Proteasomal degradation of Nck1 but not Nck2 regulates RhoA activation and actin dynamics

摘要

The ubiquitously expressed adapter proteins Nck1 /2 interact with a multitude of effector molecules to regulate diverse cellular functions including cytoskeletal dynamics. Here we show that Nck1 , but not Nck2 , is a substrate of c-Cbl -mediated ubiquitination. We uncover lysine 178 in Nck1 as the evolutionarily conserved ubiquitin acceptor site. We previously reported that synaptopodin , a proline -rich actin-binding protein, induces stress fibres by blocking the Smurf1 -mediated ubiquitination of RhoA . We now find that synaptopodin competes with c-Cbl for binding to Nck1 , which prevents the ubiquitination of Nck1 by c-Cbl . Gene silencing of c-Cbl restores Nck1 protein abundance and stress fibres in synaptopodin knockdown cells. Similarly, expression of c-Cbl -resistant Nck1 (K178R) or Nck2 containing the SH3 domain 2 of Nck1 restores stress fibres in synaptopodin -depleted podocytes through activation of RhoA signalling. These findings reveal proteasomal regulation as a key factor in the distinct and non-redundant effects of Nck on RhoA -mediated actin dynamics.