Shutdown of Achaete-scute Homolog-1 Expression by Heterogeneous Nuclear Ribonucleoprotein (hnRNP)-A2/B1 in Hypoxia

• Published in: The Journal of biological chemistry 2014-09, Vol.289 (39), p.26973-26988
• Main Authors: Kasim, Mumtaz, Benko, Edgar, Winkelmann, Aline, Mrowka, Ralf, Staudacher, Jonas J., Persson, Pontus B., Scholz, Holger, Meier, Jochen C., Fähling, Michael
• Format: Article
• Language: English
• Subjects: 3' Untranslated Regions; 5' Untranslated Regions; Animals; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - metabolism; Cell Hypoxia - genetics; Cell Line, Tumor; Gene Expression Regulation, Neoplastic; Gene Regulation; Heterogeneous-Nuclear Ribonucleoprotein Group A-B - biosynthesis; Heterogeneous-Nuclear Ribonucleoprotein Group A-B - genetics; Humans; Neoplasm Proteins - genetics; Neoplasm Proteins - metabolism; Neuroblastoma - genetics; Neuroblastoma - metabolism; Promoter Regions, Genetic; Rabbits; Rats, Wistar
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.579391

The basic helix-loop-helix transcription factor hASH1, encoded by the ASCL1 gene, plays an important role in neurogenesis and tumor development. Recent findings indicate that local oxygen tension is a critical determinant for the progression of neuroblastomas. Here we investigated the molecular mechanisms underlying the oxygen-dependent expression of hASH1 in neuroblastoma cells. Exposure of human neuroblastoma-derived Kelly cells to 1% O2 significantly decreased ASCL1 mRNA and hASH1 protein levels. Using reporter gene assays, we show that the response of hASH1 to hypoxia is mediated mainly by post-transcriptional inhibition via the ASCL1 mRNA 5′- and 3′-UTRs, whereas additional inhibition of the ASCL1 promoter was observed under prolonged hypoxia. By RNA pulldown experiments followed by MALDI/TOF-MS analysis, we identified heterogeneous nuclear ribonucleoprotein (hnRNP)-A2/B1 and hnRNP-R as interactors binding directly to the ASCL1 mRNA 5′- and 3′-UTRs and influencing its expression. We further demonstrate that hnRNP-A2/B1 is a key positive regulator of ASCL1, findings that were also confirmed by analysis of a large compilation of gene expression data. Our data suggest that a prominent down-regulation of hnRNP-A2/B1 during hypoxia is associated with the post-transcriptional suppression of hASH1 synthesis. This novel post-transcriptional mechanism for regulating hASH1 levels will have important implications in neural cell fate development and disease.