Richard S. Lewis






		Richard S. Lewis Title Associate Professor Department Molecular and Cellular Physiology Research Interests Calcium signaling by ion channels and cellular organelles; store-operated channels; calcium control of gene expression. Email rslewis@leland.stanford.edu Phone 723-9615 Fax 725-8021 Address Beckman B111A Mail Code: 5345 Faculty Research Description We are interested in molecular mechanisms of calcium signaling in T lymphocytes. The recognition of foreign antigen by a T cell opens Ca2+ channels which are essential for triggering the cell to proliferate and carry out immunologic functions. For our studies we apply a combination of techniques: patch-clamp recording to identify and characterize ion channels, video and 2-photon microscopy with fluorescent dyes to visualize ion movements and gene activation in individual cells, and molecular biology for expression of heterologous genes. Current studies include: (i) Store-operated Ca2+ channels. In T cells and virtually all other non-excitable cells, Ca2+ channels are activated by the emptying of the endoplasmic reticulum Ca2+ store. We are interested in the mechanism that links store depletion to Ca2+ channel activation, and in the role of calcium in channel regulation. We have identified four modes by which calcium controls the dynamics and magnitude of Ca2+ channel activity. Mitochondria also play a critical role in maintaining Ca2+ influx through store-operated channels by sequestering incoming Ca2+ and thereby preventing inactivation of the channels. (ii) Modulation of Ca2+ pumps. Ca2+-ATPases in the plasma membrane are responsible for eventually expelling Ca2+ from T cells after it has entered through calcium channels. The activity of the pumps is slowly upregulated following a rise in intracellular Ca2+, and this contributes to the dynamics of calcium signals. We are studying this process using a single-cell Ca2+ clamp technique that combines patch-clamp with simultaneous measurements of intracellular calcium. (iii) Ca2+ oscillations and gene expression. While Ca2+ oscillations are a common response to stimulation of many cells including T cells, little is known about their role in controlling cell behavior. To explore this question, we have developed a an automated perfusion method to produce oscillations of defined amplitude and frequency in cell populations. We find that the amplitude, duration, and dynamics of Ca2+ signals lead to differential activation of several Ca2+-sensitive transcriptional pathways in lymphocytes. These results help to explain how a multipotent messenger like calcium can achieve specificity in signaling to the nucleus. Zweifach A and Lewis RS. (1993). Mitogen-regulated Ca2+ current of T lymphocytes is activated by depletion of intracellular Ca2+ stores. Proc Natl Acad Sci 90:6295-6299. Zweifach A, Lewis RS. (1995). Slow calcium-dependent inactivation of depletion-activated calcium current. Store-dependent and independent mechanisms. J Biol Chem 270:14445-14451. Hoth M, Fanger CM, and Lewis RS. (1997). Mitochondrial regulation of store-operated calcium signaling in T lymphocytes. J Cell Biol 137:633-648. Dolmetsch RE, Lewis RS, Goodnow CC, and Healy JI. (1997). Differential activation of transcription factors induced by Ca2+ response amplitude and duration. Nature 386:855-858. Dolmetsch RE, Xu K and Lewis RS. (1998). Calcium oscillations increase the efficiency and specificity of gene expression. Nature 392:933-936. Areas of Study Cellular Neurobiology Membrane Excitability Molecular Neurobiology SBRC Ph.D.