Regulatorymechanismoftranscriptionalrepressionof the proteasomal ubiquitin receptor Rpn13

Mammalian Rpn13, as a 26S proteasome ubiquitin receptor subunit, binds to the ubiquitin substrate at the N terminal and deubiquitin enzyme UCH37 at the C end, mediates the degradation of most proteins through the ubiquitin-proteasome pathway, and is involved in the regulation of autophagy, neuron function and germ cell development.Proteasome inhibitors are important measures for tumor prevention and treatment, and targeting Rpn13 can overcome the resistance of proteasome inhibitors. However, the transcriptional repression mechanism of its gene expression is still unclear. Through the interactive analysis of gene expression profile, it was found that Rpn13 gene was highly expressed in many cancer types, especially in colon, lymphoma, pancreatic, rectal, gastric and thoracic cancers. The activity of the regulatory region -454~-58bp of the Rpn13 promoter was found to be high by the double luciferase report assay. Binding sites of multiple transcription factors, includingCTCFL(CCCTC binding factor-like),CTCF(CCCTC binding factor),NRF1(Nuclear respiratory factor 1)andFOXO3 (Forkhead box O3),were predicted on the promoter sequence of Rpn13. We constructed expression plasmids of these transcription factors, and found that they all inhibited the activity of the Rpn13 promoter. By further mutating the corresponding transcription factor binding sites of the Rpn13 promoter, CTCFL was found to bind the -63bp~-52bp sequence of the Rpn13 promoter. These studies not only analyzed the expression of Rpn13 gene in cancer tissues, but also revealed the possible transcription inhibition mechanism of Rpn13, providing useful clues for exploring the mechanism of Rpn13 in tumor occurrence and development.