Campos S P, Baumann H
Department of Molecular and Cellular Biology, Roswell Park Cancer Institute, Buffalo, New York 14263.
Mol Cell Biol. 1992 Apr;12(4):1789-97. doi: 10.1128/mcb.12.4.1789-1797.1992.
Several endocrine hormones which influence liver metabolism are known to increase in activity during the acute phase of injury or inflammation. We determined whether these hormones have the potential to influence acute-phase protein production in human and rat hepatoma cells. Catecholamines, glucagon, growth hormone, triiodothyronine, and cyclic nucleotides individually or in combination did not modulate the basal or the interleukin-1 (IL-1)-, IL-6-, and dexamethasone-stimulated levels of acute-phase plasma proteins. Insulin, however, was found to be a rapid, nonspecific, and dose-dependent inhibitor of the cytokine and glucocorticoid stimulation of acute-phase protein gene expression and to exert its effect at the transcriptional level. The insulin inhibition applied to all cytokines tested but to various degrees, depending upon the particular acute-phase gene. Insulin resulted in an early and prominent increase in the transcription of genes encoding the AP-1 components of JunA, JunB, and c-Fos, as has been observed for other growth factors. However, the effect of insulin on C/EBP beta was unexpected and paradoxical: while insulin completely inhibited the transcriptional activation of the C/EBP beta gene in cytokine- and dexamethasone-treated cells, the level of cytoplasmic C/EBP beta RNA was elevated. Quantitation of C/EBP beta mRNA by Northern (RNA) blot analysis and of C/EBP beta DNA binding activity by Southwestern (DNA-protein) blot analysis showed that insulin, when combined with cytokines and dexamethasone, stimulated both the mRNA and DNA binding activity by a factor of 1.6 compared with that of cells treated with cytokines and dexamethasone alone. Transient transfection of H-35 and HepG2 cells with a chloramphenicol acetyltransferase (CAT) gene expression vector containing the C/EBP beta response element also resulted in a 1.5-fold increase of C/EBP beta-mediated transcription in insulin-treated cells. Transfection of CAT gene constructs containing increasing lengths of heptaglobin gene 5' flanking sequences indicated that insulin inhibition of IL-6 stimulation required the presence of the region from -4100 to -1030. These results suggest that insulin has the potential to control the transcription of acute-phase genes by at least two separate mechanisms.
已知几种影响肝脏代谢的内分泌激素在损伤或炎症急性期活性会增加。我们研究了这些激素是否有可能影响人及大鼠肝癌细胞中急性期蛋白的产生。儿茶酚胺、胰高血糖素、生长激素、三碘甲状腺原氨酸和环核苷酸单独或联合使用均未调节急性期血浆蛋白的基础水平或白细胞介素 -1（IL -1）、IL -6及地塞米松刺激后的水平。然而，胰岛素被发现是细胞因子和糖皮质激素刺激急性期蛋白基因表达的一种快速、非特异性且剂量依赖性的抑制剂，并且在转录水平发挥作用。胰岛素抑制作用适用于所有测试的细胞因子，但程度各异，这取决于特定的急性期基因。胰岛素导致编码JunA、JunB和c -Fos的AP -1成分的基因转录早期显著增加，这与其他生长因子的情况一致。然而，胰岛素对C/EBPβ的影响出人意料且自相矛盾：虽然胰岛素在细胞因子和地塞米松处理的细胞中完全抑制了C/EBPβ基因的转录激活，但细胞质C/EBPβRNA水平却升高了。通过Northern（RNA）印迹分析对C/EBPβmRNA进行定量，以及通过Southwestern（DNA -蛋白）印迹分析对C/EBPβDNA结合活性进行定量，结果表明，与单独用细胞因子和地塞米松处理的细胞相比，胰岛素与细胞因子和地塞米松联合使用时，刺激了mRNA和DNA结合活性，使其增加了1.6倍。用含有C/EBPβ反应元件的氯霉素乙酰转移酶（CAT）基因表达载体对H -35和HepG2细胞进行瞬时转染，也导致胰岛素处理的细胞中C/EBPβ介导的转录增加了1.5倍。对含有不同长度七球蛋白基因5'侧翼序列的CAT基因构建体进行转染表明，胰岛素对IL -6刺激的抑制作用需要存在从 -4100至 -1030的区域。这些结果表明，胰岛素有可能通过至少两种独立机制控制急性期基因的转录。
