Protein Phosphorylation Research Group, Department of Experimental Medical Science, Lund University, BMC C11, SE 221 84 Lund, Sweden.
J Cell Biochem. 2011 May;112(5):1364-75. doi: 10.1002/jcb.23053.
AMP-activated protein kinase (AMPK) is a serine/threonine kinase that regulates cellular and whole body energy homeostasis. In adipose tissue, activation of AMPK has been demonstrated in response to a variety of extracellular stimuli. However, the upstream kinase that activates AMPK in adipocytes remains elusive. Previous studies have identified LKB1 as a major AMPK kinase in muscle, liver, and other tissues. In certain cell types, Ca(2+) /calmodulin-dependent protein kinase kinase β (CaMKKβ) has been shown to activate AMPK in response to increases of intracellular Ca(2+) levels. Our aim was to investigate if LKB1 and/or CaMKK function as AMPK kinases in adipocytes. We used adipose tissue and isolated adipocytes from mice in which the expression of LKB1 was reduced to 10-20% of that of wild-type (LKB1 hypomorphic mice). We show that adipocytes from LKB1 hypomorphic mice display a 40% decrease in basal AMPK activity and a decrease of AMPK activity in the presence of the AMPK activator phenformin. We also demonstrate that stimulation of 3T3L1 adipocytes with intracellular [Ca(2+) ]-raising agents results in an activation of the AMPK pathway. The inhibition of CaMKK isoforms, particularly CaMKKβ, by the inhibitor STO-609 or by siRNAs, blocked Ca(2+) -, but not phenformin-, AICAR-, or forskolin-induced activation of AMPK, indicating that CaMKK activated AMPK in response to Ca(2+) . Collectively, we show that LKB1 is required to maintain normal AMPK-signaling in non-stimulated adipocytes and in the presence of phenformin. In addition, we demonstrate the existence of a Ca(2+) /CaMKK signaling pathway that can also regulate the activity of AMPK in adipocytes.
AMP 激活的蛋白激酶 (AMPK) 是一种丝氨酸/苏氨酸激酶，调节细胞和全身能量稳态。在脂肪组织中，已经证明 AMPK 的激活是对各种细胞外刺激的反应。然而，在脂肪细胞中激活 AMPK 的上游激酶仍然难以捉摸。先前的研究已经确定 LKB1 是肌肉、肝脏和其他组织中 AMPK 的主要激酶。在某些细胞类型中，钙 (Ca 2+ )/钙调蛋白依赖性蛋白激酶激酶 β (CaMKKβ) 已被证明可以响应细胞内 Ca 2+ 水平的增加来激活 AMPK。我们的目的是研究 LKB1 和/或 CaMKK 是否在脂肪细胞中作为 AMPK 激酶发挥作用。我们使用了从 LKB1 表达减少到野生型 (LKB1 低表达小鼠) 20%的小鼠的脂肪组织和分离的脂肪细胞。我们表明，LKB1 低表达小鼠的脂肪细胞的基础 AMPK 活性降低了 40%，并且在 AMPK 激活剂苯甲福明存在的情况下 AMPK 活性降低。我们还证明，用细胞内 [Ca 2+ ] 升高剂刺激 3T3L1 脂肪细胞会导致 AMPK 途径的激活。抑制剂 STO-609 或 siRNA 抑制 CaMKK 同工型，特别是 CaMKKβ，阻断了 Ca 2+ ，但不是苯甲福明、AICAR 或 forskolin诱导的 AMPK 激活，表明 CaMKK 响应 Ca 2+ 激活 AMPK。总的来说，我们表明 LKB1 是维持非刺激脂肪细胞和苯甲福明存在下正常 AMPK 信号所必需的。此外，我们证明了存在一种 Ca 2+ /CaMKK 信号通路，也可以调节脂肪细胞中 AMPK 的活性。
