Activation of glutamate-cysteine ligase in lymphocytes

Thesis (Ph. D.)--University of Washington, 2000Lymphocytes are normally quiescent cells that react to receptor-based signals by developing into functional effector cells that orchestrate immune responses. In their resting state, lymphocytes are highly susceptible to oxidative stress, which can alter signal transduction, inhibiting antigen-specific responses. Glutathione (GSH), the major cellular thiol antioxidant, is required for robust lymphocyte responses. Glutamate-cysteine ligase (GLCL; E.C. 6.3.2.2) catalyzes the rate-limiting step in the biosynthesis of GSH. The studies presented herein characterize the induction of GLCL protein in lymphocytes following stimulation of proliferative responses by the mitogen phytohemagglutinin, and by cell surface receptors. Upregulation of GLCL protein is shown to be linked tightly with cell proliferation. In addition, the present work describes changes in GLCL activity following treatments that induce oxidative stress and deplete GSH in lymphocytes, and proposes a novel mechanism for the rapid activation of GLCL. Finally, this report provides evidence that the catalytic subunit of GLCL is cleaved in lymphocytes and other cells in a caspase-3 dependent fashion during programmed cell death. The site of cleavage is identified and results from initial investigations of the function of cleaved GLCL are presented. The studies described herein demonstrate that lymphocytes possess multiple mechanisms for the activation of GLCL and control of GSH biosynthesis