RESUMO
Williams-Beuren syndrome (WBS), an autosomal dominant genetic disorder, is characterized by a unique cognitive profile and craniofacial defects. WBS results from a microdeletion at the chromosomal location 7q11.23 that encompasses the genes encoding the members of TFII-I family of transcription factors. Given that the haploinsufficiency for TFII-I is causative to the craniofacial phenotype in humans, we set out to analyze the effect of post-transcriptional silencing of TFII-I during BMP-2-driven osteoblast differentiation in the C2C12 cell line. Our results show that TFII-I plays an inhibitory role in regulating genes that are essential in osteogenesis and intersects with the bone-specific transcription factor Runx2 and the retinoblastoma protein, pRb. Identification of pathways regulated by TFII-I family transcription factors may begin to shed light on the molecular determinants of WBS.
Assuntos
Antígenos de Diferenciação/biossíntese , Osteoblastos/metabolismo , Osteogênese , Interferência de RNA , Fatores de Transcrição TFII/metabolismo , Síndrome de Williams/metabolismo , Animais , Antígenos de Diferenciação/genética , Proteína Morfogenética Óssea 2/farmacologia , Células COS , Diferenciação Celular/efeitos dos fármacos , Diferenciação Celular/genética , Chlorocebus aethiops , Deleção Cromossômica , Cromossomos Humanos Par 7/genética , Cromossomos Humanos Par 7/metabolismo , Subunidade alfa 1 de Fator de Ligação ao Core/biossíntese , Subunidade alfa 1 de Fator de Ligação ao Core/genética , Humanos , Camundongos , Células NIH 3T3 , Proteína do Retinoblastoma/biossíntese , Proteína do Retinoblastoma/genética , Fatores de Transcrição TFII/genética , Síndrome de Williams/genéticaRESUMO
The multifunctional transcription factor TFII-I is tyrosine phosphorylated in response to extracellular growth signals and transcriptionally activates growth-promoting genes. However, whether activation of TFII-I also directly affects the cell cycle profile is unknown. Here we show that under normal growth conditions, TFII-I is recruited to the cyclin D1 promoter and transcriptionally activates this gene. Most strikingly, upon cell cycle arrest resulting from genotoxic stress and p53 activation, TFII-I is ubiquitinated and targeted for proteasomal degradation in a p53- and ATM (ataxia telangiectasia mutated)-dependent manner. Consistent with a direct role of TFII-I in cell cycle regulation and cellular proliferation, stable and ectopic expression of wild-type TFII-I increases cyclin D1 levels, resulting in accelerated entry to and exit from S phase, and overcomes p53-mediated cell cycle arrest, despite radiation. We further show that the transcriptional regulation of cyclin D1 and cell cycle control by TFII-I are dependent on its tyrosine phosphorylation at positions 248 and 611, sites required for its growth signal-mediated transcriptional activity. Taken together, our data define TFII-I as a growth signal-dependent transcriptional activator that is critical for cell cycle control and proliferation and further reveal that genotoxic stress-induced degradation of TFII-I results in cell cycle arrest.