The Sigma-2 Receptor and Progesterone Receptor Membrane Component 1 are Different Binding Sites Derived From Independent Genes

The sigma-2 receptor (S2R) is a potential therapeutic target for cancer and neuronal diseases. However, the identity of the S2R has remained a matter of debate. Historically, the S2R has been defined as (1) a binding site with high affinity to 1,3-di-o-tolylguanidine (DTG) and haloperidol but not to the selective sigma-1 receptor ligand (+)-pentazocine, and (2) a protein of 18-21 kDa, as shown by specific photolabeling with [H-3]-Azido-DTG and [I-125]-iodoazido-fenpropimorph ([I-125]-IAF). Recently, the progesterone receptor membrane component 1 (PGRMC1), a 25 kDa protein, was reported to be the S2R (Nature Communications, 2011, 2:380). To confirm this identification, we created PGRMC1 knockout NSC34 cell lines using the CRISPR/Cas9 technology. We found that in NSC34 cells devoid of or overexpressing PGRMC1, the maximum [H-3]-DTG binding to the S2R (B-max) as well as the DTG-protectable [I-125]-IAF photolabeling of the S2R were similar to those of wild-type control cells. Furthermore, the affinities of DTG and haloperidol for PGRMC1 (K-I = 472 mu M and 350 mu M, respectively), as determined in competition with [H-3]-progesterone, were more than 3 orders of magnitude lower than those reported for the S2R (20-80 nM). These results clarify that PGRMC1 and the S2R are distinct binding sites expressed by different genes. (C) 2015 The Authors. Published by Elsevier B.V.