Cleavage of A-CAM by endogenous proteinases in cultured lens cells and in developing chick embryos.
We describe two truncated forms of A-CAM (N-cadherin) and present evidence suggesting that both forms are proteolytically derived from the intact A-CAM molecule. The first is a membrane-bound fragment of A-CAM displaying an apparent molecular weight of 78 kDa. This polypeptide, containing the C-terminal portion of the protein, may be generated in cultured chicken lens cells, either by a short treatment with trypsin-EGTA, or by endogenous proteinase(s) during incubation in low Ca2+ medium. Immunofluorescent labeling of normal and EGTA-treated cells indicated that the 78-kDa fragment is uniformly distributed over the cell surface. Moreover, staining of developing chick embryos with pairs of antibodies which distinguish the 78-kDa fragment from intact A-CAM indicated that, at early stages of sclerotome dissociation in developing somites, a truncated derivative of the molecule is generated. The second truncated form of A-CAM is a 97-kDa polypeptide which is constitutively released by cultured lens cells into the culture medium in the presence of normal medium. We present evidence that the 97-kDa molecule is proteolytically derived from A-CAM by the action of an endogenous proteinase. We discuss possible mechanisms leading to the formation of these two truncated derivatives and their possible involvement in the physiological modulation of A-CAM-mediated interactions.
Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
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T
Volk
T
T
Volberg
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I
Sabanay
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B
Geiger
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D000936:Antigen-Antibody Complex; D015820:Cadherins / Q000302:isolation & purification / Q000378:metabolism*; D002642:Chick Embryo; D002846:Chromatography, Affinity; D005455:Fluorescent Antibody Technique; D007908:Lens, Crystalline / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism
D000906:Antibodies; D000936:Antigen-Antibody Complex; D015820:Cadherins; D010447:Peptide Hydrolases; D014357:Trypsin