Human immunodeficiency virus type 1 (HIV-1) Vpr induces cell death in mammalian and fission yeast cells, suggesting that Vpr may affect a conserved cellular process. It is unclear, however, whether Vpr-induced yeast cell death mimics Vpr-mediated apoptosis in mammalian cells. We have recently identified a number of Vpr suppressors that not only suppress Vpr-induced cell death in fission yeast, but also block Vpr-induced apoptosis in mammalian cells. These findings suggest that Vpr-induced cell death in yeast may resemble some of the apoptotic processes of mammalian cells. The goal of this study was to develop and validate a fission yeast model system for future studies of apoptosis. Similar to Vpr-induced apoptosis in mammalian cells, we show here that Vpr in fission yeast promotes phosphatidylserine externalization and induces hyperpolarization of mitochondria, leading to changes of mitochondrial membrane potential. Moreover, Vpr triggers production of reactive oxygen species (ROS), indicating that the apoptotic-like cell death might be mediated by ROS. Interestingly, Vpr induces unique morphologic changes in mitochondria that may provide a simple marker for measuring the apoptotic-like process in fission yeast. To verify this possibility, we tested two Vpr suppressors (EF2 and Hsp16) that suppress Vpr-induced apoptosis in mammalian cells in addition to a newly identified Vpr suppressor (Skp1). All three proteins abolished cell death mediated by Vpr and restored normal mitochondrial morphology in the yeast cells. In conclusion, Vpr-induced cell death in fission yeast resembles the mammalian apoptotic process. Fission yeast may thus potentially be used as a simple model organism for the future study of the apoptotic-like process induced by Vpr and other proapoptotic agents.

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The family of NADPH oxidase enzymes serve to generate reactive oxygen species (ROS), and the prototypic phagocyte‐type NADPH oxidase produces large amounts of ROS that serve a host defense role. Fibroblasts, B lymphocytes and platelets also express NOX2/gp91phox protein which leads to ROS production. Recent discovery of multiple homologues of gp91phox (e.g., NOX1, NOX4, Duox1/2) has broadened the NADPH oxidase activity in “non‐phagocytic” cells. In non‐phagocytic cells and tissues, NOX family members produce lower levels of ROS and participate in regulatory and signaling roles. We have recently shown that T cells express the phagocyte‐type NADPH oxidase which regulates T cell responses. Our new data indicate that T cells also express mRNA and protein for the calcium‐dependent, non‐phagocytic oxidase Duox1 and Duox1 produces ROS early in TCR signaling. Downregulation of Duox1 expression in primary and cultured T cells with siRNA resulted in selective changes in T cell receptor induced signal transduction. While phosphorylation of early mediators of TCR signaling (ZAP‐70, PLC‐g) was largely unaffected, TCR‐induced activation of ERK was strongly inhibited and secretion of multiple cytokines including IL‐4, IFN‐g, and TNFa was also reduced. Thus, T cells express multiple NADPH oxidases and Duox1 serves to regulate early TCR signal transduction. Supported by NIH R01 AI070823.

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