Internalization of the lymphocytic surface protein CD22 is controlled by a novel membrane proximal cytoplasmic motif.
CD22 is a key receptor on B-lymphocytes that modulates signaling during antigenic stimulation. We have defined a novel cytoplasmic motif in human CD22 that controls its unusually rapid turnover at the plasma membrane. Chimeric and mutated CD22alpha cDNA vectors were constructed and stably transfected in CD22-negative Jurkat T-lymphocytic cells. Two assays were employed to measure CD22alpha internalization: first, cytoplasmic uptake of radioiodinated anti-CD22 monoclonal antibody; and second, lethal targeting of a toxin, saporin, into cells via CD22 using bispecific F(ab')2 ([anti-CD22 x anti-saporin]) antibody. Results showed that CD22alpha lacking a cytoplasmic tail was not internalized and that replacement of the cytoplasmic tail of CD19 with that of CD22alpha resulted in a chimeric molecule that behaved like CD22alpha and internalized rapidly. Step-wise deletion of the cytoplasmic tail of CD22alpha located the internalization motif to a polar region of 11 residues (QRRWKRTQSQQ) proximal to the plasma membrane, a part of the molecule predicted to form a coil or turn structure. Interestingly, additional CD22 mutants showed that the two glutamine residues sandwiching the serine are critical to internalization but that the serine itself is not.
Chan
C H
CH
Lymphoma Research Unit, Tenovus Cancer Laboratory, Southampton General Hospital, Tremona Rd., Southampton SO16 6YD, United Kingdom.
Wang
J
J
French
R R
RR
Glennie
M J
MJ
D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018941:Antigens, CD19 / Q000235:genetics / Q000378:metabolism; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D015815:Cell Adhesion Molecules; D002462:Cell Membrane / Q000378:metabolism*; D004705:Endocytosis; D006801:Humans; D019169:Jurkat Cells; D037102:Lectins; D008214:Lymphocytes / Q000378:metabolism*; D009154:Mutation; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D051918:Sialic Acid Binding Ig-like Lectin 2; D013601:T-Lymphocytes / Q000378:metabolism
D015703:Antigens, CD; D018941:Antigens, CD19; D000944:Antigens, Differentiation, B-Lymphocyte; C497867:CD22 protein, human; D015815:Cell Adhesion Molecules; D037102:Lectins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D051918:Sialic Acid Binding Ig-like Lectin 2