Hydrogen Peroxide Induced Oxidative Stress Alters Cyclin Dependent Kinase 5 and p35/p25 Localization in Human Astroglioma Cells

Cyclin dependent kinase 5 (Cdk5), a predominantly post mitotic neuronal enzyme, is known to play a critical role in morphology, function and fate of neurons. The functional activity of Cdk5 requires an obligatory association with p35 or p25-a long lived fragment of p35 generated by cleavage by calpain. While the function of Cdk5 in the neurons has been well established, it's role in non-neuronal cells of the brain, the astroglia, especially during oxidative stress is not reported. In this study, we investigated the expression of Cdk5 and its activators p35/p25 in the human astroglioma cell line- U373 treated with H2O2 for induction of oxidative stress as an experimental model system. The cells were exposed to various doses of H2O2 and examined for its morphology and viability at different time points. Expression of Cdk5 and p35/25 was determined in control cells and in cells treated with H2O2, pretreated with calpain inhibitor- calpstatin, which inhibits cleavage of p35 to p25 and a known neuroprotective moleculelithium. We demonstrate that H2O2-induced stress causes loss in the number of cells with cytoplasmic extensions, a prelude to cell death that is associated with nuclear expression of p25 and Cdk5 while Cdk5/p35 expression is exclusively cytoplasmic in the control cells. Lithium treatment inhibited the translocalization of p25 and Cdk5 to the nucleus. We conclude that Cdk5 and its activators could be important molecular players in modulating cell morphology and viability of astroglial cells during oxidative stress.