ATP-binding cassette subfamily C (ABCC) transporter 1 (ABCC1) and 4 (ABCC4) independent of their drug efflux ability affects breast cancer biology

Abstract

Breast cancer treatment has been a challenge to date, due in part to cancer cells acquiring drug resistance. One of the mechanisms by which resistance can occur is the overexpression of drug efflux pumps such as ATP-binding cassette, subfamily C (ABCC) transporter 1(ABCC1) and 4 (ABCC4), which are members of ABC transporters. Recently research has shown that these proteins may be implicated in cancer biology independent of cytotoxic drug efflux, but so far little is known about this in regards to breast cancer. ABCC1 and ABCC4 protein levels in MDA-MB231 and MCF-7, human breast cancer derived cell lines were measured by Western blot. The role of ABCC1 and ABCC4 in cell proliferation and migration were evaluated by colony formation, MTT and scratch assays in the presence of various ABCC inhibitors – MK571, Indomethacin, Reversan, Ceefourin 1 and Ceefourin 2, inhibitors of ABCC4. Similarly the effect on proliferation, migration and invasion was monitored following knock down of ABCC1 and ABCC4 with ABCC1- and ABCC4- specific siRNAs, or overexpression using transfection with pcDNA3.1 plasmids containing the ABCC1 and ABCC4 genes. The potential correlation between ABCC1 and/or ABCC4 and the expression of Gprotein-coupled receptor 55 (GPR55), or extracellular signal-regulated kinase (ERK), or the extracellular efflux of cyclic adenosine monophosphate (cAMP), prostaglandin E2 (PGE2), sphingosine-1-phosphate (S1P) and cyteinyl leukotrienes (LTC4, LTD4 and LTE4) were investigated by Western blot and enzyme-linked immunosorbent assays. This thesis demonstrates that the expression levels of ABC transporters varies between breast cancer cell lines. Our results suggest that ABCC1 may be more involved in mediating breast cancer cell proliferation than ABCC4 and in contrary ABCC4 may be involved in mediating breast cancer cell invasion more than ABCC1. There is also an indication that both ABCC1and ABCC4 are implicated in breast cancer migration. In addition, potential correlation between ABCC1 and/or ABCC4 with cAMP or S1P efflux looks promising but further investigation is required. Taken together this thesis shows that ABCC1 and ABCC4 may be implicated in breast cancer development and progression. Further investigations are needed to validate our current results, but ABCC1 and ABCC4 could be potential therapeutic targets for breast cancer.