Induction of Ornithine Decarboxylase Activity Is a Necessary Step for Mitogen-Activated Protein Kinase Kinase–Induced Skin Tumorigenesis

Effects of lentivirus-mediated ornithine decarboxylase gene on the proliferation and apoptosis of fibroblast-like synoviocytes in rats with arthritis

OBJECTIVE

This study aimed to explore the effects of lentivirus-mediated ornithine decarboxylase (ODC) gene on the proliferation and apoptosis of fibroblast-like synoviocytes (FLSs) in rats with rheumatoid arthritis (RA).

METHODS

Twenty Lewis rats were randomized into control group (ten rats without processing) and RA group (ten rats of adjuvant-induced arthritis). The third-generation FLSs were randomized into test, control and blank groups. MTT assay and flow cytometry were employed to detect cell proliferation and apoptosis, respectively. Enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of tumor necrosis factor α (TNF-α), interferon-γ (IFN-γ), and interleukin-2 (IL-2).

RESULTS

Lewis rats in the RA group became ill from 11days on and got seriously ill 18days after modeling. However, rats in the control group had no obvious change. MTT assay showed that the test group had higher cell proliferation than the blank and control groups (P₁<0.001; P₂<0.001). Flow cytometry revealed that the apoptosis of FLSs in the test group was significantly lower than that in the blank and control groups (P₁<0.001; P₂<0.001). ELISA showed that the test group had higher TNF-α, IFN-γ and IL-2 level than the control and blank groups (all P<0.001), but no significant difference was found between the control and blank groups (all P>0.05).

CONCLUSION

The results indicated that overexpression of ODC gene promotes the proliferation while suppressing apoptosis of FLSs in rats with RA.

Destabilization of the ornithine decarboxylase mRNA transcript by the RNA-binding protein tristetraprolin

Ornithine decarboxylase (ODC) is the first and usually rate-limiting enzyme in the polyamine biosynthetic pathway. In a normal physiological state, ODC is tightly regulated. However, during neoplastic transformation, ODC expression becomes upregulated. The studies described here show that the ODC mRNA transcript is destabilized by the RNA-binding protein tristetraprolin (TTP). We show that TTP is able to bind to the ODC mRNA transcript in both non-transformed RIE-1 cells and transformed Ras12V cells. Moreover, using mouse embryonic fibroblast cell lines that are devoid of a functional TTP protein, we demonstrate that in the absence of TTP both ODC mRNA stability and ODC enzyme activity increase when compared to wild-type cells. Finally, we show that the ODC 3' untranslated region contains cis acting destabilizing elements that are affected by, but not solely dependent on, TTP expression. Together, these data support the hypothesis that TTP plays a role in the post-transcriptional regulation of the ODC mRNA transcript.

Herbacetin Is a Novel Allosteric Inhibitor of Ornithine Decarboxylase with Antitumor Activity

Ornithine decarboxylase (ODC) is a rate-limiting enzyme in the first step of polyamine biosynthesis that is associated with cell growth and tumor formation. Existing catalytic inhibitors of ODC have lacked efficacy in clinical testing or displayed unacceptable toxicity. In this study, we report the identification of an effective and nontoxic allosteric inhibitor of ODC. Using computer docking simulation and an in vitro ODC enzyme assay, we identified herbacetin, a natural compound found in flax and other plants, as a novel ODC inhibitor. Mechanistic investigations defined aspartate 44 in ODC as critical for binding. Herbacetin exhibited potent anticancer activity in colon cancer cell lines expressing high levels of ODC. Intraperitoneal or oral administration of herbacetin effectively suppressed HCT116 xenograft tumor growth and also reduced the number and size of polyps in a mouse model of APC-driven colon cancer (ApcMin/+). Unlike the well-established ODC inhibitor DFMO, herbacetin treatment was not associated with hearing loss. Taken together, our findings defined the natural product herbacetin as an allosteric inhibitor of ODC with chemopreventive and antitumor activity in preclinical models of colon cancer, prompting its further investigation in clinical trials.

Hemin inhibits cyclooxygenase-2 expression through nuclear factor-kappa B activation and ornithine decarboxylase expression in 12-O-tetradecanoylphorbol-13-acetate-treated mouse skin

Inflammation induced by various stimuli has been found to be associated with increased risk for most types of human cancer. Inflammation facilitates the initiation of normal cells, as well as the growth of initiated cells and their progression to malignancy through production of proinflammatory cytokines and diverse reactive oxygen/nitrogen species. These also activate the signaling molecules that are involved in inflammation and carcinogenesis. Our previous studies have demonstrated that hemin inhibited 7,12-dimethylbenz[a]anthracene (DMBA)-induced bacterial mutagenesis and oxidative DNA damage, reduced the level of DNA-DMBA adduct and 12-O-tetradecanoylphorobl-13-acetate (TPA)-induced tumor formation in DMBA-initiated ICR mouse skin, and inhibited myeloperoxidase and ornithine decarboxylase (ODC) activity and H(2)O(2) formation in TPA-treated mouse skin. In the present study, to further elucidate the molecular mechanisms underlying the chemopreventive activity of hemin, its effect on the expression of ODC and cyclooxygenase (COX)-2, and the activation of nuclear factor-kappa B (NF-kappaB) and mitogen-activated protein kinases (MAPKs) regulating these proteins were explored in mouse skin with TPA-induced inflammation. Topically applied hemin inhibited ear edema and epidermal thickness in mice treated with TPA. Pretreatment with hemin reduced the expression of ODC and COX-2, and also reduced NF-kappaB activation in TPA-stimulated mouse skin. In addition, hemin suppressed the TPA-induced activation of extracellular signal-regulated protein kinase (ERK) and p38 MAPK in a dose-dependent manner. Taken together, hemin inhibited TPA-induced COX-2 expression by altering NF-kappaB signaling pathway via ERK and p38 MAPK, as well as TPA-induced ODC expression in mouse skin. Thereby, hemin may be an attractive candidate for a chemopreventive agent.