A paracrine migration-stimulating factor for metastatic tumor cells secreted by mouse hepatic sinusoidal endothelial cells: identification as complement component C3b.

Selective malignant cell invasion at secondary sites mediated by organ-specific (paracrine) motility factors may be of importance in preferential organ colonization of metastatic cells. In this study we isolated and examined a migration-stimulating activity present in mouse hepatic sinusoidal endothelial cell-conditioned medium (HSE-CM). HSE-CM contains migration-stimulating activity for highly liver-metastatic (RAW117-H10) and highly lung- and liver-metastatic (RAW117-L17) mouse large cell lymphoma sublines but not for the poorly metastatic parental line (RAW117-P). A migration-stimulating factor for H10 cells was purified from HSE-CM by hydroxylapatite affinity and DEAE anion exchange chromatography, Sephacryl S-200 gel filtration, and preparative native gel electrophoresis. The activity in each of the purification fractions was measured in a Transwell chamber assay using 3-microns diameter pore filters. Upon sodium dodecyl sulfate polyacrylamide gel electrophoresis, the component migrated as a single component of M(r) > 200,000 (nonreducing conditions) or as two components or M(r) approximately 110,000 and approximately 67,000 (reducing conditions). The factor was bound to Concanavalin A-Sepharose but not to heparin- or gelatin-Sepharose affinity columns, induced mainly H10 chemotactic cell activity and some chemokinetic activity, and preferentially stimulated the chemotaxis of liver-colonizing RAW117 sublines (H10 > L17 > P). NH2-terminal amino acid sequence analysis of each subunit indicated that the HSE-CM-derived migration-stimulating factor was a proteolytic fragment of complement component C3. HSE-derived migration-stimulating factors may be important in determining the ability of RAW117 tumor cells to invade and colonize the liver.