Analysis of the mechanism intracellularly transmitting the reception signal of insulin in cultured adipocytes and hepatoma cells.

胰岛素通过与嵌入质膜的特定受体结合来调节多种细胞功能。胰岛素受体由< α >和< β > -亚基组成。< α > -亚基负责结合，< β > -亚基具有酪氨酸残基特异性的蛋白激酶活性。通过胰岛素与受体复合物的结合，已经证实了< β > -亚基的自磷酸化。然而，这种自磷酸化是否为传递胰岛素结合信号的首要步骤还存在争议。除了自身磷酸化外，还观察到依赖于胰岛素的质膜蛋白或细胞骨架蛋白的磷酸化，但尚不清楚哪一种磷酸化是最重要的。多种细胞功能已被证明受胰岛素调节。这包括1)胰岛素促进糖和氨基酸等营养物质的运输，2)胰岛素促进碳水化合物、脂质和氨基酸的合成代谢，3)胰岛素促进培养物中许多细胞的增殖。考虑到胰岛素的多种作用，假设胰岛素通过多种信号传递机制调节细胞功能更为合理。为了找到更好的实验系统来分析胰岛素的信号传递机制，我们研究了氨甲酰磷酸合成酶基因（一种尿素循环酶）在肝癌细胞和原代培养肝细胞中的表达调控。首次证实胰岛素抑制尿素循环酶的基因表达。发现糖皮质激素、胰高血糖素和儿茶酚胺对尿素循环酶有多重调控作用。分析了胰岛素等因素对3T3-L1脂肪转化的影响。通过这一分析，在肥胖调控方面取得了重要进展。

Insulin ragulates a variety of cell functions by binding to a specific receptor embedded in plasma membrane. Insulin-receptor is composed of <alpha> and <beta> -subunits. <alpha> -subunit is responsible for the binding and <beta> -subunit has protein kinase activity which is specific to tyrosine-residue. By the binding of insulin to receptor complex, auto-phosphorylation of <beta> -subunit has been demonstrated. However, it is controversial whether this auto-phosphorylation is the prime step for transmitting the signal of insulin binding. In addition to the auto-phosphorylation, phosphorylation of plasma membrane proteins or cytoskeleton proteins has been observed depending on insulin and it is not clear which phosphorylation is the most important.Various cellular functions have been demonstrated to be regulated by insulin. These include 1) transport of nutrients, such as sugars and amino acids, is stimulated by insulin, 2) anabolism of carbohydrates, lipids and amino acids is stimulated by insulin, and 3) proliferation of many cells in culture is stimulated by insulin. Considering such a variety of effects, it is more reasonable to assume many signal-transmitting mechanisms by which insulin regulate cellular functions.In order to find out better experimental systems to analyze the signal-transmitting mechanism of insulin, regulation of the expression of carbamoyl-phosphate synthetase gene (a urea cycle enzyme) in hepatoma cells and in primary cultured hepatocytes was studied. Supression of the gene expression of a urea cycle enzyme by insulin was demonstrated for the first time. A multiple-regulation of a urea cycle enzyme by glucocorticoids, glucagon and catecholamines was found. Effect of factors including insulin on the adipose conversion of 3T3-L1 was also analyzed. By this analysis, an important progress was made concerning the regulation of obesity.