ICAP-1, a novel beta1 integrin cytoplasmic domain-associated protein, binds to a conserved and functionally important NPXY sequence motif of beta1 integrin.
The cytoplasmic domains of integrins are essential for cell adhesion. We report identification of a novel protein, ICAP-1 (integrin cytoplasmic domain- associated protein-1), which binds to the 1 integrin cytoplasmic domain. The interaction between ICAP-1 and beta1 integrins is highly specific, as demonstrated by the lack of interaction between ICAP-1 and the cytoplasmic domains of other beta integrins, and requires a conserved and functionally important NPXY sequence motif found in the COOH-terminal region of the beta1 integrin cytoplasmic domain. Mutational studies reveal that Asn and Tyr of the NPXY motif and a Val residue located NH2-terminal to this motif are critical for the ICAP-1 binding. Two isoforms of ICAP-1, a 200-amino acid protein (ICAP-1alpha) and a shorter 150-amino acid protein (ICAP-1beta), derived from alternatively spliced mRNA, are expressed in most cells. ICAP-1alpha is a phosphoprotein and the extent of its phosphorylation is regulated by the cell-matrix interaction. First, an enhancement of ICAP-1alpha phosphorylation is observed when cells were plated on fibronectin-coated but not on nonspecific poly-L-lysine-coated surface. Second, the expression of a constitutively activated RhoA protein that disrupts the cell-matrix interaction results in dephosphorylation of ICAP-1alpha. The regulation of ICAP-1alpha phosphorylation by the cell-matrix interaction suggests an important role of ICAP-1 during integrin-dependent cell adhesion.
Chang
D D
DD
Department of Medicine, and Department of Microbiology and Immunology, University of California, Los Angeles, California 90095, USA. dchang@medicine.medsch.ucla.edu
Wong
C
C
Smith
H
H
Liu
J
J
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D017124:Conserved Sequence; D005353:Fibronectins; D006367:HeLa Cells; D006801:Humans; D019012:Integrin beta1 / Q000737:chemistry* / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D046911:Macromolecular Substances; D008565:Membrane Proteins; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017354:Point Mutation; D011107:Polylysine; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D005353:Fibronectins; C108257:ITGB1BP1 protein, human; D019012:Integrin beta1; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D011107:Polylysine