department of pharmacology

Clark Distelhorst, M.D.



Phone: (216) 368-4546
Fax: NA


Research in the Distelhorst Laboratory is focused on answering two fundamental questions:

• How do glucocorticosteroid hormones induce apoptosis?


Why glucocorticoid-induced apoptosis?

Glucocorticosteroid hormones ( e.g., prednisone, dexamethasone) induce apoptosis in young lymphocytes. Therefore, they are used in the treatment of virtually all types of lymphoid malignancies, including acute lymphoblastic leukemia, chronic lymphocytic leukemia, cutaneous T cell lymphoma, and non-Hodgkin lymphoma. Understanding how glucocorticoids induce apoptosis will enable us to develop novel therapies and overcome resistance to glucocorticoid-induced apoptosis, while providing novel insight into a fundamentally important mechanism of apoptosis induction. Therefore, our research is both basic and translational.


What approach are we taking to understand glucocorticoid-induced apoptosis?

Virtually all effects of steroid hormones on cells are mediated through binding to their cognate receptor proteins, which are transcription factors. Moreover, there is considerable evidence that the induction of apoptosis by glucocorticoids is mediated through the glucocorticoid receptor and involves up-regulation of one or more "death genes". Therefore, a major effort is underway in our laboratory to identify glucocorticoid-induced genes that either mediate or regulate apoptosis in lymphocytes. Through the Cancer Center 's Gene Expression Core Facility, we have performed extensive Affymetrix microarray analysis of gene expression changes induced in lymphoma cells and primary thymocytes following exposure to dexamethasone. Through this work we have identified a number of candidate "death genes", including the pro-apoptotic Bcl-2 family member bim . But there are many other interesting and important genes identified through our microarray analysis, and we are currently investigating the role of these genes in the cell death process. Our ultimate goal is to completely define the glucocorticoid-induced cell death pathway from the earliest initiation stages to the final execution stages.


• How does Bcl-2 inhibit apoptosis?


Why Bcl-2?

Bcl-2 is a 26 kDa integral membrane protein that localizes to intracellular membranes, including the endoplasmic reticulum (ER) and the outer mitochondrial membrane. It is the founding member of a large family of apoptosis regulatory proteins, and its primary role is to inhibit apoptosis. Our interest in Bcl-2 evolved from the fact that Bcl-2 inhibits glucocorticoid-induced apoptosis. But Bcl-2 inhibits most forms of apoptosis and therefore is of broad general interest in the apoptosis community. Also, Bcl-2 is fascinating since so many laboratories have studied Bcl-2, yet there is still no agreement as to how Bcl-2 regulates apoptosis.


What are we doing to understand Bcl-2's mechanism of action?

Work in our laboratory drew attention to the role of Bcl-2 on the ER. By selectively targeting Bcl-2 to either the mitochondria or the ER, we were able to show that Bcl-2 on the mitochondria can actually induce apoptosis, whereas Bcl-2 located on the ER inhibits apoptosis. Moreover, we discovered that Bcl-2 interacts with inositol 1,4,5-trisphosphate receptors (IP 3 receptors), Ca 2+ channels located on the ER membrane, and regulates the efflux of Ca 2+ ions from the ER. This is important since the Ca 2+ ion is a major second messenger involved in regulating many cellular processes, including cell proliferation and apoptosis. Our laboratory is experienced at monitoring changes in intracellular Ca 2+ at a single cell level by digital imaging and at a population level by fluorometry. This is important since dynamic changes in Ca 2+ ( e.g., oscillations, waves) encode information that regulates transcription and other cellular processes, including the activation of proteases, kinases and phosphatases. A major focus of the lab is to understand how the regulation of Ca 2+ signals by Bcl-2 governs life and death decisions in T cells. In recent work, we discovered that Bcl-2 regulates Ca 2+ signals according to the strength of T cell receptor activation, suppressing pro-apoptotic Ca 2+ signals induced by strong T cell receptor activation, while enhancing pro-survival Ca 2+ signals induced by weak T cell receptor activation.


Wang Z, Malone MH, He H, McColl KS, Distelhorst CW. Microarray analysis uncovers the induction of the pro-apoptotic BH3-only protein Bim in multiple models of glucocorticoid induced apoptosis. J. Biol. Chem. 278:23861-23867, 2003


Wang Z, Malone MH, Thomenius MJ, Zhong F, Xu F, Distelhorst CW. Dexamethasone-induced gene 2 (dig2) is a novel prosurvival stress gene induced rapidly by diverse apoptotic signals. J Biol Chem 278:27053-27058, 2003


Chen R, Valencia I, Zhong F, McColl KS, Roderick HL, Bootman MD, Berridge MJ, Conway SJ, Holmes AB, Mignery GA, Velez P, Distelhorst CW. Bcl-2 functionally interacts with inositol 1,4,5-trisphosphate receptors to regulate calcium release from the ER in response to inositol 1,4,5-trisphosphate. J Cell Biol 166:193-203, 2004. Editors Choice, Sci.STKE, 27 July 2004.


Malone M, Wang Z, Distelhorst CW. The glucocorticoid-induced gene tdag8 encodes a pro-apoptotic G protein-coupled receptor whose activation promotes glucocorticoid-induced apoptosis. J Biol Chem 279:52850-52859, 2004


Wang Z, Rong Y, Malone MH, Davis MC, Distelhorst CW. Thioredoxin-interacting protein (txnip) is a glucocorticoid-regulated primary response gene involved in mediating glucocorticoid-induced apoptosis. Oncogene 25:1903-1913, 2006


Zhong F, Davis MC, McColl KS, Distelhorst CW. Bcl-2 differentially regulates calcium signals according to the strength of T cell activation. J Cell Biol 172:127-137, 2006. Highlighted by Nicole LeBrasseur in same issue.


Swerdlow S and Distelhorst CW. Bcl-2 regulated calcium signals as common mediators of both apoptosis and autophagy. Developmental Cell 12:178-179, 2007


Davis MC, McColl K, Wang Z, Malone MH, Distelhorst CW. Dexamethasone-induced inositol 1,4,5-trisphosphate receptor elevation in murine lymphoma cells is not required for dexamethasone-mediated calcium elevation and apoptosis. J. Biol. Chem. 283:10357-65, 2008


Swerdlow S, McColl K, Rong Y, Lam M, Gupta A, Distelhorst CW. Apoptosis inhibition by Bcl-2 gives way to autophagy in glucocorticoid-treated lymphocytes. Autophagy 4:1-9, 2008


Rong Y and Distelhorst CW. Bcl-2 protein family members: Versatile regulators of calcium signaling in cell survival and apoptosis. Annual Review of Physiology 70:73-91, 2008.


Rong Y, Aromolaran AS, Bultynck G, Zhong F, Li X, McColl KS, Herlitze S, Matsuyama S, Roderick HL, Bootman MD, Mignery GA, Parys JB, De Smedt H, Distelhorst CW. Targeting Bcl-2-IP3 receptor interaction to reverse Bcl-2's inhibition of apoptotic calcium signals Molecular Cell (in press, July 25, 2008)