D. Baeckstrom et al., EXPRESSION OF THE LEUKOCYTE-ASSOCIATED SIALOGLYCOPROTEIN CD43 BY A COLON-CARCINOMA CELL-LINE, The Journal of biological chemistry, 270(23), 1995, pp. 13688-13692
The colon adenocarcinoma cell line COLO 205 secretes L-CanAg, a mucin-
like glycoprotein carrying the carcinoma-associated sialyl-Lewis a car
bohydrate epitope. In an attempt to identify its apoprotein, an NH2-te
rminal peptide sequence was obtained from purified L-CanAg. In all int
erpretable positions, this sequence showed 100% identity to the NH2-te
rminal of human CD43 (leukosialin, sialophorin), a plasma membrane bou
nd sialoglycoprotein hitherto only identified in leukocytes and other
hematopoietic cells. An antiserum against deglycosylated L-CanAg and a
n anti-CD43 antiserum both immunoprecipitated a 61-kDa band, interpret
ed as the CD43 precursor, from COLO 205 cells as well as hom the known
CD43-expressing cell line HL-60. Results from immunoprecipitations fo
llowing pulse-chase experiments and tunicamycin treatments were in agr
eement with earlier studies on the CD43 precursor. RNA blot analysis c
onfirmed the expression of CD43 by the COLO 205 cell line, whereas thr
ee other colon carcinoma cell lines were negative. The glycosylation-d
ependent monoclonal antibody Leu-22, which recognizes leukocyte CD43,
failed to bind L-CanAg, probably due to its much more extensive glycos
ylation, We conclude that L-CanAg is the secreted extracellular domain
of a novel glycoform of CD43 and that CD43, if expressed in other car
cinoma cells, may have escaped notice in studies relying on glycosylat
ion-dependent monoclonal antibodies against leukocyte CD43.