epidermal-growth-factor and Xeroderma-Pigmentosum

XPG is a causative gene underlying the photosensitive disorder xeroderma pigmentosum group G (XP-G) and is involved in nucleotide excision repair. Here, we show that XPG knockdown represses epidermal growth factor (EGF)-induced FOS transcription at the level of transcription elongation with little effect on EGF signal transduction. XPG interacted with transcription elongation factors in concert with TFIIH, suggesting that the XPG-TFIIH complex serves as a transcription elongation factor. The XPG-TFIIH complex was recruited to promoter and coding regions of both EGF-induced (FOS) and housekeeping (EEF1A1) genes. Further, EGF-induced recruitment of RNA polymerase II and TFIIH to FOS was reduced by XPG knockdown. Importantly, EGF-induced FOS transcription was markedly lower in XP-G/Cockayne syndrome (CS) cells expressing truncated XPG than in control cells expressing wild-type (WT) XPG, with less significant decreases in XP-G cells with XPG nuclease domain mutations. In corroboration of this finding, both WT XPG and a missense XPG mutant from an XP-G patient were recruited to FOS upon EGF stimulation, but an XPG mutant mimicking a C-terminal truncation from an XP-G/CS patient was not. These results suggest that the XPG-TFIIH complex is involved in transcription elongation and that defects in this association may partly account for Cockayne syndrome in XP-G/CS patients.

Topics: Cell Line, Tumor; Cockayne Syndrome; DNA Repair; DNA-Binding Proteins; Endonucleases; Epidermal Growth Factor; HEK293 Cells; HeLa Cells; Humans; Nuclear Proteins; Peptide Elongation Factor 1; Promoter Regions, Genetic; Proto-Oncogene Proteins c-fos; RNA Polymerase II; Signal Transduction; Transcription Elongation, Genetic; Transcription Factors; Transcription Factors, TFIII; Xeroderma Pigmentosum

The purpose of the present study was to determine whether skin fibroblasts from individuals, either with an inherited predisposition to cancer or with genetic disorders usually associated with a high risk of cancer, can be oncogenically transformed in vitro by a tumor promoter alone. The effects of chronic and limited applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) on several properties that are associated with transformation were examined using skin fibroblasts from individuals with polyposis coli, a familial cancer syndrome, xeroderma pigmentosum, Fanconi's anemia, and trisomy 21. The results of this study show that TPA treatment induces similar changes on cellular morphology, growth rate, saturation density, epidermal growth factor binding, and cytoskeleton in fibroblasts from both normal and genetically predisposed individuals. None of these cell lines, however, acquired anchorage-independent growth or unlimited growth potential in culture after chronic application of TPA. These observations suggest clearly that skin fibroblasts from individuals with either a genetic predisposition to or a high risk of cancer may not exist in a preneoplastic or "initiated" state susceptible to oncogenic transformation by TPA alone and that the mechanism of genetically determined cancer induction may be different from that of chemical carcinogenesis.

Topics: Cell Adhesion; Cell Division; Cell Line; Cell Transformation, Neoplastic; Cytoskeleton; Disease Susceptibility; Down Syndrome; Epidermal Growth Factor; Fanconi Anemia; Female; Fibroblasts; Humans; Intestinal Polyps; Male; Neoplasms; Phorbols; Tetradecanoylphorbol Acetate; Trypsin; Xeroderma Pigmentosum