A mutation in the extracellular cysteine-rich repeat region of the beta(3)subunit activates integrins alpha(IIb)beta(3) and alpha(V)beta(3)

Citation
H. Kashiwagi et al., A mutation in the extracellular cysteine-rich repeat region of the beta(3)subunit activates integrins alpha(IIb)beta(3) and alpha(V)beta(3), BLOOD, 93(8), 1999, pp. 2559-2568
Citations number
55
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Hematology,"Cardiovascular & Hematology Research
Journal title
BLOOD
ISSN journal
0006-4971 → ACNP
Volume
93
Issue
8
Year of publication
1999
Pages
2559 - 2568
Database
ISI
SICI code
0006-4971(19990415)93:8<2559:AMITEC>2.0.ZU;2-I
Abstract
Inside-out signaling regulates the ligand-binding function of integrins thr ough changes in receptor affinity and/or avidity. For example, alpha(IIb)be ta(3) is in a low-affinity/avidity state in resting platelets, and activati on of the receptor by platelet agonists enables fibrinogen to bind. In addi tion, certain mutations and truncations of the integrin cytoplasmic tails a re associated with a high-affinity/avidity receptor. To further evaluate th e structural basis of integrin activation, stable Chinese hamster ovary (CH O) cell transfectants were screened for high-affinity/avidity variants of a lpha(IIb)beta(3) One clone (AM-1) expressed constitutively active alpha(IIb )beta(3), as evidenced by (1) binding of soluble fibrinogen and PAC1, a lig and-mimetic alpha(IIb)beta(3) antibody; and (2) fibrinogen-dependent cell a ggregation. Sequence analysis and mutant expression in 293 cells proved tha t a single amino acid substitution in the cysteine-rich, extracellular port ion of beta(3)(T562N) was responsible for receptor activation. In fact, T56 2N also activated alpha(v)beta(3), leading to spontaneous binding of solubl e fibrinogen to 293 cells. In contrast, neither T562A nor T562Q activated a lpha(IIb)beta(3) suggesting that acquisition of asparagine at residue 562 w as the relevant variable. T562N also led to aberrant glycosylation of beta( 3), but this was not responsible for the receptor activation. The binding o f soluble fibrinogen to alpha(IIb)beta(3)(T562N) was not sufficient to trig ger tyrosine phosphorylation of pp125(FAK), indicating that additional post -ligand binding events are required to activate this protein tyrosine kinas e during integrin signaling. These studies have uncovered a novel gain-of-f unction mutation in a region of beta(3) intermediate between the ligand-bin ding region and the cytoplasmic tail, and they suggest that this region is involved in integrin structural changes during inside-out signaling. (C) 19 99 by The American Society of Hematology.