A pivotal role for endogenous TGF-β-activated kinase-1 in the LKB1/AMP-activated protein kinase energy-sensor pathway

Abstract

TGF-␤-activated kinase-1 (TAK1), also known as MAPKK kinase-7 (MAP3K7), is a candidate effector of multiple circuits in cardiac biology and disease. Here, we show that inhibition of TAK1 in mice by a cardiac-specific dominant-negative mutation evokes electrophysiological and biochemical properties reminiscent of human Wolff-Parkinson-White syndrome, arising from mutations in AMPactivated protein kinase (AMPK), most notably, accelerated atrioventricular conduction and impaired AMPK activation. To test conclusively the biochemical connection from TAK1 to AMPK suggested by this phenotype, we disrupted TAK1 in mouse embryos and embryonic fibroblasts by Cre-mediated recombination. In TAK1-null embryos, the activating phosphorylation of AMPK at T172 was blocked, accompanied by defective AMPK activity. However, loss of endogenous TAK1 causes midgestation lethality, with defective yolk sac and intraembryonic vasculature. To preclude confounding lethal defects, we acutely ablated floxed TAK1 in culture by viral delivery of Cre. In culture, endogenous TAK1 was activated by oligomycin, the antidiabetic drug metformin, 5-aminoimidazole-4-carboxamide riboside (AICAR), and ischemia, well established triggers of AMPK activity. Loss of TAK1 in culture blocked T172 phosphorylation induced by all three agents, interfered with AMPK activation, impaired phosphorylation of the endogenous AMPK substrate acetyl CoA carboxylase, and also interfered with activation of the AMPK kinase LKB1. Thus, by disrupting the endogenous TAK1 locus, we prove a pivotal role for TAK1 in the LKB1͞AMPK signaling axis, an essential governor of cell metabolism. APKs, MAPKKs (MAP2Ks), and MAP2K kinases (MAP3Ks) comprise a multitiered signaling cascade that couples extracellular cues and intracellular stresses to diverse effector pathways controlling cell growth, survival, transcription, and function (1). Among upstream members of this superfamily, TGF-␤-activated kinase-1 (TAK1)͞MA PKK kinase-7 (MAP3K7) first was identified as a mammalian kinase that complements the lack of Ste11, a MAP3K, in yeast and is activated by TGF-␤ and the relative, bone morphogenetic protein (2). Within the MAPK family, TAK1 is coupled preferentially to JNK and p38. Additional inputs for TAK1 activation include cytokine signaling and innate immunity, and additional outputs include I B kinase ␤ (3). Disruption of TAK1 by saturation mutagenesis in ES cells substantiated that TAK1 is indeed essential for a subset of TGF-␤ effects and also exerts essential functions in signaling by cytokine and Toll-like receptors (3), as proposed on earlier grounds. Additionally, the early-lethal phenotype of TAK1-null embryos, with intraembryonic and yolk sac vascular patterning defects, resembles that of mice devoid of other TGF-␤ signaling proteins, the type I receptor Alk1 and type III receptor endoglin (4).A recognized limitation of germ-line deletions is that potential gene functions may be obscured by early lethality, indirect effects, or secondary adaptations, fueling interest in lineagerestr...

TAK1 control of cell death

“…14,15 Exogenous stressors and environmental changes such as osmotic stress, UV irradiation, ischemia and nutrient withdrawal activate TAK1. 13,14,16,17 Among these stimuli, the mechanism of TAK1 activation and its role in the TNFa signaling pathway has been extensively studied. Upon TNFa stimulation, adaptor molecules including TNFa receptor type-1-associated death domain protein (TRADD), TNFa receptorassociated factor 2 and 5 (TRAF2 and TRAF5), cellular inhibitor of apoptosis 1 and 2 (cIAP1/2) and RIPK1 are recruited to the receptor complex (TNF receptor 1 (TNFR1) Complex I) (Figure 1), in which RIPK1 acquires a K63-linked or linear polyubiquitin chain by E3 ligases, TRAF2/5 cIAP1/2 or linear ubiquitin chain assembly complex containing two E3 ligases HOIL-1 and HOIP.…”

“…26,27 Drawing a link between TAK1 signaling and metabolism, studies have found that starvation and TRAIL induce autophagy in which TAK1 is actively involved by activating AMP-activated protein kinase and IKKs. 14,17,28,29 In summary, TAK1 responds to exogenous stress conditions through a variety of mechanisms including TNFa family Figure 1 TNFa induces cell survival, apoptosis and necroptosis. Upon TNFa stimulation, TNFR1 forms Complex I, in which RIPK1 acquires a polyubiquitin chain.…”

Defective Myofibroblast Formation from Mesenchymal Stem Cells in the Aging Murine Heart

“…AMPK activation was originally proposed to be dependent on Thr172 phosphorylation via action of upstream kinases including LKB1, 43,44 calmodulin-dependent protein kinase kinase II␤, 45 and Tak1. 46 However, Xie et al 47 suggested that LKB1 actually acts downstream of Tak1 in mouse fibroblasts. Because TGF-␤1 seems to be crucial in AMPK-dependent p38MAPK activation and because it is part of the FAK/Tak1/JNK pathway crucial for myofibroblast activation, 35 we chose to analyze Tak1 activation in aged fibroblasts treated with TGF-␤1 and AICAR.…”

AMP-activated protein kinase control of energy metabolism in the ischemic heart

“…1 To date, three AMPKKs have been identified in the heart, the tumor suppressor kinase LKB1, a calmodulindependent protein kinase kinase, and a TGF-b-activated kinase-1. 26 Although LKB1 and TGF-b-activated kinase-1 are highly expressed in heart, calmodulin-dependent protein kinase kinase is expressed only at low levels. 27 To date, the role of either of these AMPKKs in the control of AMPK phosphorylation and activation has not been clearly defined.…”

“…Recent evidence in endothelial cells suggests that PKC-z phosphorylates LKB1 at Ser428, resulting in an increased association of LKB1 with AMPK and consequent AMPK Thr172 phosphorylation by LKB1. 26 Whether a similar pathway exists in the heart has yet to be determined.…”