INDUCTION OF MUSCLE PROTEIN-DEGRADATION AND WEIGHT-LOSS BY A TUMOR PRODUCT

Splenocytes from mice bearing a cachexia-inducing tumor (MAC16) have b een fused with mouse myeloma cells to produce hybridomas, which have b een cloned to produce antibody reactive to a material which copurified with a lipid-mobilizing factor isolated from the same tumor. The mono clonal antibody has been used to investigate factors potentially invol ved in the development of cachexia. The major protein detectable by im munoprecipitation of a partially purified lipid-mobilizing factor was M(r) 69,000, whereas Western blotting showed two bands of Mr( )69,000 and M(r) 24,000. Although the monoclonal antibody did not neutralize l ipid-mobilizing activity in an in vitro assay, it did neutralize a ser um factor capable of protein degradation in isolated gastrocnemius mus cle. Affinity purification of MAC16 tumor homogenates using the monocl onal antibody yielded two immunoreactive bands of M(r) 69,000 and M(r) 24,000, which were further fractionated on a hydrophobic column (C-8) . This material was capable of inducing tyrosine release from isolated gastrocnemius muscle, and the effect could be blocked with the monocl onal antibody. The two immunoreactive bands from the hydrophobic colum n were capable of inducing weight loss in mice, whereas nonimmunoreact ive fractions had no effect on body weight. The M(r) 24,000 species ha d a unique amino acid sequence, whereas the M(r) 69,000 species gave t he same sequence as the M(r) 24,000 material, together with that for a lbumin. The M(r) 24,000 species contained carbohydrate, and lectin blo tting showed a strong reaction with wheat germ and Elythrina crystagal li agglutinins. This suggests that the material is a glycoprotein or p roteoglycan that shows strong binding affinity for albumin, possibly t hrough the carbohydrate residues.