THROMBOPOIETIN AND ERYTHROPOIETIN ACTIVATE INSIDE-OUT SIGNALING OF INTEGRIN AND ENHANCE ADHESION TO IMMOBILIZED FIBRONECTIN IN HUMAN GROWTH-FACTOR-DEPENDENT HEMATOPOIETIC-CELLS
A. Gotoh et al., THROMBOPOIETIN AND ERYTHROPOIETIN ACTIVATE INSIDE-OUT SIGNALING OF INTEGRIN AND ENHANCE ADHESION TO IMMOBILIZED FIBRONECTIN IN HUMAN GROWTH-FACTOR-DEPENDENT HEMATOPOIETIC-CELLS, Annals of hematology, 75(5-6), 1997, pp. 207-213
Erythropoietin (EPO) and thrombopoietin (c-MPL ligand; TPO) are struct
urally similar cytokines and support respectively, the proliferation a
nd differentiation for erythroid and megakaryocytic lineages, as well
as more primitive progenitors. We studied the effect of these cytokine
s on the induction of adhesion of human growth-factor-dependent hemato
poietic cells to immobilized fibronectin, which is a main component of
the extracellular matrix in the bone marrow. MO7ER cells that are gen
etically engineered to express human EPO receptor and MO7e cells that
express endogenous c-MPL were used. Stimulation with either TPO or EPO
induced rapid increases in adhesion of M07ER cells to fibronectin wit
hout apparent change of expression of integrins. Experiments with inhi
bitory monoclonal antibodies (mAbs) demonstrated that CD41, which has
been reported to be involved in TPO-induced adhesion of megakaryocytic
cells, is not responsible for this enhanced adhesion. Anti-beta 1 int
egrin mAb inhibited adhesion completely, while inhibition by anti-alph
a 4 integrin mAb and anti-alpha 5 integrin mAb was partial. Combinatio
n of anti-alpha 4 mAb plus anti-alpha 5 mAb completely abolished adhes
ion, as did anti-beta 1 mAb, suggesting that the adhesion is mediated
by both alpha 4 beta 1 and alpha 5 beta 1 integrins. Experiments using
inhibitors suggested that ligand binding followed by activation of in
tracellular tyrosine kinases along with PI3-kinase activation is requi
red. After stimulation of M07ER cells with either TPO or EPO, fibronec
tin-attached cells, but not cells in suspension, showed tyrosine phosp
horylation of focal adhesion kinase, which plays a central role in int
egrin-mediated signaling. These data suggest that TPO and EPO might be
involved in homing/migration to the bone marrow microenvironment by h
ematopoietic cells that express corresponding receptors.