THE ROLE OF GROWTH-FACTORS IN THE SUPPRESSION OF ACTIVE CELL-DEATH INTHE PROSTATE - AN HYPOTHESIS

Regression of the rat ventral prostate occurs when the level of Sa-dih ydrotestosterone, the trophic hormone, drops below the threshold requi red to suppress apoptosis. The induction of apoptosis in the ventral p rostate is accompanied by the increase in the steady-state level of a number of mRNAs coding for proteins that are involved in the latter st ages of apoptosis and thus represent secondary thanatogens. These incl ude proteases (cathepsins, plasminogen activators, and collagenase), c lusterin, poly(ADP)ribose polymerase, tenascin, and several unidentifi ed genes, as well as several RNases and the classical Ca2+,Mg2+-depend ent endonuclease. In addition, insulin-like growth-factor-binding prot ein 5 (IGFBP-5) is induced de novo. We propose that IGFBP-5 may serve to trigger the apoptotic process through the attenuation of the insuli n-like growth factor signalling system (which is necessary for cell su rvival), and as such, represents a primary thanatogen in the prostate.