Ratio of the expression levels of androgen receptor splice variant 7 to androgen receptor in castration refractory prostate cancer

In clinical samples, the expression of androgen receptor (AR) and of AR splice variant 7 (AR-V7) is higher in castration-resistant prostate cancer (CRPC) compared with that in hormone-sensitive prostate cancer (PCa). However, there are only a few reports on the ratio of the expression levels of AR-V7 to AR (AR-V7/AR) in prostate tissue. The present study evaluated AR-V7/AR expression in various types of human prostate tissues and CRPC cells. Pretreatment prostate tissue samples from patients with benign prostatic hyperplasia (BPH; n=18), Gleason score 7 (n=17), and Gleason score 8–10 (n=26) were collected at the time of prostate biopsy, and tissue samples from CRPC patients (n=10) were collected at the time of transurethral resection of the prostate. Furthermore, androgen-independent LNCaP cells were established. The mRNA expression levels of AR and AR-V7, cell proliferation and prostate-specific antigen (PSA) production were evaluated by reverse transcription quantitative PCR, MTS assay and chemiluminescent enzyme immunoassay, respectively. There was a significant difference in AR-V7/AR expression ratios between the CRPC group and the BPH and pre-treatment PCa groups (CRPC, 7%; BPH and pre-treatment PCa, 1%). Subsequently, we compared the AR and AR-V7 expression levels in CRPC samples with those in the pretreatment prostate tissues from the same patients. The results demonstrated that the AR-V7/AR ratio increased from 3 to 9% after CRPC onset. Furthermore, in vitro experiment demonstrated that AR-V7 expression in LNCaP cells was increased after transforming into CRPC cells. The AR-V7/AR ratio also increased from 0.05 to 0.3%. In addition, small interfering (si)-RNA-mediated knockdown of AR inhibited the proliferation of and PSA production from androgen-independent LNCaP cells; however, AR-V7 knockdown had no effect. Conversely, siRNA-mediated knockdown of both AR and AR-V7 inhibited the proliferation of VCAP cells. In summary, the findings from the present study demonstrated that AR-V7 expression and AR-V7/AR ratio were increased after the onset of CRPC, which had a limited role in CRPC cell proliferation. Further investigation is required to clarify the roles of AR other splice variants and AR-V7 in CRPC.