Seminal plasma factors induce in vitro PRL secretion in smooth muscle cells of the human prostate

Abstract

Next to the sex steroid hormone T, PRL has been shown to influence prostatic function and development. Transgenic mice overexpressing the rat PRL gene develop dramatic enlargements of the prostate gland. Proliferation and secretory activities of epithelial cells are stimulated by PRL in rodents and men. Low concentrations of human PRL (hPRL) and hPRL receptors have been observed in human prostatic epithelial cells (ECs). The aim of this study was to compare regulation of the in vitro hPRL secretion in prostatic ECs and stromal smooth muscle cells (SMCs) after stimulation with seminal plasma (SMP), containing a variety of prostatic factors. SMCs released up to 1 ng hPRL/ml (i.e., approximately 500-fold more than unstimulated SMCs and ECs). Quantification of PRL mRNA by highly sensitive quantitative RT-PCR revealed that hPRL gene expression increased 5-fold within 24 h of SMP incubation. Sex steroids (dihydrotestosterone, progesterone, 17β-estradiol), prostaglandins (PGE-1, PGE-2), and cAMP-stimulating substances (forskolin) were not responsible for induction of hPRL. Compared with endometrial SMCs, regulation of prostatic hPRL secretion was independent of progesterone and cAMP. HPLC analysis of human SMP revealed that the common action of at least two different proteins and a low molecular cofactor is required. We concluded that prostatic ECs secrete proteins acting synergistically with low-molecular-weight cofactors to induce differentiation and hPRL release in SMCs. Age-related increases in SMC-derived hPRL might contribute to the development of benign hyperplasia of the prostate.