title: Subunit S5a of the 26S proteasome is regulated by antiapoptotic signals.
abstract: We performed a functional genetic screen to find novel antiapoptotic genes that are under the regulation of the oncoprotein c-Src. Several clones were identified, including subunit S5a of the 26S proteasome. We found that S5a rescued Saos-2 cells from apoptosis induced by Src inhibitor 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1). S5a mRNA and protein levels were downregulated as a result of Src inhibition, either by siRNA or PP1. In cell lines that possess high activity of Src S5a levels were elevated. Cloning of the S5a promoter region showed that S5a transcription responds to several stimuli. Analysis of the promoter sequence revealed a binding site for Tcf/Lef-1 transcription factor. Indeed, beta-catenin significantly induced transcription from the S5a promoter, whereas EMSA studies showed that Lef-1 binds the S5a promoter-binding site. Furthermore, we also found that PP1 and LY294002, but not PD98059 inhibit the S5a promoter activity. These results suggest that S5a is regulated during apoptosis at the transcriptional level and that S5a upregulation by antiapoptotic signals can contribute to cell survival.
authors: The Hebrew University, Department of Biological Chemistry, Silberman Institute, Givat Ram, Jerusalem 91904, Israel.
authors: Yael
authors: Y
authors: Gus
authors: Rotem
authors: R
authors: Karni
authors: Alexander
authors: A
authors: Levitzki
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000502:physiology; D009025:Morpholines / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism* / Q000502:physiology*; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D016601:RNA-Binding Proteins; D015854:Up-Regulation; D051176:beta Catenin / Q000494:pharmacology; D019061:src-Family Kinases / Q000502:physiology*
chemical_list: C108123:4-amino-5-(4-methylphenyl)-7-(tert-butyl)pyrazolo(3,4-d)pyrimidine; D002867:Chromones; D005419:Flavonoids; D020672:I-kappa B Proteins; D051821:Lymphoid Enhancer-Binding Factor 1; D009025:Morpholines; C498506:PSMD4 protein, human; D011720:Pyrazoles; D011743:Pyrimidines; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D051176:beta Catenin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D019061:src-Family Kinases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one