Association of 75/80-kDa phosphoproteins and the tyrosine kinases Lyn, Fyn, and Lck with the B cell molecule CD20. Evidence against involvement of the cytoplasmic regions of CD20.
CD20, a non-glycosylated cell-surface protein expressed exclusively on B lymphocytes, is one of a family of 4-pass transmembrane molecules that also includes the beta chain of the high affinity receptor for IgE. The precise function of CD20 is unknown, although in vitro effects of CD20-specific antibodies on resting B cells indicate that it is able to transduce an extracellular signal affecting the G0/G1 cell cycle transition. Previous studies have demonstrated that CD20-initiated intracellular signals involve tyrosine kinase activation and that CD20 is tightly associated with both serine and tyrosine kinases. Here, analysis of CD20-associated molecules has revealed that CD20 is associated with the Src family tyrosine kinases p56/53lyn, p56lck, and p59fyn and with 75/80-kDa proteins phosphorylated in vivo on tyrosine residues. Mutagenesis of CD20 was performed to define regions of CD20 involved in intermolecular interactions. Mutants were analyzed in the human T lymphoblastoid cell line Molt-4, in which ectopically expressed wild-type CD20 associated with p59fyn, p56lck, and 75/80-kDa phosphoproteins. Deletion of major portions of the cytoplasmic regions of CD20 did not abolish its association with either p75/80 or tyrosine kinases. The interaction between CD20 and the Src-related kinases is therefore likely to be independent of CD20 cytoplasmic domains and may occur indirectly. The interaction may be mediated by the p75/80 phosphoproteins, which were found to be tightly associated with the Src family kinases isolated from the CD20 complex.
Deans
J P
JP
Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
Kalt
L
L
Ledbetter
J A
JA
Schieven
G L
GL
Bolen
J B
JB
Johnson
P
P
D000077329:Agammaglobulinaemia Tyrosine Kinase; D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000378:metabolism*; D018951:Antigens, CD20; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism*; D001402:B-Lymphocytes / Q000378:metabolism; D001483:Base Sequence; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D004792:Enzyme Precursors / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000378:metabolism*; D019000:Phosphotyrosine; D011233:Precipitin Tests; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051076:Proto-Oncogene Proteins c-fyn; D017384:Sequence Deletion; D000072377:Syk Kinase; D013601:T-Lymphocytes / Q000378:metabolism; D014162:Transfection; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D019061:src-Family Kinases
D015703:Antigens, CD; D018951:Antigens, CD20; D000944:Antigens, Differentiation, B-Lymphocyte; D017931:DNA Primers; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D019000:Phosphotyrosine; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C494957:FYN protein, human; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051076:Proto-Oncogene Proteins c-fyn; C000606896:SYK protein, human; D000072377:Syk Kinase; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases