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From the * Department of Medicine and the 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.
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
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