HE AMOT FAMILY OF PROTEINS BINDS AND ACTIVATES NEDD4 FAMILY LIGASES TO PROMOTE THE UBIQUITINATION OF LATS AND YAP

Abstract

Amot adaptor proteins bind and integrate signaling that controls cell po-larity and growth. All three Amot family members (Amot, AmotL1 and AmotL2) directly bind YAP; a transcriptional co-activator that controls the expression of genes involved in organ homeostasis and cell growth. Preven-tion of nuclear accumulation of YAP by either sequestration or degradation in the cytosol abolishes its transcriptional functions and is a major mechanism for growth arrest in response to cellular differentiation. This is mainly thought to be regulated by phosphorylation of YAP by the Hippo kinases LATS1/2. Recently, binding by the Amot proteins was also found to inhibit YAP by sequestering it in the cytosol through both LATS dependent and in-dependent mechanisms. This study identifies a novel mechanism whereby Amot proteins control YAP activation in a Hippo independent mechanism by coupling it to ubiquitination by Nedd4 family ligases. Amot proteins mediate the coupling of Nedd4 ligases with YAP by simultaneously binding both pro-teins via multiple PY motifs that are recognized by WW domains in both YAP and Nedd4. Binding of Nedd4 by Amot is also shown to relieve the auto-inhibition of its ligase activity. This may be a direct consequence of binding Amot or from being re-targeted in cells by Amot proteins to endosomes. Im-portantly, Amot induced ubiquitination of YAP by Nedd4 proteins is shown to enhance the residence of YAP in the nucleus and in YAP activated transcrip-tion. Taken together our data suggest that Amot couples Nedd4 family ubiq-uitin ligases with the transcriptional co-activator YAP to drive the ubiquitination and activation of YAP.