THE TUMOR SUPPRESSOR FOLLICULIN REGULATES GLYCOLYSIS BY SPECIFICALLY BINDING AND INHIBITING LACTATE DEHYDROGENASE-A

Abstract

Folliculin (FLCN) is tumor suppressor protein whose function remains a topic of debate. Germline mutations in FLCN predispose affected individuals to develop Birt-Hogg-Dubé syndrome, which is characterized by facial fibrofolliculomas, pulmonary cysts, spontaneous pneumothorax, and renal cell carcinoma. These kidney tumors exhibit an elevated glycolytic phenotype even in the presence of oxygen, an observation commonly known as the “Warburg effect.” This phenomenon is driven by the activity of lactate dehydrogenase-A (LDHA), the enzyme responsible for the interconversion of pyruvate and lactate in the terminal step of glycolysis. Our work herein shows that FLCN is a specific intracellular inhibitor of LDHA. Biochemical and biophysical analyses mapped the interaction and inhibition of LDHA activity to an unstructured loop in FLCN positioned between the amino and carboxy-terminal domains. Characterization of a minimal 10-amino acid FLCN-derived peptide demonstrated that it was sufficient to both bind and inhibit LDHA activity in vitro. Further, treatment of FLCN-deficient cells with this FLCN-derived peptide is sufficient to suppress glycolysis. Interestingly, evaluated cancer cell lines derived from solid tumors of the lung, breast, prostate, bladder, and colon also demonstrate dysregulation of LDHA activity and dissociation of FLCN-LDHA interaction. Previous work has shown that inhibition of LDHA in cancer cells leads to apoptosis. Accordingly, treatment of these cell lines with the FLCN-peptide results in apoptosis, suggesting a potential therapeutic intervention. Taken together, inhibition of LDHA by the tumor suppressor FLCN provides a mechanistic explanation for the endogenous regulation of glycolysis.