Silencing of sigma-1 receptor induces cell death in human lens cells

Sigma receptors have no known homology with other receptor systems, have no known natural ligands, but appear to play a critical role in a large diversity of cell functions. In the absence of a conventional pharmacology, siRNA technology provides a direct means of elucidating the major cell signaling pathways influenced by this receptor system. The non-transformed human lens cell line FHL124 was found to express the sigma-1 receptor (Sig-1R) and was employed for these studies. 72 h of transfection with either of the two siRNA directed against the sigma-1 receptor reduced messenger RNA and protein levels by over 70 and 60% respectively. Subsequent incubation for 96 h in culture medium (EMEM) supplemented with 5% serum gave a partial recovery of message, but there was no significant increase in protein. LDH leakage assays showed that significant cell death occurred during this time with an increased expression of Caspase-3. Thrombin (10 nM) drives the growth of lens cells with a concomitant increase in ERK and Akt phosphorylation. These increases were inhibited in the cells where knockdown had occurred but not in cells exposed to scrambled siRNA. This study establishes a central role for Sig-1R in cell survival and death.