Identification and characterization of a novel androgen receptor coregulator ARA267-alpha in prostate cancer cells

The androgen receptor (AR) is a member of the steroid receptor superfamily that binds to the androgen response element to regulate target gene transcr iption. AR may need to interact with some selected coregulators for maximal or proper androgen function. Here we report the isolation of a new AR core gulator with a calculated molecular mass of 267 kDa named the androgen rece ptor-associated protein 267-alpha (ARA267-alpha). ARA267-alpha contains 242 7 amino acids, including one Su(var)3-9, Enhancer-of-zeste, and Trithorax ( SET) domain, two LXXLL motifs, three nuclear translocation signal (NLS) seq uences, and four plant homodomain (PHD) finger domains. Northern blot analy ses reveal that ARA267-alpha is expressed predominantly in the lymph node a s 13- and 10-kilobase transcripts. HepG2 is the only cell line tested that does not express ARA267-alpha. Yeast two-hybrid and glutathione S-transfera se pull-down assays show that both the N and C terminus of ARA267-alpha int eract with the AR DNA- and ligand-binding domains. Unlike other coregulator s, such as CBP, which enhance the interaction between the N and C terminus of AR, we found that ARA267-alpha had little influence on the interaction b etween the N and C terminus of AR. Luciferase and chloramphenicol acetyltra nsferase assays show that ARA267-alpha can enhance AR transactivation in a dihydrotestosterone-dependent manner in PC-3 and H1299 cells. ARA267-alpha can also enhance AR transactivation with other coregulators, such as ARA24 or PCAF, a histone acetylase, in an additive manner. Together, our data dem onstrate that ARA267-alpha is a new AR coregulator containing the SET domai n with an exceptionally large molecular mass that can enhance AR transactiv ation in prostate cancer cells.