The AMBRA1 E3 ligase adaptor regulates Cyclin D protein stability

Here we describe AMBRA1 as the main regulator of Cyclin D protein degradation. We first identify AMBRA1 as the top candidate in a genome-wide CRISPR/Cas9 loss-of-function screen investigating the genetic basis of resistance to chemical CDK4/6 inhibition. AMBRA1 loss results in high protein levels of Cyclin D in cells and in mice. AMBRA1 loss further promotes lung cancer development in a mouse model, and low levels of AMBRA1 correlate with worse survival in lung cancer patients. Mechanistically, AMBRA1 acts as a substrate receptor for the Cullin 4 E3 ligase complex to promote ubiquitylation and proteasomal degradation of the three Cyclin D family members. Thus, AMBRA1 regulates Cyclin D protein levels and contributes to the development of cancer as well as the response of cancer cells to CDK4/6 inhibitors.