Characterization of the protein protecting RNA from Acid precipitation and its evaluation as tumor-marker in gastrointestinal and gynecological cancer.

In a previous study, we observed increased protective activity against acid precipitation of poly (U) in the serum of tumor bearing mice and hepatoma patients. In the present study we purified and partially characterized the protein responsible for this phenomenon and measured the activity in the serum of patients with various cancers. Evidence is presented that this protein forms a complex with serum ribonucleases which results in the inactivation of enzymes and protection of RNA from acid precipitation. The serum protective activity against acid precipitation of poly (U) was measured in 37 patients with gastrointestinal cancer and 79 with gynecological cancer, along with 15 male subjects with nonmalignant diseases of the gastrointestinal system, 15 with uterine leiomyoma, 19 healthy men and 30 healthy women from the hospital personnel. The mean values found in patients with various tumors were about three times higher than those found in healthy individuals, while no significant overlapping of values was observed between cancer patients and controls. On the other hand, the activity was not increased in patients with nonmalignant diseases of gastrointestinal system and uterus.