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Scatter factor protects epithelial and carcinoma cells against apoptosis induced by DNA-damaging agents
1Department of Radiation Oncology, Long Island Jewish Medical Center, The Long Island Campus for the Albert Einstein College of Medicine, New Hyde Park, New York 11040, USA.
Abstract:
Scatter factor (SF) (hepatocyte growth factor) is a cytokine that may play a role in human breast cancer invasiveness and angiogenesis. We now report that SF can block the induction of apoptosis by various DNA damaging-agents, including cytotoxic agents used in breast cancer therapy. SF protected MDA-MB-453 human breast cancer cells, EMT6 mouse mammary tumor cells and MDCK renal epithelial cells against apoptosis induced by adriamycin (ADR), X-rays, ultraviolet radiation, and other agents. Protection was observed in assays of DNA fragmentation, cell viability (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 required functional SF receptor (c-Met), but was not dependent on p53. Western blotting analysis revealed that pre-treatment of MDA-MB-453 cells with SF inhibited the ADR-induced decreases in the levels of Bcl-XL, an anti-apoptotic protein related to Bcl-2; and the dose-response and time course characteristics for SF-mediated increases in the Bcl-XL protein levels of ADR-treated cells were consistent with the degrees of protection against apoptosis observed under the same conditions. Furthermore, Bcl-XL levels were not down-regulated by ADR in MDA-MB-231 breast cancer cells, consistent with the finding that SF failed to protect these cells against ADR, despite the fact that they contain functional c-Met receptor. In contrast to Bcl-XL, SF blocked ADR-induced increases in c-Myc and inhibited the expression of p21WAF1/CIP1 and of the BRCA1 protein in MDA-MB-453 cells. However, SF did not cause significant changes in the cell cycle distribution of ADR-treated cells. These findings suggest that SF-mediated protection of human breast cancer cells may involve inhibition of one or more pathways required for the activation of apoptosis and may particularly target the anti-apoptotic mitochondrial membrane pore-forming protein Bcl-XL as a component of the protective mechanism. By implication, the accumulation of SF within human breast cancers may contribute to the development of a radio- or chemoresistant phenotype.
Insights
Scatter factor (SF) blocks apoptosis in breast cancer cells treated with chemotherapy agents. This protection, mediated by the SF receptor (c-Met) and Bcl-XL, may contribute to radio- and chemoresistance.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Signaling
Background:
- Scatter factor (SF), also known as hepatocyte growth factor, is implicated in breast cancer invasiveness and angiogenesis.
- Apoptosis induction by DNA-damaging agents is a key mechanism in breast cancer therapy.
Purpose of the Study:
- To investigate the role of SF in protecting breast cancer cells from apoptosis induced by DNA-damaging agents.
- To elucidate the molecular mechanisms underlying SF-mediated protection, including the involvement of SF receptor (c-Met) and apoptosis-related proteins.
Main Methods:
- Exposure of human breast cancer cells (MDA-MB-453, MDA-MB-231), mouse mammary tumor cells (EMT6), and renal epithelial cells (MDCK) to various DNA-damaging agents (adriamycin, X-rays, UV radiation) with or without SF pre-treatment.
- Assessment of apoptosis using assays for DNA fragmentation, cell viability (MTT), and clonogenic survival.
- Western blotting analysis to evaluate the expression levels of apoptosis-related proteins (Bcl-XL, c-Myc, p21WAF1/CIP1, BRCA1) and receptor tyrosine kinase (c-Met).
Main Results:
- SF significantly protected MDA-MB-453, EMT6, and MDCK cells against apoptosis induced by adriamycin (ADR), X-rays, and UV radiation in a dose- and time-dependent manner.
- SF-mediated protection required a functional SF receptor (c-Met) but was independent of p53.
- SF inhibited ADR-induced decreases in Bcl-XL, an anti-apoptotic protein, and blocked increases in c-Myc, p21WAF1/CIP1, and BRCA1 expression, suggesting a role in regulating apoptotic pathways.
Conclusions:
- SF confers protection to breast cancer cells against DNA-damaging agents by inhibiting key apoptotic pathways, potentially involving the anti-apoptotic protein Bcl-XL.
- SF-mediated protection may contribute to the development of radio- and chemoresistance in human breast cancers.
- Targeting SF or its downstream effectors could be a strategy to overcome therapeutic resistance in breast cancer.