Login to Access Video or Poster Abstract: MP99-14
Sources of Funding: 5R01 CA143299

Introduction

Elevated expression of miR-21, and androgen receptor (AR) regulated microRNA, is sufficient to induce castration resistant prostate cancer growth. However, the mechanism of miR-21-mediated castration resistance remains unclear. PDCD4 (programmed cell death 4) has been known as a tumor suppressor gene and also known as a potent target of miR-21. In this study, we identify PDCD4 as a check point of miR-21 induced castration resistant growth in human prostate cancer.

Methods

Hormone-sensitive prostate cancer cell lines (LNCaP, LAPC4) were used for this study. These cells were transiently transfected with miR-21 mimics, anti-PDCD4 siRNAs, or PDCD4 expression vectors (pCMV-PDCD4) and plated into three different media conditions (complete media, with Bicalutamide, androgen depleted) in order to evaluate PDCD4 function on androgen-dependent, castration resistant growth, and protein expression. In rescue experiments, cells were co-transfected with miR-21 and control or pCMV-PDCD4 vectors. Cell viability was evaluated by MTS assay. Protein expression levels were measured by western blotting.

Results

Androgen stimulation elevates miR-21 expression and reduces PDCD4 protein expression (Fig 1A). Transfection with miR-21 inhibits PDCD4 protein expression in LNCaP and LAPC4 cells (25-40%), as well as luciferase reporters that contain the predicted miR-21 targeting regions from the PDCD4 3&[prime]UTR (Fig 1B). In addition, androgen deprivation reduces miR-21 expression and increases PDCD4 protein level (Fig 1C). miR-21 inhibitor blocked miR-21-induced PDCD4 protein suppression (Fig 1B). In cell viability assay, both miR-21 or anti-PDCD4 siRNA transfected cells induced cell growth and castration resistant cell growth (Fig 2A). Moreover, miR-21 induced cell growth was inhibited by PDCD4 overexpression (Fig 2B).

Conclusions

Our results demonstrate that miR-21 regulates PDCD4 protein expression, and that PDCD4 contributes to miR-21 induced cell growth and castration resistance. Therefore, PDCD4 could be a check point of miR-21 induced castration resistance.

Funding

5R01 CA143299