Characterization of posttranslational modifications of human A33 antigen, a novel palmitoylated surface glycoprotein of human gastrointestinal epithelium.
Monoclonal antibody (mAb) A33 recognizes a differentiation antigen (A33) expressed in normal human gastrointestinal epithelium and in 95% of human colon cancers. Murine mAb A33 shows specific targeting of colon cancer in humans and a humanized A33 antibody is currently being evaluated in the clinic. The cDNA for the human A33 antigen has recently been cloned, and sequence comparison indicated that the A33 antigen is a novel human cell surface molecule of the immunoglobulin superfamily. Because mAb A33 recognizes a conformational epitope, only a partial characterization of the A33 antigen has been carried out to date. In this report we show that the A33 antigen is (I) N-glycosylated, containing approximately 8 K of N-linked carbohydrate and there is no evidence for O-glycosylation, sialylation or glycophosphatidylinositol, and (ii) S-acylated in vitro, incorporating [3H] palmitic acid linked through a hydroxylamine-sensitive thioester bond. The S-palmitoylation may be involved in regulating the internalization process initiated by binding of mAb A33 to cell surface A33 antigen.
Ritter
G
G
Ludwig Institute for Cancer Research, New York Branch at Memorial Sloan-Kettering Cancer Center, New York 10021, USA. ritterg@mskcc.org
Cohen
L S
LS
Nice
E C
EC
Catimel
B
B
Burgess
A W
AW
Moritz
R L
RL
Ji
H
H
Heath
J K
JK
White
S J
SJ
Welt
S
S
Old
L J
LJ
Simpson
R J
RJ
D000215:Acylation; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm / Q000378:metabolism*; D015153:Blotting, Western; D003110:Colonic Neoplasms / Q000276:immunology; D004064:Digestive System / Q000276:immunology*; D004591:Electrophoresis, Polyacrylamide Gel; D004848:Epithelium / Q000276:immunology; D006031:Glycosylation; D006801:Humans; D007163:Immunosorbent Techniques; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D019308:Palmitic Acid / Q000378:metabolism*; D011499:Protein Processing, Post-Translational
D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; C104258:GPA33 protein, human; C504395:Gpa33 protein, mouse; D008562:Membrane Glycoproteins; D019308:Palmitic Acid