An extra-glycolytic function for hexokinase 2 as an RNA-binding protein regulating SOX10 mRNA translation in melanoma

Several studies have reported the importance of aerobic glycolysis in melanoma development. Although metabolic benefits of glycolysis have been extensively described in tumor cells, the extra-metabolic functions linked to this energetic pathway in melanoma growth and proliferation have not been clearly established yet. Recently, some key glycolytic enzymes, such as GAPDH and PKM2, were reported to regulate mRNA translation. Translational control of gene expression is considered as a critical effector in cancer biology, representing a highly promising area of research. Here, we report that Hexokinase 2 (HK2), a glucose kinase that catalyzes the first step of glycolysis, is an RNA binding protein (RBP) that regulates mRNA translation in melanoma. We show that siRNA-mediated HK2 depletion changes the translational landscape of melanoma cells. Polysome profiling experiments and RNA-Seq indicate that the translational regulation exerted by HK2 is partly independent of the metabolic status or the glycolytic pathway. We found that HK2 specifically regulates the translation of the mRNA encoding SOX10, a transcription factor implicated in the regulation of tumor initiation, maintenance and progression in melanoma. RNA-protein interaction assays, including crosslinking immunoprecipitation (CLIP), indicate that HK2 is an RBP whose interaction with RNA is independent of its hexokinase activity or subcellular localization. We also show that HK2 specifically associates with the 5 untranslated region (5UTR) of the SOX10 mRNA, and that several deletions in this region decreases both HK2-SOX10 mRNA association and SOX10 5 UTR-mediated translation. We further show that HK2-dependent SOX10 translational regulation is involved in melanoma cell proliferation and colony formation. Collectively, our data highlight a non-metabolic function of HK2, indicating that melanoma cells may enhance glycolysis for purposes beyond simple anabolism.