Cell type-specific requirement of the MAPK pathway for the growth factor action of gastrin

Gastrin (G17) has a CCKB receptor-mediated growth-promoting effect on the A R42J rat acinar cell line that is linked to induction of both mitogen-activ ated protein kinase (MAPK) and c-fos gene expression. We investigated the m echanisms that regulate the growth factor action of G17 on the rat pituitar y adenoma cell line GH(3). Both AR42J and GH(3) cells displayed equal level s of CCKB receptor expression and similar binding kinetics of I-125-labeled G17. G17 stimulation of cell proliferation was identical in both cell line s. G17 stimulation of GH(3) cell proliferation was completely blocked by th e CCKB receptor antagonist D2 but not by the MEK inhibitor PD-98059 or the protein kinase C inhibitor GF-109203X, which completely inhibited G17 induc tion of AR42J cell proliferation. G17 induced a c-fos SRE-luciferase report er gene plasmid more than fourfold in the AR42J cells, whereas it had no ef fect in the GH(3) cells. In contrast to what we observed in the AR42J cells , G17 failed to stimulate MAPK activation and Shc tyrosyl phosphorylation a nd association with the adapter protein Grb2. Epidermal growth factor induc ed the MAPK pathway in the GH(3) cells, demonstrating the integrity of this signaling system. G17 induced Ca2+ mobilization in both the GH(3) and AR42 J cells. The calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesu lfonamide inhibited AR42J cell proliferation by 20%, whereas it completely blocked G17 induction of GH(3) cell growth. The Ca2+ ionophore ionomycin st imulated GH(3) cell proliferation to a level similar to that observed in re sponse to G17, but it had no effect on AR42J cell proliferation. Thus there are cell type specific differences in the requirement of the MAPK pathway for the growth factor action of G17. Whereas in the AR42J cells G17 stimula tes cell growth through activation of MAPK and c-fos gene expression, in th e GH(3) cells, G17 fails to activate MAPK, and it induces cell proliferatio n through Ca2+-dependent signaling pathways. Furthermore, induction of Ca2 mobilization in the AR42J cells appears not to be sufficient to sustain ce ll proliferation.