Phosphorylation of the tubulin‐binding protein, stathmin, by Cdk5 and MAP kinases in the brain

Abstract

Regulation of cytoskeletal dynamics is essential to neuronal plasticity during development and adulthood. Dysregulation of these mechanisms may contribute to neuropsychiatric and neurodegenerative diseases. The neuronal protein kinase, cyclin-dependent kinase 5 (Cdk5), is involved in multiple aspects of neuronal function, including regulation of cytoskeleton. A neuroproteomic search identified the tubulin-binding protein, stathmin, as a novel Cdk5 substrate. Stathmin was phosphorylated by Cdk5 in vitro at Ser25 and Ser38, previously identified as mitogen-activated protein kinase (MAPK) and p38 MAPKd sites. Cdk5 predominantly phosphorylated Ser38, while MAPK and p38 MAPKd predominantly phosphorylated Ser25. Stathmin was phosphorylated at both sites in mouse brain, with higher levels in cortex and striatum. Cdk5 knockout mice exhibited decreased phospho-Ser38 levels.During development, phospho-Ser25 and -Ser38 levels peaked at post-natal day 7, followed by reduction in total stathmin. Inhibition of protein phosphatases in striatal slices caused an increase in phospho-Ser25 and a decrease in total stathmin. Interestingly, the prefrontal cortex of schizophrenic patients had increased phospho-Ser25 levels. In contrast, total and phospho-Ser25 stoichiometries were decreased in the hippocampus of Alzheimer's patients. Thus, microtubule regulatory mechanisms involving the phosphorylation of stathmin may contribute to developmental synaptic pruning and structural plasticity, and may be involved in neuropsychiatric and neurodegenerative disorders. Keywords: cyclin-dependent kinase 5, mitogen-activated protein kinase, p38 MAPKd (stress-activated protein kinase 4), 3 phosphorylation, stathmin, striatum. The number of synapses on neurons in the human forebrain increases dramatically after birth and then decreases with maturity. Children have enhanced plasticity and a higher capacity for learning and memory compared with adults. During postnatal development, synapses are pruned, following over-growth (Luo and O'Leary 2005). Synaptic restructuring continues throughout adulthood and contributes to the process of aging. Strong, frequently activated connections are maintained and strengthened while weaker and less used synaptic contacts are eliminated. Reduced plasticity due to genetic or epigenetic factors can cause cognitive impairment, while excessive plasticity can cause neurological disorders

Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: A perspective

“…Stathmin is also a substrate for PAK and cdk5 [59,172]. Stathmin is phosphorylated by PAK at serine 16 and probably at serine 63 [59,172], and by cdk5 at serines 25 and 38 which are also sites for MAPK [173]. The net outcome of these inactivating phosphorylations on stathmin is net growth of microtubules.…”

Regulation of ERK Kinase by MEK1 Kinase Inhibition in the Brain

“…Mass Spectroscopy-Phosphorylation of recombinant MEK1 and site identification were conducted using similar approaches as those described previously (41,42). MEK1 was preparatively phosphorylated for site identification.…”

Distinct Roles of c-Jun N-Terminal Kinase Isoforms in Neurite Initiation and Elongation during Axonal Regeneration

“…MAPK (Leighton et al, 1993;Hayashi et al, 2006). Hypophosphorylation of stathmin was found in jnk1 Ϫ/Ϫ DRG neurons, whereas no changes were noted for regenerating jnk2 Ϫ/Ϫ or jnk3 Ϫ/Ϫ neurons (Fig.…”