SCATTER FACTOR PROTECTS EPITHELIAL AND CARCINOMA-CELLS AGAINST APOPTOSIS INDUCED BY DNA-DAMAGING AGENTS

Scatter factor (SF) (hepatocyte growth factor) is a cytokine that may play a role in human breast cancer invasiveness and angiogenesis, We n ow report that SF can block the induction of apoptosis by various DNA damaging-agents, including cytotoxic agents used in breast cancer ther apy. SF protected MDA-MB-453 human breast cancer cells, EMT6 mouse mam mary tumor cells and MDCK renal epithelial cells against apoptosis ind uced by adriamycin (ADR), X-rays, ultraviolet radiation, and other age nts. Protection was observed in assays of DNA fragmentation, cell viab ility (;MTT), and clonogenic survival. Protection of MDA-MB-453 cells against ADR was dose- and time-dependent; maximal protection required pre-incubation with 75-100 ng/ml of SF for 48 h or more. Protection re quired functional SF receptor (c-Met), but was not dependent on p53. W estern blotting analysis revealed that pre-treatment of MDA-MB-453 cel ls with SF inhibited the ADR-induced decreases in the levels of Bcl-X- L, an anti-apoptotic protein related to Bcl-2; and the dose-response a nd time course characteristics for SF-mediated increases in the Bcl-X- L protein levels of ADR-treated cells were consistent with the degrees of protection against apoptosis observed under the same conditions. F urthermore, Bcl-X-L levels were not down-regulated by ADR in MDA-MB-23 1 breast cancer cells, consistent with the finding that SF failed to p rotect these cells against ADR, despite the fact that they contain fun ctional c-Mrt receptor. In contrast to Bcl-X-L, SF blocked ADR-induced increases in c-Myc and inhibited the expression of p2(WAF1/CIP1) and of the BRCA1 protein in MDA-MB-453 cells. However, SF did not cause si gnificant changes in the cell cycle distribution of ADR-treated cells. These findings suggest that SF-mediated protection of human breast ca ncer cells may involve inhibition of one or more pathways required for the activation of apoptosis and may particularly target the anti-apop totic mitochondrial membrane pore-forming protein Bcl-X-L as a compone nt of the protective mechanism. By implication, the accumulation of SF within human breast cancers may contribute to the development of a ra dio- or chemoresistant phenotype.