Angiostatin II is the predominant glycoform in pleural effusates of rabbit VX-2 lung tumors.
Angiostatin (AST), a polypeptide with potent antiangiogenic properties, is released proteolytically from plasminogen in vivo. Plasminogen exists naturally in plasma as two glycoforms (PLGs), I and II. Recently it was shown with the use of a chick-embryo chorioallantoic membrane (CAM) assay that rabbit PLG-I and -II yield distinct ASTs-AST-I and -II, respectively-with different antiangiogenic activities. AST glycoforms were of similar molecular weight, approximately 30 to 32,000 kD, and probably consisted of kringles 1 to 3 only. AST has now been identified in the interpleural effusate released from VX-2 lung tumors in rabbits. Effusate was collected from six rabbits with high tumor burdens and fractionated by means of lysine-Sepharose chromatography. The epsilon-aminohexanoic acid-eluted protein of all effusates contained AST (kringles 1-3) at a mean concentration of 1.2 microg/mL of effusate; with regard to AST content, 97% was AST-II. A CAM assay revealed that the lysine-Sepharose-bound fraction from all interpleural effusates contained potent antiangiogenic activity. Blood and urine from rabbits with high burdens of VX-2 contained essentially only AST-II, at mean concentrations of 145 and 4 ng/mL, respectively. AST was absent from the blood of control rabbits. In an attempt to compare their uptake by VX-2, iodine 125-labeled AST-I and iodine 131-labeled AST-II were injected intravenously into tumor-bearing rabbits. AST-I entered the tumor 1.6 times faster than AST-II. As a means of accounting for the preponderance of AST-II in the interpleural effusate, we postulate that VX-2 cells release proteolytic activity to activate plasminogen but that of the two PLGs, PLG-II may be the preferred substrate for AST formation in vivo.
Hatton
Mark W C
MW
Department of Pathology and Molecular Medicine, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada.
Southward
Suzanne M R
SM
Ross
Bonnie L
BL
Legault
Kimberly
K
Marien
Lindsay
L
Korbie
Darren
D
Richardson
Mary
M
Singh
Gurmit
G
Clarke
Bryan J
BJ
Blajchman
Morris A
MA
D043168:Angiostatins; D000818:Animals; D015153:Blotting, Western; D002645:Chickens; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007457:Iodine Radioisotopes; D008175:Lung Neoplasms / Q000378:metabolism* / Q000473:pathology; D008970:Molecular Weight; D009368:Neoplasm Transplantation; D010446:Peptide Fragments / Q000032:analysis* / Q000378:metabolism; D010958:Plasminogen / Q000032:analysis* / Q000378:metabolism; D010996:Pleural Effusion / Q000737:chemistry*; D020033:Protein Isoforms / Q000032:analysis* / Q000378:metabolism; D011817:Rabbits; D014407:Tumor Cells, Cultured
D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D020033:Protein Isoforms; D043168:Angiostatins; D010958:Plasminogen