RESUMO
BACKGROUND AND OBJECTIVES: Donor factors influence the quality characteristics of red cell concentrates (RCCs) and the lesions that develop in these heterogeneous blood products during hypothermic storage. Teen male donors' RCCs contain elevated levels of biologically old red blood cells (RBCs). The aim of this study was to interrogate the quality of units of different donor ages and sexes to unravel the complex interplay between donor characteristics, long-term cold storage and, for the first time, RBC biological age. MATERIALS AND METHODS: RCCs from teen males, teen females, senior males and senior females were density-separated into less-dense/young (Y-RBCs) and dense/old RBCs (O-RBCs) throughout hypothermic storage for testing. The unseparated and density-separated cells were tested for haematological parameters, stress (oxidative and osmotic) haemolysis and oxygen affinity (p50). RESULTS: The O-RBCs obtained from teen donor samples, particularly males, had smaller mean corpuscular volumes and higher mean corpuscular haemoglobin concentrations. While biological age did not significantly affect oxygen affinity, biologically aged O-RBCs from stored RCCs exhibited increased oxidative haemolysis and decreased osmotic fragility, with teenage male RCCs exhibiting the highest propensity to haemolyse. CONCLUSION: Previously, donor age and sex were shown to have an impact on the biological age distribution of RBCs within RCCs. Herein, we demonstrated that RBC biological age, particularly O-RBCs, which are found more prevalently in male teens, to be a driving factor of several aspects of poor blood product quality. This study emphasizes that donor factors should continue to be considered for their potential impacts on transfusion outcomes.
Assuntos
Doadores de Sangue , Preservação de Sangue , Eritrócitos , Humanos , Masculino , Eritrócitos/citologia , Eritrócitos/metabolismo , Adolescente , Preservação de Sangue/métodos , Feminino , Adulto , Hemólise , Pessoa de Meia-Idade , Fatores Etários , Idoso , Senescência CelularRESUMO
BACKGROUND: Donors possess heterogeneous red cell concentrates (RCCs) in terms of the biological age of their red blood cells (RBCs) as a direct result of various donor-dependent factors influencing rates of erythropoiesis. This study aimed to estimate the median biological age of RBCs in RCCs based on donor age and sex to investigate inherent differences in blood products' biological ages over hypothermic storage using estimated median densities (EMDs). STUDY DESIGN: Sixty RCCs were collected from four donor groups; male and female teenagers (17-19 years old) and seniors (75+ years old). A Percoll density-based separation approach was used to quantify the EMDs indicative of biological age. EMD and mean corpuscular hemoglobin (MCHC) were compared by correlation analyses. RESULTS: Differences in the median biological age of RCC units were observed with male donors having significantly higher EMDs compared to females (p < .001). Teen male donors possessed the highest EMDs with significantly elevated levels of biologically aged RBCs compared to both female donor groups, regardless of storage duration (p < .05). Throughout most of the 42-day storage period, senior donors, particularly senior females, demonstrated the strongest correlation between EMD and MCHC (R2 > 0.5). CONCLUSIONS: This study provides further evidence that there are inherent differences between the biological age profiles of RBCs between blood donors of different sex and age. Our findings further highlight that biological age may contribute to RBC quality during storage and that donor characteristics need to be considered when evaluating transfusion safety and efficacy.
Assuntos
Eritrócitos , Caracteres Sexuais , Adolescente , Humanos , Masculino , Feminino , Idoso , Adulto Jovem , Adulto , Doadores de Sangue , Transfusão de Eritrócitos , Envelhecimento , Preservação de SangueRESUMO
OBJECTIVE: Dedifferentiated endometrial cancer (DDEC) is an uncommon and clinically highly aggressive subtype of endometrial cancer characterized by genomic inactivation of SWItch/Sucrose Non-Fermentable (SWI/SNF) complex protein. It responds poorly to conventional systemic treatment and its rapidly progressive clinical course limits the therapeutic windows to trial additional lines of therapies. This underscores a pressing need for biologically accurate preclinical tumor models to accelerate therapeutic development. METHODS: DDEC tumor from surgical samples were implanted into immunocompromised mice for patient-derived xenograft (PDX) and cell line development. The histologic, immunophenotypic, genetic and epigenetic features of the patient tumors and the established PDX models were characterized. The SMARCA4-deficienct DDEC model was evaluated for its sensitivity toward a KDM6A/B inhibitor (GSK-J4) that was previously reported to be effective therapy for other SMARCA4-deficient cancer types. RESULTS: All three DDEC models exhibited rapid growth in vitro and in vivo, with two PDX models showing spontaneous development of metastases in vivo. The PDX tumors maintained the same undifferentiated histology and immunophenotype, and exhibited identical genomic and methylation profiles as seen in the respective parental tumors, including a mismatch repair (MMR)-deficient DDEC with genomic inactivation of SMARCA4, and two MMR-deficient DDECs with genomic inactivation of both ARID1A and ARID1B. Although the SMARCA4-deficient cell line showed low micromolecular sensitivity to GSK-J4, no significant tumor growth inhibition was observed in the corresponding PDX model. CONCLUSIONS: These established patient tumor-derived models accurately depict DDEC and represent valuable preclinical tools to gain therapeutic insights into this aggressive tumor type.
Assuntos
Neoplasias Encefálicas , Neoplasias Colorretais , Neoplasias do Endométrio , Feminino , Humanos , Animais , Camundongos , Neoplasias do Endométrio/tratamento farmacológico , Neoplasias do Endométrio/genética , Neoplasias do Endométrio/metabolismo , Diferenciação Celular , Biomarcadores Tumorais/genética , DNA Helicases , Proteínas Nucleares/genética , Fatores de Transcrição/genética , Proteínas de Ligação a DNA/genéticaRESUMO
BACKGROUND: Blood donors at the extremes of the age spectrum (16-19 years vs. ≥75 years) are characterized by increased risks of iron deficiency and anemia, and are often underrepresented in studies evaluating the effects of donor characteristics on red blood cells (RBC) transfusion effectiveness. The aim of this study was to conduct quality assessments of RBC concentrates from these unique age groups. STUDY DESIGN: We characterized 150 leukocyte-reduced (LR)-RBCs units from 75 teenage donors, who were matched by sex, and ethnicity with 75 older donors. LR-RBC units were manufactured at three large blood collection centers in the USA and Canada. Quality assessments included storage hemolysis, osmotic hemolysis, oxidative hemolysis, osmotic gradient ektacytometry, hematological indices, and RBC bioactivity. RESULTS: RBC concentrates from teenage donors had smaller (9%) mean corpuscular volume and higher (5%) RBC concentration compared with older donors counterparts. Stored RBCs from teenage donors exhibited increased susceptibility to oxidative hemolysis (>2-fold) compared with RBCs from older donors. This was observed at all testing centers independent of sex, storage duration, or the type of additive solution. RBCs from teenage male donors had increased cytoplasmatic viscosity and lower hydration compared with older donor RBCs. Evaluations of RBC supernatant bioactivity suggested that donor age was not associated with altered expression of inflammatory markers (CD31, CD54, and IL-6) on endothelial cells. CONCLUSIONS: The reported findings are likely intrinsic to RBCs and reflect age-specific changes in RBC antioxidant capacity and physical characteristics that may impact RBC survival during cold storage and after transfusion.
Assuntos
Doadores de Sangue , Hemólise , Humanos , Masculino , Adolescente , Células Endoteliais , Eritrócitos/metabolismo , Citoplasma , Preservação de SangueRESUMO
Inactivating mutations in SMARCA4 and concurrent epigenetic silencing of SMARCA2 characterize subsets of ovarian and lung cancers. Concomitant loss of these key subunits of SWI/SNF chromatin remodeling complexes in both cancers is associated with chemotherapy resistance and poor prognosis. Here, we discover that SMARCA4/2 loss inhibits chemotherapy-induced apoptosis through disrupting intracellular organelle calcium ion (Ca2+) release in these cancers. By restricting chromatin accessibility to ITPR3, encoding Ca2+ channel IP3R3, SMARCA4/2 deficiency causes reduced IP3R3 expression leading to impaired Ca2+ transfer from the endoplasmic reticulum to mitochondria required for apoptosis induction. Reactivation of SMARCA2 by a histone deacetylase inhibitor rescues IP3R3 expression and enhances cisplatin response in SMARCA4/2-deficient cancer cells both in vitro and in vivo. Our findings elucidate the contribution of SMARCA4/2 to Ca2+-dependent apoptosis induction, which may be exploited to enhance chemotherapy response in SMARCA4/2-deficient cancers.
Assuntos
Antineoplásicos/farmacologia , Apoptose/efeitos dos fármacos , Cálcio/metabolismo , DNA Helicases/genética , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Mitocôndrias/metabolismo , Mutação , Proteínas Nucleares/genética , Fatores de Transcrição/genética , Animais , Apoptose/genética , Linhagem Celular Tumoral , DNA Helicases/metabolismo , Perfilação da Expressão Gênica/métodos , Regulação Neoplásica da Expressão Gênica , Células HEK293 , Humanos , Transporte de Íons/genética , Masculino , Camundongos Endogâmicos NOD , Camundongos Knockout , Camundongos SCID , Neoplasias/tratamento farmacológico , Neoplasias/genética , Neoplasias/metabolismo , Proteínas Nucleares/metabolismo , Fatores de Transcrição/metabolismo , Ensaios Antitumorais Modelo de Xenoenxerto/métodosRESUMO
Dedifferentiated/undifferentiated endometrial carcinoma (DDEC/UEC) is an endometrial cancer characterized by the presence of histologically undifferentiated carcinoma. Genomic inactivation of core switch/sucrose nonfermentable (SWI/SNF) complex proteins was recently identified in approximately two-thirds of DDEC/UEC. The aim of this study was to delineate the clinical behavior of SWI/SNF-deficient DDEC/UEC in comparison to SWI/SNF-intact DDEC/UEC. The study cohort consisted of 56 SWI/SNF-deficient DDEC/UEC (2 POLE-mutated), which showed either SMARCA4 (BRG1) loss, ARID1A/1B co-loss, or SMARCB1 (INI1) loss in the undifferentiated tumor, and 26 SWI/SNF-intact DDEC/UEC (4 POLE-mutated). The average age at diagnosis was 61 years for patients with SWI/SNF-deficient tumors and 64 years for SWI/SNF-intact tumors. Mismatch repair (MMR) protein deficiency was seen in 66% of SWI/SNF-deficient and 50% of SWI/SNF-intact tumors. At initial presentation, 55% of patients with SWI/SNF-deficient tumors had extrauterine disease spread in contrast to 38% of patients with SWI/SNF-intact tumors. The 2-year disease specific survival (DSS) for stages I and II disease was 65% for SWI/SNF deficient tumors relative to 100% for SWI/SNF-intact tumors (p = 0.042). For patients with stages III and IV disease, the median survival was 4 months for SWI/SNF-deficient tumors compared to 36 months for SWI/SNF-intact tumors (p = 0.0003). All six patients with POLE-mutated tumors, including one with stage IV SWI/SNF-deficient tumor were alive with no evidence of disease. Among the patients with advanced stage SWI/SNF-deficient tumors, 68% (21 of 31) received adjuvant or neoadjuvant chemotherapy (platinum/taxane-based) and all except the patient with a POLE-mutated tumor (20 of 21) experienced disease progression either during chemotherapy or within 4 months after its completion. These findings show that core SWI/SNF-deficiency defines a highly aggressive group of undifferentiated cancer characterized by rapid disease progression that is refractory to conventional platinum/taxane-based chemotherapy. This underscores the importance of accurate clinical recognition of this aggressive tumor and the need to consider alternative systemic therapy for these tumors.
Assuntos
Carcinoma/genética , Neoplasias do Endométrio/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Carcinoma/metabolismo , Carcinoma/patologia , DNA Helicases/genética , DNA Helicases/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Neoplasias do Endométrio/metabolismo , Neoplasias do Endométrio/patologia , Feminino , Humanos , Imuno-Histoquímica , Pessoa de Meia-Idade , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Estudos Retrospectivos , Proteína SMARCB1/genética , Proteína SMARCB1/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Plasticity of neoplasia, whereby cancer cells attain stem-cell-like properties, is required for disease progression and represents a major therapeutic challenge. We report that in breast cancer cells NANOG, SNAIL and NODAL transcripts manifest multiple isoforms characterized by different 5' Untranslated Regions (5'UTRs), whereby translation of a subset of these isoforms is stimulated under hypoxia. The accumulation of the corresponding proteins induces plasticity and "fate-switching" toward stem cell-like phenotypes. Mechanistically, we observe that mTOR inhibitors and chemotherapeutics induce translational activation of a subset of NANOG, SNAIL and NODAL mRNA isoforms akin to hypoxia, engendering stem-cell-like phenotypes. These effects are overcome with drugs that antagonize translational reprogramming caused by eIF2α phosphorylation (e.g. ISRIB), suggesting that the Integrated Stress Response drives breast cancer plasticity. Collectively, our findings reveal a mechanism of induction of plasticity of breast cancer cells and provide a molecular basis for therapeutic strategies aimed at overcoming drug resistance and abrogating metastasis.
Assuntos
Regiões 5' não Traduzidas/genética , Neoplasias da Mama/genética , Regulação Neoplásica da Expressão Gênica/genética , Biossíntese de Proteínas/genética , Isoformas de RNA/genética , Antineoplásicos/farmacologia , Neoplasias da Mama/tratamento farmacológico , Neoplasias da Mama/patologia , Hipóxia Celular , Linhagem Celular Tumoral , Fator de Iniciação 2 em Eucariotos/genética , Fator de Iniciação 2 em Eucariotos/metabolismo , Feminino , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Células MCF-7 , Proteína Homeobox Nanog/genética , Proteína Nodal/genética , Fosforilação/efeitos dos fármacos , Fatores de Transcrição da Família Snail/genéticaRESUMO
Epithelial-to-mesenchymal transition (EMT) is a physiological process that is vital throughout the human lifespan. In addition to contributing to the development of various tissues within the growing embryo, EMT is also responsible for wound healing and tissue regeneration later in adulthood. In this review, we highlight the importance of EMT in the development and normal functioning of the female reproductive organs (the ovaries and the uterus) and describe how dysregulation of EMT can lead to pathological conditions, such as endometriosis, adenomyosis, and carcinogenesis. We also summarize the current literature relating to EMT in the context of ovarian and endometrial carcinomas, with a particular focus on how molecular mechanisms and the tumor microenvironment can govern cancer cell plasticity, therapy resistance, and metastasis.
RESUMO
Epithelial-to-mesenchymal transition (EMT) is an important physiologic process that drives tissue formation during development, but also contributes to disease pathogenesis, including fibrosis and cancer metastasis. Elevated expression of the FOXC1 transcription factor has been detected in several metastatic cancers that have undergone EMT. Therefore, mechanistic insight into the role of FOXC1 in the initiation of the EMT process was sought. It was determined that although Foxc1 transcript expression was elevated following TGFß1-induced EMT of NMuMG cells, FOXC1 was not required for this induction. RNA sequencing revealed that the mRNA levels of FGF receptor 1-isoform IIIc (Fgfr1-IIIc), normally activated upon TGFß1 treatment, were reduced in Foxc1 knockdown cells, and overexpression of Foxc1 was sufficient to induce Fgfr1-IIIc expression, but not EMT. Chromatin immunoprecipitation experiments demonstrated that FOXC1 binds to an Fgfr1 upstream regulatory region and that FOXC1 activates an Fgfr1 promoter element. Furthermore, elevated expression of Foxc1 led to increased Fgfr1-IIIc transcript. Foxc1 knockdown impaired the FGF2-mediated three-dimensional migratory ability of NMuMG cells, which was rescued by expression of FGFR1. In addition, elevated expression of FOXC1 and FGFR1 was also observed in migratory mesenchymal MDA-MB-231 breast cancer cells. Together, these results define a role for FOXC1 in specifying an invasive mesenchymal cell type by promoting FGFR1 isoform switching following induction of TGFß1-mediated EMT. Mol Cancer Res; 15(10); 1341-53. ©2017 AACR.
Assuntos
Neoplasias da Mama/genética , Fatores de Transcrição Forkhead/genética , Receptor Tipo 1 de Fator de Crescimento de Fibroblastos/genética , Análise de Sequência de RNA/métodos , Fator de Crescimento Transformador beta1/farmacologia , Animais , Neoplasias da Mama/metabolismo , Linhagem Celular Tumoral , Movimento Celular , Transição Epitelial-Mesenquimal/efeitos dos fármacos , Feminino , Fatores de Transcrição Forkhead/metabolismo , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Camundongos , Invasividade Neoplásica , Isoformas de RNA/genéticaRESUMO
Dedifferentiated carcinoma of the endometrium or the ovary is an aggressive epithelial malignancy that comprises an endometrioid carcinoma together with an undifferentiated carcinoma. We recently reported that inactivation of BRG1 or INI1, core subunits of the switch/sucrose non-fermenting (SWI/SNF) complex, was the likely molecular event underlying dedifferentiation in about half of dedifferentiated carcinomas. In this study, we performed a genomic screen that included other members of the SWI/SNF complex to better delineate the molecular basis in the remainder of these tumours. We identified concurrent inactivating mutations involving ARID1A and ARID1B in 12 of 24 BRG1/INI1-intact, 0 of 3 INI1-deficient and 0 of 16 BRG1-deficient dedifferentiated carcinomas. All ARID1A and ARID1B co-mutated tumours displayed loss of ARID1A expression in the undifferentiated component with 11 of 12 tumours also displaying absent staining in the endometrioid component. ARID1B expression was absent in the undifferentiated component in all 12 tumours, whereas the corresponding endometrioid component showed intact expression. Clinically, ARID1A/ARID1B co-inactivated tumours showed similar aggressive behaviour to BRG1 or INI1-inactivated tumours. Given that ARID1A and ARID1B are the only known DNA-binding subunits of the SWI/SNF-A complex, additional inactivation of ARID1B in an ARID1A-deficient background appears to represent an alternative mechanism of disruption of SWI/SNF-mediated transcriptional regulation, resulting in arrested cellular differentiation in endometrial and ovarian endometrioid cancer.
Assuntos
Carcinoma Endometrioide/genética , Proteínas de Ligação a DNA/genética , Neoplasias do Endométrio/genética , Proteínas Nucleares/genética , Neoplasias Ovarianas/genética , Fatores de Transcrição/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Biomarcadores Tumorais/genética , Carcinoma Endometrioide/patologia , Neoplasias do Endométrio/patologia , Feminino , Humanos , Pessoa de Meia-Idade , Neoplasias Ovarianas/patologiaRESUMO
AIMS: Dedifferentiated endometrial carcinoma (DDEC) is defined by the presence of an undifferentiated carcinoma together with an endometrioid carcinoma. Inactivation of SMARCA4 (BRG1) and inactivation of SMARCB1 (INI1) were recently described as potential mechanisms underlying the histological dedifferentiation. The aim of this study was to characterize the immunophenotypic features of DDECs, particularly in cases with prototypical histological and molecular features (BRG1/INI1 deficiency). METHODS AND RESULTS: We evaluated PAX8, oestrogen receptor (ER) and p53 immunostaining in the endometrioid and the undifferentiated components of 20 BRG1/INI1-deficient DDECs and 15 BRG1/INI1-intact DDECs, and compared the results with those of 23 grade 3 endometrioid carcinomas. The differentiated endometrioid component was positive for PAX8 and/or ER in 19 of 20 BRG1/INI1-deficient DDECs, whereas the corresponding undifferentiated component of all 20 tumours showed a complete absence of PAX8 and ER staining. All except one of the BRG1/INI1-deficient tumours showed a wild-type p53 staining pattern. PAX8 and ER expression in the undifferentiated component was absent in 67% and 80% of BRG1/INI1-intact DDECs, respectively, whereas 47% of the BRG1/INI1-intact DDECs showed a mutated p53 staining pattern. In comparison, absent PAX8 expression and absent ER expression were each observed in the more solid area of 48% and 48% of grade 3 endometrioid carcinomas. CONCLUSIONS: The consistent absence of PAX8 and ER expression in molecularly defined (BRG1/INI1-deficient) DDECs suggests that the loss of PAX8 and ER expression is a fundamental feature of dedifferentiation. The frequent findings of a mutated p53 staining pattern in BRG1/INI1-intact DDECs indicate that BRG1/INI1-intact DDECs may be biologically different from BRG1/INI1-deficient tumours.
Assuntos
Biomarcadores Tumorais/análise , Carcinoma Endometrioide/patologia , DNA Helicases/deficiência , Neoplasias do Endométrio/patologia , Proteínas Nucleares/deficiência , Proteína SMARCB1/deficiência , Fatores de Transcrição/deficiência , Adulto , Idoso , Idoso de 80 Anos ou mais , Desdiferenciação Celular , Feminino , Humanos , Imuno-Histoquímica , Imunofenotipagem , Pessoa de Meia-Idade , Fator de Transcrição PAX8/análise , Fator de Transcrição PAX8/biossíntese , Receptores de Estrogênio/análise , Receptores de Estrogênio/biossíntese , Proteína Supressora de Tumor p53/análise , Proteína Supressora de Tumor p53/biossínteseRESUMO
Dedifferentiated endometrial carcinoma is an aggressive type of endometrial cancer that contains a mix of low-grade endometrioid and undifferentiated carcinoma components. We performed targeted sequencing of eight dedifferentiated carcinomas and identified somatic frameshift/nonsense mutations in SMARCA4, a core ATPase of the switch/sucrose non-fermenting (SWI/SNF) complex, in the undifferentiated components of four tumors. Immunohistochemical analysis confirmed the loss of SMARCA4 in the undifferentiated component of these four SMARCA4-mutated cases, whereas the corresponding low-grade endometrioid component showed retained SMARCA4 expression. An expanded survey of other members of the SWI/SNF complex showed SMARCB1 loss in the undifferentiated component of two SMARCA4-intact tumors, and all SMARCA4- or SMARCB1-deficient tumors showed concomitant loss of expression of SMARCA2. We subsequently examined the expression of SMARCA2, SMARCA4, and SMARCB1 in an additional set of 22 centrally reviewed dedifferentiated carcinomas and 31 grade 3 endometrioid carcinomas. Combining the results from the index and the expansion set, 15 of 30 (50%) of the dedifferentiated carcinomas examined showed either concurrent SMARCA4 and SMARCA2 loss (37%) or concurrent SMARCB1 and SMARCA2 loss (13%) in the undifferentiated component. The loss of SMARCA4 or SMARCB1 was mutually exclusive. All 31 grade 3 endometrioid carcinomas showed intact expression of these core SWI/SNF proteins. The majority (73%) of the SMARCA4/SMARCA2-deficient and half of SMARCB1/SMARCA2-deficient undifferentiated component developed in a mismatch repair-deficient molecular context. The observed spatial association between SWI/SNF protein loss and histologic dedifferentiation suggests that inactivation of these core SWI/SNF proteins may contribute to the development of dedifferentiated endometrial carcinoma.
Assuntos
Desdiferenciação Celular/fisiologia , Proteínas Cromossômicas não Histona/biossíntese , Neoplasias do Endométrio/patologia , Fatores de Transcrição/biossíntese , Idoso , Proteínas Cromossômicas não Histona/genética , Análise Mutacional de DNA , Neoplasias do Endométrio/genética , Neoplasias do Endométrio/mortalidade , Feminino , Humanos , Imuno-Histoquímica , Estimativa de Kaplan-Meier , Pessoa de Meia-Idade , Análise de Sequência com Séries de Oligonucleotídeos , Análise Serial de Tecidos , Fatores de Transcrição/genéticaRESUMO
Using a combination of biochemical, structural probing and rapid kinetics techniques we reveal for the first time that the universally conserved translational GTPase (trGTPase) HflX binds to the E-site of the 70S ribosome and that its GTPase activity is modulated by peptidyl transferase centre (PTC) and peptide exit tunnel (PET) binding antibiotics, suggesting a previously undescribed mode of action for these antibiotics. Our rapid kinetics studies reveal that HflX functions as a ribosome splitting factor that disassembles the 70S ribosomes into its subunits in a nucleotide dependent manner. Furthermore, our probing and hydrolysis studies show that the ribosome is able to activate trGTPases bound to its E-site. This is, to our knowledge, the first case in which the hydrolytic activity of a translational GTPase is not activated by the GTPase activating centre (GAC) in the ribosomal A-site. Furthermore, we provide evidence that the bound state of the PTC is able to regulate the GTPase activity of E-site bound HflX.
Assuntos
Proteínas de Escherichia coli/metabolismo , GTP Fosfo-Hidrolases/metabolismo , Proteínas de Ligação ao GTP/metabolismo , Proteínas Ativadoras de GTPase/genética , Ribossomos/genética , Sítios de Ligação/genética , Escherichia coli/genética , Proteínas de Escherichia coli/genética , GTP Fosfo-Hidrolases/genética , Proteínas de Ligação ao GTP/genética , Proteínas Ativadoras de GTPase/metabolismo , Hidrólise , Cinética , Peptidil Transferases/genética , Peptidil Transferases/metabolismo , Ligação Proteica , Ribossomos/enzimologiaRESUMO
The universally conserved GTPase HflX is a putative translation factor whose GTPase activity is stimulated by the 70S ribosome as well as the 50S but not the 30S ribosomal subunit. However, the details and mechanisms governing this interaction are only poorly understood. In an effort to further elucidate the functional mechanism of HflX, we examined its interaction with the 70S ribosome, the two ribosomal subunits (50S and 30S), as well as its ability to interact with guanine nucleotides in the respective ribosomal complexes using a highly purified in vitro system. Binding studies reported here demonstrate that HflX not only interacts with 50S and 70S particles, but also with the 30S subunit, independent of the nucleotide-bound state. A detailed pre-steady-state kinetic analysis of HflX interacting with a non-hydrolyzable analog of mant-GTP, coupled with an enzymatic probing assay utilizing limited trypsinolysis, reveal that HflX·GTP exists in a structurally distinct 50S- and 70S-bound form that stabilizes GTP binding up to 70 000-fold and that may represent the "GTPase-activated" state. This activation is likely required for efficient GTP-hydrolysis, and may be similar to that observed in elongation factor G. Results reported here address the surprising low affinity of free HflX for GTP and suggest that cellular HflX will mainly exist in the HflX·GTP·ribosome-bound form. A minimal model for the functional cycle of HflX is proposed.