The Journal of Experimental Medicine
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© The Rockefeller University Press, 0022-1007/1997/3/1035/ $5.00
The Journal of Experimental Medicine, Volume 185, Number 6, March 17, 1997 1035-1042

Articles

Signal Transducer and Activator of Transcription-3 (STAT3) Is Constitutively Activated in Normal, Self-renewing B-1 Cells but Only Inducibly Expressed in Conventional B Lymphocytes

James G. Karras*, Zihua Wang*, Li Huo*, Robert G. Howard*, David A. Frank§, and Thomas L. Rothstein*,{ddagger}

From the * Department of Medicine and the {ddagger} Department of Microbiology and the Evans Memorial Department of Clinical Research, Boston University Medical Center, Boston, Massachusetts 02118; and § Division of Hematological Malignancies, Dana-Farber Cancer Institute, Boston, Massachusetts 02115

Cytokine and growth factor receptor engagement leads to the rapid phosphorylation and activation of latent, cytosolic signal transducers and activators of transcription (STAT) proteins, which then translocate to the nucleus where they regulate transcriptional events from specific promoter sequences. STAT3 expression in particular has been associated with Abl, Src, and HTLV-1 transformation of normal cells. B-1 lymphocytes are self-renewing, CD5+ B cells that display a propensity for malignant transformation and are the normal counterpart to human chronic lymphocytic leukemias. Further, B-1 cells are characterized by aberrant intracellular signaling, including hyperresponsiveness to phorbol ester PKC agonists. Here we demonstrate that B-1 lymphocytes constitutively express nuclear activated STAT3, which is not expressed by unmanipulated conventional (B-2) lymphocytes. In contrast, STAT3 activation is induced in B-2 cells after antigen receptor engagement in a delayed fashion (after 3 h). Induction of STAT3 is inhibited by both the serine/threonine protein kinase inhibitor H-7 and the immunosuppressive drug rapamycin and requires de novo protein synthesis, demonstrating novel coupling between sIg and STAT proteins that differs from the classical paradigm for STAT induction by cytokine receptors. The inability of prolonged stimulation of conventional B-2 cells with anti-Ig, a treatment sufficient to induce CD5 expression, to result in sustained STAT3 activation suggests that STAT3 is a specific nuclear marker for B-1 cells. Thus, STAT3 may play a role in B cell antigen-specific signaling responses, and its constitutive activation is associated with a normal cell population exhibiting intrinsic proliferative behavior.

Address correspondence to Thomas L. Rothstein, Department of Medicine, Evans-556, Boston Medical Center, 88 East Newton St., Boston, MA 02118.

1Abbreviations used in this paper: CHX, cycloheximide; CNTF, ciliary neurotrophic factor; EMSA, electrophoretic mobility shift assay; PKC, protein kinase C; SIE, sis-inducible element; SIF, sis-inducible factor; STAT, signal transducers and activators of transcription; TI-2, T cell–independent type II.


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