2030 - RIBONUCLEASE INHIBITOR (RNH1) REGULATES HEMATOPOIETIC CELL SPECIFIC TRANSLATION

Abstract

Regulation of gene expression is important for normal development and is mainly controlled at the level of transcription. However, recent studies show that ribosomal proteins (RPs) regulate specific gene expression by selectively facilitating translation of specific mRNAs. Indeed, in Diamond- Blackfan anemia (DBA) and 5q– syndrome, mutations in RP genes lead to a specific defect in erythroid gene translation and cause anemia. How mutations in RP genes leads to hematopoietic specific defects is largely unknown. Similar to transcription factors the existence of cell type specific translation regulators remain elusive. Here, we report that Ribonuclease inhibitor (RNH1) regulates hematopoietic cell specific translation. Recently, we published that RNH1 is a ribosomal associated protein and regulates erythropoiesis by regulating GATA1 mRNA translation. In this study, we found that RNH1-deficiency in human hematopoietic origin cells such as erythroid leukemia cells, monocytic cells and T lymphocytes decreased polysome formation but not in non-hematopoietic origin cells such as HEK293, HaCat, HeLa cells. Similarly, OP-Puro incorporation experiments in mice revealed that RNH1-deficency leads to translation defect in hematopoietic cells but not in non- hematopoietic cells. At molecular level, we found that RNH1 binds to ribosomes and regulates RPs gene expression at translation level independent of mTOR signaling. Interestingly, it has been shown that RNH1 expression is translationally down regulated in RPS19 knockdown cells, which is frequently mutated in DBA patients. Supporting RNH1 role in translation, over expression of RNH1 rescues erythroid and translation defects in RPS19 knockdown cells. Collectively, our result unravels the existence of cell type specific translation regulators and may partially explain cell type specific defects caused by mutations in RP genes.