Biomedical subjects

Jeffrey Hildebrand

Publications and source records attributed to Jeffrey Hildebrand.

3 recordsLinked to original sources

PubMed2003

Homeodomain interacting protein kinase 2 promotes apoptosis by downregulating the transcriptional corepressor CtBP.

Genetic knockout of the transcriptional corepressor CtBP in mouse embryo fibroblasts upregulates several genes involved in apoptosis. We predicted, therefore, that a propensity toward apoptosis might be regulated through changes in cellular CtBP. To identify pathways involved in this regulation, we screened a mouse embryo cDNA library with an E1A-CtBP complex and identified the homeodomain interacting protein kinase 2 (HIPK2), which had previously been linked to UV-directed apoptosis through its ability to phosphorylate p53. Expression of HIPK2 or exposure to UV irradiation reduced CtBP levels via a proteosome-mediated pathway. The UV effect was prevented by coexpression of kinase-inactive HIPK2 or reduction in HIPK2 levels via siRNA. Mutation of the residue phosphorylated by HIPK2 prevented UV- and HIPK2-directed CtBP clearance. Finally, reduction in CtBP levels, either by genetic knockout or siRNA, promoted apoptosis in p53-deficient cells. These findings provide a pathway for UV-induced apoptosis in cells lacking p53.

Alcohol Oxidoreductases↗

PubMed2003

C-terminal-binding protein corepresses epithelial and proapoptotic gene expression programs.

The genesis of carcinoma cells often involves epithelial-to-mesenchymal transitions and the acquisition of apoptosis resistance, but it is unclear whether these alterations are controlled coordinately or independently. Our previously reported effects of adenovirus E1a in human tumor cells raised the possibility that the E1a-interacting corepressor protein C-terminal-binding protein (CtBP) might selectively repress epithelial cell adhesion and proapoptotic genes. Here, we report that CtBP-knockout cells were hypersensitive to apoptosis. Correspondingly, microarray analysis of CtBP-knockout vs. CtBP-rescued mouse embryo fibroblasts revealed that many epithelial-specific and proapoptotic genes were indeed regulated by CtBP. Neither the apoptosis nor the repression activities of CtBP required histidine-315, suggesting that the proposed dehydrogenase activity is not essential for CtBP function. The results presented herein establish two functional roles of CtBP: to corepress epithelial genes, thus permitting epithelial-to-mesenchymal transitions, and to modulate the cellular threshold for apoptotic responses.

Alcohol Oxidoreductases↗

PubMed2003

Opposed regulation of corepressor CtBP by SUMOylation and PDZ binding.

The transcription corepressor CtBP is often recruited to the target promoter via interaction with a conserved PxDLS motif in the interacting repressor. In this study, we demonstrate that CtBP1 was SUMOylated and that its SUMOylation profoundly affected its subcellular localization. SUMOylation occurred at a single Lys residue, Lys428, of CtBP1. CtBP2, a close homolog of CtBP1, lacked the SUMOylation site and was not modified by SUMO-1. Mutation of Lys428 into Arg (K428R) shifted CtBP1 from the nucleus to the cytoplasm, while it had little effect on its interaction with the PxDLS motif. Consistent with a change in localization, the K428R mutation abolished the ability of CtBP1 to repress the E-cadherin promoter activity. Notably, SUMOylation of CtBP1 was inhibited by the PDZ domain of nNOS, correlating with the known inhibitory effect of nNOS on the nuclear accumulation of CtBP1. This study identifies SUMOylation as a regulatory mechanism underlying CtBP1-dependent transcriptional repression.

Alcohol Oxidoreductases↗