Hormone status selects for spontaneous somatic androgen receptor variants that demonstrate specific ligand and cofactor dependent activities in autochthonous prostate cancer

We have used the autochthonous transgenic adenocarcinoma of mouse prostate (TRAMP) model to investigate the relationship between somatic mutation in t he androgen receptor (AR) and the emergence of androgen-independent prostat e cancer. Here we report the identification, isolation, and characterizatio n of distinct classes of AR variants from spontaneous prostate tumors in th e TRAMP model. Using cDNA cloning, single stranded conformation polymorphis m and sequencing strategies, 15 unique somatic mutations in the AR were ide ntified in prostate tumors obtained from eight TRAMP mice between 24 and 29 weeks of age. At least one mutation was isolated from each mouse. All muta tions:were single base substitutions, 10 were missense and 5 were silent. N ine mutations in the AR were identified in tumors of four mice that were ca strated at 12 weeks of age. Interestingly, the majority of mutations (seven out of nine, 78%) identified in the androgen-independent tumors colocalize d in the AR transactivation domain. The remaining mutations colocalized in the AR ligand binding domain. In general, the AR variants demonstrated prom oter-, cell-, and cofactor-specific activities in response to various hormo nes. All AR variants isolated in this study maintained strong sensitivity f or androgens, and four AR variants isolated from castrated mice demonstrate d increased activities in the absence of ligand. The K638M and F677S varian ts demonstrated increased activities in response to androgen, and K638M als o demonstrated increased response to estradiol, In the presence of AR coact ivator ARA70 the E231G variant demonstrated increased activity in response to both androgen and estradiol. However, in the presence of AR coactivator ARA160 the E231G variant was selectively responsive to androgen. Collective ly these analyses not only indicate that somatic mutations in the AR gene o ccur spontaneously in TRAMP tumors but also how changes in the hormonal env ironment may drive the selection of spontaneous somatic mutations that prov ide a growth advantage.