Genistein differentially modulates androgen-responsive gene expression and activates JNK in LNCaP cells

Abstract

Genistein, the predominant isoflavone in soy, may be chemopreventive in prostate cancer (CaP). It downregulates the prostate-specific antigen (PSA) and androgen receptor (AR) in androgen responsive cells. However, the extent of the down-regulation and whether genistein has a general effect on all androgen responsive genes (ARGs) are unclear. We investigated the ability of genistein to modulate ARG expression by the synthetic androgen R1881 in LNCaP cells. Given that there is important crosstalk between AR and mitogen activated protein kinase (MAPK) signaling, we also investigated whether genistein activates the MAPK end targets c-Jun N-terminal kinase (JNK) and c-Jun. Changes in ARG expression were determined by Western analysis and semi-quantitative RT-PCR. The activation of JNK and c-Jun was investigated by Western analysis and a solid phase kinase assay. The PSA protein and mRNA expression were both down-regulated by genistein. In contrast, KLK4 was upregulated at the mRNA, but down-regulated at the protein level. NKX3.1 mRNA levels did not change significantly, but protein levels were significantly down-regulated. STAMP2 mRNA levels slightly increased whereas the protein expression was down-regulated. The AR mRNA expression changed significantly only at high concentrations of genistein when it was down-regulated, whereas AR protein levels were decreased at low concentrations of genistein. The solid phase kinase assay indicated a transient activation of JNK by genistein, which was supported by Western analysis. Thus genistein differentially modulates ARG mRNA expression, but has an inhibitory role on the ARG protein levels. The activation of the JNK pathway which inhibits AR signaling may provide a mechanism for the overall inhibition of protein levels.

Prostatic soy isoflavone concentrations exceed serum levels after dietary supplementation

“…In models pertaining to PCA, genistein inhibits receptor tyrosine kinases, nuclear factor kappa B (NF-kB) and vitamin D-24-hydroxylase thus induces apoptosis (10, 13) and enhances calcitriol action to inhibit proliferation of PCA cells (29, 37). Genistein activates tumor suppressor genes (12, 15), inhibits metastasis (13), modulates androgen-responsive gene expression (14), and down-regulates prostate-specific antigen (PSA) (9) and the androgen receptor (7). …”

Soy isoflavones and prostate cancer: A review of molecular mechanisms

“…These results provide evidence to support the inhibitory effect of genistein on AR expression and/or transcriptional activity. However, some in vitro studies demonstrated stimulatory effects of isoflavones particularly genistein at certain low doses [190–192]. The cause of these controversial results is not clear.…”

Differential Effects of Genistein on Prostate Cancer Cells Depend on Mutational Status of the Androgen Receptor

“…Although in a number of in vitro studies genistein downregulated AR transcription and PSA protein expression in PCa cells and inhibited their growth [24,26,27], stimulatory effects have been also reported [45–47]. However, most of these studies have some methodological limitations.…”