Tumour promoter mediated altered expression and regulation of ornithine decarboxylase and S-adenosylmethionine decarboxylase in H-ras-transformed fibrosarcoma cell lines

Alterations in cellular growth are important in the progression of malignan t disease. Cell growth regulation by tumour promoters can be complex. The p resent study demonstrates a novel link between alterations in phorbol ester tumour promoter mediated regulation during malignant conversion and the ex pression of ornithine decarboxylase and S-adenosylmethionine decarboxylase, key rate-limiting and regulatory activities in the biosynthesis of polyami nes. H-ras-transformed mouse 10 T 1/2 cell lines exhibiting increasing mali gnant potential were investigated for possible phorbol ester tumour promote r mediated changes in ornithine decarboxylase (ODC) and S-adenosylmethionin e decarboxylase (SAMDC) gene expression. Selective induction of ODC and SAM DC gene expression was observed, since in contrast to nontransformed parent al 10 T1/2 cells, ras-transformed cells capable of benign tumour formation (NR3 cells) and ras-transformed cells capable of metastasis formation (C2 c ells) exhibited marked alterations in the levels of ODC and SAMDC gene expr ession. Increased ODC gene and SAMDC gene expression in response to phorbol -12-myristate-13-acetate (PMA) treatment was found to involve transcription al events in both NR3 cells and in C2 cells. Post-transcriptional events al so played a role in the regulation of ODC gene expression in NR3 cells and in C2 cells, and in the regulation of SAMDC gene expression in C2 cells but not in NR3 cells. In NR3 cells, alterations in ODC and in SAMDC gene expre ssion was an event requiring de novo protein synthesis, whereas in highly m alignant C2 cells, protein synthesis inhibition following cycloheximide tre atment in cooperation with PMA resulted in an augmentation of both ODC and SAMDC gene expression. Evidence is presented to suggest that the PMA-mediat ed alterations in ODC and in SAMDC gene expression in NR3 cells and in C2 c ells involved protein kinase C - mediated events. The status of the cellula r polyamine levels was also an important determinant of the PMA-mediated al terations that occurred in ODC and in SAMDC expression in these H-ras trans formed cells. Collectively, these results suggest that PMA can modulate ODC and SAMDC expression in H-ras transformed cells and that the mechanisms in volved in the PMA- mediated regulation of ODC and SAMDC gene expression cha nges as a function of H-ras mediated cellular transformation and malignant progression. This study further suggests a mechanism of PMA stimulation of transformed cells wherein early alterations in the regulatory control of OD C and SAMDC gene expression are important and critical.