S-adenosytmethionine decarboxylase gene expression is regulated by the cAMP signal transduction pathway in H-ras transformed fibrosarcoma cells capable of malignant progression

The hypothesis that H-ras transformed cells contain alterations in signalli ng pathways important in controlling the expression of S-adenosylmethionine decarboxylase, (SAMDC) a highly regulated activity in the biosynthesis of polyamines was tested. Mouse 10 T1/2 fibroblasts and H-ras transformed cell lines of varying degrees of malignant potential were treated with agents w hich affect cAMP levels within cells. Elevations in SAMDC expression were n oted in H-ras transformed metastatic C3 cells, which were not observed in e ither parental, nontransformed III T1/2 fibroblast cells? or in ras transfo rmed NR3 cells, which are only capable of benign tumour formation. Forskoli n, a stimulator of cAMP synthesis, was able to increase SAMDC enzyme activi ty but the response which occurred was dependent upon the cellular phenotyp e expressed. Actinomycin D pre-treatment of C3 cells prior to exposure to f orskolin did not abrogate the elevation observed in SAMDC gene expression s uggesting that this was not a transcriptional process mediated event. Forsk olin pre-treatment of C3 eel Is did result in a marked increase in the hair -life of SAMDC mRNA transcripts suggesting a role for post-transcriptional stabilization. Furthermore, cycloheximide treatment of malignant C3 cells r esulted in elevated SAMDC mRNA levels. Treatment of malignant C3 cells with both cycloheximide and forskolin together resulted in a further additive e levation in SAMDC message levels. Cycloheximide treatment alone was found t o affect the half-life of SAMDC mRNA through a mechanism of post-transcript ional stabilization. Additionally, altered SAMDC gene expression in C3 cell s which occurred in response to cAMP alterations, was enhanced by stimulati on of a protein kinase C pathway suggesting possible interactions between p rotein kinase C- and cAMP-mediated pathways which affect the regulation of SAMDC expression in highly malignant C3 cells. These results demonstrate ab errant regulation of signalling pathways involved in controlling SAMDC gene expression in H-ras transformed cells capable of malignant progression and provide further insight into the altered growth regulatory program associa ted with H-ras mediated cellular transformation and malignant progression. (C) 2001 Wiley-Liss, Inc.