Molecular and Cellular Pharmacology, Vol 4, No 1 (2012)

hnRNP A18: A New Pathway to Regulate Protein Translation in Cancer Cells

Abstract

Intracellular changes that lead to modification of normal gene expression and protein metabolism patterns are a hallmark of cancer cells. These changes confer specific growth advantages and unlimited replicative potential that are necessary for a continuously dividing cancer cell. Targeting the refueling capacity of actively proliferating cancer cells by limiting the amount of protein synthesized provides an attractive mechanism to prevent cancer progression. New anti cancer therapies targeting the protein translation regulator mammalian Target Of Rapamycin (mTOR) highlight the importance of this signaling pathway for cancer progression. Here, we describe an alternative mechanism to regulate protein translation in cancer cells. In contrast to mTOR which predominantly targets the general translational machinery, the heterogenous Ribonucleoprotein A18 (hnRNP A18) regulates the translation of specific mRNA transcripts in response to cellular stress such as hypoxia and UV radiation. hnRNP A18 mediates this effect by binding to an hnRNP A18 signature motif in the 3'UTR of targeted transcripts important for cancer progression such as HIF-a, RPA, TRX, eIF5A and ATR. hnRNP A18 interacts with the general translational machinery by binding to eIF4G, thus bridging the 3'UTR to the 5'UTR to initiate translation. hnRNP A18 is over expressed in several human cancers and can immortalize murine primary cells. hnRNP A18 could thus, as mTOR, be targeted to prevent protein translation in cancer cells.

Keywords: protein translation; cancer cells; mammalian Target Of Rapamycin (mTOR); heterogenous Ribonucleoprotein A18 (hnRNP A18); cellular stress; cancer progression

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