p66Shc-dependent apoptosis requires Lck and CaMKII activity

p66Shc, an adaptor molecule which enhances reactive oxygen species (ROS) production by mitochondria, promotes T-cell apoptosis by inducing mitochondrial dysfunction and impairing Ca(2+) homeostasis. We have addressed the potential role of Lck, a kinase which has been implicated in T-cell apoptosis induced by a number of stimuli, in the proapoptotic activity of p66Shc. Lck deficiency in Jurkat T cells overexpressing p66Shc leads to impaired apoptotic responses to supraphysiological increases in [Ca(2+)](c). This defect could be rescued by reconstitution of Lck expression, indicating that Lck is required for p66Shc-dependent apoptosis. Furthermore, p66Shc phosphorylation on serine 36 (S36), an event on which the proapoptotic function of p66Shc depends, requires Lck. p66Shc-dependent mitochondrial dysfunction, altered Ca(2+) homeostasis and S36 phosphorylation require moreover the activity of CaMKII, a Ca(2+)/calmodulin-dependent kinase known to be implicated in the proapoptotic activity of Lck in T cells. The results suggest that increases in [Ca(2+)](c) lead to CaMKII activation and subsequent Lck-dependent p66Shc phosphorylation on S36. This event causes both mitochondrial dysfunction and impaired Ca(2+) homeostasis, which synergize in promoting Jurkat T-cell apoptosis.