Cloning and characterization of mouse 5'-AMP-activated protein kinase {gamma}3 subunit

Research Division, Joslin Diabetes Center, and Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02215 Submitted 25 July 2003 ; accepted in final form 17 September 2003 Naturally occurring mutations in the regulatory -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 -subunit in AMPK function. In this study we cloned the mouse AMPK 3 subunit and revealed that there are two transcription start sites, which result in a long form, 3L (AF525500 ) and a short form, 3S (AF525501 ). AMPK 3L is the predominant form in mouse and is specifically expressed in mouse skeletal muscle at the protein level. In skeletal muscle, AMPK 3 shows higher levels of expression in fast-twitch white glycolytic muscle (type IIb) compared with fast-twitch red oxidative glycolytic muscle (type IIa), whereas 3 is undetectable in soleus muscle, a slow-twitch oxidative muscle with predominantly type I fibers. AMPK 3 can coimmunoprecipititate with both and AMPK subunits. Overexpression of 3S and 3L in mouse tibialis anterior muscle in vivo has no effect on 1 and 2 subunit expression and does not alter AMPK 2 catalytic activity. However, 3S and 3L overexpression significantly increases AMPK 1 phosphorylation and activity by 50%. The increase in AMPK 1 activity is not associated with alterations in glycogen accumulation or glycogen synthase expression. In conclusion, the 3 subunit of AMPK is highly expressed in fast-twitch glycolytic skeletal muscle, and wild-type 3 functions in the regulation of 1 catalytic activity, but it is not associated with changes in muscle glycogen concentrations. adenosine 5'-monophosphate-activated protein kinase; AMPK 3 short form; AMPK 3 long form; cystathionine -synthase domain Address for reprint requests and other correspondence: L. J. Goodyear, Joslin Diabetes Center, One Joslin Place, Boston, MA 02215 (E-mail: laurie.goodyear{at}joslin.harvard.edu ).