HIG2 and Hypoxic Regulation of Protein Synthesis

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DESCRIPTION (provided by applicant): Hypoxia is a unique patho-physiologic stress of the solid tumor that has been shown both experimentally and clinically to influence tumor aggressiveness, metastatic potential and response to therapy. The mechanisms for these phenomena have not been determined, but are thought to be at least partially dependent upon gene and protein expression changes induced by hypoxia. Investigators have identified many components of the hypoxic stress response cascade starting from hypoxic sensing, to transcriptional changes, to protein expression changes and post-translational protein modifications. Tumor cells that are unable to start new hypoxia-responsive mRNA transcription grow poorly in model tumors (HIF knockouts). Likewise, cells that fail to express the hypoxic target protein vascular endothelial growth factor also grow poorly in model tumors (VEGF knockouts). The conclusion can therefore be made that studying other components of the stress response cascade is reasonable, because blocking them could have similarly profound impact on tumor growth. We propose to investigate if HIG2 can influence stress-dependent protein synthesis because we have evidence that HIG2 is associated with translational machinery during hypoxia. We have previously identified HIG2 as a novel 63 amino acid proteins that is robustly induced by hypoxia in a wide variety of normal cells and tumor cell lines. We now show that the HIG2 protein co-localizes with members of the cytoplasmic "Stress granule". Stress granules have been shown to regulate protein translation in response to heat shock, and we suggest that they serve a similar function during hypoxia. This grant proposal is based upon the hypothesis that HIG2 plays an important function in regulating protein synthesis during hypoxia through its association with components of the stress granule. To address this hypothesis, we propose to 1) Identify the mechanism by which HIG2 is targeted to the stress granule, 2) Determine binding partners for HIG2 during hypoxia and 3) Establish the functional significance of HIG2 within the stress granule during tumor formation. These experiments should determine if HIG2 is necessary for hypoxia-dependent translational control, and how important this control is to the survival of ceils within the hypoxic regions of human tumors.