A novel functional role for the highly conserved alpha-subunit KVGFFKR motif distinct from integrin alphaIIbbeta3 activation processes.
BACKGROUND
The highly conserved integrin alpha-subunit membrane-proximal motif KVGFFKR plays a decisive role in modulating the activation of integrin alphaIIbbeta3. Previously, we have shown that a platelet permeable palmityl (pal)-peptide with this seven amino acid sequence can directly activate alphaIIbbeta3 leading to platelet aggregation.


OBJECTIVE
To investigate further the role of the KVGFFKR motif in integrin alphaIIbbeta3 function.


METHODS
We used two sequence-specific complementary model systems, palmityl pal-peptides in platelets, and mutant alphaIIbbeta3-expressing Chinese Hamster Ovary (CHO) cell lines.


RESULTS
In platelets we show that the two phenylalanine amino acids in pal-KVGFFKR (pal-FF) peptide are critical for stimulating platelet aggregation. Pal-FF peptide treatment of platelets also gives rise to a tyrosine phosphorylation signal despite the presence of inhibitors of fibrinogen binding. In CHO cells, a double alanine substitution, alphaIIb(F992A, F993A)beta3, induces constitutive integrin activation but prevents actin stress fiber formation upon adhesion to fibrinogen, suggesting that alphaIIbbeta3-mediated cytoskeletal reorganization is also dependent on F992 and F993. This further highlights a critical role for the two phenylalanine residues in both of these alphaIIbbeta3-mediated processes.


CONCLUSIONS
In addition to regulating integrin alphaIIbbeta3 activation state, the KVGFFKR motif also influences cytoskeletal reorganization. This activity is critically determined by F992 and F993 within the seven amino acid sequence.
Aylward
K
K
Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin, Ireland.
Meade
G
G
Ahrens
I
I
Devocelle
M
M
Moran
N
N
D020816:Amino Acid Motifs; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D006801:Humans; D008856:Microscopy, Fluorescence; D010455:Peptides / Q000737:chemistry; D010649:Phenylalanine / Q000737:chemistry; D010766:Phosphorylation; D015539:Platelet Activation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D014162:Transfection
D010455:Peptides; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010649:Phenylalanine