Transformation by H-ras can result in aberrant regulation of ornithine decarboxylase gene expression by transforming growth factor-?1

Polyamines and related signaling pathways in cancer

Polyamines are aliphatic compounds with more than two amino groups that play various important roles in human cells. In cancer, polyamine metabolism dysfunction often occurs, and regulatory mechanisms of polyamine. This review summarizes the existing research on the metabolism and transport of polyamines to study the association of oncogenes and related signaling pathways with polyamines in tumor cells. Drugs that regulate enzymes have been developed for cancer treatment, and in the future, more attention should be paid to treatment strategies that simultaneously modulate polyamine metabolism and carcinogenic signaling pathways. In addition, the polyamine pathway is a potential target for cancer chemoprevention. As an irreversible suicide inhibitor of the ornithine decarboxylase (a vital enzyme of polyamine synthesis), Difluoro-methylornithine had been shown to have the chemoprevention effect on cancer. Therefore, we summarized and analyzed the chemoprophylaxis effect of the difluoromethylornithine in this systematic review.

Inhibitory effects of the ginsenoside Rg3 on phorbol ester-induced cyclooxygenase-2 expression, NF-kappaB activation and tumor promotion

Our previous studies demonstrated the anti-oxidant and anti-tumor promotional properties of the methanol extract of heat-processed Panax ginseng C.A. Meyer [Cancer Lett. 150 (2000) 41]. In the present work, we have evaluated anti-inflammatory as well as anti-tumor promoting effects of Rg(3), a major ginsenoside derived from heat-processed ginseng. Pretreatment of dorsal skins of female ICR mice with Rg(3) significantly inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ornithine decarboxylase activity and 7,12-dimethylbenz[a]anthracene-initiated papilloma formation. In another experiment, Rg(3) pretreatment abrogated the expression of cyclooxygenase-2 in TPA-stimulated mouse skin. Rg(3) also inhibited the TPA-induced activation of the eukaryotic transcription factor, NF-kappaB in both mouse skin and cultured human pro-myelocytic leukemia (HL-60) cells. Moreover, Rg(3) exerted potent inhibitory effects on the activation of another transcription factor, activator protein-1 (AP-1) that is responsible for c-jun and c-fos oncogenic transactivation. Based on these findings, it is likely that the anti-tumor promoting activity of Rg(3) is mediated possibly through down-regulation of NF-kappaB and AP-1 transcription factors.

Growth factor-mediated altered expression and regulation of S-adenosylmethionine decarboxylase in a H-ras transformed cell line capable of malignant progression

Mammalian S-adenosylmethionine decarboxylase (SAMDC) is a regulatory activity, which is involved in the biosynthesis of polyamines. The polyamines, namely putrescine, spermidine, and spermine, are essential for mammalian cell proliferation. SAMDC expression was examined in a H-ras transformed cell capable of metastasis formation. Serum stimulation of these cells resulted in increased SAMDC mRNA and enzyme activity expression. The effect of several physiologically relevant growth factors on SAMDC expression was also determined. SAMDC mRNA expression was increased in response to epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) stimulation but was unaffected by transforming growth factor beta(1) (TGF-beta(1)) and platelet derived growth factor (PDGF). Increased SAMDC enzyme activity occurred in response to exposure to EGF, bFGF, TGF-beta(1), and PDGF. The EGF and bFGF mediated alterations in SAMDC mRNA expression were apparently not due to alterations in the transcriptional apparatus but occurred partly through post-transcriptional mechanisms involving increased SAMDC message stability. EGF and bFGF were able both to cooperate with cycloheximide, an inhibitor of protein synthesis, to augment the expression of SAMDC mRNA. Furthermore, studies with NIH-3T3 fibroblasts transfected with either the normal basic fibroblast growth factor coding sequence that lacks a known secretory signal sequence or a chimeric bFGF sequence that targets the growth factor to the secretory pathway revealed that increased SAMDC expression occurred only in those cells which contained the chimeric bFGF sequence that targets the growth factor to the secretory pathway suggesting that the increase in expression of SAMDC occurs through an autocrine mechanism. Increased ornithine decarboxylase (ODC) expression was found to occur in both types of bFGF transfected cells suggesting that altered ODC expression in response to bFGF stimulation may occur through both autocrine and intracrine mechanisms. In addition, a correlation was found to exist between SAMDC expression and regulation in response to growth factor stimulation and malignant potential. This correlation supports the view that growth factor induced alterations in SAMDC expression, although not sufficient on their own to induce metastasis, are important in the promotion and establishment of events important to the phenotype expressed by H-ras transformed cells capable of malignant progression.