CD44 MEDIATES HYALURONAN-BINDING BY HUMAN MYELOID KG1A AND KG1 CELLS

Hyaluronan-binding function of the CD44 molecule has not been so far d etected in myeloid cells. In order to study pure populations of primit ive myeloid cells, we investigated the hyaluronan-binding function of the CD44 molecule from three myeloid cell lines: KG1a KG1 and HMO. Bot h KG1a and KG1 cells express the CD34 antigen characteristic of the he matopoietic stem cells, and HL60 cells do not; accordingly, KG1a and K G1 cells are generally considered as the most primitive, and HL60 cell s as the mast mature of these cell lines. Measurement of cell adhesion to hyaluronan-coated surfaces, using Cr-51-labeled cells, and of aggr egate formation in hyaluronan-containing solutions, showed that 45% of KG1 cells and 22-24% of KG1a spontaneously bind to hya[uronan whereas HMO cells do not, either spontaneously or after treatment with a phor bol ester. Hyaluronan binding by KG1a and KG1 cells is mediated by CD4 4, because if is specifically abolished by monoclonal antibodies to th is molecule. The binding might require phosphorylation by protein kina se C, and perhaps also by protein kinase A, because it is prevented by staurosporine, that inhibits these enzymes. TPA, that activates prote in kinase C, rises to 80% the proportion of KG1 and KG1a cells which b ind hyaluronan; this activation is dependent on protein synthesis for it is abrogated by cyclophosphamide, a protein synthesis inhibitor. Bi nding of TPA-treated cells to hyaluronan is only partly inhibited by m onoclonal antibody to CD44: this suggests that TPA may induce synthesi s of a hyaluronan-binding protein distinct from CD44. Considering the abundance of hyaluronan in human bone-marrow, these results suggest th at CD44 may be involved in mediating precursor-stroma interaction.