GALECTIN-3 INHIBITS GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR (GM-CSF)-DRIVEN RAT BONE-MARROW CELL-PROLIFERATION AND GM-CSF-INDUCED GENE-TRANSCRIPTION

The expression of galectin-3 (formerly known as IgE-binding protein or Mac-2) in rat bone marrow IBM) was investigated by FACS, immunocytoch emical and immunoblot analysis. The functional significance of rat rec ombinant galectin-3 on mouse recombinant granulocyte-macrophage colony -stimulating factor (GM-CSF)-driven proliferation of macrophage progen itors tors and gene transcription was further examined. Immunocytochem ical analysis of in situ BM sections demonstrated galectin-3 in myelop oietic cells and surrounding stroma, whereas erythropoietic and lympho poietic environments essentially Lacked galectin-3 expression. FACS an alysis demonstrated that incubation of freshly isolated BMC with lacto se, a competing ligand for galectin-3 binding to glycoconjugates, decr eased binding of antigalectin antibodies to cells primarily expressing the myeloid antigen recognized by mAb His-54. Similarly, lectin-media ted binding of exogenous galectin-3 to myeloid lineage cells was also demonstrated. Immunoblot analysis of BM eluates demonstrated galectin- 3 both in the extracellular matrix and in a lactose elutable form, bou nd to the surface of BMC. [H-3]Thymidine incorporation studies on BMC cultured in the presence of galectin-3 demonstrated suppression of GM- CSF-induced proliferation by galectin-3. In addition, differential dis play analysis of immediate early gene expression in BMC cultured in th e presence of galectin-3 revealed a 76.2% inhibition oi GM-CSF-induced gene transcription by galectin-3 assessed by the number of PCR-fragme nts generated. Our data suggest a role for galectin-3 in the organizat ion of myelopoietic compartments in rat BM and regulation of the actio n of growth factors on myelopoietic precursor cells.