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/
Jp. Deans et al., 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/, The Journal of biological chemistry, 270(38), 1995, pp. 22632-22638
CD20, a non-glycosylated cell-surface protein expressed exclusively on
B lymphocytes, is one of a family of 4-pass transmembrane molecules t
hat also includes the beta chain of the high affinity receptor for IgE
. The precise function of CD20 is unknown, although in vitro effects o
f CD20-specific antibodies on resting B cells indicate that it is able
to transduce an extracellular signal affecting the G(0)/G(1) cell cyc
le 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, an
alysis of CD20-associated molecules has revealed that CD20 is associat
ed with the Src family tyrosine kinases p56/53(lyn), p56(lck), and p59
(fyn) and with 75/80-kDa proteins phosphorylated in vivo on tyrosine r
esidues. Mutagenesis of CD20 was performed to define regions of CD20 i
nvolved in intermolecular interactions. Mutants were analyzed in the h
uman T lymphoblastoid cell line Molt-4, in which ectopically expressed
wild-type CD20 associated with p59(fyn), p56(lck), and 75/80-kDa phos
phoproteins. Deletion of major portions of the cytoplasmic regions of
CD20 did not abolish its association with either p75/80 or tyrosine ki
nases, The interaction between CD20 and the Src-related kinases is the
refore likely to be independent of CD20 cytoplasmic domains and may oc
cur indirectly, The interaction may be mediated by the p75/80 phosphop
roteins, which were found to be tightly associated with the Src family
kinases isolated from the CD20 complex.