GROWTH OF THE ANDROGEN-DEPENDENT TUMOR OF THE PROSTATE - ROLE OF ANDROGENS AND OF LOCALLY EXPRESSED GROWTH MODULATORY FACTORS

The crucial role played by androgens in the growth of prostatic carcin oma is now well established. However, the mechanisms of this prolifera tive action are still poorly understood. Experiments have been perform ed to clarify: (1) the metabolism of androgens in prostatic tumor cell s; and (2) the role played by locally produced growth factors in the a utocrine regulation of prostatic tumor cell proliferation and the poss ible regulation exerted by testosterone (T) on the activity of these f actors. These studies have been performed by utilizing the human andro gen-responsive prostatic cancer LNCaP cell line. (1) By incubating LNC aP cells with different C-14-labeled androgenic precursors, it has bee n shown that all the major key enzymes involved in the metabolism of a ndrogens (5 alpha-reductase, 17 beta-hydroxysteroid-oxidoreductase, 3 alpha- and 3 beta-hydroxysteroid-oxidoreductases) are present and acti ve in these cells. In particular, the 5 alpha-reductase, which convert s T and Delta(4) to DHT and 5 alpha-A respectively, seems to be more a ctive when Delta(4) is the substrate, suggesting a preference for this precursor. (2) The hypothesis that LNCaP cells might produce LHRH (or a LHRH-like peptide) has been verified by RT-PCR, performed in the pr esence of a pair of specific oligonucleotide primers. A cDNA band of t he expected size (228 bp), which specifically hybridized with a P-32-l abeled LHRH oligonucleotide probe, has been obtained in LNCaP cells. T o clarify the possible role played by this factor in the regulation of tumor growth, LNCaP cells, cultured in steroid-free conditions, have been treated with a LHRH antagonist; the treatment resulted in a signi ficant increase of cell proliferation. Taken together, these data indi cate that a LHRH (or EHRH-like) growth modulatory system is expressed in LNCaP cells and plays an inhibitory role in the regulation of tumor cell proliferation. This system seems to be regulated in a negative w ay by steroids. Growth factors endowed with stimulatory activity, such as EGF and TGF alpha, have also been shown to be produced by LNCaP ce lls. The present studies show that the immunoprecipitation of the EGF receptor with a specific monoclonal antibody (Ab225) reveals a protein band of the expected size (170 kDa) which is phosphorylated even in b asal conditions. Moreover, the treatment of LNCaP cells, cultured in s erum-free conditions, either with a monoclonal antibody against the EG F receptor, or with immunoneutralizing antibodies against EGF and TGF alpha, results in a significant decrease of cell proliferation. These observations clearly confirm the expression, in prostatic tumor cells, of an EGF/TGF alpha loop which exerts a stimulatory action on cell pr oliferation. T seems to exert a positive regulation on this loop, at l east in terms of EGF receptor concentration.