BMP-6 inhibits human bone marrow B lymphopoiesis—Upregulation of Id1 and Id3

Objective In mammals, factors produced by bone marrow (BM) stromal cells are instrumental in orchestrating the developmental process of B lymphocytes. Bone morphogenetic proteins (BMPs) are multifunctional cytokines previously found to regulate hematopoietic stem cells. In the present study, we have explored the role of BMP-6 in human B progenitor cells. Materials and Methods In vitro B lymphopoiesis of CD10+ B progenitor cells from human BM was evaluated in the presence or absence of BMP-6 in short- or long-term coculture on MS-5 stromal cells, by tracking CFSE-labeled CD10+ B progenitor cells or by quantification of CD19+ cells. DNA synthesis in the pre–B cell line Nalm-6 was measured by 3H-thymidine incorporation. BMP-6-induced phosphorylation of Smad1/5/8 was determined by Western blot analysis, whereas elevation of Id1-Id4 mRNA levels and basal BMP-6 mRNA levels were measured by real-time and conventional RT-PCR, respectively. Results By in vitro coculture of CD10+ B progenitor cells or monoculture of Nalm-6 cells, we found that BMP-6 inhibited B lymphopoiesis by impeding cell proliferation. Furthermore, in CD10+ B progenitors as well as in Nalm-6 cells, BMP-6 rapidly induced phosphorylation of Smad1/5/8, followed by an upregulation of Id1 and Id3 mRNA levels. Finally, we demonstrated that human bone marrow stromal cells express BMP-6 mRNA whereas B progenitor cells did not. Conclusions We suggest that BMP-6, produced by the BM, may participate to fine-tune the balance between proliferation, apoptosis, and differentiation in human B progenitor cells during BM B lymphopoiesis.