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

Area of Science:

• Pharmacology
• Cell Biology
• Molecular Biology

Background:

• Sigma-2 receptors are implicated in tumor proliferation and neurodegenerative diseases.
• Sigma-2 receptor was recently identified as transmembrane protein 97 (TMEM97).
• TMEM97 forms a complex with progesterone receptor membrane component 1 (PGRMC1) and the LDL receptor, involved in LDL internalization.

Purpose of the Study:

• To investigate the role of TMEM97 and PGRMC1 in mediating sigma-2 ligand-induced cell death.
• To determine if sigma-1 receptor or the DTG residual binding site (RBS) are involved in sigma-2 ligand cytotoxicity.
• To assess the impact of TMEM97 and PGRMC1 on sigma-2 ligand internalization.

Main Methods:

• Cell viability and caspase-3 assays were performed in control, TMEM97 KO, PGRMC1 KO, and double KO cell lines.
• Sigma-2 and sigma-1 receptor ligands were used to assess cytotoxicity.
• Binding affinities (Ki) on the DTG RBS and internalization rates of a fluorescent sigma-2 ligand (SW120) were measured.

Main Results:

• Knockout of TMEM97, PGRMC1, or both did not affect the EC50 of sigma-2 ligands, indicating these proteins do not mediate cytotoxicity.
• Sigma-1 receptor ligands did not block sigma-2 ligand cytotoxicity.
• Binding affinities on the DTG RBS did not correlate with cytotoxicity potency.
• Knocking out TMEM97, PGRMC1, or both reduced the initial internalization rate of SW120, but later concentrations were identical, suggesting internalization is not the primary driver of cell death.

Conclusions:

• Sigma-2 receptor/TMEM97 and PGRMC1 do not mediate sigma-2 ligand cytotoxicity.
• The sigma-1 receptor and DTG RBS are not fully responsible for sigma-2 ligand cytotoxicity.
• The initial internalization process of sigma-2 ligands does not appear to mediate their cell-killing effect.
• Further research is needed to elucidate the mechanisms of sigma-2 ligand cytotoxicity.