Cloning and characterization of mouse 5′-AMP-activated protein kinase γ3 subunit

Naturally occurring mutations in the regulatory γ-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 γ-subunit in AMPK function. In this study we cloned the mouse AMPKγ3 subunit and revealed that there are two transcription start sites, which result in a long form, γ3L (AF525500) and a short form, γ3S (AF525501). AMPKγ3L is the predominant form in mouse and is specifically expressed in mouse skeletal muscle at the protein level. In skeletal muscle, AMPKγ3 shows higher levels of expression in fast-twitch white glycolytic muscle (type IIb) compared with fast-twitch red oxidative glycolytic muscle (type IIa), whereas γ3 is undetectable in soleus muscle, a slow-twitch oxidative muscle with predominantly type I fibers. AMPKγ3 can coimmunoprecipititate with both α and β AMPK subunits. Overexpression of γ3S and γ3L in mouse tibialis anterior muscle in vivo has n...