Ubiquitin-dependent proteasomal degradation of AMPK gamma subunit by Cereblon inhibits AMPK activity.

Cereblon (CRBN), a substrate receptor for Cullin-ring E3 ubiquitin ligase (CRL), is a major target protein of immunomodulatory drugs. An earlier study demonstrated that CRBN directly interacts with the catalytic alpha subunit of AMP-activated protein kinase (AMPK), a master regulator of energy homeostasis, down-regulating the enzymatic activity of AMPK. However, it is not clear how CRBN modulates AMPK activity. To investigate the mechanism of CRBN-dependent AMPK inhibition, we measured protein levels of each AMPK subunit in brains, livers, lungs, hearts, spleens, skeletal muscles, testes, kidneys, and embryonic fibroblasts from wild-type and Crbn(-/-) mice. Protein levels and stability of the regulatory AMPKgamma subunit were increased in Crbn(-/-) mice. Increased stability of AMPKgamma in Crbn(-/-) MEFs was dramatically reduced by exogenous expression of Crbn. In wild-type MEFs, the proteasomal inhibitor MG132 blocked degradation of AMPKgamma. We also found that CRL4(CRBN) directly ubiquitinated AMPKgamma. Taken together, these findings suggest that CRL4(CRBN) regulates AMPK through ubiquitin-dependent proteasomal degradation of AMPKgamma.