Cdk5 Regulates the Organization of Nestin and Its Association with p35

Abstract

The intermediate filament protein nestin is characterized by its specific expression during the development of neuronal and myogenic tissues. We identify nestin as a novel in vivo target for cdk5 and p35 kinase, a critical signaling determinant in development. Two cdk5-specific phosphorylation sites on nestin, Thr-1495 and Thr-316, were established, the latter of which was used as a marker for cdk5-specific phosphorylation in vivo. Ectopic expression of cdk5 and p35 in central nervous system progenitor cells and in myogenic precursor cells induced elevated phosphorylation and reorganization of nestin. The kinetics of nestin expression corresponded to elevated expression and activation of cdk5 during differentiation of myoblast cell cultures and during regeneration of skeletal muscle. In the myoblasts, a disassembly-linked phosphorylation of Thr-316 indicated active phosphorylation of nestin by cdk5. Moreover, cdk5 occurred in physical association with nestin. Inhibition of cdk5 activity-either by transfection with dominant-negative cdk5 or by using a specific cdk5 inhibitorblocked myoblast differentiation and phosphorylation of nestin at Thr-316, and this inhibition markedly disturbed the organization of nestin. Interestingly, the interaction between p35, the cdk5 activator, and nestin appeared to be regulated by cdk5. In differentiating myoblasts, p35 was not complexed with nestin phosphorylated at Thr-316, and inhibition of cdk5 activity during differentiation induced a marked association of p35 with nestin. These results demonstrate that there is a continuous turnover of cdk5 and p35 activity on a scaffold formed by nestin. This association is likely to affect the organization and operation of both cdk5 and nestin during development.

Nestin expression in repopulating mesangial cells promotes their proliferation

“…44 Phosphorylation of nestin by different kinases leads to disassembly of nestin filaments during mitosis 44 or development of neuronal precursor cells. 45 This role of nestin during MC proliferation is further supported by the additional findings that nestin expression is clearly regulated during cell-cycle progression and that nestin knockdown by siRNA does affect cell-cycle progression in cultured MCs. In cultured MCs, nestin is markedly increased around nuclei of dividing cells and is strongly upregulated during S-and G2-phases compared with S1-phase.…”

p53, Apaf-1, caspase-3, and -9 are dispensable for Cdk5 activation during cell death

“…18 However, Cdk5 is not restricted to neurons. It is also prominent in the testis, where its level is high but its function is unknown (our unpublished data), developing muscle, 19,20 bFGF-stimulated bovine aortic endothelial cell proliferation, 21 and differentiating monocytes. 22,23 Cdk5 is activated in dying cells, including both developing tissues (interdigital areas of mouse limbs, 24 differentiating rat lens, 4 and mouse brain 5 ) and adult tissues (regressing mouse prostate following androgen withdrawal and atrophic mouse ovaries 5 ).…”

Nestin Is Not Essential for Development of the CNS But Required for Dispersion of Acetylcholine Receptor Clusters at the Area of Neuromuscular Junctions

“…Recent in vitro studies have shown that nestin can protect neural progenitors against oxidant-induced cell death through interaction with Cdk5 (Sahlgren et al, 2006). Indeed, nestin can serve as a scaffold for Cdk5 and is able to regulate its kinase activity in vitro (Sahlgren et al, 2003(Sahlgren et al, , 2006.…”