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1.
Am J Med Genet A ; 179(9): 1884-1894, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31313512

RESUMO

Brachyolmia is a skeletal dysplasia characterized by short spine-short stature, platyspondyly, and minor long bone abnormalities. We describe 18 patients, from different ethnic backgrounds and ages ranging from infancy to 19 years, with the autosomal recessive form, associated with PAPSS2. The main clinical features include disproportionate short stature with short spine associated with variable symptoms of pain, stiffness, and spinal deformity. Eight patients presented prenatally with short femora, whereas later in childhood their short-spine phenotype emerged. We observed the same pattern of changing skeletal proportion in other patients. The radiological findings included platyspondyly, irregular end plates of the elongated vertebral bodies, narrow disc spaces and short over-faced pedicles. In the limbs, there was mild shortening of femoral necks and tibiae in some patients, whereas others had minor epiphyseal or metaphyseal changes. In all patients, exome and Sanger sequencing identified homozygous or compound heterozygous PAPSS2 variants, including c.809G>A, common to white European patients. Bi-parental inheritance was established where possible. Low serum DHEAS, but not overt androgen excess was identified. Our study indicates that autosomal recessive brachyolmia occurs across continents and may be under-recognized in infancy. This condition should be considered in the differential diagnosis of short femora presenting in the second trimester.

2.
Eur J Hum Genet ; 27(10): 1611-1618, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31278393

RESUMO

The developmental and epileptic encephalopathies (DEE) are a heterogeneous group of chronic encephalopathies frequently associated with rare de novo nonsynonymous coding variants in neuronally expressed genes. Here, we describe eight probands with a DEE phenotype comprising intellectual disability, epilepsy, and hypotonia. Exome trio analysis showed de novo variants in TRPM3, encoding a brain-expressed transient receptor potential channel, in each. Seven probands were identically heterozygous for a recurrent substitution, p.(Val837Met), in TRPM3's S4-S5 linker region, a conserved domain proposed to undergo conformational change during gated channel opening. The eighth individual was heterozygous for a proline substitution, p.(Pro937Gln), at the boundary between TRPM3's flexible pore-forming loop and an adjacent alpha-helix. General-population truncating variants and microdeletions occur throughout TRPM3, suggesting a pathomechanism other than simple haploinsufficiency. We conclude that de novo variants in TRPM3 are a cause of intellectual disability and epilepsy.

3.
Eur Heart J ; 40(35): 2964-2975, 2019 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-31170290

RESUMO

AIMS: Calmodulinopathies are rare life-threatening arrhythmia syndromes which affect mostly young individuals and are, caused by mutations in any of the three genes (CALM 1-3) that encode identical calmodulin proteins. We established the International Calmodulinopathy Registry (ICalmR) to understand the natural history, clinical features, and response to therapy of patients with a CALM-mediated arrhythmia syndrome. METHODS AND RESULTS: A dedicated Case Report File was created to collect demographic, clinical, and genetic information. ICalmR has enrolled 74 subjects, with a variant in the CALM1 (n = 36), CALM2 (n = 23), or CALM3 (n = 15) genes. Sixty-four (86.5%) were symptomatic and the 10-year cumulative mortality was 27%. The two prevalent phenotypes are long QT syndrome (LQTS; CALM-LQTS, n = 36, 49%) and catecholaminergic polymorphic ventricular tachycardia (CPVT; CALM-CPVT, n = 21, 28%). CALM-LQTS patients have extremely prolonged QTc intervals (594 ± 73 ms), high prevalence (78%) of life-threatening arrhythmias with median age at onset of 1.5 years [interquartile range (IQR) 0.1-5.5 years] and poor response to therapies. Most electrocardiograms (ECGs) show late onset peaked T waves. All CALM-CPVT patients were symptomatic with median age of onset of 6.0 years (IQR 3.0-8.5 years). Basal ECG frequently shows prominent U waves. Other CALM-related phenotypes are idiopathic ventricular fibrillation (IVF, n = 7), sudden unexplained death (SUD, n = 4), overlapping features of CPVT/LQTS (n = 3), and predominant neurological phenotype (n = 1). Cardiac structural abnormalities and neurological features were present in 18 and 13 patients, respectively. CONCLUSION: Calmodulinopathies are largely characterized by adrenergically-induced life-threatening arrhythmias. Available therapies are disquietingly insufficient, especially in CALM-LQTS. Combination therapy with drugs, sympathectomy, and devices should be considered.

4.
Am J Hum Genet ; 105(1): 213-220, 2019 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-31230721

RESUMO

De novo variants represent a significant cause of neurodevelopmental delay and intellectual disability. A genetic basis can be identified in only half of individuals who have neurodevelopmental disorders (NDDs); this indicates that additional causes need to be elucidated. We compared the frequency of de novo variants in patient-parent trios with (n = 2,030) versus without (n = 2,755) NDDs. We identified de novo variants in TAOK1 (thousand and one [TAO] amino acid kinase 1), which encodes the serine/threonine-protein kinase TAO1, in three individuals with NDDs but not in persons who did not have NDDs. Through further screening and the use of GeneMatcher, five additional individuals with NDDs were found to have de novo variants. All eight variants were absent from gnomAD (Genome Aggregation Database). The variant carriers shared a non-specific phenotype of developmental delay, and six individuals had additional muscular hypotonia. We established a fibroblast line of one mutation carrier, and we demonstrated that reduced mRNA levels of TAOK1 could be increased upon cycloheximide treatment. These results indicate nonsense-mediated mRNA decay. Further, there was neither detectable phosphorylated TAO1 kinase nor phosphorylated tau in these cells, and mitochondrial morphology was altered. Knockdown of the ortholog gene Tao1 (Tao, CG14217) in Drosophila resulted in delayed early development. The majority of the Tao1-knockdown flies did not survive beyond the third instar larval stage. When compared to control flies, Tao1 knockdown flies revealed changed morphology of the ventral nerve cord and the neuromuscular junctions as well as a decreased number of endings (boutons). Furthermore, mitochondria in mutant flies showed altered distribution and decreased size in axons of motor neurons. Thus, we provide compelling evidence that de novo variants in TAOK1 cause NDDs.

5.
Am J Hum Genet ; 104(3): 530-541, 2019 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-30827496

RESUMO

Acetylation of the lysine residues in histones and other DNA-binding proteins plays a major role in regulation of eukaryotic gene expression. This process is controlled by histone acetyltransferases (HATs/KATs) found in multiprotein complexes that are recruited to chromatin by the scaffolding subunit transformation/transcription domain-associated protein (TRRAP). TRRAP is evolutionarily conserved and is among the top five genes intolerant to missense variation. Through an international collaboration, 17 distinct de novo or apparently de novo variants were identified in TRRAP in 24 individuals. A strong genotype-phenotype correlation was observed with two distinct clinical spectra. The first is a complex, multi-systemic syndrome associated with various malformations of the brain, heart, kidneys, and genitourinary system and characterized by a wide range of intellectual functioning; a number of affected individuals have intellectual disability (ID) and markedly impaired basic life functions. Individuals with this phenotype had missense variants clustering around the c.3127G>A p.(Ala1043Thr) variant identified in five individuals. The second spectrum manifested with autism spectrum disorder (ASD) and/or ID and epilepsy. Facial dysmorphism was seen in both groups and included upslanted palpebral fissures, epicanthus, telecanthus, a wide nasal bridge and ridge, a broad and smooth philtrum, and a thin upper lip. RNA sequencing analysis of skin fibroblasts derived from affected individuals skin fibroblasts showed significant changes in the expression of several genes implicated in neuronal function and ion transport. Thus, we describe here the clinical spectrum associated with TRRAP pathogenic missense variants, and we suggest a genotype-phenotype correlation useful for clinical evaluation of the pathogenicity of the variants.

6.
Eur J Hum Genet ; 27(5): 738-746, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30679813

RESUMO

Determining pathogenicity of genomic variation identified by next-generation sequencing techniques can be supported by recurrent disruptive variants in the same gene in phenotypically similar individuals. However, interpretation of novel variants in a specific gene in individuals with mild-moderate intellectual disability (ID) without recognizable syndromic features can be challenging and reverse phenotyping is often required. We describe 24 individuals with a de novo disease-causing variant in, or partial deletion of, the F-box only protein 11 gene (FBXO11, also known as VIT1 and PRMT9). FBXO11 is part of the SCF (SKP1-cullin-F-box) complex, a multi-protein E3 ubiquitin-ligase complex catalyzing the ubiquitination of proteins destined for proteasomal degradation. Twenty-two variants were identified by next-generation sequencing, comprising 2 in-frame deletions, 11 missense variants, 1 canonical splice site variant, and 8 nonsense or frameshift variants leading to a truncated protein or degraded transcript. The remaining two variants were identified by array-comparative genomic hybridization and consisted of a partial deletion of FBXO11. All individuals had borderline to severe ID and behavioral problems (autism spectrum disorder, attention-deficit/hyperactivity disorder, anxiety, aggression) were observed in most of them. The most relevant common facial features included a thin upper lip and a broad prominent space between the paramedian peaks of the upper lip. Other features were hypotonia and hyperlaxity of the joints. We show that de novo variants in FBXO11 cause a syndromic form of ID. The current series show the power of reverse phenotyping in the interpretation of novel genetic variances in individuals who initially did not appear to have a clear recognizable phenotype.

7.
J Am Heart Assoc ; 7(16): e009706, 2018 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-30369311

RESUMO

Background Congenital long- QT syndrome ( LQTS ) is a genetic disorder characterized by prolongation of the corrected QT interval ( QT c) on an ECG . The aim of the present study was to estimate the prevalence of pathogenic and likely pathogenic sequence variants in patients who had at least 1 ECG with a QT c ≥500 ms. Methods and Results Telemark Hospital Trust is a community hospital within the Norwegian national health system, serving ≈173 000 inhabitants. We searched the ECG database at Telemark Hospital Trust, Norway, from January 2004 to December 2014, and identified 1531 patients with at least 1 ECG with a QT c ≥500 ms. At the time of inclusion in this study (2015), 766 patients were alive. A total of 733 patients were invited to participate, and 475 accepted. The 17 genes that have been reported to cause monogenic LQTS were sequenced among the patients. Pro- QT c score was calculated for each patient. A molecular genetic cause of LQTS was detected in 31 (6.5%) of 475 patients. These patients had a lower pro- QT c score than those without pathogenic or likely pathogenic variants (1.7±1.0 versus 2.8±1.6; P<0.001). Conclusions Compared with the general population, hospitalized patients with a QT c ≥500 ms in at least 1 ECG recording had an increased likelihood for pathogenic and likely pathogenic variants in LQTS genes. We recommend increased awareness of the possibility of LQTS in patients with at least 1 ECG with a QT c ≥500 ms.

8.
Genet Med ; 2018 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-30158690

RESUMO

PURPOSE: Defects in the cohesin pathway are associated with cohesinopathies, notably Cornelia de Lange syndrome (CdLS). We aimed to delineate pathogenic variants in known and candidate cohesinopathy genes from a clinical exome perspective. METHODS: We retrospectively studied patients referred for clinical exome sequencing (CES, N = 10,698). Patients with causative variants in novel or recently described cohesinopathy genes were enrolled for phenotypic characterization. RESULTS: Pathogenic or likely pathogenic single-nucleotide and insertion/deletion variants (SNVs/indels) were identified in established disease genes including NIPBL (N = 5), SMC1A (N = 14), SMC3 (N = 4), RAD21 (N = 2), and HDAC8 (N = 8). The phenotypes in this genetically defined cohort skew towards the mild end of CdLS spectrum as compared with phenotype-driven cohorts. Candidate or recently reported cohesinopathy genes were supported by de novo SNVs/indels in STAG1 (N = 3), STAG2 (N = 5), PDS5A (N = 1), and WAPL (N = 1), and one inherited SNV in PDS5A. We also identified copy-number deletions affecting STAG1 (two de novo, one of unknown inheritance) and STAG2 (one of unknown inheritance). Patients with STAG1 and STAG2 variants presented with overlapping features yet without characteristic facial features of CdLS. CONCLUSION: CES effectively identified disease-causing alleles at the mild end of the cohensinopathy spectrum and enabled characterization of candidate disease genes.

9.
Am J Hum Genet ; 101(5): 768-788, 2017 Nov 02.
Artigo em Inglês | MEDLINE | ID: mdl-29100089

RESUMO

Calcium/calmodulin-dependent protein kinase II (CAMK2) is one of the first proteins shown to be essential for normal learning and synaptic plasticity in mice, but its requirement for human brain development has not yet been established. Through a multi-center collaborative study based on a whole-exome sequencing approach, we identified 19 exceedingly rare de novo CAMK2A or CAMK2B variants in 24 unrelated individuals with intellectual disability. Variants were assessed for their effect on CAMK2 function and on neuronal migration. For both CAMK2A and CAMK2B, we identified mutations that decreased or increased CAMK2 auto-phosphorylation at Thr286/Thr287. We further found that all mutations affecting auto-phosphorylation also affected neuronal migration, highlighting the importance of tightly regulated CAMK2 auto-phosphorylation in neuronal function and neurodevelopment. Our data establish the importance of CAMK2A and CAMK2B and their auto-phosphorylation in human brain function and expand the phenotypic spectrum of the disorders caused by variants in key players of the glutamatergic signaling pathway.


Assuntos
Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/genética , Deficiência Intelectual/genética , Mutação/genética , Animais , Encéfalo/patologia , Linhagem Celular , Exoma/genética , Feminino , Ácido Glutâmico/genética , Células HEK293 , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Neurônios/patologia , Fosforilação/genética , Transdução de Sinais/genética
10.
Mol Genet Metab ; 121(1): 51-56, 2017 05.
Artigo em Inglês | MEDLINE | ID: mdl-28377240

RESUMO

BACKGROUND: Rare sequence variants in at least five genes are known to cause monogenic obesity. In this study we aimed to investigate the prevalence of, and characterize, rare coding and splice site variants in LEP, LEPR, MC4R, PCSK1 and POMC in patients with morbid obesity and normal weight controls. METHOD: Targeted next-generation sequencing of all exons in LEP, LEPR, MC4R, PCSK1 and POMC was performed in 485 patients with morbid obesity and 327 normal weight population-based controls from Norway. RESULTS: In total 151 variants were detected. Twenty-eight (18.5%) of these were rare, coding or splice variants and five (3.3%) were novel. All individuals, except one control, were heterozygous for the 28 variants, and the distribution of the rare variants showed a significantly higher carrier frequency among cases than controls (9.9% vs. 4.9%, p=0.011). Four variants in MC4R were classified as pathogenic or likely pathogenic. CONCLUSION: Four cases (0.8%) of monogenic obesity were detected, all due to MC4R variants previously linked to monogenic obesity. Significant differences in carrier frequencies among patients with morbid obesity and normal weight controls suggest an association between heterozygous rare coding variants in these five genes and morbid obesity. However, additional studies in larger cohorts and functional testing of the novel variants identified are required to confirm the findings.


Assuntos
Variação Genética , Sequenciamento de Nucleotídeos em Larga Escala/métodos , Obesidade Mórbida/genética , Análise de Sequência de DNA/métodos , Adolescente , Adulto , Distribuição por Idade , Estudos de Casos e Controles , Criança , Feminino , Predisposição Genética para Doença , Humanos , Leptina/genética , Masculino , Pessoa de Meia-Idade , Taxa de Mutação , Noruega , Pró-Opiomelanocortina/genética , Pró-Proteína Convertase 1/genética , Receptor Tipo 4 de Melanocortina/genética , Receptores para Leptina/genética , Adulto Jovem
11.
Tidsskr Nor Laegeforen ; 135(20): 1833-7, 2015 Nov 03.
Artigo em Inglês, Norueguês | MEDLINE | ID: mdl-26534809

RESUMO

BACKGROUND: New DNA-sequencing technology is revolutionising medical diagnostics. Through the use of exome sequencing, it is now possible to sequence all human genes in parallel. This technology has been widely used in research over the last few years and is now also being applied to diagnostics. The aim of this study was to systematically examine initial experiences with diagnostic exome sequencing in Norway. MATERIAL AND METHOD: This is a retrospective observational study of the results of all exome sequencing performed by the Section of Medical Genetics at Telemark Hospital between December 2012 and October 2014, and includes 125 persons in 46 families. The majority of these families were being investigated for a syndrome (n = 35, 76%) or neurological disease (n = 9, 20%). RESULTS: Exome sequencing detected pathogenic sequence variants in 15 of 46 probands, and variants of unknown significance in 12 probands. Of the 100 patients who stated their wishes regarding feedback of any incidental findings, six indicated that they did not wish to receive such information. There were no incidental findings in this study, but neither were such sequence variants actively looked for. INTERPRETATION: Exome sequencing can enable more patients with syndromes or neurological diseases to receive a causal diagnosis, and to receive this diagnosis at an earlier stage. However, the patients in this study were quite highly selected, and the results must therefore be interpreted with caution.


Assuntos
Exoma , Doenças Genéticas Inatas/diagnóstico , Sequenciamento de Nucleotídeos em Larga Escala , Doenças do Sistema Nervoso , Análise de Sequência de DNA , Humanos , Consentimento Livre e Esclarecido , Doenças do Sistema Nervoso/diagnóstico , Doenças do Sistema Nervoso/genética , Noruega , Estudos Retrospectivos , Síndrome
12.
FEBS Open Bio ; 4: 321-7, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24918045

RESUMO

More than 1700 mutations in the low density lipoprotein receptor (LDLR) gene have been found to cause familial hypercholesterolemia (FH). These are commonly divided into five classes based upon their effects on the structure and function of the LDLR. However, little is known about the mechanism by which mutations in the transmembrane domain of the LDLR gene cause FH. We have studied how the transmembrane mutation G805R affects the function of the LDLR. Based upon Western blot analyses of transfected HepG2 cells, mutation G805R reduced the amounts of the 120 kDa precursor LDLR in the endoplasmic reticulum. This led to reduced amounts of the mature 160 kDa LDLR at the cell surface. However, significant amounts of a secreted 140 kDa G805R-LDLR ectodomain fragment was observed in the culture media. Treatment of the cells with the metalloproteinase inhibitor batimastat largely restored the amounts of the 120 and 160 kDa forms in cell lysates, and prevented secretion of the 140 kDa ectodomain fragment. Together, these data indicate that a metalloproteinase cleaved the ectodomain of the 120 kDa precursor G805R-LDLR in the endoplasmic reticulum. It was the presence of the polar Arg805 and not the lack of Gly805 which led to ectodomain cleavage. Arg805 also prevented γ-secretase cleavage within the transmembrane domain. It is conceivable that introducing a charged residue within the hydrophobic membrane lipid bilayer, results in less efficient incorporation of the 120 kDa G805R-LDLR in the endoplasmic reticulum membrane and makes it a substrate for metalloproteinase cleavage.

13.
Biochem J ; 457(1): 99-105, 2014 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-24144304

RESUMO

PCSK9 (proprotein convertase subtilisin/kexin type 9) binds to the LDLR (low-density lipoprotein receptor) at the cell surface and disrupts recycling of the LDLR. However, PCSK9 also interacts with the LDLR in the ER (endoplasmic reticulum). In the present study we have investigated the role of PCSK9 for the transport of the LDLR from the ER to the cell membrane. A truncated LDLR consisting of the ectodomain (ED-LDLR) was used for these studies to avoid PCSK9-mediated degradation of the LDLR. The amount of secreted ED-LDLR was used as a measure of the amount of ED-LDLR transported from the ER. From co-transfection experiments of various PCSK9 and ED-LDLR plasmids, PCSK9 increased the amount of WT (wild-type) ED-LDLR in the medium, but not of an ED-LDLR lacking the EGF (epidermal growth factor)-A repeat or of a Class 2a mutant ED-LDLR which fails to exit the ER. Mutant PCSK9s which failed to undergo autocatalytic cleavage or failed to exit the ER, failed to increase the amount of WT-ED-LDLR in the medium. These mutants also reduced the amount of WT-ED-LDLR intracellularly, which could partly be prevented by the proteasome inhibitor lactacystine. WT-ED-LDLR promoted autocatalytic cleavage of pro-PCSK9. The findings of the present study indicate that the binding of WT-ED-LDLR to pro-PCSK9 in the ER promotes autocatalytic cleavage of PCSK9, and autocatalytically cleaved PCSK9 acts as a chaperone to promote the exit of WT-ED-LDLR from the ER.


Assuntos
Retículo Endoplasmático/metabolismo , Chaperonas Moleculares/fisiologia , Pró-Proteína Convertases/fisiologia , Receptores de LDL/metabolismo , Serina Endopeptidases/fisiologia , Catálise , Membrana Celular/metabolismo , Células Hep G2 , Homeostase , Humanos , Pró-Proteína Convertase 9 , Pró-Proteína Convertases/química , Domínios e Motivos de Interação entre Proteínas/fisiologia , Isoformas de Proteínas/química , Isoformas de Proteínas/fisiologia , Precursores de Proteínas/química , Precursores de Proteínas/fisiologia , Transporte Proteico , Proteólise , Receptores de LDL/química , Serina Endopeptidases/química
14.
J Lipid Res ; 54(6): 1560-6, 2013 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-23509406

RESUMO

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the LDL receptor (LDLR) at the cell surface and reroutes the internalized LDLR to intracellular degradation. In this study, we have shown that PCSK9-mediated degradation of the full-length 160 kDa LDLR generates a 17 kDa C-terminal LDLR fragment. This fragment was not generated from mutant LDLRs resistant to PCSK9-mediated degradation or when degradation was prevented by chemicals such as ammonium chloride or the cysteine cathepsin inhibitor E64d. The observation that the 17 kDa fragment was only detected when the cells were cultured in the presence of the γ-secretase inhibitor DAPT indicates that this 17 kDa fragment undergoes γ-secretase cleavage within the transmembrane domain. The failure to detect the complementary 143 kDa ectodomain fragment is likely to be due to its rapid degradation in the endosomal lumen. The 17 kDa C-terminal LDLR fragment was also generated from a Class 5 mutant LDLR undergoing intracellular degradation. Thus, one may speculate that an LDLR with bound PCSK9 and a Class 5 LDLR with bound LDL are degraded by a similar mechanism that could involve ectodomain cleavage in the endosome.


Assuntos
Lipoproteínas LDL/metabolismo , Mutação , Pró-Proteína Convertases/metabolismo , Proteólise , Receptores de LDL/metabolismo , Serina Endopeptidases/metabolismo , Secretases da Proteína Precursora do Amiloide/genética , Secretases da Proteína Precursora do Amiloide/metabolismo , Células Hep G2 , Humanos , Lipoproteínas LDL/genética , Pró-Proteína Convertase 9 , Pró-Proteína Convertases/genética , Estrutura Terciária de Proteína , Receptores de LDL/genética , Serina Endopeptidases/genética
15.
Atherosclerosis ; 225(2): 370-5, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23102784

RESUMO

OBJECTIVE: To study whether mutations in the SORT1 gene could be a cause of autosomal dominant hypercholesterolemia and to study the effect of sortilin on the binding and internalization of low density lipoprotein (LDL). METHODS: 842 unrelated hypercholesterolemic subjects without mutations in genes known to cause autosomal dominant hypercholesterolemia, were screened for mutations in the SORT1 gene by DNA sequencing. Transfections of wild-type or mutant SORT1 plasmids in HeLa T-REx cells and the use of siRNA were used to study the effect of sortilin on the number of cell-surface LDL receptors and on the binding and internalization of LDL. RESULTS: A total of 45 mutations in the SORT1 gene were identified of which 15 were missense mutations. Eight of these were selected for in vitro studies, of which none had a major impact on the amount of LDL bound to the cell surface. There was a positive correlation between the amount of sortilin on the cell surface and the amount of LDL bound. The observation that a mutant sortilin which is predominantly found on the cell surface rather than in post-Golgi compartments, bound very high amounts of LDL, indicates that sortilin does not increase the binding of LDL through an intracellular mechanism. Rather, our data indicate that sortilin binds LDL on the cell surface. CONCLUSION: Even though sortilin binds and internalizes LDL by receptor-mediated endocytosis, mutations in the SORT1 gene are unlikely to cause autosomal dominant hypercholesterolemia and may only have a marginal effect on plasma LDL cholesterol levels.


Assuntos
Proteínas Adaptadoras de Transporte Vesicular/genética , Membrana Celular/metabolismo , LDL-Colesterol/sangue , Hiperlipoproteinemia Tipo II/genética , Mutação , Proteínas Adaptadoras de Transporte Vesicular/metabolismo , Adulto , Idoso , Análise Mutacional de DNA , Endocitose , Feminino , Predisposição Genética para Doença , Células HeLa , Humanos , Hiperlipoproteinemia Tipo II/metabolismo , Masculino , Pessoa de Meia-Idade , Fenótipo , Ligação Proteica , Estrutura Terciária de Proteína , Interferência de RNA , Receptores de LDL/metabolismo , Fatores de Risco , Índice de Gravidade de Doença , Transfecção
16.
Transl Res ; 160(2): 125-30, 2012 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-22683370

RESUMO

Secreted proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low-density lipoprotein receptor (LDLR) at the cell surface and disrupts the normal recycling of the LDLR. When human PCSK9 is injected into LDLR-deficient mice, PCSK9 is still rapidly cleared by the liver. This finding may suggest that PCSK9 is physiologically also cleared by receptors other than the LDLR. An alternative explanation could be that PCSK9 has undergone modifications during purification and is cleared by scavenger receptors on liver endothelial sinusoidal cells when injected into mice. If the only mechanism for clearing PCSK9 in humans is through the LDLR, one would expect that differences in the number of LDLRs would affect the plasma levels of low-density lipoprotein cholesterol (LDLC) and PCSK9 in a similar fashion. In this study, levels of LDLC and PCSK9 were measured in familial hypercholesterolemia (FH) homozygotes, FH heterozygotes, and normocholesterolemic subjects. The ratio between the levels of LDLC and PCSK9 was 1.7-fold higher in FH heterozygotes and 3-fold higher in FH homozygotes than in the normocholesterolemic subjects. Thus, defective LDLRs have a greater impact on the levels of LDLC than on the levels of PCSK9. By assuming that the rate of PCSK9 synthesis is similar in the 3 groups, this finding suggests that in humans, plasma PCSK9 is also cleared by LDLR-independent mechanisms.


Assuntos
LDL-Colesterol/sangue , Hiperlipoproteinemia Tipo II/metabolismo , Pró-Proteína Convertases/sangue , Receptores de LDL/metabolismo , Serina Endopeptidases/sangue , Adolescente , Adulto , Animais , Remoção de Componentes Sanguíneos , Feminino , Genótipo , Heterozigoto , Homozigoto , Humanos , Hiperlipoproteinemia Tipo II/genética , Hiperlipoproteinemia Tipo II/terapia , Lipídeos/sangue , Masculino , Camundongos , Pessoa de Meia-Idade , Regiões Promotoras Genéticas/genética , Pró-Proteína Convertase 9 , Pró-Proteína Convertases/genética , Serina Endopeptidases/genética , Adulto Jovem
17.
Mol Genet Metab ; 105(1): 149-54, 2012 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-22078455

RESUMO

In this study we have characterized a naturally occurring truncated form of the low density lipoprotein receptor (LDLR). Western blot analysis of transfected cells indicated that the truncated form (∆N-LDLR) is a degradation product of the full-length LDLR generated by cleavage in the linker region between ligand-binding repeats 4 and 5 of the ligand-binding domain. The cleavage of the linker was not caused by components of the culture media, as heat inactivation of the media did not prevent cleavage. Rather, it is assumed that cleavage was caused by an enzyme secreted from the cells. Biotinylation experiments showed that ∆N-LDLR is located on the cell surface and is detectable approximately 5 h after synthesis of the full-length LDLR. Flow cytometric analysis showed that ∆N-LDLR was not able to bind and internalize low density lipoprotein (LDL). ∆N-LDLR appeared to be equally stable as the full-length LDLR. Thus, generation of ∆N-LDLR does not appear to be the first signal for degradation of the LDLR. The existence of two functionally different populations of LDLRs on the cell surface, of which ∆N-LDLR constitutes 28%, must be taken into account when interpreting results of experiments to study LDLRs on the cell surface. Furthermore, if the cleavage of the linker between ligand-binding repeats 4 and 5 could be prevented by an enzyme inhibitor, this could represent a novel therapeutic strategy to increase the number of functioning LDLRs and thereby decrease the levels of plasma LDL cholesterol.


Assuntos
Proteólise , Receptores de LDL/metabolismo , Animais , Células CHO , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Cricetinae , Cricetulus , Meios de Cultura , Complexo de Golgi/efeitos dos fármacos , Complexo de Golgi/metabolismo , Humanos , Ligantes , Proteínas Mutantes/metabolismo , Inibidores de Proteases/farmacologia , Estabilidade Proteica/efeitos dos fármacos , Estrutura Terciária de Proteína , Transporte Proteico/efeitos dos fármacos , Proteólise/efeitos dos fármacos , Receptores de LDL/antagonistas & inibidores , Receptores de LDL/química , Deleção de Sequência
18.
Hum Mol Genet ; 21(6): 1402-9, 2012 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-22156580

RESUMO

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the epidermal growth factor homology domain repeat A of the low-density lipoprotein receptor (LDLR) at the cell surface and disrupts recycling of the internalized LDLR. As a consequence, the LDLR is rerouted to the lysosomes for degradation. Although PCSK9 may bind to an LDLR lacking the ligand-binding domain, at least three ligand-binding repeats of the ligand-binding domain are required for PCSK9 to reroute the LDLR to the lysosomes. In this study, we have studied the binding of PCSK9 to an LDLR with or without the ligand-binding domain at increasingly acidic conditions in order to mimic the milieu of the LDLR:PCSK9 complex as it translocates from the cell membrane to the sorting endosomes. These studies have shown that PCSK9 is rapidly released from an LDLR lacking the ligand-binding domain at pH in the range of 6.9-6.1. A similar pattern of release at acidic pH was also observed for the binding to the normal LDLR of mutant PCSK9 lacking the C-terminal domain. Together these data indicate that an interaction between the negatively charged ligand-binding domain of the LDLR and the positively charged C-terminal domain of PCSK9 is required for PCSK9 to remain bound to the LDLR during the early phase of endosomal acidification as the LDLR translocates from the cell membrane to the sorting endosome.


Assuntos
Ácidos/metabolismo , Endossomos/metabolismo , Pró-Proteína Convertases/metabolismo , Receptores de LDL/metabolismo , Serina Endopeptidases/metabolismo , Animais , Western Blotting , Células CHO , Membrana Celular/metabolismo , Células Cultivadas , Cricetinae , Humanos , Concentração de Íons de Hidrogênio , Rim/citologia , Rim/metabolismo , Lisossomos/metabolismo , Mutagênese Sítio-Dirigida , Mutação/genética , Pró-Proteína Convertase 9 , Pró-Proteína Convertases/genética , Ligação Proteica , Estrutura Terciária de Proteína , Transporte Proteico , Receptores de LDL/genética , Serina Endopeptidases/genética , Transdução de Sinais
19.
Biochem Biophys Res Commun ; 415(4): 642-5, 2011 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-22079632

RESUMO

Newly synthesized low density lipoprotein receptors (LDLRs) exit the endoplasmic reticulum (ER) as the first step in the secretory pathway. In this study we have generated truncating deletions and substitutions within the 50 amino acid cytoplasmic domain of the LDLR in order to identify residues required for the exit from the ER. Western blot analysis was used to determine the relative amounts of the 120 kDa precursor form of the LDLR located in the ER and the 160 kDa mature form that has exited the ER. These studies have shown that the exit of an LDLR lacking the cytoplasmic domain, is markedly reduced. Moreover, the longer the cytoplasmic domain, the more efficient is the exit from the ER. At least 30 residues were required for the LDLR to efficiently exit the ER. Mutations in the two di-acidic motifs ExE(814) and/or ExD(837) had only a small effect on the exit from the ER. The requirement for a certain length of the cytoplasmic domain for efficient exit from the ER, could reflect the distance needed to interact with the COPII complex of the ER membrane or the requirement for the LDLR to undergo dimerization.


Assuntos
Citoplasma/metabolismo , Retículo Endoplasmático/metabolismo , Receptores de LDL/metabolismo , Sequência de Aminoácidos , Substituição de Aminoácidos , Animais , Células CHO , Cricetinae , Humanos , Dados de Sequência Molecular , Mutação , Estrutura Terciária de Proteína , Transporte Proteico , Receptores de LDL/química , Receptores de LDL/genética , Deleção de Sequência
20.
J Lipid Res ; 52(10): 1787-94, 2011 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-21771976

RESUMO

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low density lipoprotein receptor (LDLR) at the cell surface and disrupts the normal recycling of the LDLR. In this study, we investigated the role of the C-terminal domain for the activity of PCSK9. Experiments in which conserved residues and histidines on the surface of the C-terminal domain were mutated indicated that no specific residues of the C-terminal domain, apart from those responsible for maintaining the overall structure, are required for the activity of PCSK9. Rather, the net charge of the C-terminal domain is important. The more positively charged the C-terminal domain, the higher the activity toward the LDLR. Moreover, replacement of the C-terminal domain with an unrelated protein of comparable size led to significant activity of the chimeric protein. We conclude that the role of the evolutionary, poorly conserved C-terminal domain for the activity of PCSK9 reflects its overall positive charge and size and not the presence of specific residues involved in protein-protein interactions.


Assuntos
Endossomos/metabolismo , Receptores de LDL/metabolismo , Serina Endopeptidases/química , Serina Endopeptidases/metabolismo , Alanina/química , Alanina/metabolismo , Sequência de Aminoácidos , Endossomos/química , Células Hep G2 , Histidina/química , Histidina/metabolismo , Humanos , Dados de Sequência Molecular , Pró-Proteína Convertase 9 , Pró-Proteína Convertases , Ligação Proteica , Receptores de LDL/química , Células Tumorais Cultivadas
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