Mutation of the Cytoplasmic Domain of the Integrin Subunit

doi:10.1074/jbc.270.16.9550

Mutation of the Cytoplasmic Domain of the Integrin Subunit

DIFFERENTIAL EFFECTS ON CELL SPREADING, RECRUITMENT TO ADHESION PLAQUES, ENDOCYTOSIS, AND PHAGOCYTOSIS (*)

From the (1) Departments of Biochemistry and
(2) Anatomy, University of Helsinki, Helsinki, Finland and the
(3) Department of Vascular Biology, The Scripps Research Institute, La Jolla, California

^§ Postdoctoral fellow of the Arthritis Foundation during these studies. To whom correspondence should be addressed:
Div. of Biochemistry, Dept. of Biosciences, P. O. Box 5 (Unioninkatu 35), 00014 University of Helsinki, Finland.
Tel.: 358-191-7793; Fax: 358-191-7769; E-mail: Jari.Ylanne{at}csc.fi.

Abstract

The cytoplasmic domain of the β subunit of the αβ₃integrin is required for cell spreading on fibrinogen. Here we report that deletion of six amino acids from the COOH terminus of the β₃(ITYRGT) totally abolished cell spreading and formation of adhesion plaques, whereas retaining Ilepartially preserved these functions. We further found that substitution of Tyrwith Ala also abolished αβ₃-mediated cell spreading.

The effects of these and other mutations on additional functions of αβ₃were also studied. Progressive truncations of β₃, in which stop codons were inserted at amino acid positions 759-756, caused partial defects in the recruitment of αβ₃to preestablished adhesion plaques and a gradual decrease in the ability of αβ₃to mediate internalization of fibrinogen-coated particles. The Tyr Ala substitution mutant was almost totally inactive in both of these assays. Point mutations at Tyr, and at a conserved area close to the transmembrane domain of β₃, decreased integrin recruitment to preestablished adhesion plaques but allowed αβ₃-mediated formation of these structures and partial cell spreading. Deletion of the cytoplasmic domain of β₃did not affect the constitutive endocytosis of αβ₃.

Footnotes

↵* This study was supported in part by grants from the Academy of Finland (to J. Y., C. G. G., and I. V.), the Finnish Cancer Society (to C. G. G.), the Sigrid Jusélius Foundation (to C. G. G.), the Finnish Society of Science and Letters (to J. Y.), the Ella and Georg Ehrnrooth Foundation (to J. Y.), the Walter and Lisi Wahl Foundation (to J. Y.), and by National Institutes of Health Grants HL48728 and HL28235 (to M. H. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

CHO

Chinese hamster ovary

PCR

polymerase chain reaction

PBS

phosphate-buffered saline.