INDUCTION OF PROGRAMMED CELL-DEATH IN HUMAN HEMATOPOIETIC-CELL LINES BY FIBRONECTIN VIA ITS INTERACTION WITH VERY LATE ANTIGEN-5

Extracellular matrix (ECM) molecules such as fibronectin (FN), collage ns, and laminin have important roles in hematopoiesis. However, little is known about the precise mechanisms by which ECM molecules regulate proliferation of human hematopoietic progenitor cells. In this study, we have investigated the effects of ECM molecules, particularly of FN , on the proliferation of a myeloid leukemia cell line, M07E, which pr oliferates in response to either human granulocyte/macrophage colony-s timulating factor (GM-CSF) or stem cell factor (SCF). The [H-3]thymidi ne incorporation and cell enumeration assays showed that FN strikingly inhibited GM-CSF- or SCF-induced proliferation of M07E cells in a dos e-dependent manner, whereas little or no inhibition was induced by col lagen types I and IV. The growth suppression of M07E cells was not due to the inhibitory effect of FN on ligand binding or very early events in the signal transduction pathways from the GM-CSF or SCF receptors. DNA content analysis using how cytometry after staining with propidiu m iodide revealed that the treatment of M07E cells with FN did not blo ck the entry of the cells into the cell cycle after stimulation with G M-CSF or SCF, whereas the treatment resulted in the appearance of subd iploid peak. Furthermore, FN was found to induce oligonucleosomal DNA fragmentation and chromatin condensation in the cells even in the pres ence of GM-CSF or SCF, suggesting the involvement of programmed cell d eath (apoptosis) in the FN-induced growth suppression. The growth supp ression or apoptosis induced by FN was rescued by the addition of eith er anti-FN antibody, anti-very late antigen 5 monoclonal antibody (ant i-VLA5 mAb), or GRGDSP peptide, but not by that of anti-VLA4 mAb or GR GESP peptide, suggesting that the FN effects on M07E cells were mediat ed through VLA5. In addition, the FN-induced apoptosis was detectable in VLA5-positive human hematopoietic cell lines other than M07E cells, but not in any of the VLA5-negative cell lines. These results suggest that FN is capable of inducing apoptosis via its interaction with VLA 5, and also raise the possibility that the FN-VLA5 interaction may con tribute, at least in part, to negative regulation of hematopoiesis.