Hexokinase 2 is an RNA-binding protein that regulates mRNA translation independently of glycolysis and induces melanoma cell proliferation
Although metabolic benefits of glycolysis have been extensively described in tumor cells, the extra-metabolic functions linked to this energetic pathway in tumor growth and cell 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 at the outer mitochondrial membrane (OMM), is an RNA-binding protein (RBP) that regulates mRNA translation in melanoma cell lines. Polysome profiling experiments followed by RNA sequencing 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 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 enzymatic activity, its ability to bind glucose or its association with the OMM. HK2 directly interacts with the 5' untranslated region (5'UTR) of the SOX10 mRNA through a stem-loop RNA secondary structure. Using RNA-protein proximity ligation assays and a fluorescence-based ribosome-bound mRNA mapping method (RIBOmap), we found that high glucose conditions, which promotes the release of HK2 from the OMM, induces an increase in HK2-SOX10 mRNA interaction and SOX10 mRNA translation in the cytoplasm. We further showed that HK2-dependent SOX10 mRNA translation is involved in melanoma cell proliferation and colony formation. Collectively, our data highlight a non-metabolic function of HK2 acting as an RBP and translation regulator. Overall design: We performed transcriptome and translatome analysis (RNA-Seq) on A375 melanoma cells cultured in galactose- or glucose-containing medium depleted or not of the glycolytic enzymes HK2, GAPDH, PKM2.