Functional analysis of mutations in the γ2 subunit of AMP-activated protein kinase associated with cardiac hypertrophy and Wolff-Parkinson-White syndrome

Abstract

Mutations in the gene encoding the γ2 subunit of the AMP-activated protein kinase (AMPK) have recently been shown to cause cardiac hypertrophy and ventricular pre-excitation (Wolff-Parkinson-White syndrome). We have examined the effect of four of these mutations on AMPK activity. The mutant γ2 polypeptides are all able to form functional complexes following co-expression with either α1β1 or α2β1 in mammalian cells. None of the mutations caused any detectable change in the phosphorylation of threonine 172 within the α subunit of AMPK. Consequently, in the absence of an appropriate stimulus the mutant complexes, like the wild-type complex, exist in an inactive form demonstrating that the mutations do not lead to constitutive activation of the kinase. Three of the mutations we studied occur within the cystathionine β-synthase (CBS) domains of γ2. Two of these mutations lead to a marked decrease in AMP dependence, whereas the third reduces AMP sensitivity. These findings suggest that the CBS domains play an important role in AMP-binding within the complex. In contrast, a fourth mutation, which lies between adjacent CBS domains, has no significant effect on AMPK activity in vitro. These results indicate that mutations in γ2 have different effects on AMPK function, suggesting that they may lead to abnormal development of the heart through distinct mechanisms.