Clark Distelhorst, M.D.
Professor
WRB3-301
Phone: (216) 368-4546
Fax: NA
E-mail: cwd@case.edu
Research
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.
SELECTED REFERENCES:
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)