SUN-LB134 Androgen Receptor Phosphorylated at Serine 815 in Mouse and Human Prostates

Androgen receptor (AR) regulates male sexual development and maintenance. AR forms a homodimer in the cytoplasm and monomerizes following hormonal activation, translocating to the nucleus in Cos-1 cells (Shizu et al. Scientific reports. 2019). Utilizing Ser815 of AR, the conserved phosphorylation residue within the ligand binding domains of steroid hormone receptors (NR3C), whether and how this phosphorylation regulates AR functions was investigated. While, like AR WT, a phosphomimic AR S815D mutant formed a homodimer in the cytoplasm, unlike the WT, this mutant remained as a homodimer in the cytoplasm even after hormone treatment. Apparently, Ser815 phosphorylation disabled AR’s capability to monomerize and nuclear translocate in Cos-1 cells. A phospho-Ser815 peptide antibody was used to detect phosphorylation of endogenous AR in mouse as well as human prostates. Immunohistochemistry showed phosphorylation present in both the cytoplasm and nucleus. Mouse prostates were cell fractionated in cell membrane, mitochondria, endoplasmic reticulum (ER) and cytosolic fractions for subsequent Western blot analysis. While AR was found in all of these fractions, phosphorylated AR was only detected in the ER and cytosolic fractions. A cDNA microarray analysis of PC-3 cells with ectopic expression of AR S815D suggested that phosphorylated AR may regulate ER stress.