title: Strong association of bovine IgM with microvilli and their microfilament core from 13762 ascites tumor cells.
abstract: Microfilament cores, obtained by extracting 13762 mammary ascites tumor cell microvilli with Triton X-100, contain a major glycoprotein migrating at an apparent molecular weight of 80 kDa by dodecyl sulfate-polyacrylamide gel electrophoresis. The 80-kDa component is a disulfide-linked multimer, as demonstrated by velocity sedimentation and agarose-acrylamide gel electrophoresis analyses under nonreducing conditions. This 80-kDa species is not metabolically labeled, as is a minor 80-kDa glycoprotein found in the cores, membranes, and an isolated transmembrane complex with actin. Antibodies prepared against the 80-kDa glycoprotein react strongly with bovine IgM and more weakly with rat IgM. These antibodies were used to demonstrate that the 80-kDa component is present in microvilli, microvillar microfilament cores, and microvillar membranes only if the microvilli are prepared in the presence of calf serum. The 80-kDa component, purified by velocity sedimentation in dodecyl sulfate, reacts with anti-rat IgM by immunoblot analyses. Moreover, immunoprecipitation of detergent extracts of microvilli with anti-rat IgM specifically sediments the 80-kDa component. The 80-kDa glycoprotein fractionates with the actin-containing transmembrane complex prepared by gel filtration of Triton-solubilized microvillar membranes. These results indicate that the disulfide-linked, multi-meric 80-kDa component is bovine IgM, which binds strongly to a cell-surface component of the microvilli, and is indirectly associated with the microfilament cores. Thus, the IgM provides a marker by which the transmembrane complexes to the microfilaments can be identified.
authors.affiliation: Department of Anatomy and Cell Biology, University of Miami School of Medicine, Florida 33101.
authors.forename: X H
authors.initials: XH
authors.lastname: Ye
authors.forename: T N
authors.initials: TN
authors.lastname: Metcalf
authors.forename: D M
authors.initials: DM
authors.lastname: Andrews
authors.forename: C A
authors.initials: CA
authors.lastname: Carraway
authors.forename: K L
authors.initials: KL
authors.lastname: Carraway
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media; D007075:Immunoglobulin M / Q000378:metabolism*; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism / Q000648:ultrastructure*; D008970:Molecular Weight; D011233:Precipitin Tests; D011485:Protein Binding; D051381:Rats
chemical_list: D003470:Culture Media; D007075:Immunoglobulin M; D008562:Membrane Glycoproteins