CROSS-LINKING OF INTEGRINS INDUCES TYROSINE PHOSPHORYLATION OF THE PROTOONCOGENE PRODUCT VAV AND THE PROTEIN-TYROSINE KINASE SYK IN HUMAN FACTOR-DEPENDENT MYELOID CELLS
A. Gotoh et al., CROSS-LINKING OF INTEGRINS INDUCES TYROSINE PHOSPHORYLATION OF THE PROTOONCOGENE PRODUCT VAV AND THE PROTEIN-TYROSINE KINASE SYK IN HUMAN FACTOR-DEPENDENT MYELOID CELLS, Cell growth & differentiation, 8(6), 1997, pp. 721-729
Attachment to extracellular matrix is important in the regulation of p
roliferation and differentiation of hematopoietic stem and progenitor
cells. Post-ligand occupancy events of integrin receptors in myeloid c
ells are largely unknown. We examined early signaling events after sti
mulation of integrin receptors (outside-in signal) using a cross-linki
ng system in a growth factor-dependent myeloid cell line, M07e. alpha
4, alpha 5, and beta 1 integrin cross-linking induced a similar patter
n of transient tyrosine phosphorylation of cellular proteins. The appr
oximate molecular weights of these phosphoproteins were M-r 150,000, M
-r 120,000-125,000, M-r 95,000, M-r 70,000, M-r 60,000, and M-r 40,000
-50,000. Vav, Syk, and Erk2 were identified as some of the tyrosine-ph
osphorylated proteins, and their weights were M-r 95,000, M-r 70,000,
and M-r 40,000-50,000, respectively. Erk2 and Vav were also tyrosine-p
hosphorylated by stimulation with Steel factor (SLF) and granulocyte m
acrophage colony-stimulating factor, whereas tyrosine phosphorylation
of Syk was not induced by stimulation with these cytokines. The degree
of tyrosine phosphorylation of Vav through integrin engagement was al
most equal to that by SLF stimulation, whereas that of Erk2 was much w
eaker than with SLF stimulation. Upon integrin engagement, antibodies
raised against Syk coprecipitated several tyrosine-phosphorylated prot
eins. In vitro binding assays demonstrated that, among these Syk- asso
ciated proteins, pp40, which differed from Erks, Crk, and Crk1, binds
Syk through SH2 domains of Syk and is a prominent tyrosine-phosphoryla
ted protein in integrin cross-linked cells. These results suggest that
tyrosine phosphorylation of Vav and Erk2 in myeloid cells might be re
gulated by both integrins and cytokines in the bone marrow microenviro
nment, whereas Syk might be involved in a distinct pathway from that s
hared between integrins and cytokines in myeloid cells.