Processing of cdk5 activator p35 to its truncated form (p25) by calpain in acutely injured neuronal cells.
Recently, it was shown that conversion of cdk5 activator protein p35 to a C-terminal fragment p25 promotes a deregulation of cdk5 activity, which may contribute to neurodegeneration in Alzheimer's disease. In this study, we present evidence that calpain is a protease involved in the conversion of p35 to p25. To activate calpain, rat cerebellar granule neurons were treated with maitotoxin (MTX). A C-terminus-directed anti-p35 antibody detected that p35 conversion to p25 paralleled the formation of calpain-generated alpha-spectrin (alpha-fodrin) breakdown products (SBDP's) in a maitotoxin-dose-dependent manner. Two calpain inhibitors (MDl28170 and SJA6017) reduced p35 processing but were unchanged when exposed to the caspase inhibitor carbobenzoxy-Asp-CH(2)OC(=O)-2, 6-dichlorobenzene or the proteasome inhibitors (lactacystin and Z-Ile-Glu(OtBu)Ala-Leu-CHO). p35 protein was also degraded to p25 when rat brain lysate was subjected to in vitro digestion with purified mu- and m-calpains. Additionally, in a rat temporary middle cerebral artery occlusion model, p35 processing to p25 again paralleled SBDP formation in the ischemic core. Lastly, in malonate-injured rat brains, the ipsilateral side showed a striking correlation of SBDP formation with p35 to p25 conversion and tau phosphorylation (at Ser202 and Thr205) increase. These data suggest that calpain is a major neuronal protease capable of converting p35 to p25 and might play a pathological role of activating cdk5 and its phosphorylation of tau in Alzheimer's disease.
Nath
R
R
Department of Neuroscience Therapeutics, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Company, 2800 Plymouth Road, Ann Arbor, Michigan 48105, USA.
Davis
M
M
Probert
A W
AW
Kupina
N C
NC
Ren
X
X
Schielke
G P
GP
Wang
K K
KK
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000378:metabolism* / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D020925:Hypoxia-Ischemia, Brain; D008297:Male; D008314:Malonates / Q000494:pharmacology; D008387:Marine Toxins / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D035964:Oxocins; D010766:Phosphorylation; D020033:Protein Isoforms; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury; D013997:Time Factors; D016875:tau Proteins / Q000378:metabolism; D000095702:Polyether Toxins
D002118:Calcium; D002154:Calpain; D008314:Malonates; D008387:Marine Toxins; D009419:Nerve Tissue Proteins; D035964:Oxocins; D020033:Protein Isoforms; D016875:tau Proteins; C089495:neuronal Cdk5 activator (p25-p35); C030290:malonic acid; C020394:maitotoxin; D000095702:Polyether Toxins