Inhibition of Tumor Cell Proliferation by σ Ligands Is Associated with K⁺ Channel Inhibition and p27^kip1 Accumulation

Abstract

Previous studies have shown that receptors are overexpressed in tumor cells. However, the role of receptors remains enigmatic. Recently, we and others have demonstrated that -1 receptor modulates K ϩ channels in pituitary. In the present report, patch-clamp and Western blot assays were used in small cell lung cancer (SCLC, NCI-H209, and NCI-H146) and leukemic (Jurkat) cell lines to investigate the effects of ligands on voltage-gated K ϩ channels and cell proliferation. The ligands (ϩ)-pentazocine, igmesine, and 1,3-di(2-tolyl)guanidine (DTG) all reversibly inhibited voltage-activated K ϩ currents in both cell lines. The potency of ligand-induced inhibition (10 M) was igmesine ϭ (ϩ)-pentazocine Ͼ DTG, pointing to the involvement of -1 receptors. Addition of the K ϩ channel blockers tetraethylammonium (TEA) and 4-aminopyridin or one of cited ligands in the culture media reversibly inhibited Jurkat cell growth. Interestingly, K ϩ channel blockers and ligands caused an accumulation of the cyclin-dependent kinase inhibitor p27 kip1 and a decrease in cyclin A expression in Jurkat and SCLC cells, whereas no effect could be detected on p21 cip1 . Moreover, ligands and TEA had no effect on caspase 3 activity. Accordingly, incubation of cells with ligands did not provoke DNA laddering. These data demonstrate that ligands and voltage-dependent channel blockers inhibit cell growth through a cell cycle arrest in the G 1 phase but not via an apoptotic mechanism. Altogether, these results indicate that the -1 receptor-induced inhibition of the cell cycle is, at least in part, the consequence of the inhibition of K ϩ channels.

Cancer Cell Cycle Modulated by a Functional Coupling between Sigma-1 Receptors and Cl– Channels

“…The same modulation of cell cycle-controlling proteins was also observed for cells challenged with igmesine (Fig. 4) and other sigma ligands (25), suggesting a common pathway.…”

“…In a previous work, we have demonstrated that the pharmacological activation of these receptors by igmesine blocked tumor cell cycle through a mechanism involving the inhibition voltage-dependent K ϩ channels (25). Altogether, our data showing the modulation of both potassium and chloride flux across the membrane by sigma ligands indicate that the sigma-1 receptors modulate the RVD process.…”

“…Accumulation-We have previously demonstrated that the pharmacological activation of sigma-1 receptors inhibits cell cycle progress through the accumulation of the CDK inhibitor p27 and the subsequent down-regulation of cyclin A (25). In the present study, we show that the incubation of jurkat cells with either igmesine (40 M) or NPPB (100 M) produces a strong inhibition of cell growth over 3 days (Fig.…”

“…In the light of these data, we showed that the cell incubation with NPPB, a classical blocker of VRCC and RVD, inhibits proliferation in SCLC and jurkat cells. The cell cycle arrest provoked by NPPB is underlined in both SCLC and Jurkat cells by an accumulation of the CDK inhibitor p27, but not p21 cip1 (not shown), and the subsequent decrease in cyclin A, which is consistent with a blockade in the G 1 phase (25,26,48,49). Interestingly, we had previously demonstrated that the sigma receptor ligands and K ϩ channel blockers provoke a cell cycle arrest with the same modulation profile, i.e.…”

“…We then demonstrated that the activation of sigma-1 receptors by highly selective ligands provoked the arrest of the cell cycle progression in the G 1 phase in cancer cells. This effect was partly linked to the inhibition of voltage-dependent potassium channels (25,26). In the present work, we have examined in leukemic and SCLC 3 cells a putative interaction between sigma-1 receptors and volume-regulated chloride currents (VRCC) that have been involved in the control of the cell cycle (27-29).…”