Yu Haiyan, Fujii Nobuharu, Hirshman Michael F, Pomerleau Jason M, Goodyear Laurie J
Research Division, Joslin Diabetes Center, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02215, USA.
Am J Physiol Cell Physiol. 2004 Feb;286(2):C283-92. doi: 10.1152/ajpcell.00319.2003. Epub 2003 Sep 24.
Naturally occurring mutations in the regulatory gamma-subunit of 5'-AMP-activated protein kinase (AMPK) can result in pronounced pathological changes that may stem from increases in muscle glycogen levels, making it critical to understand the role(s) of the gamma-subunit in AMPK function. In this study we cloned the mouse AMPKgamma3 subunit and revealed that there are two transcription start sites, which result in a long form, gamma3L (AF525500) and a short form, gamma3S (AF525501). AMPKgamma3L is the predominant form in mouse and is specifically expressed in mouse skeletal muscle at the protein level. In skeletal muscle, AMPKgamma3 shows higher levels of expression in fast-twitch white glycolytic muscle (type IIb) compared with fast-twitch red oxidative glycolytic muscle (type IIa), whereas gamma3 is undetectable in soleus muscle, a slow-twitch oxidative muscle with predominantly type I fibers. AMPKgamma3 can coimmunoprecipititate with both alpha and beta AMPK subunits. Overexpression of gamma3S and gamma3L in mouse tibialis anterior muscle in vivo has no effect on alpha1 and alpha2 subunit expression and does not alter AMPKalpha2 catalytic activity. However, gamma3S and gamma3L overexpression significantly increases AMPKalpha1 phosphorylation and activity by approximately 50%. The increase in AMPKalpha1 activity is not associated with alterations in glycogen accumulation or glycogen synthase expression. In conclusion, the gamma3 subunit of AMPK is highly expressed in fast-twitch glycolytic skeletal muscle, and wild-type gamma3 functions in the regulation of alpha1 catalytic activity, but it is not associated with changes in muscle glycogen concentrations.
5'-AMP 激活蛋白激酶（AMPK）调节性γ亚基的自然发生突变可导致明显的病理变化，这些变化可能源于肌肉糖原水平的升高，因此了解γ亚基在 AMPK 功能中的作用至关重要。在本研究中，我们克隆了小鼠 AMPKγ3 亚基，发现有两个转录起始位点，分别产生长形式γ3L（AF525500）和短形式γ3S（AF525501）。AMPKγ3L 是小鼠中的主要形式，在蛋白质水平上特异性表达于小鼠骨骼肌中。在骨骼肌中，与快缩红氧化糖酵解肌（IIa 型）相比，AMPKγ3 在快缩白糖酵解肌（IIb 型）中的表达水平更高，而在比目鱼肌中未检测到γ3，比目鱼肌是一种主要由 I 型纤维组成的慢缩氧化肌。AMPKγ3 可与 AMPK 的α和β亚基共免疫沉淀。在体内小鼠胫前肌中过表达γ3S 和γ3L 对α1 和α2 亚基的表达没有影响，也不会改变 AMPKα2 的催化活性。然而，γ3S 和γ3L 的过表达显著增加了 AMPKα1 的磷酸化和活性，增幅约为 50%。AMPKα1 活性的增加与糖原积累或糖原合酶表达的改变无关。总之，AMPK 的γ3 亚基在快缩糖酵解骨骼肌中高度表达，野生型γ3 在调节α1 催化活性中起作用，但与肌肉糖原浓度的变化无关。
