OR26-3 USP19 Deubiquitinating Enzyme Functions as a Novel Co-Chaperone of Hsp90 to Regulate Glucocorticoid Receptor Levels

Ubiquitin specific protease 19 (USP19) is a deubiquitinating enzyme involved in metabolism. Its expression is upregulated in skeletal muscle in many conditions of muscle wasting. Genetic inactivation of USP19 (USP19KO) in mice protects from muscle atrophy and diet induced obesity and insulin resistance. We previously reported that the protection against muscle atrophy in USP19KO is due at least in part to reduction in muscle glucocorticoid receptor (GR) levels and signaling. Here, we report that USP19KO mice show > 50% decrease in GR protein level in multiple tissues with no observed changes in GR mRNA levels. Overexpression of the endoplasmic reticulum or cytosol-localized isoforms of USP19 in cells resulted in increased GR protein levels, while knockdown by siRNA or knockout by CRISPR-Cas9 resulted in decreased GR protein levels. Intriguingly, GR was not more ubiquitinated in the absence of USP19. Furthermore, expression of a catalytically inactive form of USP19 also increased GR protein levels and exposure of cells to a small molecule inhibitor of USP19 enzymatic activity had no effects on levels of GR. Deletion analysis revealed that the N-terminal CS domains of USP19, which are structurally similar to the p23 co-chaperone of HSP90, were required for increasing levels of GR. Since HSP90 is known to regulate GR folding and stability, this suggested that USP19 may function as a p23 like co-chaperone. Indeed, overexpression of USP19 not only increased GR levels, but translocation to the nucleus and transcriptional activity of a reporter gene. Using a novel BRET assay, we observed that USP19 interacts indirectly with GR through binding with HSP90. This interaction with HSP90 is critically dependent on the CS2 domain of USP19 and can be competed by expression of the p23 co-chaperone of HSP90. We have therefore identified a novel co-chaperone-like mechanism through which USP19 regulates GR protein stability independent of its catalytic activity. Targeting the interaction of USP19 with the GR-HSP90 complex could be a strategy to decrease GR levels, reduce glucocorticoid signalling and prevent muscle atrophy. Presentation: Monday, June 13, 2022 11:30 a.m. - 11:45 a.m.