The impact of the RNA-binding protein hnRNP-A1 on translation in inflammation-associated tumorigenesis

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The inflammatory tumor microenvironment is shaped by infiltrating immune cells, most notably macrophages, which release pro-inflammatory mediators that contribute to malignant transformation. In line, inflammatory conditions are widely accepted to support the process of tumorigenesis. We have previously shown that macrophage-associated inflammatory conditions, in addition to inducing transcriptional changes, elicit translational changes in tumor cells that foster tumor development. Preliminary data imply that hnRNP-A1 could play an important role in the regulation of cap-independent translation changes under these conditions. Thus, we now aim to identify and characterize inflammation-induced translational changes in tumor cells that depend on the RNA-binding protein hnRNP-A1. Using polysomal fractionation, we will assess hnRNP-A1-dependent translational changes in tumor cells under inflammatory conditions. In addition, we will determine the exact binding sites of hnRNP-A1 on its mRNA targets by PAR-CLIP (photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation) analysis. Combining both approaches we will identify translationally regulated hnRNP-A1 targets that interact with hnRNP-A1 via their 5' untranslated region. These targets will be analyzed for the presence of internal ribosome entry site (IRES)-elements facilitating cap-independent initiation of translation. Determination of shared sequences or structural motifs will predict hnRNP-A1 responsive IRESs. Further analyses aim at identifying potential co-IRES trans-acting factors (ITAFs) contributing the IRES-dependent translation of selected hnRNP-A1 targets. Finally, the elucidation of the macrophage-dependent inflammatory factors contributing to the altered IRES-activities and the contributing signaling cascades will provide the basis for translation-targeted interventions.