Human secreted proteins SLURP‐1 and SLURP‐2 control the growth of epithelial cancer cells via interactions with nicotinic acetylcholine receptors

Background and purpose Nicotinic acetylcholine receptors (nAChRs) are a promising target for development of new anticancer therapies. Our purpose is to study effects of human proteins SLURP-1 and SLURP-2, antagonists of nAChRs, on human epithelial cancer cells. Experimental approach Growth of epithelial cancer cells (A431, SKBR3, MCF-7, A549, HT-29) exposed to SLURP-1, SLURP-2, mecamylamine, atropine, timolol and gefitinib was investigated by WST-1 test. Expression levels of SLURP-1, α7-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 analyzed by Western-blotting. Key results SLURP-1 and SLURP-2 significantly inhibited growth of A431, SKBR3, MCF-7, and HT-29 cells at concentrations above 1 nM (to 40-70 % of a number of viable cells in 24 h). Antiproliferative effect on A549 cells was observed only for SLURP-1. Antiproliferative activity of SLURPs on A431 cells was concluded to be associated with nAChRs, but not with β-adrenergic or EGF receptors. Action of gefitinib and SLURPs was additive and resulted in near to complete inhibition of A431 cell proliferation during 24 h. Exposure of A431 cells to recombinant SLURP-1 down-regulates α7-nAChR expression and induces secretion of endogenous SLURP-1 from intracellular depot increasing its concentration in the extracellular media. Conclusion and implications SLURPs inhibit growth of epithelial cancer cells in vitro and require further investigation as potential agents for anticancer therapy.