Neurotoxicity induces cleavage of p35 to p25 by calpain

Abstract

Cyclin-dependent kinase 5 (cdk5) and its neuron-specific activator p35 are required for neurite outgrowth and cortical lamination. Proteolytic cleavage of p35 produces p25, which accumulates in the brains of patients with Alzheimer's disease. Conversion of p35 to p25 causes prolonged activation and mislocalization of cdk5. Consequently, the p25/cdk5 kinase hyperphosphorylates tau, disrupts the cytoskeleton and promotes the death (apoptosis) of primary neurons. Here we describe the mechanism of conversion of p35 to p25. In cultured primary cortical neurons, excitotoxins, hypoxic stress and calcium influx induce the production of p25. In fresh brain lysates, addition of calcium can stimulate cleavage of p35 to p25. Specific inhibitors of calpain, a calcium-dependent cysteine protease, effectively inhibit the calcium-induced cleavage of p35. In vitro, calpain directly cleaves p35 to release a fragment with relative molecular mass 25,000. The sequence of the calpain cleavage product corresponds precisely to that of p25. Application of the amyloid beta-peptide A beta(1-42) induces the conversion of p35 to p25 in primary cortical neurons. Furthermore, inhibition of cdk5 or calpain activity reduces cell death in A beta-treated cortical neurons. These observations indicate that cleavage of p35 to p25 by calpain may be involved in the pathogenesis of Alzheimer's disease.

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

“…Inhibition of calpain activation, which blocks p25 production and Cdk5 activation, prevents neuronal cell death. 29,31,32,35,41,42 Here we document the generation of p25 during cell death, as we had previously suggested. 28 We also establish that calpainmediated Cdk5/p25 activation coincides with cell death in both non-neuronal and neuronal systems, suggesting the generality of the role of Cdk5 in cell death.…”

“…Induction of p25 is a reliable indicator and measure of Cdk5 activation. 28,29,31 In A9, it took 12 h to activate caspase-3 ( Figure 2B, a) and induce p25 (Cdk5 activation - Figure 2B, b). As expected, the level of Cdk5 protein was constant for the 18 h in both C8 and A9 ( Figure 2B, c, data for 8, 15, and 18 h not shown).…”

“…The association between Cdk5 activation and cell death is seen in pathology: rat lungs infected with Streptococcus pneumoniae, 25 mouse limbs infected with Leishmania major, 26 preterm lamb lungs after ventilation, 27 cyclophosphamide-treated mouse embryos, 28 and several neurodisorders and neuronal injuries. [29][30][31][32][33][34][35][36][37] The regulatory signals and mechanisms by which Cdk5 is activated remain undefined.…”

A role for calpain-dependent cleavage of TDP-43 in amyotrophic lateral sclerosis pathology

“…The samples were boiled at 100 1C for 5 min. Fifty microliters of the recombinant TDP-43 or mutant TDP-43 protein, which were synthesized by the TNT T7 Quick Coupled Transcription/Translation Systems, were homogenized by sonication in 450 ml of extraction buffer (5 mM cysteine and 150 mM imidazole, pH 7.5) 57 . The homogenate was centrifuged at 1,000 g for 10 min at 4 1C.…”

Calpain inhibition rescues troponin T3 fragmentation, increases Cav1.1 , and enhances skeletal muscle force in aging sedentary mice

“…Calpain‐1 mediates proteolysis of various cellular proteins, including cytoskeletal proteins (Campbell & Davies, 2012). Calpain‐1 overactivation causes irreversible cell damage, contributing to the pathology of cerebral and cardiac ischemia, Alzheimer's disease, arthritis, and cataracts (Wang & Yuen, 1994; Lee et al ., 2000). Calpains may be activated by muscle microinjuries throughout the lifespan, particularly at later stages, when increased susceptibility to trauma may activate calpains (Faulkner et al ., 1993; Salazar et al ., 2010).…”