GROWTH-FACTOR REGULATION OF GENE-EXPRESSION IN THE HUMAN PROSTATIC-CARCINOMA CELL-LINE LNCAP

In order to characterize the effects of growth factors on the regulation of expression of the genes coding for prostatic differentiation markers, prostatic acid phosphatase and prostate-specific antigen, we studied changes occurring in the biosynthesis of these enzymes in LNCaP prostatic cancer cells treated with growth factors. Epidermal growth factor was found to reduce the secretion of prostatic acid phosphatase and prostate-specific antigen by the cells, as the result of lowered steady-state levels of the corresponding messenger RNAs (mRNAs). In addition, epidermal growth factor (EGF) interfered with the androgen regulation of these genes. EGF evoked these changes in a concentration- and time-dependent fashion, in both the presence and absence of serum and most likely through interactions with the epidermal growth factor receptor, inasmuch as similar effects were achieved by treating the cells with transforming growth factor alpha. The regulation of the human glandular kallikrein 1 gene was quite similar to the regulation of the prostate-specific antigen gene. In addition to the expression of the genes coding for prostatic secretory proteins, the amount of the human androgen receptor mRNA was down-regulated by EGF. This reduction was more pronounced than the autologous down-regulation of human androgen receptor (hAR) mRNA by androgen and could be maintained for at least 5 days. In the presence of androgen, some of the effects of EGF and transforming growth factor alpha on the levels of androgen-regulated mRNAs may be due to down-regulation of the expression of the hAR gene. Transforming growth factor beta1, which blocked the growth induction of LNCaP cells by EGF, increased the level of prostatic acid phosphatase and hAR mRNAs, but when given to the cells together with EGF its up-regulatory effect could not be discerned. In summary, regulation of the prostatic acid phosphatase and prostate-specific antigen genes is a complex matter, inasmuch as androgens and growth factors regulate the levels of the mRNAs originating from them. Furthermore, the interactions between the androgen-regulatory system and the growth factor-regulatory systems are likely to be at multiple levels in prostatic cells, as suggested by the modulation of the hAR gene expression by these growth factors.