Calmodulin Binding and Cdk5 Phosphorylation of p35 Regulate Its Effect on Microtubules

Abstract

In the nervous system, Cdk5 and its neuronal activator p35 are involved in the control of various activities, including neuronal differentiation and migration. Recently, we have reported that p35 is a microtubule-associated protein that regulates microtubule dynamics ( 2؉ -specific manner, suggesting that p35 may be involved in the Ca 2؉ /CaMmediated inhibition of microtubule assembly. Second, p35 phosphorylation by Cdk5 interferes with the microtubule-binding and polymerizing activities of p35. Using a mutational approach, we found that only phosphorylation at Thr-138, one of the two residues primarily phosphorylated in vivo, inhibits the polymerizing activity. In PC12 cells, expression of p35 promotes nerve growth factor-induced neurite outgrowth under a Cdk5 inhibitory condition. Such p35 activity is impaired by the phosphomimetic mutation of Thr-138. These data suggest that Thr-138 phosphorylation plays a critical role in the control of the p35 functions in microtubule assembly and neurite outgrowth.

A 24-Residue Peptide (p5), Derived from p35, the Cdk5 Neuronal Activator, Specifically Inhibits Cdk5-p25 Hyperactivity and Tau Hyperphosphorylation

“…The p10 interaction in vivo with other cellular proteins, such as tubulin (microtubules) and calmodulin (31,74), may protect the activity of the Cdk5-p35 complex (and not the Cdk5-p25 complex) from p5 inhibition. In our experiments (Fig.…”

Structural Basis for the Association of MAP6 Protein with Microtubules and Its Regulation by Calmodulin

“…Interestingly, this kind of regulation has already been observed for the microtubule-associated protein p35, which is also regulated by site-specific phosphorylations and Ca 2ϩ -CaM with MT overlapping binding sites (41). Similar mechanisms of CaM regulation were again suggested for Tau (42)(43)(44).…”

Peptides Derived from Neuronal Cell Cycle like Kinase 5 Activator p35, in Neurodegeneration; Pathology and Therapy

“…The situation in cells, with numerous interacting proteins, differs fundamentally, however. It has been demonstrated that p35, with its p10 N-terminal "domain" interacts with other proteins such as microtubules, actin, munc18 and others forming a multimeric complex [6,7,31,33,34]. We suggest that binding of macromolecules to the p10 domain favors a p35 conformational change such that it competes successfully for the Cdk5 catalytic site and sustains activity.…”

“…In the brain, expression of p35 and p39 increases with development till adult; in fetus and adult p35 is phosphorylated by Cdk5 at Ser 8 which localizes a cytoplasmic Cdk5/p35 whereas in the fetus, phosphorylation of tyrosine 138 by tyrosine kinases, results in degradation of p35 via the proteosomeubiquitin pathway [4]. In the adult, however, Cdk5/p35 is restively more stable since neither site is phosphorylated as p35 acts to bundle microtubules and actin [6,7]. These regulatory options have profound effects on the role of Cdk5 in health and disease [8][9][10][11] (Figure 1).…”

“…It is intriguing that in several neurodegenerative disorders (AD, ALS, PD, HD) a hyperactive Cdk5 is detected in the brain at autopsy [6,7] and has been shown to be upstream of the pathways leading to plaques, tangles and inflammation in cultured neurons and model mice [8][9][10][11]. It does so when p35 is not phosphorylated and has been cleaved due to neuronal insults increasing intracellular calcium concentration inducing activation of calpain and cleavage into the myristolated p10 fragment and p25, a deregulated hyperactive Cdk5 [12].…”