The neuronal cyclin-dependent kinase 5 activator p35Nck5a and Cdk5 activity in monocytic cells

Cyclin-dependent kinase 5 (Cdk5) and its activator p35Nck5a are an odd but interesting couple. Recent work has established that in spite of their names, Cdk5 is clearly not cyclin-dependent, while p35Nck5a is not exclusively neuronal. Indeed, p35Nck5a and/or Cdk5 activity has been demonstrated to be present in human and rat promyelocytic cell lines, and in normal human monocytes. Further, monocytes from mice in which p35Nck5a gene was deleted do not express non-specific esterase, an enzyme present in normal monocytes, while transfection of Cdk5 together with p35Nck5a into myeloblastic cells leads to the expression of this marker of the monocytic phenotype. Thus, the Cdk5/p35Nck5a complex appears to play an important role in monocytic differentiation.