Human CD1d associates with prolyl-4-hydroxylase during its biosynthesis.
Recent studies have shown that the CD1 family of proteins present various glycolipid antigens to subsets of T cells. CD1d is expressed on human intestinal epithelial cells (IEC) and exists in two biochemical forms: 37-kDa, beta2-microglobulin (beta2m) independent, nonglycosylated, and 47-kDa, beta2m dependent, glycosylated forms. The biosynthetic pathways and the mechanisms of generation of these two biochemically distinct forms of CD1d in human IEC are unknown. Using a human colonic cell line, T84, transfected with CD1d, the biosynthesis of CD1d was investigated. Pulse-chase metabolic labeling studies of T84 transfected with wild type CD1d demonstrated that CD1d was a stable protein over a 4-day chase period. During the first 24 h of the chase, a novel 65-kDa glycoprotein was co-immunoprecipitated with CD1d. Microsequencing of this protein identified the glycoprotein as the alpha and beta subunits of the resident endoplasmic reticulum protein, prolyl-4-hydroxylase (P4H), an enzyme responsible for hydroxyl modification of proline residues. To study if either one or both biochemical forms of CD1d contained hydroxyproline residues, amino acid composition analysis of the 37 and 48 kDa was performed, and demonstrated that only the 37-kDa, but not the 48-kDa form of CD1d, contained hydroxyproline residues. These studies demonstrate that CD1d exhibits a prolonged association with P4H and that the 37-kDa form contains hydroxyproline residues. This suggests that P4H association with CD1d during its biosynthesis results in a novel post-translational modification of CD1d.
Kim
H S
HS
Division of Gastroenterology, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115, USA.
Colgan
S P
SP
Pitman
R
R
Hershberg
R M
RM
Blumberg
R S
RS
D018949:Antigens, CD1 / Q000032:analysis / Q000096:biosynthesis*; D055610:Antigens, CD1d; D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology; D008970:Molecular Weight; D011393:Procollagen-Proline Dioxygenase / Q000032:analysis*; D011499:Protein Processing, Post-Translational; D014407:Tumor Cells, Cultured
D018949:Antigens, CD1; D055610:Antigens, CD1d; C526877:CD1D protein, human; D011393:Procollagen-Proline Dioxygenase