Signal transduction by the alpha 6 beta 4 integrin: distinct beta 4 subunit sites mediate recruitment of Shc/Grb2 and association with the cytoskeleton of hemidesmosomes.
We have examined the mechanism of signal transduction by the hemidesmosomal integrin alpha 6 beta 4, a laminin receptor involved in morphogenesis and tumor progression. Immunoprecipitation and immune complex kinase assays indicated that antibody- or laminin-induced ligation of alpha 6 beta 4 causes tyrosine phosphorylation of the beta 4 subunit in intact cells and that this event is mediated by a protein kinase(s) physically associated with the integrin. Co-immunoprecipitation and GST fusion protein binding experiments showed that the adaptor protein Shc forms a complex with the tyrosine-phosphorylated beta 4 subunit. Shc is then phosphorylated on tyrosine residues and recruits the adaptor Grb2, thereby potentially linking alpha 6 beta 4 to the ras pathway. The beta 4 subunit was found to be phosphorylated at multiple tyrosine residues in vivo, including a tyrosine-based activation motif (TAM) resembling those found in T and B cell receptors. Phenylalanine substitutions at the beta 4 TAM disrupted association of alpha 6 beta 4 with hemidesmosomes, but did not interfere with tyrosine phosphorylation of Shc and recruitment of Grb2. These results indicate that signal transduction by the alpha 6 beta 4 integrin is mediated by an associated tyrosine kinase and that phosphorylation of distinct sites in the beta 4 tail mediates assembly of the hemidesmosomal cytoskeleton and recruitment of Shc/Grb2.
Mainiero
F
F
Department of Pathology, Kaplan Comprehensive Cancer Center, New York University School of Medicine, NY 10016, USA.
Pepe
A
A
Wary
K K
KK
Spinardi
L
L
Mohammadi
M
M
Schlessinger
J
J
Giancotti
F G
FG
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism; D000954:Antigens, Surface / Q000378:metabolism*; D002448:Cell Adhesion / Q000502:physiology; D015815:Cell Adhesion Molecules / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D004252:DNA Mutational Analysis; D003896:Desmosomes / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D051380:GRB2 Adaptor Protein; D006801:Humans; D039161:Integrin alpha6beta4; D039663:Integrin beta4; D016023:Integrins / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014162:Transfection; D018909:src Homology Domains; D000097794:Kalinin
D048868:Adaptor Proteins, Signal Transducing; D015703:Antigens, CD; D000951:Antigens, Neoplasm; D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D051380:GRB2 Adaptor Protein; D039161:Integrin alpha6beta4; D039663:Integrin beta4; D016023:Integrins; D011505:Protein-Tyrosine Kinases; D011506:Proteins; D011994:Recombinant Proteins; D000097794:Kalinin; C495948:GRB2 protein, human; C495950:Grb2 protein, rat