Inducible Tyrosine Phosphorylation of the β3 Integrin Requires the αv Integrin Cytoplasmic Tail

Scott D Blystone,Frederik P Lindberg,Matthew P Williams,Kevin P Mchugh,Eric J Brown

doi:10.1074/jbc.271.49.31458

Scott D Blystone, Frederik P Lindberg + Show 3 more

Open Access

https://doi.org/10.1074/jbc.271.49.31458

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Abstract

We have found that the integrin beta3 chain can be phosphorylated on tyrosine residues in K562 cells transfected with alphavbeta3. Tyrosine phosphorylation of the beta3 cytoplasmic tail is induced by adhesion to alphavbeta3-specific ligand or antibody or by incubation in manganese-containing buffer. Under the same conditions, beta5 does not become tyrosine-phosphorylated in K562 transfected with alphavbeta5. Phosphorylation of the beta3 subunit requires the simultaneous presence of the alphav subunit cytoplasmic tail, because neither the alphaIIb subunit nor a truncated alphav subunit is sufficient to permit phosphorylation of beta3 when coexpressed as a heterodimer with beta3. Finally, tyrosine phosphorylation of the beta3 cytoplasmic tail occurs on both human and murine beta3 and is inducible in the ovarian carcinoma OV10 as well, independent of expression of integrin-associated protein (CD47). Tyrosine phosphorylation of the beta3 integrin subunit facilitates association of Grb-2, an adaptor protein leading to activation of the Ras signaling pathway, and may contribute to the unique functional and signaling capabilities of alphavbeta3.

Highlights

One puzzling aspect of integrin biology is the apparent redundancy in ligand specificity of many integrins
An hypothesis to resolve this overlap in ligand binding is that outside-in signaling differs when distinct integrins are ligated by a single extracellular matrix protein. ␤3 integrins may have a unique place in integrin biology because of the myriad functional and signaling capabilities that have been ascribed to them. ␤3 integrins mediate diverse functions such as clot retraction in platelets [2], calcium fluxes in endothelial cells [3, 4], tumor metastasis in melanoma cells [5,6,7,8], phagocytosis in macrophages [1, 9], activation of neutrophils [10, 11], and adhesion and migration in many cell types [1, 12,13,14]
Tyrosine phosphorylation of the ␤3 cytoplasmic tail (CT) is not unique to K562 cells nor their transforming agent because phosphorylation of ␤3 could be induced in an ovarian carcinoma cell line overexpressing ␣v␤3

Summary

Introduction

One puzzling aspect of integrin biology is the apparent redundancy in ligand specificity of many integrins. Upon examination of tyrosine-phosphorylated proteins contained in ␣v␤3 immunoprecipitations from ␣v␤3-transfected K562 cells incubated with Mn2ϩ, we repeatedly found a single, prominent, 95-kDa tyrosine-phosphorylated protein. Direct amino acid sequencing identified this protein as the human ␤3 integrin subunit itself, a result confirmed by reprobing blots with mAb specific for ␤3.

Results

Conclusion