Cross-linking of Surface IgM in the Burkitt's Lymphoma Cell Line ST486 Provides Protection against Arsenite- and Stress-induced Apoptosis That Is Mediated by ERK and Phosphoinositide 3-Kinase Signaling Pathways

doi:10.1074/jbc.M208779200

Cross-linking of Surface IgM in the Burkitt's Lymphoma Cell Line ST486 Provides Protection against Arsenite- and Stress-induced Apoptosis That Is Mediated by ERK and Phosphoinositide 3-Kinase Signaling Pathways*

From the Department of Microbiology and Immunology, Cornell University, Ithaca, New York 14853

Abstract

The ST486 cell line, derived from a human Burkitt's lymphoma, is a model for antigen-induced clonal deletion in germinal center B-lymphocytes, with apoptosis induced upon cross-linking of surface IgM. Moreover, this cell line is highly sensitive to the induction of apoptosis by many chemicals, including sodium arsenite, a significant environmental contaminant with immunotoxic activity. In contrast to arsenite and other chemicals, surface IgM cross-linking induces apoptosis in ST486 cells with delayed kinetics. Moreover, the initial signaling events following IgM stimulation are associated with cell survival and proliferation and include activation of the extracellular-signal regulated kinase (ERK) and the phosphoinositide 3-kinase (PI3K) pathways. We examined the question of whether IgM-mediated activation of the ERK and PI3K pathways can influence the apoptotic response of ST486 cells following exposure to arsenite and selected drugs with different molecular targets, including cycloheximide, etoposide, and camptothecin, and a physical stress, hyperthermia. Our findings show that IgM-stimulated cells are significantly protected against arsenite and drug-induced apoptosis during a window of several hours after surface IgM cross-linking, as evidenced by an inhibition of cleavage of poly(ADP-ribose) polymerase and lack of morphological changes indicative of apoptosis. Significantly, surface IgM cross-linking also protects against arsenite-induced mitochondrial depolarization as well as caspase-9 cleavage. Furthermore, we demonstrate that this IgM-mediated protection requires the activation of the ERK and PI3K pathways, because inhibition of either pathway blocks the ability of antigen receptor activation to protect against apoptosis. Our study also provides evidence for p90^S6 ribosomal kinase as a point of convergence between the two signaling pathways resulting in the phosphorylation of the pro-apoptotic Bcl-2 family member Bad at serine 112. This investigation demonstrates, for the first time, that specific signals transduced by activation of the B-cell receptor protect cells at a common point of regulation in the apoptotic pathways for diverse stresses.

Footnotes

↵* This work was supported by Grant R01ES010815 from the NIEHS, National Institutes of Health (to D. E. M.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ To whom correspondence should be addressed: Dept. of Microbiology and Immunology, C4–101 Veterinary Medical Center, Cornell University, Ithaca, NY 14853. Tel.: 607-253-4047; Fax: 607-253-3384; E-mail: dem10@cornell.edu.
Published, JBC Papers in Press, December 2, 2002, DOI 10.1074/jbc.M208779200
Abbreviations:

BL

Burkitt's lymphoma

MAPK

mitogen-activated protein kinase

ERK

extracellular signal-regulated kinase

MEK

MAPK/ERK kinase

MEKK

MEK kinase

JNK

c-Jun amino-terminal kinase

AKT

protein kinase B/AKT

PDK1

3-phosphoinositide-directed kinase-1

Δψ_m

mitochondrial membrane potential

BCR

B-cell antigen receptor

PARP

poly(ADP-ribose) polymerase

PI3K

phosphoinositide 3-kinase

RSK

p90^S6 ribosomal kinase

CTD

carboxyl-terminal domain of p90^S6 ribosomal kinase: NTD, amino-terminal domain of p90^S6 ribosomal kinase

mTOR

mammalian target of rapamycin

AKTi5

1L-6-hydroxymethyl-chiro-inositol 2-[(R)-2-O-methyl]-3-O-octadecylcarbonate

mClCCP

carbonyl cyanide m-chlorophenylhydrazone

GC

germinal center

FADD

Fas-associated death domain, FLIP, FADD-inhibitory protein
- Received August 27, 2002.
- Revision received November 18, 2002.
The American Society for Biochemistry and Molecular Biology, Inc.