The platelet-endothelial cell adhesion molecule-1 (PE-CAM-1), defined by the CD31 monoclonal antibody (MoAb), was initially described as a cell-cell adhesion molecule mediating both homotypic and heterotypic adhesion. In this report, we show that enriched CD34+ human hematopoietic progenitor cell populations, containing early myeloid, erythroid, and multipotential progenitor cells, are CD31+. Analyses of CD34+ cell lines representing early myeloid, multipotential, and pre- pre-B-lymphoid progenitors indicate that precursors of both myeloid and B-lymphoid cells express PECAM-1 at high levels. Three-color flow- cytometric analyses also show that normal human bone marrow CD31+ CD34+ subsets coexpress myeloid (CD33) or B-lymphoid (CD19, CD10) markers. Except for the monocytic cell line, U937, all CD34- cell lines tested, which represent more mature stages of the myeloid, erythroid, and lymphoid lineages, expressed substantially lower or negligible levels of PECAM-1. Western blotting studies indicated that the CD31 MoAb, JC/70A, detected molecules in the 120- to 140-kD molecular weight range on the monocytic CD34- CD33+ CD31+ cell line, U937; on the CD34+ CD31+ CD33+ CD19- multipotential/lymphomyeloid precursor cell lines, KG1 and KG1B; on the CD34+ CD31+ CD19+ CD10+ CD33- precursor pre-pre-B-cell line, MIK-ALL; and on a CD34(+)-enriched precursor cell population from normal human bone marrow. A single molecular weight species was generally observed with enriched membrane preparations, whereas two PECAM-1 molecules were present in whole-cell lysates of cell lines and the CD34+ bone marrow cell subset. Preliminary studies show that a proportion of the PECAM-1 molecules on the lymphomyeloid/multipotential progenitor cell line, KG1, and on the monocytic cell line, U937, binds to heparin-sepharose. A soluble form of PECAM-1 also binds heparin- sepharose. The high level of expression of PECAM-1 on CD34+ cells suggests that this glycoprotein may function as a heterotypic adhesion molecule, possibly mediating multipotential, myeloid, and early-B- lymphoid precursor cell interactions with stromal cells and extracellular matrix molecules via heparan sulfate proteoglycans. It may also act as a homotypic adhesion molecule by interacting with PECAM- 1 on bone marrow stromal macrophage-like cells and endothelial cells or on endothelial cells during stem/progenitor cell migration. Thus, this molecule has the potential importance of directing both lineage commitment and trafficking of early hematopoietic progenitor cells.
Sensitivity of Monocytic Cell Lines to Verapamil in vitro
