Transferrin in the Rat Prostate Dunning Tumor1

A major protein of the rat Dunning prostate tumor has been purified. It has physicochemical properties and an amino acid composition similar to that of transferrin. Furthermore, the isolated tumor protein reacts with antiserum to authentic rat transferrin. Immunoperoxidase staining with rabbit anti-rat transferrin localizes transferrin within tumor acinar glands. Rocket ¡mmunoelectrophoresis indicates that transferrin con stitutes 30 to 40% of tumor fluid protein, but accounts for only ~9% of total serum protein. In normal rat prostate cytosols, the level of transferrin is at least 200 times lower than in tumor cytosol. Nevertheless, dorsal and lateral prostate show variable peroxidase staining indicating the presence of immunoreactive transferrin within acinar glands of these normal tissues. While intense staining for transferrin was found in the interstium of all regions of the normal prostate, transferrin was not detected within acinar glands of coagulating gland, ventral prostate, or seminal vesicle. Immunocytochemical localization of albumin indicates a distribution similar to that of transferrin in normal and neoplastic rat prostate. However, unlike transferrin, the albumin content was lower in tumor fluid than in serum. It is suggested that the high level of transferrin in tumor fluid may be due to selective uptake by the tumor from serum.