Sumo and Ubiquitin Ligases Regulate Hepatocyte Nuclear Factor - 1 Beta Transcriptional Activity

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Title: Sumo and Ubiquitin Ligases Regulate Hepatocyte Nuclear Factor - 1 Beta Transcriptional Activity
Author: McNally, Brian Timothy
Abstract: Hepatocyte nuclear factor -1beta (HNF -1β ) is a homeodomain -containing transcription factor that regulates tissue -specific gene expression in the kidney , liver , and other organs . Humans with heterozygous mutations of HNF -1β develop maturity -onset diabetes of the young type 5 (MODY5 ) associated with cystic abnormalities of the kidney . A yeast two -hybrid screen was performed to identify proteins that interact with HNF -1β The SUMO E2 ligase , Ubc9 , SUMO E3 ligases , PIAS1 and PIASgamma , and the ubiquitin E3 ligase , Arkadia , were isolated as putative interacting proteins . SUMOylation of transcription factors affects their subcellular localization , intracellular transport , stability , and transcriptional activity . Ubiquitination of transcription factors has been shown to alter their stability and transcriptional activity . Immunostaining of the adult mouse kidney showed that HNF -1β co -localized with Ubc9 , PIAS1 , and PIASgamma in the nuclei of renal tubular epithelial cells . Immunostaining also showed that Arkadia localized to the nuclei of renal tubules . Overexpression of Ubc9 , PIAS1 , or PIASgamma inhibited the activity of the Pkhd1 promoter , a known HNF -1β target . Expression of catalytically inactive Ubc9 or PIASgamma mutants also inhibited Pkhd1 promoter activity , suggesting that repression of HNF -1β transcriptional activity is SUMOylation -independent . In contrast to the repressive effect of SUMO ligases , overexpression of Arkadia stimulated Pkhd1 promoter activity in an HNF -1β ; -dependent fashion . Immunoprecipitation of epitope -tagged SUMO or ubiquitin resulted in co -precipitation of HNF -1β , indicating that HNF -1β is both SUMOylated and ubiquitinated in vivo . In summary , the E2 and E3 SUMO ligases Ubc9 , PIAS1 , and PIASgamma repressed HNF -1β transcriptional activity via SUMOylation -dependent and -independent mechanisms . The E3 ubiquitin ligase Arkadia stimulated HNF -1β transcriptional activity .Together , these results demonstrated that HNF -1β is covalently modified by SUMO and ubiquitin , and these modifications had opposing effects on HNF -1β transcriptional activity . In addition , insights into the regulation of HNF -1β and ubsequent effects on target gene expression may lead to a greater understanding of the mechanisms that lead to renal cystogenesis .
URI: http : / /hdl .handle .net /2152 .5 /279
Date: 2007-05-27

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Sumo and Ubiquitin Ligases Regulate Hepatocyte Nuclear Factor - 1 Beta Transcriptional Activity. Graduate School of Biomedical Sciences. Available electronically from http : / /hdl .handle .net /2152 .5 /279 .

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