Human Secreted Proteins SLURP-1 and SLURP-2 Control the Growth of Epithelial Cancer Cells via interaction with Nicotinic Acetylcholine Receptors.

Background and PurposeNicotinic acetylcholine receptors (nAChRs) are a promising target for development of new anticancer therapies. Here we have investigated the effects of the endogenous human proteins SLURP-1 and SLURP-2, antagonists of nAChRs, on human epithelial cancer cells. Experimental ApproachGrowth of epithelial cancer cells (A431, SKBR3, MCF-7, A549, HT-29) exposed to SLURP-1, SLURP-2, mecamylamine, atropine, timolol and gefitinib was measured by the WST-1 test. Expression levels of SLURP-1, 7-nAChR and EGF receptors and their distribution in cancer cells were studied by confocal microscopy and flow cytometry. Secretion of endogenous SLURP-1 by A431 cells under treatment with recombinant SLURP-1 was analysed by Western-blotting. Key ResultsSLURP-1 and SLURP-2 significantly inhibited growth of A431, SKBR3, MCF-7 and HT-29 cells at concentrations above 1nM, to 40-70% of the control, in 24h. Proliferation of A549 cells was inhibited only by SLURP-1. The anti-proliferative activity of SLURPs on A431 cells was associated with nAChRs, but not with -adrenoceptors or EGF receptors. Action of gefitinib and SLURPs was additive and resulted almost complete inhibition of A431 cell proliferation during 24h. Exposure of A431 cells to recombinant SLURP-1 down-regulated 7-nAChR expression and induced secretion of endogenous SLURP-1 from intracellular depots, increasing its concentration in the extracellular media. Conclusions and ImplicationsSLURPs inhibit growth of epithelial cancer cells in vitro and merit further investigation as potential agents for anticancer therapy.