The DExH-box RNA helicase RHAU is a Nuclear Protein Involved in Transcription and mRNA Decay

RHAU (RNA helicase-associated with AU-rich element) is a DExH protein that was originally identified as a factor accelerating AU-rich element-mediated mRNA degradation. The finding that RHAU is predominantly localized in the nucleus, despite that mRNA degradation occurs in cytoplasm, prompted us to consider nuclear functions of RHAU. In HeLa cells, RHAU was localized throughout the nucleoplasm with some concentration in nuclear speckles in a manner dependent on ATPase activity. Transcriptional arrest altered its localization to nucleolar caps where it was colocalized with other RNA helicases, p68 and p72, suggesting that RHAU is involved in transcription-related RNA metabolism in the nucleus. To see whether RHAU affects global gene expression either transcriptionally or posttranscriptionally, we performed microarray analysis using total RNA prepared from RHAU-depleted HeLa cell lines, measuring both steady-state mRNA levels and mRNA half-lives by ActinomycinD-chase. We found that most transcripts whose steady-state levels were affected by RHAU knockdown did not show changes in their half-lives, suggesting the involvement of transcriptional regulation for these transcripts. We propose that RHAU has dual functions involved in synthesis and degradation of mRNA in different subcellular compartments.

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Iwamoto F, Stadler M, Chalupníková K, Oakeley E, Nagamine Y