Human secreted protein SLURP-1 abolishes nicotine-induced proliferation, PTEN down-regulation and α7-nAChR expression up-regulation in lung cancer cells

Human Ly-6/uPAR-related protein-1 (SLURP-1) is an allosteric negative modulator of the alpha 7-type nicotinic acetylcholine receptor (alpha 7-nAChR), one of the key receptors promoting nicotine-induced proliferation of lung cancer cells. Incubation of lung adenocarcinoma A549 cells with recombinant SLURP-1 (rSLURP-1) at concentrations > 10 nM resulted in the significant decrease of the cell growth (similar to 70%), while treatment of normal lung-derived WI-38 fibroblasts with rSLURP-1 did not influence the cell proliferation up to 1 mu M of the protein. rSLURP-1 fully abolished the nicotine-induced increase of the cell proliferation, down-regulation of the expression of PTEN (the negative regulator of the AKT pathway, controlling the growth, survival, and proliferation of cancer cells), and up-regulation of the alpha 7-nAChR expression in the A549 cells. Using the siRNA against alpha 7-nAChR and inhibitors of different cell-surface receptors, we showed that rSLURP-1 antiproliferative effect in A549 cells is connected with alpha 7-nAChR, epidermal growth factor receptors, and beta-adrenergic receptors. Moreover, we found that downstream effectors of rSLURP-1 are IP3 receptors and the STAT3 transcription factor. Implication of the IP3 receptors and PTEN in the rSLURP-1 antiproliferative activity points on the AKT-mediated signaling pathway. Co-application of rSLURP-1 with gefitinib and bortezomib (currently used anticancer drugs) resulted in an additive suppression of the A549 cells proliferation up to similar to 44% and 35%, respectively. Thus, rSLURP-1 could be considered a promising prototype of drugs to prevent nicotine-induced pathologies and cancer treatment.