Autocrine effect of DHT on FGF signaling and cell proliferation in LNCaP cells: Role of heparin/heparan-degrading enzymes

BACKGROUND. LNCaP cells are androgen-sensitive human prostate cancer cells. They are characterized by a bell-shaped growth curve in response to increa sing doses of dihydrotestosterone (DHT) in culture. At a low concentration of DHT (0.1 nM), these cells show an increase in proliferation, but their g rowth is arrested at a high concentration (100 nM) of DHT. Results of our p revious study demonstrated that the inhibitory effect of DHT at a high conc entration was mediated through the action of TGF-beta 1. The objective of t he present study was to elucidate the mechanism of the proliferative effect of DHT in LNCaP cells. METHODS AND RESULTS. DHT stimulated LNCaP proliferation only when cells wer e cultured in the presence of serum. In serum-free cultures, the characteri stic DHT-induced proliferation was not observed. The addition of neutralizi ng antibody against FGF-2 (basic fibroblast growth factor) was able to inhi bit this DHT-induced proliferation. These results suggest that the prolifer ative effect of DHT was mediated through the action of FGF-2. However, resu lts of the reverse transcriptase polymerase chain reaction indicated that L NCaP cells did not express FGF-2 message. As a result, the source of FGF-2 in these cultures must be the serum supplemented in the culture media. FGF- 2 can bind to heparin sulfate chains within the extracellular matrix (ECM). In cultures treated with exogenous heparin, these proliferative effect of DHT was abolished. These results led to the development of the hypothesis t hat DHT treatment mediates the release of FGF-2 entrapped in the ECM throug h increased heparinase activity. The addition of heparinase to cultures of LNCaP cells, in the absence of DHT, was able to stimulate cell proliferatio n. Moreover, 0.1 nM DHT caused a significant increase in heparinase activit y. CONCLUSIONS. These results provide a possible mechanism for DHT action in L NCaP cells. In the absence of DHT, FGF-2 in culture was trapped in the extr acellular matrix and was not available to interact with LNCaP cells. Howeve r, in the presence of 0.1 nM DHT, heparinase activity in the culture was el evated and, as a result, it liberated the trapped FGF-2 which, in turn, sti mulated proliferation in LNCaP cells. Prostate 44:124-132, 2000. (C) 2000 W iley-Liss, Inc.