CAMP AND PMA ENHANCE THE EFFECTS OF IGF-I IN THE PROLIFERATION OF ENDOMETRIAL ADENOCARCINOMA CELL-LINE HEC-1-A BY ACTING AT THE G(1) PHASE OF THE CELL-CYCLE

The present study was undertaken to determine whether endometrial canc er cell line HEC-1-A differ from nontransformed cells, in that the cAM P and protein kinase C pathways may enhance IGF-I effects in mitogenes is by acting at the G(1) phase of the cell cycle instead of G(0). Immu nofluorescence staining of HEC-1-A cells using the proliferating cell nuclear antigen (PCNA) monoclonal antibody and flow cytometric analysi s determined that HEC-1-A cells do not enter the G(0) phase of the cel l cycle when incubated in a serum-free medium. Approximately 51% of th e cells were in G(1), 12% were in S and 37% in G(2) phase of the cell cycle prior to treatment. Forskolin and phorbol-12-myristate 13-acetat e (PMA) were used to stimulate cAMP production and protein kinase C ac tivity, respectively. IGF-I, forskolin and PMA each increased (P < 0.0 1) [H-3]-thymidine incorporation in a dose and time dependent manner. The interaction of forskolin and PMA with IGF-I was then determined. C ells preincubated with forskolin or PMA followed by incubation with IF G-I incorporated significantly more (P < 0.01) [H-3]-thymidine into DN A than controls or any treatment alone. It is concluded that forskolin and, to a lesser extent, PMA exert their effect at the G(1) phase of the cycle to enhance IGF-I effects in cell proliferation.