NUCLEOTIDE EXCISION-REPAIR IS NOT REQUIRED FOR THE ANTIAPOPTOTIC FUNCTION OF INSULIN-LIKE-GROWTH-FACTOR-1

The expression of ERCC1, a member of the nucleotide excision repair (N ER) family, is enhanced in cells transfected with insulin-like growth factor 1 (IGF-1) receptors. Of interest, an excellent concordance betw een ERCC1 expression and NER-mediated cell survival has been demonstra ted. The two aims of the present study were to determine the signaling pathways used by IGF-1 to confer protection against apoptotic cell de ath in Chinese hamster ovary (CHO) cells and to assess the role of NER in this IGF-1 action. Experiments with pharmacological inhibitors ind icated that phosphatidylinositol 3-kinase (PI 3-kinase) but not mitoge n-activated protein kinase (ERK1/ERK2) mediates IGF-1 antiapoptotic ac tivity. Using two series of CHO cells that have altered expression of ERCC1 or XPB/ERCC3, we examined IGF-1's ability to delay apoptotic dea th and reduction of mitochondrial oxidative function mediated by growt h factor withdrawal. IGF-1 effectively blocked apoptosis, concomitant with increased MTT activity, in a pair of CHO cell lines expressing in active ERCC1 (43-3B cells) and the transfected line of the mutant carr ying the expressed human ERCC1 gene (83-G5 cells). Similarly, repair-d eficient UV24 cells, which lack XPB/ERCC3, and their parental line AA8 were also responsive to the IGF-1's antiapoptotic capacity. In the pr esence of IGF-1, these cell lines became resistant to the cleavage of poly(ADP-ribose) polymerase, a key player in DNA damage recognition an d DNA repair. These results suggest that PI 3-kinase activation plays a determinant role in the antiapoptotic function of IGF-1, but that fu nctional NER does not play a critical part in mediating this IGF-1 res ponse. (C) 1998 Academic Press.