RESUMO
ABSTRACT: Fibrinogen, involved in coagulation, is a soluble protein composed of two sets of disulfide-bridged Aα, Bß, and γ-chains. In this review, we present the clinical implications of the αC domain of the molecule in Alzheimer's disease, hereditary renal amyloidosis and a number of thrombotic and hemorrhagic disorders. In Alzheimer's disease, amyloid beta peptide (Aß) is increased and binds to the αC domain of normal fibrinogen, triggering increased fibrin(ogen) deposition in patients' brain parenchyma. In hereditary renal amyloidosis, fibrinogen is abnormal, with mutations located in the fibrinogen αC domain. The mutant αC domain derived from fibrinogen degradation folds incorrectly so that, in time, aggregates form, leading to amyloid deposits in the kidneys. In these patients, no thrombotic tendency has been observed. Abnormal fibrinogens with either a point mutation in the αC domain or a frameshift mutation resulting in absence of a part of the αC domain are often associated with either thrombotic events or bleeding. Mutation of an amino acid into cysteine (as in fibrinogens Dusart and Caracas V) or a frameshift mutation yielding an unpaired cysteine in the αC domain is often responsible for thrombotic events. Covalent binding of albumin to the unpaired cysteine via a disulphide bridge leads to decreased accessibility to the fibrinolytic enzymes, hence formation of poorly degradable fibrin clots, which explains the high incidence of thrombosis. In contrast, anomalies due to a frameshift mutation in the αC connector of the molecule, provoking deletion of a great part of the αC domain, are associated with bleeding.
RESUMO
MicroRNAs (miRNAs) in the AGO-containing RISC complex control messenger RNA (mRNA) translation by binding to mRNA 3' untranslated region (3'UTR). The relationship between miRNAs and other regulatory factors that also bind to mRNA 3'UTR, such as CPEB1 (cytoplasmic polyadenylation element-binding protein), remains elusive. We found that both CPEB1 and miR-15b control the expression of WEE1, a key mammalian cell cycle regulator. Together, they repress WEE1 protein expression during G1 and S-phase. Interestingly, the 2 factors lose their inhibitory activity at the G2/M transition, at the time of the cell cycle when WEE1 expression is maximal, and, moreover, rather activate WEE1 translation in a synergistic manner. Our data show that translational regulation by RISC and CPEB1 is essential in cell cycle control and, most importantly, is coordinated, and can be switched from inhibition to activation during the cell cycle.
Assuntos
Proteínas de Ciclo Celular/metabolismo , MicroRNAs/fisiologia , Proteínas Nucleares/metabolismo , Proteínas Tirosina Quinases/metabolismo , Fatores de Transcrição/fisiologia , Fatores de Poliadenilação e Clivagem de mRNA/fisiologia , Sequência de Bases , Proteínas de Ciclo Celular/genética , Pontos de Checagem da Fase G2 do Ciclo Celular , Células HeLa , Humanos , Proteínas Nucleares/genética , Proteínas Tirosina Quinases/genética , Interferência de RNARESUMO
PLZF, the promyelocytic leukaemia zinc-finger protein, is a transcriptional repressor essential to development. In some acute leukaemias, a chromosomal translocation fusing the PLZF gene to that encoding the retinoic acid receptor RARalpha gives rise to a fusion protein, PLZF-RARalpha, thought to be responsible for constitutive repression of differentiation-associated genes in these cells. Repression by both PLZF and PLZF-RARalpha is sensitive to the histone deacetylase inhibitor TSA, and PLZF was previously shown to interact physically with HDAC1, a class I histone deacetylase. We here asked whether class II histone deacetylases, known to be generally involved in differentiation processes, participate in the repression mediated by PLZF and PLZF-RARalpha, and found that PLZF interacts with HDAC4 in both GST-pull-down and co-immunoprecipitation assays. Furthermore, HDAC4 is indeed involved in PLZF and PLZF-RARalpha-mediated repression, since an enzymatically dead mutant of HDAC4 released the repression, as did an siRNA that blocks HDAC4 expression. Taken together, our data indicate that recruitment of HDAC4 is necessary for PLZF-mediated repression in both normal and leukaemic cells.
Assuntos
Proteínas de Ligação a DNA/fisiologia , Histona Desacetilases/fisiologia , Leucemia Promielocítica Aguda/metabolismo , Proteínas Repressoras/fisiologia , Fatores de Transcrição/fisiologia , Transcrição Gênica/fisiologia , Animais , Células HeLa , Humanos , Imuno-Histoquímica , Fatores de Transcrição Kruppel-Like , Camundongos , Células NIH 3T3 , Proteínas de Neoplasias/fisiologia , Proteínas de Fusão Oncogênica/fisiologia , Proteína com Dedos de Zinco da Leucemia PromielocíticaRESUMO
Deciphering the mechanisms underlying skeletal muscle differentiation in mammals is an important challenge. Cell differentiation involves complex pathways regulated at both transcriptional and post-transcriptional levels. Recent observations have revealed the importance of small (20-25 base pairs) non-coding RNAs (microRNAs or miRNAs) that are expressed in both lower organisms and in mammals. miRNAs modulate gene expression by affecting mRNA translation or stability. In lower organisms, miRNAs are essential for cell differentiation during development; some miRNAs are involved in maintenance of the differentiated state. We have shown that miR-181, a microRNA that is strongly upregulated during differentiation, participates in establishing the muscle phenotype. Moreover, our results suggest that miR-181 downregulates the homeobox protein Hox-A11 (a repressor of the differentiation process), thus establishing a functional link between miR-181 and the complex process of mammalian skeletal muscle differentiation. Therefore, miRNAs can be involved in the establishment of a differentiated phenotype - even when they are not expressed in the corresponding fully differentiated tissue.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento/genética , MicroRNAs/genética , Desenvolvimento Muscular/genética , Músculo Esquelético/citologia , Animais , Proteínas Argonautas/fisiologia , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Proteínas de Homeodomínio/fisiologia , Humanos , Mamíferos , Camundongos , Músculo Esquelético/embriologia , Músculo Esquelético/metabolismo , Mioblastos/citologia , Oligonucleotídeos Antissenso/farmacologia , Interferência de RNA , Complexo de Inativação Induzido por RNA/genética , Ribonuclease III/fisiologiaRESUMO
Acetylation is a post-translational modification that influences the activity of numerous proteins in vitro. Among them, the myogenic transcription factor MyoD shows an increased transcriptional activity in vitro when acetylated on two lysines (K): lysines 99 and 102. Here, we have investigated the biological relevance of this acetylation in vivo. Using specific antibodies, we show that endogenous MyoD is acetylated on lysines 99 and 102 in myoblasts. Moreover, we show the functional importance of acetylation in live animals by using a mutant of MyoD in which lysines 99 and 102 were replaced by arginines (R). Knock-in embryos homozygous for the MyoD(R99,102) allele expressed slightly reduced levels of MyoD but developed normally. However, the knock-in homozygous adult mice showed a phenotype that was almost identical to that of MyoD-knockout animals, including delayed muscle regeneration in vivo and an increased number of myoblasts but with reduced differentiation potential in vitro. Together, these results show the importance of MyoD acetylation for adult myogenesis.
Assuntos
Células-Tronco Embrionárias/metabolismo , Desenvolvimento Muscular , Músculo Esquelético/fisiologia , Proteína MyoD/fisiologia , Mioblastos/metabolismo , Acetilação , Alelos , Animais , Diferenciação Celular , Proliferação de Células , Células Cultivadas , Homozigoto , Lisina/metabolismo , Camundongos , Camundongos Transgênicos , Músculo Esquelético/embriologia , Músculo Esquelético/metabolismo , Proteína MyoD/genética , Proteína MyoD/metabolismo , Fenótipo , TransfecçãoRESUMO
Tumor necrosis factor-alpha (TNF-alpha) and lymphotoxin-beta receptor (LTbetaR) signaling both play important roles in inflammatory and immune responses through activation of NF-kappaB. Using various deficient mouse embryonic fibroblast cells, we have compared the signaling pathways leading to NF-kappaB induction in response to TNF-alpha and LTbetaR activation. We demonstrate that LTbetaR ligation induces not only RelA/p50 dimers but also RelB/p50 dimers, whereas TNF-alpha induces only RelA/p50 dimers. LTbetaR-induced binding of RelB/p50 requires processing of p100 that is mediated by IKKalpha but is independent of IKKbeta, NEMO/IKKgamma, and RelA. Moreover, we show that RelB, p50, and p100 can associate in the same complex and that TNF-alpha but not LTbeta signaling increases the association of p100 with RelB/p50 dimers in the nucleus, leading to the specific inhibition of RelB DNA binding. These results suggest that the alternative NF-kappaB pathway based on p100 processing may account not only for the activation of RelB/p52 dimers but also for that of RelB/p50 dimers and that p100 regulates the binding activity of RelB/p50 dimers via at least two distinct mechanisms depending on the signaling pathway involved.