Expression of 5'-AMP-activated protein kinase with starvation in murine thymocytes

The 5'-AMP-activated protein kinase (AMPK) is a key enzyme in the protection of cells during energy crisis. AMPK is a heterotrimer consisting of a catalytic α (α1, 2) subunit and two regulatory subunits, β (β1, 2) and γ (γ1-3). To elucidate the role of AMPK in thymocytes with starvation, we investigated the expression of AMPK in murine thymocytes. The main isoforms expressed were α2, β1, and γ1, of which expression increased time-dependently with starvation, together with an increase in the amount of the active form of AMPK, phospho-AMPKα. In cultured thymocytes, expression of AMPK was induced by dexamethasone, but not by a low glucose concentration in medium. Increased expression was inhibited by glucocorticoid receptor antagonist RU486. Phosphorylation of AMPKα showed an increase with low glucose concentration, but not with dexamethasone. These results suggest that increased expression of AMPK in starved mouse thymocytes is induced by an increase in glucocorticoids and that activation is induced by hypoglycemia.

Hydrogen peroxide induces expression and activation of AMP-activated protein kinase in a dental pulp cell line

AIM

To investigate the effects of hydrogen peroxide on cell viability and expression and activation of AMP-activated protein kinase (AMPK) in rat dental pulp cell line RPC-C2A.

METHODOLOGY

RPC-C2A cells derived from rat dental pulp were maintained in MEM supplemented with 10% FBS at 37 degrees C, in a humidified atmosphere at 5% CO(2). Cells were cultured in the presence or absence of H(2)O(2) for up to 60 min at concentrations of from 0.1 to 3.0 mmol L(-1). Cell viability was analysed by WST-1 reduction assay. Expression of AMPK subunit isoforms was analysed by Western blotting using antibodies to the catalytic alpha1 and regulatory beta1 and gamma1 subunit isoforms. The effect of silencing AMPKalpha1 on cell viability was determined using siRNA.

RESULTS

Exposure to H(2)O(2) decreased cell viability in a time- and dose-dependent manner. The catalytic AMPKalpha1 subunit and its activated form, phospho-AMPKalpha, increased with exposure to H(2)O(2) in a time- and dose-dependent manner, whereas the regulatory beta1 and gamma1 subunits showed no change. Downregulation of AMPKalpha1 resulted in a reduction in cell viability in H(2)O(2)-treated cells at a concentration of 0.1 mmol L(-1) for 30 min incubation, indicating an increased sensitivity to H(2)O(2).

CONCLUSIONS

Reactive oxygen induced energy fuel gauge enzyme AMPKalpha expression and its activation by phosphorylation in RPC-C2A cells, suggesting that AMPK is essential for protection against H(2)O(2)-induced nonapoptotic cell death. Therefore, AMPK may be a therapeutic modulation target for treatment of the dentine-pulp complex injured by reactive oxygen.

Hypoxia induces expression and activation of AMPK in rat dental pulp cells

AMP-activated protein kinase (AMPK) is a stress-responsive enzyme involved in cell adaptation to an energy crisis. We hypothesized that hypoxia suppresses oxidative phosphorylation and ATP production, resulting in AMPK activation to protect cells. We investigated the effects of hypoxia on cell proliferation, the expression of AMPK and hypoxia-inducible factor 1alpha (HIF-1alpha), the activation of AMPK, and the relationship between AMPK and HIF-1alpha expression in rat dental pulp RPC-C2A cells. AMPK in the cells was composed of catalytic alpha1, and regulatory beta1 and gamma1 subunit isoforms. Cell proliferation was initially suppressed under hypoxia, but it increased thereafter, together with an increase in the expression of AMPK and HIF-1alpha, and the activation of AMPK. Down-regulation of AMPKalpha1 by siRNA inhibited cell proliferation under both normoxia and hypoxia, revealing that AMPK induction and activation were required for cell proliferation, although HIF-1alpha expression under hypoxia was not affected.

Geldanamycin, a heat-shock protein 90-binding agent, induces thymocyte apoptosis through destabilization of Lck in presence of 12-O-tetradecanoylphorbol 13-acetate

Geldanamycin, a heat-shock protein 90 (Hsp90)-binding agent, modulates various cellular activities. The present study found that, although geldanamycin by itself had no effect on thymocyte viability, it induced apoptosis in thymocytes with a reduction of the mitochondrial transmembrane potential (DeltaPsim) in the presence of 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C (PKC). This apoptosis depended on transcription and translation, and on activation of caspase-8 and -3. Geldanamycin treatment in the presence of TPA also enhanced destabilization of Lck. This destabilization was independent of transcription and translation. It was inhibited, however, by conventional PKC inhibitors, preventing apoptosis. Proteasome inhibitor affected neither the degradation of Lck nor DNA fragmentation, although they inhibited reduction of DeltaPsim. These results suggest that the ubiquitin-proteasome system is not involved in Lck destabilization, and that DeltaPsim reduction is not directly related to the progression of apoptosis. Furthermore, inhibition of Lck in the presence of TPA induced apoptosis in thymocytes. Our findings suggest that Hsp90 modulates thymocyte apoptosis in concert with PKC through the destabilization of Lck and in a caspase-8- and -3-dependent manner.

MODULATION OF DEXAMETHASONE-INDUCED THYMOCYTE APOPTOSIS BY HEAT-SHOCK PROTEIN 90-BINDING AGENTS

Heat-shock protein 90 (HSP90) is known to affect a variety of cellular activities. The present study showed that the HSP90-binding agents, geldanamycin, herbimycin A and radicicol, inhibited the murine thymocyte apoptosis induced by dexamethasone and was accompanied by the inhibition of the reduction of the mitochondrial transmembrane potential (delta psi m). HSP90-binding agents did not inhibit etoposide-induced apoptosis. The inhibition of dexamethasone-induced apoptosis was in part due to the interference of HSP90 with the glucocorticoid receptor, resulting in the inhibition of nuclear translocation of the receptor. The expression of inositol 1,4,5-triphosphate receptors, which were shown to be involved in dexamethasone-induced apoptosis, did not participate in the inhibition of apoptosis.

[Prophylactic and chemotherapeutic efficacy of pivmecillinam (PMPC) against infections after TUR-P and prostatectomy]

The prophylactic and chemotherapeutic efficacy of PMPC against infections after TUR-P has been investigated. Bacteriological evaluation: PMPC , 200-300 mg/day for 2-12 weeks, was administered to 49 patients, who had over 10(3)CFU/ml of microorganisms after CET or CEC treatment for 3-7 days. The eradication rate of microorganisms was 40.8% after 2 weeks, 52.2% after 4 weeks, 64.1% after 6 weeks, 65.0% after 8 weeks and 70.6% after 12 weeks. Effectiveness on pyuria : The improvement rate of pyuria against 59 patients who had over 10(5)/hpf of pyuria , was 15.3% after 2 weeks, 16.4% after 4 weeks, 25.4% after 6 weeks, 58.5% after 8 weeks, 72.7% after 10 weeks and 75.0% after 12 weeks. Overall clinical efficacy on PMPC was examined in 26 patients. The results of efficacy were 27.3% after 2 weeks, 48.0% after 4 weeks, 50.0% after 6 weeks, 69.2% after 8 weeks, 75.0% after 10 weeks and 77.0% after 12 weeks. The clinical response was evaluated according to a criterion for clinical evaluation of antimicrobial agent on chronic complicated UTI proposed by UTI committee in Japan. No severe adverse effect including allergic reaction was found. Following administration of PMPC , three patients experienced adverse gastric reactions, and drug administration was discontinued at week 6 or 8. PMPC was effective as a prophylactic chemotherapeutic drug against infections after TUR-P and prostatectomy.