PROJECT SUMMARY (ABSTRACT) An evolving concept that contributes to our understanding of resistance to androgen deprivation therapy (ADT) or androgen receptor (AR) antagonists in advanced prostate cancer (PCa) is the ability of cells to evade AR blockade and turn on compensatory hormone receptor signaling for survival. Preclinical and clinical studies by us and others have demonstrated that induction of glucocorticoid receptor (GR) expression confers resistance to AR-targeted therapy. Elegant studies by others in the hormone receptors field have shown that posttranslational modifications (PTM) on nuclear hormone receptors can amplify or alter their canonical activity to favor cancer cell survival or drug resistance. One such PTM is, phosphorylation. We published that pan-AKT inhibition blocks GR induction/activity and overcomes GR- mediated resistance to AR-targeted therapy (ARi). We observed this in a setting of both ligand-dependent and ligand-independent GR signaling. Furthermore, preliminary proteomics studies show that GR phosphorylation is expressed with progression to castrate-resistant PCa (CRPC) and increases significantly in enzalutamide-resistant CRPC. This increase also correlated with an increase in AKT1 expression. We found that AKT1 is directly bound to GR, which validates the finding by others. Pharmacologic inhibition specific for AKT1 or knockdown of AKT1 significantly decreased pGR(s134) but not total GR. In addition, inhibition of AKT1 inhibited pGR(s134) expression in the nucleus with or without ligand. When cells were exposed to a GR-specific modulator (GRM), CORT134, in combination with enzalutamide and the presence/absence of ligands, we only observed suppression of cell proliferation in CRPC but not very effective in enzalutamide-resistant CRPC. Conversely, AKT1 inhibition decreased pGR(s134) in the nucleus, with/without ligand, and was also associated with inhibition of cell proliferation. Phospho-site mutation on pGR(s134) was also associat