Patel A R, Wang J Y
Department of Surgery, University of Maryland Medical School and Baltimore Veterans Affairs Medical Center, Baltimore, Maryland 21201, USA.
Am J Physiol. 1999 Feb;276(2):G441-50. doi: 10.1152/ajpgi.1999.276.2.G441.
Activator protein 1 (AP-1) is a group of dimeric transcription factors composed of protooncogene (Jun and Fos) subunits that bind to a common DNA site, the AP-1 binding site. The proteins of c-Jun, JunB, and Fos are essential for initiation of the cell cycle. Conversely, the activation of the junD gene slows cell growth in some cell types. The current study tests the hypothesis that polyamines influence cell growth by altering the balance of positive and negative Jun/AP-1 activities in intestinal epithelial cells. Studies were conducted in the IEC-6 cell line derived from rat small intestinal crypt cells. Administration of alpha-difluoromethylornithine (DFMO), a specific inhibitor for polyamine synthesis, for 4 and 6 days completely depleted cellular polyamine levels, while AP-1 binding activity was significantly increased. Spermidine, when given together with DFMO, restored AP-1 binding activity toward normal. The increased AP-1 complexes in polyamine-deficient cells were dramatically supershifted by the anti-JunD antibody but not by antibodies against c-Jun, JunB, or Fos proteins. There were significant increases in JunD mRNA and protein in DFMO-treated cells, although expression of the c-fos, c-jun, and junB genes decreased. The increase in JunD/AP-1 activity in DFMO-treated cells was associated with a significant decrease in cell division. Exposure of control quiescent cells to 5% dialyzed serum increased c-Jun/AP-1 but not JunD/AP-1 activities. DFMO prevented the stimulation of c-Jun/AP-1 activity induced by 5% dialyzed serum. These results indicate that 1) polyamine depletion is associated with an increase in AP-1 binding activity and 2) the increase in AP-1 activity in the DFMO-treated cells was primarily contributed by an increase in the JunD/AP-1. These findings suggest that polyamines regulate cell growth at least partially by modulating the balance of positive and negative Jun/AP-1 activities in the intestinal mucosa.
活化蛋白1（AP-1）是一组由原癌基因（Jun和Fos）亚基组成的二聚体转录因子，它们结合到一个共同的DNA位点，即AP-1结合位点。c-Jun、JunB和Fos蛋白对于细胞周期的启动至关重要。相反，junD基因的激活在某些细胞类型中会减缓细胞生长。当前的研究检验了这样一个假说，即多胺通过改变肠道上皮细胞中正负Jun/AP-1活性的平衡来影响细胞生长。研究是在源自大鼠小肠隐窝细胞的IEC-6细胞系中进行的。给予α-二氟甲基鸟氨酸（DFMO），一种多胺合成的特异性抑制剂，4天和6天可使细胞内多胺水平完全耗尽，而AP-1结合活性显著增加。当与DFMO一起给予亚精胺时，AP-1结合活性恢复到正常水平。多胺缺乏细胞中增加的AP-1复合物被抗JunD抗体显著超迁移，但不被针对c-Jun、JunB或Fos蛋白的抗体超迁移。DFMO处理的细胞中JunD mRNA和蛋白显著增加，尽管c-fos、c-jun和junB基因的表达下降。DFMO处理的细胞中JunD/AP-1活性的增加与细胞分裂的显著减少相关。将对照静止细胞暴露于5%透析血清中会增加c-Jun/AP-1活性，但不会增加JunD/AP-1活性。DFMO可阻止5%透析血清诱导的c-Jun/AP-1活性的刺激。这些结果表明：1）多胺耗竭与AP-1结合活性增加有关；2）DFMO处理细胞中AP-1活性的增加主要是由JunD/AP-1的增加所致。这些发现提示多胺至少部分地通过调节肠道黏膜中正负Jun/AP-1活性的平衡来调节细胞生长。
