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Post‐translational modification and intracellular localization of a splice product of CD46 cloned from human testis: role of the intracellular domains in O‐glycosylation
Author(s) -
Tomoko Hara,
Yasuhiko Suzuki,
Teruki Nakazawa,
H Nishimura,
Shigeharu Nagasawa,
Miyuki Nishiguchi,
Misako Matsumoto,
Minoru Hatanaka,
Masaya Kitamura,
Tsukasa Seya
Publication year - 1998
Publication title -
immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.297
H-Index - 133
eISSN - 1365-2567
pISSN - 0019-2805
DOI - 10.1046/j.1365-2567.1998.00455.x
Subject(s) - chinese hamster ovary cell , gene isoform , biology , glycosylation , hamster , sperm , microbiology and biotechnology , alternative splicing , biochemistry , gene , genetics , receptor
We obtained a unique CD46 cDNA, ST c /CY4, from the human testis, the predicted amino acid sequence of which suggested the presence of a novel isoform of CD46. This message was present predominantly in the testis, andthe predicted isoform possessed a short (11 amino acids) transmembrane section (TM) and an unidentified cytoplasmic tail (CY). When expressed in Chinese hamster ovary (CHO) cells, this CD46 isoform underwent no O‐glycosylation and was mostly retained in the endoplasmic reticulum. This unusual behaviour of the new isoform was due in part to the short TM and the unusual sequences of the CY. The molecular mass of this isoform was 42 000, approximately 20 000 smaller than conventional CD46. These properties of the ST c /CY4 isoform were similar to those of sperm CD46. The only difference between sperm CD46 and the ST c /CY4 isoform expressed on CHO cells was that only the latter possessed N‐linked sugars of high mannose types. Since the ST c /CY4 isoform may behave like sperm CD46 in cellular localization and post‐translational modification, studies of sperm–egg interassociation were performed using hamster eggs and CHO cell clones expressing various isoforms including the ST c /CY4. Rosette formation was seen most effectively between hamster eggs and ST c /CY4‐expressing CHO cells. These results infer that O‐glycosylation perturbs CD46‐mediated sperm‐binding to eggs and thus sperm CD46 lacking O‐linked sugars can serve as an adhesion molecule. The possible role of CD46 in fertilization and the structural differences between sperm and conventional CD46 are discussed.