TMEM97 and PGRMC1 do not mediate sigma-2 ligand-induced cell death

• Published in: Cell death discovery Vol. 5; no. 1; p. 58
• Main Authors: Zeng, Chenbo, Weng, Chi-Chang, Schneider, Jr, Mark E, Puentes, Laura, Riad, Aladdin, Xu, Kuiying, Makvandi, Mehran, Jin, Linda, Hawkins, William G, Mach, Robert H
• Format: Journal Article
• Language: English
• Published: United States Springer Nature B.V 28.01.2019; Nature Publishing Group UK
• Subjects: Apoptosis; Binding sites; Cancer; Caspase; Caspase-3; Cell death; Cytotoxicity; Internalization; Ligands; Low density lipoprotein; Neurodegenerative diseases; Pentazocine; Progesterone; Receptor density
• ISSN: 2058-7716; 2058-7716
• DOI: 10.1038/s41420-019-0141-2

Sigma-2 receptors have been implicated in both tumor proliferation and neurodegenerative diseases. Recently the sigma-2 receptor was identified as transmembrane protein 97 (TMEM97). Progesterone receptor membrane component 1 (PGRMC1) was also recently reported to form a complex with TMEM97 and the low density lipoprotein (LDL) receptor, and this trimeric complex is responsible for the rapid internalization of LDL. Sigma-2 receptor ligands with various structures have been shown to induce cell death in cancer cells. In the current study, we examined the role of TMEM97 and PGRMC1 in mediating sigma-2 ligand-induced cell death. Cell viability and caspase-3 assays were performed in control, TMEM97 knockout (KO), PGRMC1 KO, and TMEM97/PGRMC1 double KO cell lines treated with several sigma-2 ligands. The data showed that knockout of TMEM97, PGRMC1, or both did not affect the concentrations of sigma-2 ligands that induced 50% of cell death (EC ), suggesting that cytotoxic effects of these compounds are not mediated by TMEM97 or PGRMC1. Sigma-1 receptor ligands, (+)-pentazocine and NE-100, did not block sigma-2 ligand cytotoxicity, suggesting that sigma-1 receptor was not responsible for sigma-2 ligand cytotoxicity. We also examined whether the alternative, residual binding site (RBS) of 1,3-Di- -tolylguanidine (DTG) could be responsible for sigma-2 ligand cytotoxicity. Our data showed that the binding affinities ( ) of sigma-2 ligands on the DTG RBS did not correlate with the cytotoxicity potency (EC ) of these ligands, suggesting that the DTG RBS was not fully responsible for sigma-2 ligand cytotoxicity. In addition, we showed that knocking out TMEM97, PGRMC1, or both reduced the initial internalization rate of a sigma-2 fluorescent ligand, . However, concentrations of internalized became identical later in the control and knockout cells. These data suggest that the initial internalization process of sigma-2 ligands does not appear to mediate the cell-killing effect of sigma-2 ligands. In summary, we have provided evidence that sigma-2 receptor/TMEM97 and PGRMC1 do not mediate sigma-2 ligand cytotoxicity. Our work will facilitate elucidating mechanisms of sigma-2 ligand cytotoxicity.