Lymphoma cell-mediated degradation of sulfated proteoglycans in the subendothelial extracellular matrix: relationship to tumor cell metastasis

Abstract

Cloned lines of the methylcholanthrene-induced DBA/2 low-metastatic T-lymphoma Eb line and its highly metastatic variant ESb line were compared for the ability to degrade proteoglycans in the subendothelial extracellular matrix (ECM) produced by cultured endothelial cells. The ECM was metabolically labeled with Na2(35)SO4, and the tumor cell-mediated release of labeled degradation products was analyzed by gel filtration. More than 90% of the labeled material released upon incubation of ESb cells with the ECM, either when exposed or covered with vascular endothelial cells, was in the form of low-Mr, heparan sulfate-containing fragments (Mr approximately 10(4)) compared to high-Mr sulfated proteoglycans (mostly excluded from Sepharose 6B) released by incubation with the low-metastatic Eb cells. The same high- and low-Mr degradation products were obtained by incubation of the ECM with a serum-free medium conditioned by the low (Eb)- and high (ESb)-metastatic sublines, respectively. The high-Mr proteoglycans released by incubation of the ECM with Eb-conditioned medium was further degraded into Mr 10(4) glycosaminoglycan fragments upon a subsequent incubation with ESb-conditioned medium. These fragments were smaller than glycosaminoglycan side chains released by treatment of the ECM with papain or alkaline borohydride, suggesting an ESb-specific endoglycosidase activity. The higher ability of the ESb over the Eb cells to solubilize the glycosaminoglycan scaffolding of the sub-endothelial ECM may, among other properties, facilitate their hematogenous dissemination and extravasation.