Abstract
1. The Src homology protein tyrosine phosphatase SHP2 is associated with cytoskeletal maintenance, cell division, and cell differentiation, but the role of SHP2 during central nervous system injury requires further definition. We therefore characterized the role of SHP2 during nitric oxide (NO)-induced programmed cell death (PCD). 2. Employing primary hippocampal neurons from mice with a dominant negative SHP2 mutant to render the phosphatase site of the SHP2 protein biologically inactive, but functionally capable of binding substrate, neuronal injury was evaluated by trypan blue, DNA fragmentation, membrane phosphatidyl serine (PS) exposure, mitogen-activated protein (MAP) kinase phosphorylation, and cysteine protease activity. NO was administered through the NO generators SIN-1 (300 microM) or NOC-9 (300 microM). 3. Following NO exposure, neuronal survival decreased from 89 +/- 3% in untreated controls to 37 +/- 2% in wild-type neurons and to 21 +/- 4% in SHP2 mutant neurons. In sister cultures following NO exposure, this increased susceptibility to neuronal injury paralleled enhanced genomic DNA degradation and membrane PS exposure with PCD induction increasing in SHP2 mutant neurons by approximately 42% during specified time periods when compared to wild-type neurons. Interestingly, modulation of the MAP kinase p38 appears to represent an initial level of neuronal protection employed by SHP2. In addition, both the rate and degree of caspase 1- and caspase 3-like activities in SHP2 mutant neurons were significantly increased over a 24-h course when compared to wild-type neurons. Inhibition of caspase 1- and caspase 3-like activities reversed the progression of neuronal PCD, suggesting that inhibition of cysteine protease activity is a downstream mechanism for SHP2 to afford neuronal protection. 4. Our work supports the premise that the tyrosine phosphatase SHP2 plays a dominant role during NO-induced PCD and may offer a potential molecular "checkpoint" against neurodegenerative disease.