Initiation Factor eIF2-independent Mode of c-Src mRNA Translation Occurs via an Internal Ribosome Entry Site

• Published in: The Journal of biological chemistry 2010-02, Vol.285 (8), p.5713-5725
• Main Authors: Allam, Heba, Ali, Naushad
• Format: Article
• Language: English
• Subjects: 5' Untranslated Regions; c-Src; cap-independent Translation; Carcinoma, Hepatocellular - genetics; Carcinoma, Hepatocellular - metabolism; Carcinoma, Hepatocellular - pathology; Cell Transformation, Neoplastic - genetics; Cell Transformation, Neoplastic - metabolism; Cell-Free System - metabolism; Eukaryotic Initiation Factor-2 - metabolism; Genes, src; HeLa Cells; Humans; Internal Ribosome Entry Site; Neoplasm Metastasis; Peptide Chain Initiation, Translational; Protein Synthesis and Degradation; Ribosome Subunits, Small, Eukaryotic - genetics; Ribosome Subunits, Small, Eukaryotic - metabolism; RNA Caps - genetics; RNA Caps - metabolism; RNA Folding; RNA/Ribosome Assembly; Stress, Physiological; Translation; Translation/Control; Translation/Regulation Eukaryote
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.029462

Overexpression and activation of the c-Src protein have been linked to the development of a wide variety of cancers. The molecular mechanism(s) of c-Src overexpression in cancer cells is not clear. We report here an internal ribosome entry site (IRES) in the c-Src mRNA that is constituted by both 5′-noncoding and -coding regions. The inhibition of cap-dependent translation by m7GDP in the cell-free translation system or induction of endoplasmic reticulum stress in hepatoma-derived cells resulted in stimulation of the c-Src IRES activities. Sucrose density gradient analyses revealed formation of a stable binary complex between the c-Src IRES and purified HeLa 40 S ribosomal subunit in the absence of initiation factors. We further demonstrate eIF2-independent assembly of 80 S initiation complex on the c-Src IRES. These features of the c-Src IRES appear to be reminiscent of that of hepatitis C virus-like IRESs and translation initiation in prokaryotes. Transfection studies and genetic analysis revealed that the c-Src IRES permitted initiation at the authentic AUG351, which is also used for conventional translation initiation of the c-Src mRNA. Our studies unveiled a novel regulatory mechanism of c-Src synthesis mediated by an IRES element, which exhibits enhanced activity during cellular stress and is likely to cause c-Src overexpression during oncogenesis and metastasis.