Characterization of the molecular mechanism for Cereblon as a negative regulator of AMP-activated protein kinase

Abstract

Cereblon (CRBN), a primary target of immunomodulatory drugs (IMiDs), functions as a substrate receptor in the CUL4-RBX1-DDB1-CRBN (known as CRL4CRBN) E3 ubiquitin ligase complex. Binding of IMiDs to CRBN redirects the CRL4CRBN E3 ubiquitin ligase to recruit or displace its substrates. An earlier study demonstrated that CRBN directly interacts with the catalytic α 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. The present study showed that protein levels and stability of the regulatory AMPKγ subunit were increased in Crbn-/- mice. Increased stability of AMPKγ in Crbn-/- MEFs was dramatically reduced by exogenous expression of Crbn. In wild-type MEFs, the proteasomal inhibitor MG132 blocked degradation of AMPKγ. Moreover, AMPKγ was directly ubiquitinated by CRL4CRBN, and depletion of CRBN suppressed the ubiquitination of AMPKγ. I also found that thalidomide had no effect on the function of CRBN as a negative regulator of AMPK. The N-terminal region and C-terminal tail of CRBN, which is distinct from the IMiD binding site, were critical for interaction with the AMPKα subunit. Taken together, these findings suggest that CRL4CRBN regulates AMPK through ubiquitin-dependent proteasomal degradation of AMPK γ independently of CRBN-IMiDs binding.