Identification Of A Met-Eif4g1 Translational Regulation Axis That Controls Hif-1 Alpha Levels Under Hypoxia

Poor oxygenation is a common hallmark of solid cancers that strongly associates with aggressive tumor progression and treatment resistance. While a hypoxia-inducible factor 1 alpha (HIF-1 alpha)-associated transcriptional overexpression of the hepatocyte growth factor (HGF) receptor tyrosine kinase (RTK) MET has been previously documented, any regulation of the HIF-1a system through MET downstream signaling in hypoxic tumors has not been yet described. By using MET-driven in vitro as well as ex vivo tumor organotypic fresh tissue models we report that MET targeting results in depletion of HIF-1 alpha and its various downstream targets. Mechanistically, we provide evidence that MET regulates HIF-1 alpha levels through a protein translation mechanism that relies on phosphorylation modulation of the eukaryotic initiation factor 4G1 (eIF4G1) on serine 1232 (Ser-1232). Targeted phosphoproteomics data demonstrate a significant drop in eIF4G1 Ser-1232 phosphorylation following MET targeting, which is linked to an increased affinity between eIF4G1 and eIF4E. Since phosphorylation of eIF4G1 on Ser-1232 is largely mediated through mitogen-activated protein kinase (MAPK), we show that expression of a constitutively active K-RAS variant is sufficient to abrogate the inhibitory effect of MET targeting on the HIF-1 alpha pathway with subsequent resistance of tumor cells to MET targeting under hypoxic conditions. Analysis of The Cancer Genome Atlas data demonstrates frequent co-expression of MET, HIF-1 alpha and eIF4G1 in various solid tumors and its impact on disease-free survival of non-small cell lung cancer patients. Clinical relevance of the MET-eIF4G1-HIF-1 alpha pathway is further supported by a co-occurrence of their expression in common tumor regions of individual lung cancer patients.