Characterization of the Major Heparan Sulfate Proteoglycan Secreted by Bovine Aortic Endothelial Cells in Culture: Homology to the large molecular weight molecule of basement membranes

Abstract

To determine the precise architecture and functional characteristics of the subendothelial basal lamina, detailed information of the molecules contained in this structure is required. To this end, we have studied low passage bovine aortic endothelial cells and have isolated the major heparan sulfate-containing proteoglycan from the growth medium of the cells maintained under static culture conditions. This large macromolecule consists of a core protein approximately 500,000 daltons in mass and two to three glycan side chains as revealed by carbon/platinum rotary shadow casting. Specific antibodies raised by immunization of rabbits with the native or deglycosylated bovine molecule could be isolated from an immunoadsorption column prepared with a preparation isolated from the murine Engelbreth-Holm-Swarm tumor. The antibodies purified by immunoaffinity react with basement membranes of blood vessels, lung, liver, or skin, and this reactivity is indistinguishable, at least for the organs studied, from the reactivity of antibodies specific for the Engelbreth-Holm-Swarm tumor-derived high molecular weight heparan sulfate proteoglycan isolated previously. Immunoelectron microscopy of frozen ultrathin tissue sections from the kidney indicates localization of the epitope(s) also in the basement membranes of the renal glomeruli and tubuli. The close structural relationship and homology between the aortic endothelial cell product can be demonstrated even more convincingly by two-dimensional peptide mapping procedures. The peptide patterns from the bovine and mouse products of approximately 500 kDa are nearly indistinguishable. Maps of polypeptides of molecular masses ranging from 400 to 150 kDa, which are found in the bovine as well mouse tumor preparation, are clearly related to each other and suggest that this proteoglycan is quite sensitive to degradation by tissue proteases. Thus the data presented here strongly suggest that the large proteoglycan previously isolated and described as a tumor cell product can be produced by normal cells.