Neuronal cytoskeleton and protein phosphorylation in the nervous system

Telephone: (301) 402-2124

E-mail: panth@ninds.nih.gov

Office: Building 36, Room 4D20

Mailing Address:

National Institute Neurological Disorders & Stroke (NINDS)
36 Convent Drive, MSC 4130 

Bethesda, Maryland 20892-4130

Topographic regulation of cytoskeletal protein phosphorylation in normal neurons and during neurodegeneration

CDK5: Expression, regulation and its role in nerve cell function

Under a variety of neuropathological conditions, such as ALS, Alzheimer's, and Picks disease, hyperphosphorylation of cytoskeletal proteins, such as neurofilament proteins (NFPs), has been found in abnormal aggregates within cell bodies, usually correlated with massive neuronal cell death. The major questions relate to the factors that regulate the compartmentalization of cytoskeletal protein phosphorylation in neurons and the nature of the mechanisms responsible for their breakdown in neurodegenerative disorders. Two experimental approaches have been taken to date. First, we have shown that proline directed kinases (MAP kinase and cdk5) are primarily responsible for the extensive axonal phosphorylation of multiple KSP repeat sites in MAPs and NF-M/NF-H tail domains. We have also demonstrated that these kinases are activated by signal transduction cascades in cell cultures and phosphorylate NF-M and NF-H KSP repeats. One source of exogenous signals are the glia responsible for myelination, and we observed that MAPK (ErK1/2) and cdk5 kinase activities in brain and sciatic nerve extracts are down regulated compared to wild type mice. Second, we have shown that cytoskeletal extracts of mammalian and squid nervous tissues yield macromolecular complexes of cytoskeletal protein substrates (NFPs, tubulin, actin, MAPS, tau) associated with proline and non-proline directed kinases as well as phosphatases. Moreover, in the squid giant fiber system, extracted axonal complexes exhibit active phosphorylation of endogenous substrates whereas similar complexes derived from cell bodies are relatively inactive. To study the nature of this difference, we are currently evaluating various phosphatases to determine whether differences in their activities are responsible for this compartment-specific pattern of phosphorylation.  In addition, role of cdk5 in nervous system function and its regulation is being investigated.