Cultured hepatoma cells for the study of enzyme regulation: induction of ornithine decarboxylase by insulin and asparagine

Endogenous ornithine decarboxylase/polyamine system mediated the antagonist role of insulin/PEG-CMCS preconditioning against heart ischemia/reperfusion injury in diabetes mellitus

INTRODUCTION

Insulin has shown antioxidation and cytoprotective effects to decrease heart ischemia/reperfusion injury (HI/RI) in diabetes mellitus (DM), but the role of insulin/poly(ethylene glycol)-carboxymethyl chitosan (PEG-CMCS) on HI/RI in DM is not known. This research explored whether insulin/PEG-CMCS revealed a protective effect on HI/RI in DM through ornithine decarboxylase (ODC)/polyamine systems.

MATERIALS AND METHODS

Diabetes was induced via streptozotocin (STZ) in Sprague Dawley (SD) rats, which suffered from HI via blocking the left circumflex artery for 45 minutes, followed by 2 hours of reperfusion. α-Difluoromethylornithine-ethylglyoxal bis (guanylhydrazone) (DFMO-EGBG) and insulin/PEG-CMCS were administered to diabetic rats to explore their roles on severity of HI/RI.

RESULTS

Insulin could be fleetly and efficiently loaded via the nanocarrier PEG-CMCS at pH =6, showing efficient loading and stable release. In addition, insulin/PEG-CMCS showed significant hypoglycemic activity in diabetic rats. On the other hand, ischemia/reperfusion obviously augmented the contents of creatine kinase (CK), lactic dehydrogenase (LDH), putrescine (Pu), myocardial infarct size, and NF-κB and spermidine/spermine N'-acetyltransferase (SSAT) expressions and decreased the levels of spermine (Sp), polyamine pools (PAs), heart rate (HR), coronary blood flow (CF), left ventricular developed pressure (LVDP), and ODC expression, compared with Sham. Administration of insulin and insulin/PEG-CMCS both reduced the contents of CK, LDH, Pu, myocardial infarct size, and NF-κB and SSAT expressions and increased the levels of Sp, PAs, HR, CF, LVDP, and ODC expression, while insulin/PEG-CMCS significantly indicated the protective results, and DFMO-EGBG showed the opposite effects.

CONCLUSION

The research showed that insulin/PEG-CMCS could play a protective effect on HR/RI in diabetic rats via its antioxidative, antiapoptotic, and anti-inflammatory roles and modulating ODC/polyamine systems.

Insulin signal transduction pathways and insulin-induced gene expression

Insulin regulates metabolic activity, gene transcription, and cell growth by modulating the activity of several intracellular signaling pathways. Insulin activation of one mitogen-activated protein kinase cascade, the MEK/ERK kinase cascade, is well described. However, the effect of insulin on the parallel p38 pathway is less well understood. The present work examines the effect of inhibiting the p38 signaling pathway by use of specific inhibitors, either alone or in combination with insulin, on the activation of ERK1/2 and on the regulation of gene transcription in rat hepatoma cells. Activation of ERK1/2 was induced by insulin and was dependent on the activation of MEK1, the kinase upstream of ERK in this pathway. Treatment of cells with p38 inhibitors also induced ERK1/2 activation/phosphorylation. The addition of p38 inhibitors followed by insulin addition resulted in a greater than additive activation of ERK1/2. The two genes studied, c-Fos and Pip92, are immediate-early genes that are dependent on the ERK1/2 pathway for insulin-regulated induction because the insulin effect was inhibited by pretreatment with a MEK1 inhibitor. The addition of p38 inhibitors induced transcription of both genes in a dose-dependent manner, and insulin stimulation of both genes was enhanced by prior treatment with p38 inhibitors. The ability of the p38 inhibitors to induce ERK1/2 and gene transcription, both alone and in combination with insulin, was abolished by prior inhibition of MEK1. These data suggest possible cross-talk between the p38 and ERK1/2 signaling pathways and a potential role of p38 in insulin signaling.

Ethanol's effect on tissue polyamines and ornithine decarboxylase activity: a concise review

An extraordinarily diverse literature describes the cellular/tissue systems in which the molecular effects of both acute and chronic alcohol exposure seem to be mediated by changes in polyamine levels and/or ornithine decarboxylase (ODC) activity. The single unifying factor that links most of these studies is that they all, in some way, involve tissues that are undergoing relatively rapid cell division. Non-dividing cells expressing the NMDA receptor are a notable exception in that ethanol and the polyamines seem to act via discrete regions of that receptor. Under most cellular conditions, ODC activity is a reflection of the relative tissue polyamine content, and an increase in ODC activity and polyamine content seems to be one of the early events in the progression of quiescent cells toward cell division. Thus, it is not surprising that ethanol, which has been widely reported to delay cell division, should be found to interact with the ODC/polyamine pathway. Perhaps the most unique aspect of these studies is the fact that, with rare exception, both acute and chronic ethanol exposure have been found to slow growth and to lower tissue polyamine (putrescine) content. Furthermore, in most studies, the ethanol-induced suppression of cell division could be overcome by the administration of exogenous putrescine. These data suggest that the ethanol-induced suppression of cell division resulted from the loss of putrescine. In addition, because the cells were able to respond to the exogenous putrescine, the studies suggest that the signaling pathway remained intact beyond the polyamine synthesis step.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical changes, early brain growth suppression and impaired detour learning in nicotine-treated chicks

Fetal growth suppression associated with chronic maternal intake of cigarette smoke is frequently observed in humans and studies using animal models suggest that in utero nicotine exposure is an important component of this growth suppression. The developing fetal central nervous system (CNS) is sensitive to the growth inhibitory effect of nicotine and morphological as well as functional CNS deficits may result from fetal nicotine exposure. The studies presented here show that nicotine exposure during early embryonic development ultimately inhibits the ability of 7-11 day old chicks to learn a detour task. The brain growth suppression caused by nicotine is paralleled by a failure of the early embryo brain to express the normal developmental increase in ornithine decarboxylase (ODC) activity. This biochemical change may be germane to the mechanism of nicotine-induced growth inhibition and/or nicotine-induced behavioral changes because the appropriate expression of ODC activity is essential to normal growth and differentiation in the fetal CNS. In the chick embryo, nicotine exposure alters several important signaling pathways that regulate ODC expression. For example, nicotine exposure lowers embryonic brain glucose levels and causes significant decreases in whole brain cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels and in cyclic AMP binding proteins (protein kinase-A regulatory activity). Also, in cultured chick cells, nicotine inhibits the ability of a potent mitogen (insulin) to induce ODC activity, but, paradoxically, in ovo nicotine exposure increased insulin binding and stimulated insulin receptor autophosphorylation in brain membranes.

Effect of cocaine, ethanol or nicotine on ornithine decarboxylase activity in early chick embryo brain

Fetal drug exposure causes multiple deficits in the developing child. For both humans and animal models, the single most common drug-related problem is fetal growth suppression. This defect is associated with significant perinatal morbidity and mortality and may also be related to significant behavioral problems appearing later in life. Studies focussed on the molecular mechanism of fetal drug effects in placental models are complicated by multiple interactions of the drug with mother, placenta and fetus. Using early (76-168 h) chick embryos as a non-placental model, and three common drugs of abuse (nicotine, ethanol and cocaine) it was found that each drug suppressed the peak in fetal brain ornithine decarboxylase (ODC) activity that normally occurs at 120 h of development. For each drug, the decrease in ODC activity at 120 h was followed by a small but significant increase in ODC. Thus, although the drug-treated embryos were smaller in size, they appeared to be undergoing compensatory growth and, in fact, became equal in weight to the vehicle-treated animals, if allowed to hatch.

Insulin and phorbol myristic acetate induce ornithine decarboxylase in Reuber H35 rat hepatoma cells by different mechanisms

Reuber H35 rat hepatoma cells respond to insulin or to tumor promoting phorbol esters with an increase in ornithine decarboxylase enzyme activity. This occurs in a time- and dose-dependent manner with both types of agonist. We report here that the increase in ornithine decarboxylase activity with optimal concentrations of both agonists is additive. Furthermore, the initial increase is dependent on continued RNA and protein synthesis. We also find that both of these agonists cause an increase in mRNA coding for ornithine decarboxylase in a time- and dose-dependent manner which suggests that the increase in enzyme activity can be accounted for by the increase in transcript levels. The difference in the time course of induction by the agonists, the additivity of induction by the two agonists, the differential sensitivity of induction to cycloheximide and RNA synthesis inhibitors, and the observation that phorbol myristic acetate causes a further increase in ornithine decarboxylase activity and transcript levels in cells already maximally induced by insulin suggest that these two agonists act through separate mechanisms.

Induction of ornithine decarboxylase activity by insulin and growth factors is mediated by amino acids

The polypeptide growth factors, nerve growth factor, epidermal growth factor, and platelet-derived growth factor, as well as insulin do not induce ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) unless a minimal concentration of an ornithine decarboxylase-inducing amino acid, such as asparagine, is present in the medium. The effects of the growth factors were studied in appropriately responsive cell lines: pheochromocytoma (PC12) cells for nerve and epidermal growth factors, fibroblasts (NIH 3T3) for platelet-derived growth factor, and fibroblasts and hepatoma (KRC-7) cells for insulin. The nonmetabolizable amino acid analog alpha-aminoisobutyric acid can replace asparagine, indicating that the covalent modification of the inducing amino acid is not necessary for the induction of ornithine decarboxylase by these growth factors. For the same intracellular concentration of the inducing amino acid, the presence of the growth factors induces higher levels of ornithine decarboxylase. The evidence indicates that these growth factors do not induce ornithine decarboxylase by raising the intracellular concentration of amino acids but rather act synergistically with the inducing amino acid. Evidence is provided that the induction of polyamine-dependent growth by these growth factors is mediated by amino acids. The relationship of these results to the A and N amino acid transport systems and to the Na+ influxes in relation to growth is discussed.