THE FANCONI ANEMIA POLYPEPTIDE, FAC, NORMALIZES p53 INDUCTION IN A TRANSFECTED HEMATOPOIETIC CELL LINE. • 930

Abstract

Fanconi anemia (FA) is an autosomal recessive disease marked by developmental defects, bone marrow failure, and cancer susceptibility. FA cells are hypersensitive to DNA crosslinking and alkylating agents and accumulate in the G2 phase of the cell cycle in response to these agents. FA cells also display genomic instability, suggesting a possible defect in the p53 pathway. To test the effect of heterologous expression of FAC cDNA upon drug-induced cytotoxicity, G2 accumulation, and p53 induction in FA cells, we compared two isogenic FA cells lines: HSC536N (mock), a FA type C cell line sensitive to MMC, and the same cell line transfected (corrected) with wild type FAC cDNA [HSC536N (+FAC)]. HSC536N (+FAC) cells showed a 30-fold increase in resistance to MMC concentration. Similarly, increases in resistance were observed following exposure to cisplatin, carboplatin and cyclophosphamide. In addition, HSC536N (+FAC) cells showed a two fold lower G2 accumulation following MMC treatment. To analyze the possible interaction of FAC with the p53 pathway, we analyzed p53 induction in mock and corrected cell lines following exposure to MMC. HSC536N (mock) cells induced p53 at lower MMC concentrations than HSC536N (corrected). Caffeine, a known G2 checkpoint inhibitor, not only inhibited G2 accumulation seen in both cell lines but also caused the resistant HSC536N (+FAC) to become as sensitive to MMC as HSC536N(mock) cell line. We conclude that the FAC protein has a specific cytoprotective effect and may function as a cell cycle related protein of G2 phase of the cell cycle.