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Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
During early B lymphopoiesis, developing B cells maintain lineage
commitment despite the local presence of myeloid lineage-promoting
cytokines such as GM-CSF and IL-3. Previous observations suggest that
the B cell-specific transcription factor Pax5A (paired box 5A
transcription factor) plays a role in maintaining B cell lineage
commitment by limiting expansion and survival of early
IL-3/GM-CSF-dependent myeloid lineage cells. To define a mechanism by
which Pax5A can exert these inhibitory effects on myeloid lineage
differentiation, an inducible form of the Pax5A protein was expressed
in the myeloid cell line FDC-P1. This cell line models myeloid
progenitors in that it responds to the survival and growth-potentiating
effects of IL-3 and GM-CSF. We observed that enforced expression of
Pax5A selectively suppressed proliferation in response to GM-CSF, but
not IL-3. This effect was associated with specific down-regulation of
GM-CSFR
-chain, but not
-chain expression. These data provide a
molecular mechanism to enforce commitment to the B cell lineage despite
the presence of GM-CSF, a factor that has been shown to convert early
developing B cells to the myeloid lineage. Furthermore, they indicate a
role for B cell Pax5A expression in maintaining rather than directing
commitment to the B cell lineage.
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