Sigma-2 receptor (TMEM97) (σ2R or S2R)

The Sigma‑2 receptor is an integral membrane protein now identified as TMEM97, distinct from the classical G protein-coupled or ion channel receptors. It is characterized by four transmembrane domains and localizes primarily to the endoplasmic reticulum. The sigma‑2 receptor plays a key role in regulating cellular cholesterol homeostasis, cell proliferation, apoptosis, neurite outgrowth, and neuronal regeneration. It forms part of a trimeric complex with the LDL receptor and PGRMC1 that mediates internalization of lipoproteins. Sigma‑2 receptors are highly expressed in various cancers—including breast, ovarian, lung, brain, bladder, colon cancers—and serve as valuable biomarkers for tumor identification and assessment of proliferative status. Radiolabeled ligands targeting sigma‑2 have been developed for PET imaging ([^18F]ISO‑1), which correlates with tumor growth rates. In neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease—as well as psychiatric conditions like schizophrenia—the sigma‑2 receptor modulates processes including autophagy/protein trafficking. Experimental drugs such as Elayta/CT1812 target this pathway by preventing amyloid-beta oligomer binding to neurons. Despite its name "receptor," no endogenous ligand has been identified; its mechanism appears modulatory rather than classical signal transduction. The field continues to explore its full therapeutic potential across oncology and neurology.[1][6][8]

Other names

TMEM97Sigma intracellular receptor 2S2R

Modulation of cholesterol trafficking and homeostasis. Displacement/prevention of amyloid-beta oligomer binding to neurons in Alzheimer’s disease.