Identification of a metabolite-protein interaction network in the regulation of mTOR signal transduction and cell growth

Abstract

Mechanistic target of rapamycin (mTOR) is a key protein kinase that integrates external signals, such as growth factors and nutrients, to control critical biological events, including growth and survival. Dysregulation of the mTOR signaling network reported in major human diseases, such as cancer, is tightly linked to aberrant mTOR activation. Substantial efforts to identify protein subunits interacting with mTOR have led to the identification of two multiprotein complexes, mTORC1 and mTORC2, although endogenous metabolite-mTOR interactions remain largely unknown at present. Here I have demonstrated direct binding of 13-S-hydroxyoctadecadienoic acid (13-S-HODE), an oxygenated metabolite of linoleic acid, to mTOR. By employing a series of biophysical and biochemical analyses, I elucidated that specific interactions of 13-S-HODE with the catalytic ATP-binding domain of mTOR prevented its kinase activity in an ATP-competitive manner. Moreover, direct treatment with 13-S-HODE inhibited the normal fibroblast cells as well as hyperactivity of mTOR mutants in vitro and growth of cultured endometrial cancer cells with hyperactive MTOR mutations. Overexpression of human arachidonate 15-lipoxygenase (ALOX15) that catalyzes synthesis of 13-S-HODE led to suppression of both mTORC1 and mTORC2 pathways in cells as well as in vivo growth of endometrial tumor xenografts. The collective results support a direct link between polyunsaturated fatty acid metabolism and the mTOR signaling network, providing novel insights into regulation of cancer cell growth through metabolic reprogramming