| Research Abstract |
Insulin-like growth factor-I (IGF-I) is a potent mitogenic and a differentiation inducing polypeptide growth factor, and is considered to be a significant autocrine-paracrine factor involved in cellular proliferation of normal and malignant tissues. Recently, IGF-I receptors have been characterized in human normal prostate epithelial cells, hyperplastic prostate cells, and rat prostate cancer cells. Furthermore, a family of at least six proteins with high binding affinity for IGFs, the IGF binding proteins (IGFBPs), are described which are different form IGF receptors and are considered to control the proliferative and mitogenic effects of IGFs.
The androgen-dependent prostatic carcinoma cell line, LNCaP-FGC (FGC), its derived androgen-independent sublines, LNCaP-r and LNO,and the androgen-independent cell lines PC-3and TSU-PRI (TSU) were used. The breast cancer cell line MCF-7 cell line served as control cell line for IGF responsiveness. The effects of IGF-I or androgens on the growth
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of the cells were assessed by the use of a test based on the enzymatic reduction of the tetrazolium salt MTT.Conditioned medium proteins were separated on sodium dodecylsulfate-polyacrylamide gel and transferred to nitrocellulose paper and IGFBPs were detected by Western blotting. IGF-I recceptor content of membrane preparated was determined by saturation analysis. The data were calculated by multiple-point Scatchard analyzes.
IGF-I stimulated MCF-7 cells dose-dependently (1-100ng/ml). Under the same conditions FGC,LNCaP-r, LNO,and PC-3 cell lines did not respond to IGF-I,whereas it slightly stimulated growth of the TSU line. Androgen addition to IGF-I did not influence the cell growth of the andfrogen-dependent FGC cell line. High affinity IGF-I receptors were demonstrated in all cell lines lested, the receptor content of the FGC line being lower than the other androgen-independent cell lines. All prostatic cancercell lines secreted IGFBP-2, whereas IGFBP-3 and/or IGFBP-4 were also detected in the medium of LNCaP-r, PC-3 and TSU cultures.
In spite of the presence of high affinity IGF receptors, with one exception (TSU), IGF-I had no effect on cell proliferation of the prostatic cancer cell lines tested. As has been described for other tissues, IGFBP-2 may be a factor that inhibits the biological activity of IGF-I in these cell lines, whereas some other IGFBPs, such as IGFBP-4 may enhance IGF-I responsiveness of the cells. It is therefore suggested that IGFBPs regulate IGF-I mediated cell proliferation of prostate cancer cells. Less
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