RESUMO
The Wilms' tumor 1 protein WT1 is a transcriptional regulator that is involved in cell growth and differentiation. The transcriptional corepressor BASP1 interacts with WT1 and converts WT1 from a transcriptional activator to a repressor. Here, we demonstrate that the N-terminal myristoylation of BASP1 is required in order to elicit transcriptional repression at WT1 target genes. We show that myristoylated BASP1 binds to nuclear PIP2, which leads to the recruitment of PIP2 to the promoter regions of WT1-dependent target genes. BASP1's myristoylation and association with PIP2 are required for the interaction of BASP1 with HDAC1, which mediates the recruitment of HDAC1 to the promoter and elicits transcriptional repression. Our findings uncover a role for myristoylation in transcription, as well as a critical function for PIP2 in gene-specific transcriptional repression through the recruitment of histone deacetylase.
Assuntos
Núcleo Celular/metabolismo , Histona Desacetilase 1/metabolismo , Lipoilação/fisiologia , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Fosfatidilinositol 4,5-Difosfato/metabolismo , Proteínas Repressoras/metabolismo , Transcrição Gênica/fisiologia , Proteínas WT1/metabolismo , Núcleo Celular/genética , Histona Desacetilase 1/genética , Humanos , Células K562 , Proteínas de Membrana/genética , Proteínas do Tecido Nervoso/genética , Fosfatidilinositol 4,5-Difosfato/genética , Regiões Promotoras Genéticas/fisiologia , Ligação Proteica , Proteínas Repressoras/genética , Proteínas WT1/genéticaRESUMO
The Wilms' tumour suppressor protein WT1 plays a central role in the development of the kidney and also other organs. WT1 can act as a transcription factor with highly context-specific activator and repressor functions. We previously identified Brain Acid Soluble Protein 1 (BASP1) as a transcriptional cosuppressor that can block the transcriptional activation function of WT1. WT1 and BASP1 are co-expressed during nephrogenesis and both proteins ultimately become restricted to the podocyte cells of the adult kidney. Here, we have analysed the WT1/BASP1 complex in a podocyte precursor cell line that can be induced to differentiate. Chromatin immunoprecipitation revealed that WT1 and BASP1 occupy the promoters of the Bak, c-myc and podocalyxin genes in podocyte precursor cells. During differentiation-dependent upregulation of podocalyxin expression BASP1 occupancy of the podocalyxin promoter is reduced compared to that of WT1. In contrast, the repressive WT1/BASP1 occupancy of the c-myc and Bak promoters is maintained and these genes are downregulated during the differentiation process. We provide evidence that the regulation of BASP1 promoter occupancy involves the sumoylation of BASP1. Our results reveal a dynamic cooperation between WT1 and BASP1 in the regulation of gene expression during differentiation.