CELL BIOLOGY AND METABOLISM
Identification of a Novel AMP-activated Protein Kinase β Subunit Isoform That Is Highly Expressed in Skeletal Muscle*

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The AMP-activated protein kinase (AMPK) is a member of a growing family of related kinases, including the SNF1 complex in yeast, which respond to nutritional stress. AMPK is a heterotrimeric complex of a catalytic subunit (α) and two regulatory subunits (β and γ), and proteins related to all three subunits have been identified in the SNF1 complex. We have used the two-hybrid system in order to identify proteins interacting with the catalytic subunit (α2). Using this approach, we have isolated a novel AMPKβ isoform, which we designate AMPKβ2. The N-terminal region of β2 differs significantly from that of the previously characterized isoform (β1), suggesting that this region could play a role in isoform-specific AMPK activity. Comparison of the C-terminal sequences of β1 and β2 with their related proteins in yeast identifies two highly conserved regions predicted to be involved in binding of the α and γ subunits. The expression of β1 and β2 was examined in a number of tissues, revealing that the β1 isoform is highly expressed in liver with low expression in skeletal muscle, whereas the opposite pattern is observed for the β2 isoform. These results suggest that the β isoforms have tissue-specific roles, which may involve altered responses to upstream signaling and/or downstream targeting of the AMPK complex.

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This work was supported by the Medical Research Council (United Kingdom) and by a studentship from GlaxoWellcome (to C. T.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) AJ224515 and AJ224538.