BOMBESIN STIMULATES THE MOTILITY OF HUMAN PROSTATE-CARCINOMA CELLS THROUGH TYROSINE PHOSPHORYLATION OF FOCAL ADHESION KINASE AND OF INTEGRIN-ASSOCIATED PROTEINS

Bombesin-like peptides, including the mammalian homologue gastrin-rele asing peptides, are highly expressed and secreted by neuroendocrine ce lls in prostate carcinoma (PCa) tissues and are likely to be related t o the progression of this disease, In the present study, we show that bombesin enhances the migration of androgen-independent PCa cells (PC- 3) in vitro, while not affecting their adhesion to extracellular matri x proteins, The bombesin-increased motility of PC-3 cells occurs throu gh its receptor, and, as shown with inhibitors, it likely requires act ivation of both protein tyrosine kinases (PTKs) and protein kinases C (PKCs), Because the focal adhesion kinase pp125(FAK) plays a key role in adhesion/motility and is highly expressed in advanced PCa, we exami ned whether in PC-3 cells bombesin signal transduction triggers the ty rosine phosphorylation of this PTK and of associated integrins and sig naling proteins likely to be present in focal adhesion plaques, pp125( FAK) tyrosine phosphorylation was stimulated by bombesin and mimicked by PKC activation with the tumor-promotor phorbol 12-myristate-13-acet ate (PMA). Moreover, this effect of bombesin on pp125(FAK) tyrosine ph osphorylation requires the presence of both active PKC and cytoskeleto n integrity since this signal was abolished by down-regulating PKCs in duced by prolonged PMA treatment or by PKC inhibition with GP 109203X, as well as by disruption of the cytoskeleton with cytochalasin D. We also show that bombesin increases the tyrosine phosphorylation of a 95 -kDa protein (pp95) which was co-immunoprecipitated with the alpha v a nd beta (3 and 5) subunits, forming integrin receptors with alpha v in PC-3 cells. The protein pp95 is distinct from the endogenously tyrosi ne-phosphorylated beta 3 subunit. In addition, upon bombesin treatment , the beta 1, beta 3 and beta 5 integrin subunits co-immunoprecipitate d with pp125(FAK) and major phosphotyrosine (pY)-containing proteins o f 125 and 68-70 kDa, likely corresponding to pp125(FAK) and paxillin. Together our data suggest that, in addition to PKC activation, tyrosin e phosphorylation of pp125(FAK) and integrin-associated proteins may p lay an important role in bombesin signaling, triggering the processes of PCa cell motility and invasion. (C) 1997 Wiley-Liss, Inc.