Association of a functional prostaglandin E2-protein kinase A coupling with responsiveness of metastatic Lewis lung carcinoma variants to prostaglandin E2 and to prostaglandin E2-producing nonmetastatic Lewis lung carcinoma variants

Cloned Lewis lung carcinoma (LLC) variants were used in an in vitro migration model for dissemination, to determine if prostaglandin E2 (PGE2) produced by nonmetastatic LLC cells could directly stimulate dissemination of metastatic LLC cells and to identify an intracellular mechanism for such an effect. The migration of metastatic LLC clones was stimulated not only by exogenous PGE2 but also by nonmetastatic LLC cells, by their production of a migration-stimulatory factor which was sensitive to indomethacin and anti-PGE2 antibodies. Nonmetastatic LLC clones were unresponsive to migration stimulation by PGE2. The results of in vivo metastasis studies were consistent with those of in vitro migration studies. In vivo lung metastasis was increased by PGE2, as well as by nonmetastatic cells when they were either admixed with the metastatic LLC inoculum, irradiated and injected adjacent to the metastatic LLC tumor, or localized in chambers and implanted s.c. into mice given injections of metastatic LLC cells. Indomethacin blocked metastasis stimulation by nonmetastatic cells. The in vitro PGE2 stimulation of metastatic LLC cells appeared to be linked to a cyclic AMP (cAMP) response, since migration could also be stimulated by dibutyryl-cyclic AMP and blockage of a cAMP response with nicotinic acid ablated the PGE2 stimulation of migration. In vivo metastasis could be stimulated by elevation of cAMP with aminophylline. The differential responsiveness of metastatic versus nonmetastatic LLC cells to PGE2 could not be due to PGE2-adenylate cyclase coupling, since PGE2 increased the cAMP levels in cultures of both metastatic and nonmetastatic LLC cells. There was, however, a difference in the cyclic AMP-dependent protein kinase (PKA) response to PGE2, with PKA activity of metastatic LLC being stimulated by PGE2 and by the adenylate cyclase-stimulator forskolin, whereas PKA of nonmetastatic LLC was not stimulated by these cAMP elevators, suggesting a dysfunction in the cAMP-PKA coupling.