Cell surface proteoglycan of mammary epithelial cells. Protease releases a heparan sulfate-rich ectodomain from a putative membrane-anchored domain

• Published in: The Journal of biological chemistry Vol. 260; no. 7; pp. 4103 - 4109
• Main Authors: Rapraeger, A, Bernfield, M
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 10-04-1985; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Biological and medical sciences; Cell membranes. Ionic channels. Membrane pores; Cell structures and functions; Centrifugation, Density Gradient; Chondroitin Sulfate Proteoglycans - analysis; Chromatography, Gel; Epithelium - analysis; Female; Fundamental and applied biological sciences. Psychology; Glycosaminoglycans - analysis; Heparan Sulfate Proteoglycans; Heparin - metabolism; Heparitin Sulfate - analysis; Mammary Glands, Animal - cytology; Mice; Molecular and cellular biology; Peptide Hydrolases - metabolism; Proteoglycans - analysis; Sulfates - metabolism; Proteoglycan; Cell culture; Membrane protein; Proteinase; Rodentia; Glycoproteins; Cell surface; Vertebrata; Mammalia; Mouse; Epithelial cell; Mammary gland; Molecular accessibility
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)89237-7

Heparan sulfate-rich proteoglycan is present on the surface of NMuMG mouse mammary epithelial cells. All of this cell surface fraction is lipophilic, assessed by intercalation into lipid vesicles, and requires proteolytic cleavage to be released from the cell surface. No proteoglycan is competitively displaced by heparin. The cell surface lipophilic proteoglycan constitutes 52-55% of the total cellular proteoglycan while the remaining proteoglycan is apparently intracellular, comprising a nonlipophilic fraction (35%) and a small (10-13%) lipophilic fraction. Trypsin or chymotrypsin cleaves a labile site between the region of the cell surface proteoglycan bearing the glycosaminoglycan chains and the cell-associated portion of the core protein, producing a proteoglycan that is nonlipophilic, has an increased bouyant density, and is smaller than the parent molecule. We refer to this proteoglycan as the ectodomain of the cell surface proteoglycan. The correlation between its cell surface location and lipophilic properties suggests that a hydrophobic domain of its core protein may anchor this proteoglycan in the plasma membrane. In vivo, the proteoglycan may be cleaved from this putative anchor, generating nonlipophilic proteoglycan present as a matrix component, or it may remain a membrane component, anchoring the cell directly to the extracellular matrix.