Effects of heat shock and a carcinogen (1,2-dimethylhydrazine) on the time-dependent p53 protein concentration in the rat serum

Background: We have studied the expression of the cytoplasmic (soluble) form of p53 protein in animals exposed both to heat shock and to a carcinogen. Methods: Rats were treated with hyperthermia (2 h at 45°C) or with a carcinogen (1,2-dimethylhydrazine, DMH, 20 mg/kg weekly for 5 weeks). The results were evaluated by the determination of the serum levels of proteins that were isolated by the method described. Results: Hyperthermia caused an increase in concentrations of 90, 70 and 53-kD proteins 2 h after exposure. Concentrations of the first two proteins decreased up to the end of the second week. The 53-kD protein could be detected in serum even on day 21 after the treatment. After exposure of rats to a carcinogen, a significant increase in blood levels of 64 and 53-kD proteins was found. The 64-kD protein accumulated in DMH-treated tumor-free rats, whereas high blood levels of p53 protein were found in cancer-bearing rats. Conclusions: p53 protein should be considered as a protein related to pathological changes in the organism, i.e., as a stress response protein. The increased expression of this protein may be manifested in different biological processes, including tumorigenesis and inflammatory diseases. In such cases, the over-expression of p53 protein may serve as a part of a cellular defense mechanism which has developed as a reaction of the organism to stress.