Fukushi Kambe

AMP-activated protein kinase (AMPK) is a key regulator of glucose and fatty acid homeostasis. In muscle cells, AMPK stimulates mitochondrial fatty acid oxidation and ATP production. The thyroid hormone T3 increases cellular oxygen consumption and is considered to be a major regulator of mitochondrial activities. In this study, we examined the possible involvement of AMPK in the stimulatory action of T3 on mitochondria. Treatment of C2C12 myoblasts with T3 rapidly led to phosphorylation of AMPK. Acetyl-coenzyme A carboxylase, a direct target of AMPK, was also phosphorylated after T3 treatment. Similar results were obtained with 3T3-L1, FRTL-5, and HeLa cells. Stable expression of T3 receptor (TR)-α or TRβ in Neuro2a cells enhanced this effect of T3, indicating the involvement of TRs. Because HeLa cells express only Ca2+/calmodulin-dependent protein kinase kinase-β (CaMKKβ), one of two known AMPK kinases, it was suggested that the effect of T3 is mediated by CaMKKβ. Indeed, experiments using a CaMKK inhibitor, STO-609, and an isoform-specific small interfering RNA demonstrated the CaMKKβ-dependent phosphorylation of AMPK. Furthermore, T3 was found to rapidly induce intracellular Ca2+ mobilization in HeLa cells, and a Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), suppressed T3- as well as ionomycin-dependent phosphorylation of AMPK. In addition, T3-dependent oxidation of palmitic acids was attenuated by BAPTA, STO-609, and the small interfering RNA for CaMKKβ, indicating that T3-induced activation of AMPK leads to increased fatty acid oxidation. These results demonstrate that T3 nontranscriptionally activates AMPK via intracellular Ca2+ mobilization and CaMKKβ activation, thereby stimulating mitochondrial fatty acid oxidation.

An important role for the cyclin-dependent kinase inhibitors (CDKIs), p27Kip1 and p57Kip2, in the proliferation and differentiation of adrenal cells has been suggested by their knockout mice, which display adrenal hyperplasia. Adrenal development and function are primarily regulated by ACTH. In the present study, we investigated the effects of ACTH on the expression of p27Kip1, p57Kip2 and proliferating cell nuclear antigen (PCNA) in rat adrenals. Male Wistar rats were treated with dexametha-sone (Dex) to inhibit endogenous ACTH secretion. ACTH was then administered to the rats, and the adrenals were examined by Western blot and immunohisto-chemical analyses. Dex treatment induced shrinkage of adrenals where no PCNA-expressing cells were detected, but most of the cells expressed p27Kip1. Subsequent ACTH treatment resulted in the marked suppression of p27Kip1 expression, specifically in adrenocortical cells at 12 h after the stimulus. At 48 h, the p27Kip1 suppression still continued in the cortex, while the PCNA-expressing cells appeared mainly around the zona glomerulosa and increased at 72 h. At this time, the p27Kip1-expressing cells also appeared in the same zone. In contrast to p27Kip1, the expression of p57Kip2 was not detected in the Dex-treated adrenal. However, its expression was markedly induced by ACTH in the zona glomerulosa at 48 and 72 h. The results demonstrate that the primary site for mitogenic action of ACTH in rat adrenocortex is the zona glomerulosa, and that ACTH modulates proliferation of adrenocortical cells by regulating p27Kip1 and p57Kip2 expression in a time- and site-specific manner.

Objective—Cyclosporin A (CsA) and tacrolimus (FK506) are widely used as immunosuppressants. However, their use has been hampered by various adverse effects, such as acceleration of atherosclerosis. Interleukin (IL)-8, a chemotactic cytokine, plays an important role in pathogenesis of atherosclerosis. We thus investigated whether synthesis of IL-8 from primary human aortic smooth muscle cells is influenced by CsA and FK506.Methods and Results—Northern blot analysis revealed that CsA increased IL-8 mRNA level and enhanced its increase by epidermal growth factor or tumor necrosis factor-α. In contrast, FK506 had no effect on the mRNA level. IL-8 accumulation in culture media was also increased by CsA. Stability of IL-8 mRNA was not affected by CsA, whereas luciferase reporter gene assay using the human IL-8 promoter revealed that CsA significantly augmented the promoter activity. Electrophoretic mobility shift assay showed that binding activity of activator protein (AP)-1 was increased by CsA, and introduction of a mutation into the AP-1 site in the promoter abolished its CsA-dependent activation. The increased AP-1 binding activity was accompanied by c-Fos synthesis.Conclusions—CsA stimulates synthesis of IL-8 via activation of AP-1 in human aortic smooth muscle cells, providing a novel aspect of biological effects of CsA on the cells.

Adrenocorticotropic hormone receptor (ACTHR) is expressed predominantly in the adrenal glands, and its expression is upregulated by its own ligand, ACTH, via a cAMP-dependent pathway. In the present study, we characterized the 5'-regulatory region of human ACTHR gene to elucidate the molecular mechanisms underlying its adrenal-specific and ACTH/cAMP-dependent expression. The promoter region (-1017/+47 when the transcription start site is regarded as + 1) and its serial 5'-deletions (-764/+47, -503/+-47, -214/+47 and -56/+47) were ligated into the upstream of a luciferase (luc) reporter gene. These constructs were transfected into adrenocortical Y1 cells or non-adrenal JEG3 and Cos-1 cells. In all the cell lines, the luc activity gradually increased with serial 5'-deletions and the maximum activity was conferred by - 56/+ 47. However, the magnitude of luc activity of each deletion construct in non-adrenal cells was much less than that in Y1 cells, suggesting that the promoter functions in an adrenal-specific manner. We identified two Steroidogenic Factor (SF)-1-binding sites at -209 and -35. Electrophoretic mobility shift assay (EMSA) demonstrated that both sites bind to SF-1. Mutation of both sites significantly decreased the activity of -214/+47 promoter in Y1 cells. Transfection of SF-1-expressing plasmid into non-adrenal cells significantly increased the promoter activity, suggesting that SF-1 plays a role in the tissue-specific expression of human ACTHR gene. We identified the region, -764 to -503, that was required for the forskolin/cAMP responsiveness of the promoter. This region contains one AP-1 site. EMSA revealed that the binding of AP-1 to this site increased significantly upon treatment of Y1 cells with forskolin. Mutation of the site abolished the forskolin-responsiveness. In non-adrenal cells, the forskolin-responsiveness was observed only when SF-1-expressing plasmid was cotransfected. This is the first demonstration that both AP-1 and SF-1 are required for the cAMP-dependent induction of human ACTHR gene.

We employed cDNA representational difference analysis to identify new genes that are upregulated by 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) in a human hepatoblastoma cell line HepG2. We isolated s...

Objective: Thyroid hormone modifies cardiac action potentials and outward potassium currents directly and indirectly e.g. through β-adrenergic signaling pathway. We thus examined the expression of six voltage-gated potassium channel α-subunits in the rat left ventricle under hypo- and hyperthyroid status, and tested roles of β-adrenergic signaling pathway in their expressions under both status. Methods: Hypothyroidism and hyperthyroidism were induced by administration of methimazole (MMI) for 4 weeks and by injection of l-thyroxine (T₄) to the MMI-treated rats for the last 7 days, respectively. To distinguish the effects of T₄ and the β-adrenergic system, propranolol (Pro) was administered to the MMI-treated rats together with T₄, and isoproterenol (Iso) was injected to MMI-treated rats for the last 7 days. The mRNA levels of Kv1.2, Kv1.4, Kv1.5, Kv2.1, Kv4.2 and Kv4.3 in the left ventricles were determined by ribonuclease protection assay. Results: MMI treatment induced hypothyroidism and resulted in a significant decrease in the mRNA levels of Kv1.5, Kv2.1 and Kv4.2 (19%, 77% and 61% of control value, respectively; n=6, p4 administration induced hyperthyroidism and cardiac hypertrophy, and it increased the Kv1.5 and Kv2.1 mRNA levels over the control value (212% and 140%, respectively; n=6, p4. In contrast, the Kv1.2 and Kv1.4 mRNA levels increased in hypothyroid rats (161% and 186% of control value, respectively; n=6, pn=6, p4-induced hypertrophy. Iso induced cardiac hypertrophy. Pro or Iso by itself did not alter Kv mRNA levels except for Kv1.2, the message of which was decreased by Iso. Conclusion: Thyroid hormone differentially regulates the expression of Kv1.4, Kv1.5, Kv2.1 and Kv4.2 mRNA levels in the rat left ventricle. This effect is not mediated through β-adrenergic signaling pathway. On the other hand, the reduction in Kv1.2 mRNA level was associated with cardiac hypertrophy induced by T₄ or Iso.

Tumor necrosis factor (TNF) -α is present in synovial fluid of patients with rheumatoid arthritis. It induces the expression of chemotactic cytokines (chemokines) such as interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) in synovial cells. Based on our recent finding that reactive oxygen intermediates play important roles in mediating TNF-α action, we examined the effect of an antioxidant flavonoid, quercetin, on TNF-α-induced expression of IL-8 and MCP-1 in cultured human synovial cells. Quercetin suppressed the TNF-α-induced increase in the mRNAs for IL-8 and MCP-1 in a dose dependent manner. H₂O₂-mediated induction of these genes was also inhibited by quercetin. Electrophoretic mobility shift assays revealed that quercetin inhibited the activation of NF-κB by TNF-α. These results demonstrate for the first time that quercetin suppresses TNF-α-mediated stimulation of IL-8 and MCP-1 expression, at least in part, by inhibiting the activation of NF-κB.

Regulation of the ACTH receptor (R) in the adrenal gland by its own ligand “ACTH” has beena matter of controversy. In the present study, whether ACTH regulates the expression of mRNA for its own receptor in the adrenal gland was studied in human subjects and in rats in vivo. In the human study, adrenal adenoma tissues as well as adjacent normal tissues were obtained at surgery from two patients with typical Cushing's syndrome. Northern blot analysis revealed two ACTH-R mRNA species with 4.0kb and 2.0kb. ACTH-R mRNAs in the adenoma tissues were much more abundant than those in the normal tissues from the two patients, suggesting that the mRNA in normal adrenal tissue is either suppressed by cortisol excess or the absence of ACTH. To examine the mechanism involved in ACTH-R mRNA regulation, the changes in the receptor mRNA caused by ACTH were studied in dexamethasone-treated rats. Administration of dexamethasone for 5 days resulted in a marked decrease in ACTH-R mRNA to an undetectable level. A bolus administration of ACTH_1-24 intravenously or ACTH-Z_1-24 intramuscularly to the dexamethasone-treated rat did not cause any significant change in ACTH-R mRNA from 0.5 to 12h after the administration. However, a significant increase in the receptor mRNA was observed at 24h after the ACTH-Z_1-24 and the level was further increased until 48h followed by a sustained increase at 72h when it was given once every 24h. These data suggest that the ACTH-receptor is increased by ACTH at a pretranslational level. Although it remains to be studied whether the increased receptor mRNA level in the adenoma tissues of the patients with Cushing's syndrome is a general phenomenon, the results suggest that the regulatory mechanism of the receptor in the adenoma is different from that in normal tissue and this could contribute to the pathogenesis of autonomous production of cortisol.