Endoplasmic reticulum factor ERLIN2 regulates cytosolic lipid content in cancer cells

Increased de novo lipogenesis is a hallmark of aggressive cancers. Lipid droplets, the major form of cytosolic lipid storage, have been implicated in cancer cell proliferation and tumorigenesis. Recently, we identified the ERLIN2 [ER (endoplasmic reticulum) lipid raft-associated 2) gene that is amplified and overexpressed in aggressive human breast cancer. Previous studies demonstrated that ERLIN2 plays a supporting oncogenic role by facilitating the transformation of human breast cancer cells. In the present study, we found that ERLIN2 supports cancer cell growth by regulating cytosolic lipid droplet production. ERLIN2 is preferably expressed in human breast cancer cells or hepatoma cells and is inducible by insulin signalling or when cells are cultured in lipoprotein-deficient medium. Increased expression of ERLIN2 promotes the accumulation of cytosolic lipid droplets in breast cancer cells or hepatoma cells in response to insulin or overload of unsaturated fatty acids. ERLIN2 regulates activation of SREBP (sterol regulatory element-binding protein) 1c, the key regulator of de novo lipogenesis, in cancer cells. ERLIN2 was found to bind to INSIG1 (insulin-induced gene 1), a key ER membrane protein that blocks SREBP activation. Consistent with the role of ERLIN2 in regulating cytosolic lipid content, down-regulation of ERLIN2 in breast cancer or hepatoma cells led to lower cell proliferation rates. The present study revealed a novel role for ERLIN2 in supporting cancer cell growth by promoting the activation of the key lipogenic regulator SREBP1c and the production of cytosolic lipid droplets. The identification of ERLIN2 as a regulator of cytosolic lipid content in cancer cells has important implications for understanding the molecular basis of tumorigenesis and the treatment of cancer.