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c-Src-mediated phosphorylation of hnRNP K drives translational activation of specifically silenced mRNAs
Antje Ostareck-Lederer1, Dirk H Ostareck, Christophe Cans
1European Molecular Biology Laboratory, Heidelberg, Germany. aostareck@anadyspharma.de
Abstract:
hnRNPK and hnRNP E1/E2 mediate translational silencing of cellular and viral mRNAs in a differentiation-dependent way by binding to specific regulatory sequences. The translation of 15-lipoxygenase (LOX) mRNA in erythroid precursor cells and of the L2 mRNA of human papilloma virus type 16 (HPV-16) in squamous epithelial cells is silenced when either of these cells is immature and is activated in maturing cells by unknown mechanisms. Here we address the question of how the silenced mRNA can be translationally activated. We show that hnRNP K and the c-Src kinase specifically interact with each other, leading to c-Src activation and tyrosine phosphorylation of hnRNP K in vivo and in vitro. c-Src-mediated phosphorylation reversibly inhibits the binding of hnRNP K to the differentiation control element (DICE) of the LOX mRNA 3' untranslated region in vitro and specifically derepresses the translation of DICE-bearing mRNAs in vivo. Our results establish a novel role of c-Src kinase in translational gene regulation and reveal a mechanism by which silenced mRNAs can be translationally activated.
Insights
Messenger RNA translation is silenced in immature cells and activated during maturation. This study reveals how the c-Src kinase phosphorylates hnRNP K, activating silenced messenger RNAs.
Area of Science:
- Molecular Biology
- Gene Regulation
- Cellular Differentiation
Background:
- Heterogeneous nuclear ribonucleoproteins (hnRNP K and hnRNP E1/E2) silence cellular and viral messenger RNAs (mRNAs) during cell differentiation.
- The mechanisms for activating silenced mRNAs in maturing cells remain largely unknown.
Purpose of the Study:
- To elucidate the mechanism by which silenced mRNAs become translationally activated during cellular maturation.
- To identify the role of c-Src kinase in the translational regulation of specific mRNAs.
Main Methods:
- Investigated the interaction between hnRNP K and c-Src kinase using in vivo and in vitro assays.
- Analyzed the effect of c-Src-mediated phosphorylation on hnRNP K binding to the differentiation control element (DICE) of 15-lipoxygenase (LOX) mRNA.
- Assessed the impact of this phosphorylation on the translation of DICE-bearing mRNAs in vivo.
Main Results:
- hnRNP K and c-Src kinase were found to specifically interact, leading to c-Src activation and tyrosine phosphorylation of hnRNP K.
- c-Src-mediated phosphorylation reversibly inhibited hnRNP K binding to the DICE in the 3' untranslated region of LOX mRNA.
- This phosphorylation specifically derepressed the translation of DICE-bearing mRNAs in vivo.
Conclusions:
- Established a novel role for c-Src kinase in the translational gene regulation of specific mRNAs.
- Revealed a mechanism involving c-Src-mediated phosphorylation of hnRNP K that activates translationally silenced mRNAs during cellular differentiation.