A novel function of SMC1 as a transporter of xenobiotics.

Abstract

e14107 Background: Structural Maintenance of Chromosome 1 (SMC1) is a component of the cohesin complex involved in the DNA-damage repair. Studies have shown that it is overexpressed in Colon Ca, Glioblastoma ,Triple-negative breast cancer (TNBC) and contributes to their characteristic drug resistance. Because of its structural homology to the ABC-membrane transporter proteins (mediate multi-drug resistance in cancer cells by catalyzing ATP-dependent efflux of many structurally unrelated amphiphilic xenobiotics) and because of its marked over-expression in tissues of knockout mice lacking the other known transporter RLIP76 (RALBP1), the present studies were directed at determining whether SMC1 was present in plasma membrane and could function as a multi-drug transporter capable of mediating multi-drug resistance. Methods: The intracellular localization of SMC1 was performed by immunocytochemistry in fixed and live H358 cells (human non small cell lung cancer cells). We demonstrated, for the first time that SMC1 can be purified to apparent homogeneity using a GS-E affinity chromatography method. Transport activity of SMC1 was tested by reconstituting purified SMC1 into artificial liposomes, later transfected into H358 and TNBC cells with confirmed SMC1 overexpression. Accumulation and efflux of amphiphilic chemo drugs were compared to control cells. Results: Immunofixation studies demonstrated no detectable immunological cross-reactivity between SMC1 and Ralbp1.SMC1 was found in the plasma membrane ,cytosol and nucleus.The uptake of Doxorubicin and Vinblastine in transfected cells was significantly lower and were two-fold resistant to DOX as compared with controls. These cells, when treated with SMC1 antibody/antisense also confirmed increased drug cytotoxicity as well as apoptosis. Conclusions: This study provides convincing evidence for the distribution of SMC1 in the plasma membrane, cytosol, and nucleus. It functions as a drug-transporter reducing intracellular accumulation of chemotherapy drugs in cancer cells.These findings indicate a dual role in defending these from apoptosis and suggest that strategies aimed at inhibiting SMC1 could be useful in reversing intrinsic or acquired drug-resistance of cancer cells.