Calmodulin binds to p21(Cip1) and is involved in the regulation of its nuclear localization.

p21(Cip1), first described as an inhibitor of cyclin-dependent kinases, has recently been shown to have a function in the formation of cyclin D-Cdk4 complexes and in their nuclear translocation. The dual behavior of p21(Cip1) may be due to its association with other proteins. Different evidence presented here indicate an in vitro and in vivo interaction of p21(Cip1) with calmodulin: 1) purified p21(Cip1) is able to bind to calmodulin-Sepharose in a Ca(2+)-dependent manner, and this binding is inhibited by the calmodulin-binding domain of calmodulin-dependent kinase II; 2) both molecules coimmunoprecipitate when extracted from cellular lysates; and 3) colocalization of calmodulin and p21(Cip…