AICAR induces cyclooxygenase-2 expression through AMP-activated protein kinase-transforming growth factor-beta-activated kinase 1-p38 mitogen-activated protein kinase signaling pathway.

AMP-activated protein kinase (AMPK), a critical signaling molecule for regulating energy homeostasis, might bi-directionally regulate inflammation, and its action mechanism leading to inflammation is not fully understood. We utilized 5-aminoimidazole-4-carboxamide riboside (AICAR) as a pharmacological activator of AMPK to unveil the effects of and signaling cascades mediated by AMPK on cyclooxygenase (COX)-2 gene expression in rat aortic vascular smooth muscle cells (VSMCs), murine macrophage cell line (J774), and human umbilical vein endothelial cells (HUVECs). Biochemical approaches were further conducted to elucidate interactions among signaling molecules. We found that AICAR could induce COX-2 protein expression in the cell types tested. This event was mediated by COX-2 gene transcription, and abrogated by compound C and 5'-iodotubercidin, suggesting the essential role of AMPK in COX-2 induction. Pharmacological and biochemical studies indicated that p38 mitogen-activated protein kinase (MAPK) activation is the common downstream signal of AMPK in COX-2 expression in all three cell types. Furthermore, we also found that TAK1 is associated with AMPKalpha2, and this binding requires an interaction between the kinase domains of both molecules. Notably data of TAK1 phosphorylation indicate that the activating state is enhanced upon AMPK activation in vivo and in vitro. Our data for the first time prove a pivotal role of TAK1 in the AMPK signaling axis. Such interaction gives AMPK an additional pathway for regulating cellular functions. Via a downstream p38 MAPK signaling cascade, AMPK-dependent TAK1 activation leads to the expression of the inflammatory COX-2 gene in various cell types.

Chang MY ，Ho FM ，Wang JS ，Kang HC ，Chang Y ，Ye ZX ，Lin WW ... -  《-》

Inhibition of lipopolysaccharide-induced inducible nitric oxide synthase and cyclooxygenase-2 gene expression by 5-aminoimidazole-4-carboxamide riboside is independent of AMP-activated protein kinase.

Recent studies suggest AMP-activated protein kinase (AMPK), an enzyme involved in energy homeostasis, might be a novel signaling pathway in regulating inflammatory response, but the precise intracellular mechanisms are not fully understood. In this study, we have demonstrated that 5-aminoimidazole-4-carboxamide riboside (AICAR), an activator of AMPK, inhibited lipopolysaccharide (LPS)-induced protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in macrophages and microglial cells at the gene transcription level. Data obtained from electrophoretic mobility shift assay (EMSA) and promoter activity assay have further confirmed the ability of AICAR to block LPS-mediated NF-kappaB, AP-1, CREB, and C/EBPbeta activation. However, AICAR did not affect LPS-mediated IKK, ERK, and p38 activation. Regardless of the ability of AICAR to activate AMPK, the inhibitory effects of AICAR on iNOS and COX-2 expression were not associated with AMPK. An adenosine kinase inhibitor 5'-iodotubercidin, which effectively abolished AMPK activation caused by AICAR, did not reverse the anti-inflammatory effect of AICAR. Moreover, another AMPK activator metformin was not able to mimic the effects of AICAR. Direct addition of AICAR in EMSA assay interrupted binding of NF-kappaB, CREB, and C/EBPbeta to specific DNA elements. Taken together, this study demonstrates that the anti-inflammatory effects of AICAR against LPS-induced iNOS and COX-2 gene transcription are not associated with AMPK activation, but might be resulting from the direct interference with DNA binding to transcription factors.

Kuo CL ，Ho FM ，Chang MY ，Prakash E ，Lin WW ... -  《-》

AMP-activated protein kinase inhibits angiotensin II-stimulated vascular smooth muscle cell proliferation.

Nagata D ，Takeda R ，Sata M ，Satonaka H ，Suzuki E ，Nagano T ，Hirata Y ... -  《-》

AMPK activation enhances PPARα activity to inhibit cardiac hypertrophy via ERK1/2 MAPK signaling pathway.

Activation of adenosine monophosphate-activated protein kinase (AMPK) has been shown to inhibit cardiac hypertrophy through peroxisome proliferators-activated receptor-α (PPARα) signaling pathway, but the detailed mechanism remains unclear. A rat model of cardiac hypertrophy created by transaortic constriction (TAC) was used to investigate the mechanism involved in regulation of PPARα activity by AMPK. It was observed that treatment with AICAR (5-aminoimidazole 1 carboxamide ribonucleoside), an AMPK activator, significantly inhibited cardiac hypertrophy in vivo and in vitro. Phosphorylated extracellular signal regulated protein kinase (phospho-ERK1/2) and phospho-p38 mitogen-activated protein kinase (MAPK) protein levels were significantly up-regulated, while PPARα protein level was down-regulated in TAC rats. AICAR treatment reversed the changes of PPARα and phospho-ERK1/2, but increased phospho-p38 MAPK protein level in TAC rats. Similar changes of PPARα and phospho-ERK1/2 protein levels were observed in the hypertrophied cardiomyocytes induced by phenylephrine treatment. Epidermal growth factor (EGF, ERK1/2 activator), but not SB203580 (p38 inhibitor) blocked the up-regulation of PPARα protein level induced by AICAR. Luciferase assay showed that AICAR increased PPARα transcriptional activity which was abrogated by EGF, but not by SB203580. These results demonstrate that AMPK activation enhances the activity of PPARα to inhibit cardiac hypertrophy through ERK1/2, but not p38 MAPK, signaling pathway.

Meng R ，Pei Z ，Zhang A ，Zhou Y ，Cai X ，Chen B ，Liu G ，Mai W ，Wei J ，Dong Y ... -  《-》

Adiponectin inhibits insulin-like growth factor-1-induced cell migration by the suppression of extracellular signal-regulated kinase 1/2 activation, but not Akt in vascular smooth muscle cells.

Motobayashi Y ，Izawa-Ishizawa Y ，Ishizawa K ，Orino S ，Yamaguchi K ，Kawazoe K ，Hamano S ，Tsuchiya K ，Tomita S ，Tamaki T ... -  《-》