The xeroderma pigmentosum group E gene product DDB2 is a specific target of cullin 4A in mammalian cells.
The damaged-DNA binding protein DDB consists of two subunits, DDB1 (127 kDa) and DDB2 (48 kDa). Mutations in the DDB2 subunit have been detected in patients suffering from the repair deficiency disease xeroderma pigmentosum (group E). In addition, recent studies suggested a role for DDB2 in global genomic repair. DDB2 also exhibits transcriptional activity. We showed that expression of DDB1 and DDB2 stimulated the activity of the cell cycle regulatory transcription factor E2F1. Here we show that DDB2 is a cell cycle-regulated protein. It is present at a low level in growth-arrested primary fibroblasts, and after release the level peaks at the G(1)/S boundary. The cell cycle regulation of DDB2 involves posttranscriptional mechanisms. Moreover, we find that an inhibitor of 26S proteasome increases the level of DDB2, suggesting that it is regulated by the ubiquitin-proteasome pathway. Our previous study indicated that the cullin family protein Cul-4A associates with the DDB2 subunit. Because cullins are involved in the ubiquitin-proteasome pathway, we investigated the role of Cul-4A in regulating DDB2. Here we show that DDB2 is a specific target of Cul-4A. Coexpression of Cul-4A, but not Cul-1 or other highly related cullins, increases the ubiquitination and the decay rate of DDB2. A naturally occurring mutant of DDB2 (2RO), which does not bind Cul-4A, is not affected by coexpression of Cul-4A. Studies presented here identify a specific function of the Cul-4A gene, which is amplified and overexpressed in breast cancers.
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Department of Biochemistry and Molecular Biology (M/C 536), University of Illinois at Chicago, Chicago, Illinois 60612, USA.
Bondar
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Shiv
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Raychaudhuri
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D000818:Animals; D015153:Blotting, Western; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D044842:Cullin Proteins; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004260:DNA Repair; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005347:Fibroblasts / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D009363:Neoplasm Proteins / Q000378:metabolism*; D010447:Peptide Hydrolases; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012323:RNA Processing, Post-Transcriptional; D012260:Ribonucleases / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D014452:Ubiquitins / Q000494:pharmacology
C114234:CUL4A protein, human; D018797:Cell Cycle Proteins; D044842:Cullin Proteins; C091435:DDB1 protein, human; C117669:DDB2 protein, human; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D009363:Neoplasm Proteins; D011500:Protein Synthesis Inhibitors; D014157:Transcription Factors; D014452:Ubiquitins; D004247:DNA; D003513:Cycloheximide; D012260:Ribonucleases; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease