Human G3BP1 interacts with β-F1-ATPase mRNA and inhibits its translation

Summary The post-transcriptional regulation of nuclear mRNAs that encode core components of mitochondria has relevant implications in cell physiology. The mRNA that encodes the catalytic subunit of the mitochondrial H + -ATP synthase subunit (ATP5B, -F1-ATPase) is localized in a large ribonucleoprotein (RNP) complex (-F1–RNP), which is subjected to stringent translational control during development and the cell cycle, and in carcinogenesis. Because downregulation of -F1-ATPase is a conserved feature of most prevalent human carcinomas, we have investigated the molecular composition of the human -F1–RNP. By means of an improved affinity-chromatography procedure and protein sequencing we have identified nine RNA-binding proteins (RNABPs) of the -F1– RNP. Immunoprecipitation assays of Ras-GAP SH3 binding protein 1 (G3BP1) and fluorescent in-situ hybridization of mRNA indicate a direct interaction of the endogenous G3BP1 with mRNA of -F1-ATPase (-F1 mRNA). RNA-bridged trimolecular fluorescence complementation (TriFC) assays confirm the interaction of G3BP1 with the 3-UTR of -F1 mRNA in cytoplasmic RNA-granules. Confocal and high-resolution immunoelectron-microscopy experiments suggest that the -F1–RNP is sorted to the periphery of mitochondria. Molecular and functional studies indicate that the interaction of G3BP1 with -F1 mRNA inhibits its translation at the initiation level, supporting a role for G3BP1 in the glycolytic switch that occurs in cancer.