Identification of a keratin-associated protein that localizes to a membrane compartment

Author:

Chou C F1,Riopel C L1,Omary M B1

Affiliation:

1. Palo Alto Veterans Administration Medical Center, and the Gastroenterology Division at Stanford University, School of Medicine, 3801 Miranda Avenue, GI 111, Palo Alto, CA 94304, U.S.A.

Abstract

We describe the characterization of an acidic glycoprotein (molecular mass approximately 85 kDa) that associates with keratin intermediate filaments of ‘simple’-type epithelia. Using a number of anti-keratin monoclonal antibodies, the 85 kDa glycoprotein was identified by co-immunoprecipitation with keratin polypeptides 8 and 18 (K8/18) from the human colonic epithelial cell line HT29 and several other epithelial cell lines. This Keratin-Associated Protein (termed KAP85) was readily detected after in vitro galactosylation of K8/18 immunoprecipitates obtained from mitosis-arrested cells. Its solubilization and detection were dependent on the detergent used, and it was barely detected after in vitro galactosylation of asynchronously growing G0/G1-phase cells. Its poor in vitro galactosylation in G0/G1-phase cells is likely a reflection of the lack of available terminal N-acetylglucosamine residues, since it can be labelled to a similar extent in G0/G1- and G2/M-phase cells using NaIO4/NaB3H4. Glycosidase digestion showed that KAP85 contains high mannose and complex oligosaccharides. Fractionation of total cellular K8/18 into soluble and cytoskeletal insoluble pools showed that KAP85 associates exclusively with the cytoskeletal K8/18 pool. Subcellular fractionation showed that KAP85 co-localizes with a plasma-membrane-enriched fraction that includes the transferrin receptor and KS-1 antigen. Our results demonstrate in vitro evidence of a membrane-associated glycoprotein (KAP85) which may serve as an attachment site for filamentous K8/18.

Publisher

Portland Press Ltd.

Subject

Cell Biology,Molecular Biology,Biochemistry

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