Jang Byeong-Churl, Muñoz-Najar Ursula, Paik Ji-Hye, Claffey Kevin, Yoshida Minoru, Hla Timothy
Center for Vascular Biology, Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06030-3501, USA.
J Biol Chem. 2003 Jan 31;278(5):2773-6. doi: 10.1074/jbc.C200620200. Epub 2002 Dec 4.
Cyclooxygenase (COX)-2, the inducible prostaglandin synthase, is overexpressed in cancer and chronic inflammatory diseases. Post-transcriptional regulation of COX-2 mRNA is important in controlling the expression of the COX-2 gene. Here, we report that leptomycin B (LMB), a specific inhibitor of the nuclear export factor CRM1 potently inhibits the stabilization of COX-2 mRNA in MDA-MB-231 human mammary cancer cells. However, COX-2 promoter-driven reporter gene expression is not inhibited by LMB, suggesting that LMB acts at the post-transcriptional level. Subcellular fractionation experiments indicate that LMB inhibited the time-dependent export of COX-2 mRNA into the membrane-bound polysomal compartment at the endoplasmic reticulum. LMB suppressed COX-2 expression by interleukin-1beta in HT-29 human colon cancer cells and in human umbilical vein endothelial cells but had no effect on COX-2 expression induced by Escherichia coli lipopolysaccharide in monocytic THP-1 cells. These data suggest that the nuclear export of COX-2 mRNA may be rate-liming in a cell-specific manner. LMB may be useful to control COX-2 expression in various human diseases in which COX-2 plays a pathogenetic role.
环氧化酶（COX）-2，即诱导型前列腺素合酶，在癌症和慢性炎症性疾病中过度表达。COX-2 mRNA的转录后调控对于控制COX-2基因的表达很重要。在此，我们报道，核输出因子CRM1的特异性抑制剂雷帕霉素B（LMB）能有效抑制MDA-MB-231人乳腺癌细胞中COX-2 mRNA的稳定性。然而，LMB并不抑制COX-2启动子驱动的报告基因表达，这表明LMB在转录后水平发挥作用。亚细胞分级分离实验表明，LMB抑制了COX-2 mRNA在内质网中向膜结合多核糖体区室的时间依赖性输出。LMB抑制了HT-29人结肠癌细胞和人脐静脉内皮细胞中白细胞介素-1β诱导的COX-2表达，但对单核细胞THP-1细胞中大肠杆菌脂多糖诱导的COX-2表达没有影响。这些数据表明，COX-2 mRNA的核输出可能以细胞特异性方式成为限速步骤。LMB可能有助于控制COX-2在各种COX-2起致病作用的人类疾病中的表达。
