Thyroid Hormone Activates Adenosine 5′-Monophosphate-Activated Protein Kinase via Intracellular Calcium Mobilization and Activation of Calcium/Calmodulin-Dependent Protein Kinase Kinase-β

• Published in: Molecular endocrinology (Baltimore, Md.) Md.), 2008-04, Vol.22 (4), p.893-903
• Main Authors: Yamauchi, Masako, Kambe, Fukushi, Cao, Xia, Lu, Xiuli, Kozaki, Yasuko, Oiso, Yutaka, Seo, Hisao
• Format: Article
• Language: English
• Subjects: 3T3-L1 Cells; Acetyl-CoA Carboxylase - metabolism; AMP-Activated Protein Kinases; Animals; Benzimidazoles - pharmacology; Blotting, Western; Calcium - metabolism; Calcium-Calmodulin-Dependent Protein Kinase Kinase - genetics; Calcium-Calmodulin-Dependent Protein Kinase Kinase - metabolism; Cell Line; Egtazic Acid - analogs & derivatives; Egtazic Acid - pharmacology; Enzyme Activation - drug effects; Fatty Acids - metabolism; HeLa Cells; Humans; Immunohistochemistry; Mice; Multienzyme Complexes - metabolism; Naphthalimides - pharmacology; Oxidation-Reduction - drug effects; Phosphorylation - drug effects; Protein-Serine-Threonine Kinases - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA, Small Interfering - genetics; Signal Transduction - drug effects; Thyroid Hormone Receptors alpha - genetics; Thyroid Hormone Receptors alpha - metabolism; Thyroid Hormone Receptors beta - genetics; Thyroid Hormone Receptors beta - metabolism; Thyroid Hormones - pharmacology; Transfection
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/me.2007-0249

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.