Wnt expression and canonical Wnt signaling in human bone marrow B lymphopoiesis.
BACKGROUND
The early B lymphopoiesis in mammals is regulated through close interactions with stromal cells and components of the intracellular matrix in the bone marrow (BM) microenvironment. Although B lymphopoiesis has been studied for decades, the factors that are implicated in this process, both autocrine and paracrine, are inadequately explored. Wnt signaling is known to be involved in embryonic development and growth regulation of tissues and cancer. Wnt molecules are produced in the BM, and we here ask whether canonical Wnt signaling has a role in regulating human BM B lymphopoiesis.


RESULTS
Examination of the mRNA expression pattern of Wnt ligands, Fzd receptors and Wnt antagonists revealed that BM B progenitor cells and stromal cells express a set of ligands and receptors available for induction of Wnt signaling as well as antagonists for fine tuning of this signaling. Furthermore, different B progenitor maturation stages showed differential expression of Wnt receptors and co-receptors, beta-catenin, plakoglobin, LEF-1 and TCF-4 mRNAs, suggesting canonical Wnt signaling as a regulator of early B lymphopoiesis. Exogenous Wnt3A induced stabilization and nuclear accumulation of beta-catenin in primary lineage restricted B progenitor cells. Also, Wnt3A inhibited B lymphopoiesis of CD133+CD10- hematopoietic progenitor cells and CD10+ B progenitor cells in coculture assays using a supportive layer of stromal cells. This effect was blocked by the Wnt antagonists sFRP1 or Dkk1. Examination of early events in the coculture showed that Wnt3A inhibits cell division of B progenitor cells.


CONCLUSIONS
These results indicate that canonical Wnt signaling is involved in human BM B lymphopoiesis where it acts as a negative regulator of cell proliferation in a direct or stroma dependent manner.
Døsen
Guri
G
Department of Immunology, Institute for Cancer Research, Rikshospitalet-Radiumhospitalet Medical Center, Medical Faculty, University of Oslo, Norway. guri.dosen@rr-research.no
Tenstad
Ellen
E
Nygren
Marit Kveine
MK
Stubberud
Heidi
H
Funderud
Steinar
S
Rian
Edith
E
D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D001854:Bone Marrow Cells / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002478:Cells, Cultured; D018920:Coculture Techniques; D051157:Frizzled Receptors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D038041:Lymphopoiesis / Q000187:drug effects; D051379:Mice; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D013234:Stem Cells / Q000187:drug effects / Q000378:metabolism; D017154:Stromal Cells / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D051153:Wnt Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism; D051185:gamma Catenin / Q000235:genetics / Q000378:metabolism
D051157:Frizzled Receptors; D012333:RNA, Messenger; D014157:Transcription Factors; D051153:Wnt Proteins; D051176:beta Catenin; D051185:gamma Catenin