REGULATION OF ION CHANNELS BY APOPTOSIS TRIGGER PROTEINS

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Apoptosis or programmed cell death can be induced by a variety of stimuli. Apoptosis is considered to be involved in many physiological and clinical phenomena, including ischemic injury, many forms of cancer, and neurodegenerative diseases, such as Alzheimer's disease, amyotrophic lateral sclerosis, and some prion-related disorders. Many apoptosis-inducing stimuli and gene products have been identified. The molecular mechanisms by which these stimuli trigger the cell-death program are, however, only poorly understood. The research program proposed here will focus on how an apoptosis-trigger gene, reaper, promotes cell death in electrically excitable cells. The reaper gene is expressed in cells destined to undergo apoptosis 1 to 2 hours before the cell death program starts. A sequence comparison of the N-termini of Reaper and a "A-type" voltage-dependent potassium channel (ShB) shows that the Reaper protein could work as an inactivation ball to block potassium channels. Our preliminary results indeed show that the full-length Reaper protein blocks voltage-dependent potassium channels by inducing very stable inactivation. Our preliminary results also show that Reaper slows down the inactivation process of voltage-dependent sodium channels. The proposed research program will examine how the Reaper protein alters functional properties of voltage-dependent ion channels to promote apoptosis. The central hypothesis is that Reaper alters properties of the plasma membrane ion channels to promote depolarization and that this depolarization facilitates apoptosis. We will test this hypothesis using heterologously expressed ion channels in Xenopus oocytes as well as native mammalian channels. We will examine how induced expression Reaper affects the ion channel properties and membrane potential in mammalian cells. The results expected from the proposed research will establish how some apoptosis-trigger proteins promote cell-death and the results may be useful in designing therapeutic interventions to treat the diseases that involve apoptosis.