STUDIES ON GROWTH SIGNALS DERIVED FROM PROTEIN NUTRITION

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Recent knowledge of molecular biology indicates that cell growth and proliferation are required growth signals and its signal transduction. Although growth of young animals is related to nutritional status, the interaction between nutrition and growth-related signal transduction has not been studied thoroughly. The aim of our study is to determine whether protein nutrition affects signal transduction for cell growth in the tissues of growing animals depending on its nutritional quality. For this purpose, we examined expression of several growth-related genes and DNA synthesis in tissues of growing rats under a variety of nutritional conditions. The results obtained under this project are ; (1) The levels of c-myc and insulin-like growth factor-1 (IGF-1) mRNA in the liver of growing rats varied in a reciprocal manner in response to changes in either quantity or quality of diet. In contrast to many previous works the c-myc mRNA increased in the liver of malnourished rats in which growth was arrested. (2) Feeding of casein diet to the rats maintained on protein-free diet caused rapid decrease in the level of c-myc mRNA and induced the DNA synthesis in the liver. The level of IGF-1 mRNA increased rapidly under this condition. (3) Zein diet, which lacks tryptophan and lysine, did not change the c-myc and the IGF-1 mRNA levels nor induced DNA synthesis in the liver unless it was supplemented with tryptophan and lysine. (4) The level of c-myc mRNA increased rapidly more than 18-fold when amino acids were removed from the medium indicating that the expression of c-myc was regulated directory by nutritional environment.In conclusion, lemphasize the possibility that nutrition not only supplies material for body components but also affects the signal transduction for cell growth in young growing rats.