Can an autocrine loop explain sex-hormone-dependent tumor growth? A brief overview

Sex hormones and their related compounds have been known to regulate the target cell growth positively or negatively in the receptor-dependent manner. The molecular mechanism of these complicated events, especially sex hormone-dependent growth enhancement, has been studied extensively. In MCF-7 cells, estrogen-induced autocrine loop has been demonstrated to play the important role for estrogen-dependent growth. Androgen has been also found to promote the growth of SC-3 cell through the induction of an autocrine growth factor (FGF 8). The blockade of FGF 8 activity resulted in a complete inhibition of androgen-dependent growth of SC-3 cells, suggesting that FGF 8 acts as an essential component of androgen-dependent growth. However, the constitutional expression of FGF 8 failed to convert SC-3 cells from an androgen-dependent to an androgen-independent phenotype. These observations would suggest that sex hormone-induced autocrine loop is an obligatory but not sufficient component for the growth of sex hormone-dependent tumor.