HOXB13-mediated suppression of p21WAF1/CIP1 regulates JNK/c-Jun signaling in prostate cancer cells.

Many prostate cancer (PCa) patients die of recurrent disease due to the emergence of hormone-independent cancer cells of which the mechanism is not fully understood. Our previous studies demonstrated that most castration- resistant prostate cancers (CRPC) overexpress the HOXB13 transcription factor to confer positive growth signals. Since HOXB13 also suppresses p21WAF1/CIP1 (p21) expression, we studied the correlation between HOXB13 and p21 in selected samples of PCa. While there was no statistically significant correlation between expression of HOXB13 and p21, HOXB13-deficient tumors had three times higher odds for expressing p21 than HOXB13-positive tumors. Moreover, CRPC showed more negative correlation than hormone-dependent PCa (HDPC). Further in vitro proliferation assay demonstrated that androgen did not affect the growth-suppressive function of p21 in androgen-dependent PCa cells, suggesting that p21 seems to override the growth-promoting function of androgen and suppression of p21 expression by HOXB13 is an important step in PCa cell survival under no androgen influence. HOXB13 also inhibited AP-1 signals via suppressed expression of JNK/c-Jun. While HOXB13 suppressed p21 expression via regulation of JNK signals, alteration of p21 expression also affected c-Jun and AP-1 activity. Taken together, overexpression of HOXB13 in CRPC is an important step in avoiding the growth-suppressive effect of p21 in a harsh condition such as an androgen-deprived environment.

Evaluation of HOXB13 as a molecular marker of recurrent prostate cancer.

Many patients with prostate cancer have disease recurrence following surgical removal of tumors and fail to respond to androgen ablation therapy. Despite the existence of a number of clinical/pathological factors, it is not possible to predict which patients will fall into this category. The results of our previous studies demonstrated that the HOXB13 homeodomain protein plays a key role in the development of prostate cancer and the progression of this malignancy. In addition, HOXB13 has been reported to predict estrogen-resistant breast cancer tumors. The purpose of this study was to investigate whether HOXB13 could be used as a molecular marker to predict prostate cancer recurrence. To examine the role of HOXB13 as a molecular marker with clinical/pathological data, the expression of HOXB13 was compared using immunohistochemistry in 57 organ-confined prostate cancer tumors obtained by radical prostatectomy. There was no significant correlation between the expression of HOXB13 and most clinical/pathological parameters, including tumor margin, invasion, pathological stage and risk level. The HOXB13 expression levels correlated with the Gleason score and there was a positive correlation with the pre-operative prostate specific antigen (PSA) levels. Accordingly, the tumor specimens from 4 patients who ultimately had biochemical failure (PSA >0.2 ng/ml), all showed a high expression of HOXB13, while their risk levels were either intermediate or high. This is the first study to report that HOXB13, together with other clinical/pathological factors, can be used as a molecular marker to predict the progression of prostate cancer.