Altered growth-regulation of prostatic epithelial-cells by human papillomavirus-induced transformation

Six lines of human papillomavirus (HPV)-transformed prostatic epithelial cells, clonally-derived from transfection of three different parental cell strains, were analyzed for their ability to respond to stimulatory and inhibitory factors known to regulate prostatic cell growth. The cell lines were tested in a serum-free medium that was developed specifically for analysis of low-density growth of prostatic cells in order to mitigate any effects of autocrine factors. This medium has been used previously to characterize the growth regulatory pathways of primary cultures of prostatic epithelial cells derived from normal, benign prostatic hyperplasia (BPH), or adenocarcinoma tissues, as well as an SV40-transformed cell line (pRNS-1-1) that was derived from the same parental cell strain as four of the HPV-transformed lines used in the present study. The responses of the HPV-transformed cell lines to three essential mitogens in the medium - epidermal growth factor (EGF), bovine pituitary extract (BPE) and insulin-like growth factor (IGF) - were similar to those of primary cultures and pRNS-1-1, except that two of the HPV-transformed cell lines were IGF-independent for growth. The presence or absence of cholera toxin (CT), which acts synergistically with peptide growth factors, only mildly affected the proliferation of HPV-transformed cells, which is also true for primary cultures and pRNS-1-1. However, while hydrocortisone (HC) also has only minimal effect on the growth of primary cultures and pRNS-1-1, four of the HPV-transformed lines were very dependent on HC for growth. With regard to growth-inhibitory factors, all of the cell lines (HPV- or SV40- transformed) were insensitive to tumor necrosis factor-alpha (TNFalpha), which is a common feature of transformed cells. However, the cell lines remained sensitive to the growth-inhibitory properties of retinoic acid (RA) and transforming growth factor-beta (TGF(beta)). The HPV-transformed cell lines were also inhibited by 1,25(OH)(2) vitamin D-3 [1,25(OH)(2)D-3], although pRNS-1-1 cells were not. Perhaps the most unexpected finding in our study was the apparent loss of responsiveness of all of the transformed lines to fibroblast growth factor (FGF). Alterations in FGF pathways have been described for prostatic cancer cell lines and changes in expression of FGF or receptors may be involved in prostatic carcinogenesis. Our study demonstrates that the availability of primary cultures, SV40- and HPV- transformed cell lines and a well-defined culture system will provide an opportunity to characterize the processes involved in malignant transformation of prostatic cells.