Isolation and identification of a human serum fibronectin-like protein elevated during malignant disease

A human DNA-binding protein, designated MAD-2, has recently been found to be elevated in the serum from patients with malignant diseases. MAD-2 has been purified approximately 500-fold from peritoneal and pleural fluids collected from cancer patients. Immunodiffusion studies have indicated that MAD-2 is immunochemically identical to human plasma fibronectin. The purified material has been resolved by sodium dodecyl sulfate gel electrophoresis into two major protein chains with molecular weights in the range of 200,000 to 210,000 in either the presence or absence of disulfide bond-reducing agents. These results suggest that MAD-2 is a fibronectin fragment which has been generated through proteolysis. A quantitative assay system capable of detecting ng quantities of MAD-2 has been developed and used to verify the presence of elevated MAD-2 levels in DNA-binding protein fractions isolated from the serum of individuals with malignant diseases.