Evidence for a differential functional regulation of the two beta(3)-integrins alpha(V)beta(3) and alpha(IIb)beta(3).
The functional regulation of integrins is a major determinant of cell adhesion, migration and tissue maintenance. The binding of cytoskeletal proteins to various sites of integrin cytoplasmic domains is a key mechanism of this functional regulation. Expression of recombinant integrin alpha(IIb)beta(3) and alpha(M)beta(2) lacking the GFFKR-region in CHO cells results in constitutively activated integrins. In contrast, CHO cells stably expressing either a GFFKR-deleted alpha(V(del))beta(3) or a FF to AA-substituted alpha(V(AA))beta(3) do not reveal a constitutively activated integrin. Adhesion to immobilized fibrinogen is strongly impaired in alpha(V(del))beta(3) or alpha(V(AA))beta(3)-expressing cells, whereas it is not impaired in alpha(IIb)beta(3) and alpha(M)beta(2), both lacking the GFFKR-region. In a parallel plate flow chamber assay, alpha(V)beta(3)-expressing cells adhere firmly to fibrinogen and spread even at shear rates of 15 to 20 dyn/cm(2), whereas alpha(V(del))beta(3) or alpha(V(AA))beta(3) cells are detached at 15 dyn/cm(2). Actin stress fiber formation and focal adhesion plaques containing alpha(V)beta(3) are observed in alpha(V)beta(3) cells but not in alpha(V(del))beta(3) or alpha(V(AA))beta(3)-expressing cells. As an additional manifestation of impaired outside-in signaling, phosphorylation of pp125(FAK) was reduced in these cells. In summary, we report that the GFFKR-region of the alpha(V)-cytoplasmic domain and in particular two phenylalanines are essential for integrin alpha(V)beta(3) function, especially for outside-in signaling. Our results suggest that the two beta(3)-integrins alpha(IIb)beta(3) and alpha(V)beta(3) are differentially regulated via their GFFKR-region.
Ahrens
I G
IG
Department of Cardiology and Angiology, Internal Medicine III, University of Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany. iahrens@gmx.de
Moran
N
N
Aylward
K
K
Meade
G
G
Moser
M
M
Assefa
D
D
Fitzgerald
D J
DJ
Bode
C
C
Peter
K
K
D000818:Animals; D016466:CHO Cells; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D002478:Cells, Cultured; D017124:Conserved Sequence; D006224:Cricetinae; D039302:Integrin alphaVbeta3 / Q000502:physiology*; D009154:Mutation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D015398:Signal Transduction / Q000502:physiology
D039302:Integrin alphaVbeta3; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011994:Recombinant Proteins