A transcription-independent role for HIF-1α in modulating microprocessor assembly.

Microprocessor is an essential nuclear complex responsible for the initial RNase-mediated cleavage of primary miRNA, which is a tightly controlled maturation process that requires the proper assembly of Drosha and DGCR8. Unlike previously identified mechanisms directly targeting the enzymatic subunit Drosha, current knowledge about the biological ways of controlling miRNA nuclear maturation through DGCR8 is less addressed. In this study, we unveiled that the microprocessor assembly is governed by a master gene regulator HIF-1α irrespective of its canonical transcriptional activity. First, a widespread protein binding of HIF-1α with DGCR8 instead of Drosha was observed in response to biological stimulations. Similar protein interactions between their corresponding orthologues in model organisms were also observed. After dissecting the essential protein domains, we noticed that HIF-1α suppresses microprocessor assembly via binding to DGCR8. Furthermore, our results showed that HIF-1α hijacks monomeric DGCR8 thus reducing its dimer formation prior to microprocessor assembly, and consequently, the suppressed microprocessor formation and nuclear processing of primary miRNA were demonstrated. In conclusion, here we unveiled the mechanism of how microprocessor assembly is regulated by HIF-1α, which not only demonstrates a non-transcriptional function of nuclear HIF-1α but also provides new molecular insights into the regulation of microprocessor assembly through DGCR8.