ARK5 Regulates Subcellular Localization of hnRNP A1 During Hypertonic Stress

Abstract

During cellular stress, the regulation of protein synthesis is a key adaptive mechanism used by cells to survive. In response to various stresses, heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), an RNA binding protein principally found within the nucleus, is phosphorylated and consequently accumulates in the cytoplasm. Among other roles, cytoplasmic hnRNP A1 functions as an auxiliary translation factor for internal ribosome entry site (IRES)-mediated translation of specific mRNA, including the anti-apoptotic protein B-cell lymphoma-extra large (Bcl-xL). To identify which kinases control the cytoplasmic accumulation of hnRNP A1, an RNAi-based kinome-wide screen was performed in hypertonically stressed U2OS cells, from which AMPK-related kinase 5 (ARK5) was identified as a potential regulator of hnRNP A1’s localization. Here we show that ARK5 directly phosphorylates hnRNP A1 and that the inhibition of ARK5 expression blocks the stress induced cytoplasmic accumulation of hnRNP A1, modulates expression of Bcl-xL protein and increases cell viability. Our data points to a novel role for ARK5 and provides further insight into the mechanisms regulating cellular stress response.