Cooper J T, Stroka D M, Brostjan C, Palmetshofer A, Bach F H, Ferran C
Sandoz Center for Immunobiology, Deaconess Hospital, Harvard Medical School, Boston, Massachusetts 02215, USA.
J Biol Chem. 1996 Jul 26;271(30):18068-73. doi: 10.1074/jbc.271.30.18068.
The A20 gene product is a novel zinc finger protein originally described as a tumor necrosis factor alpha (TNF)-inducible early response gene in human umbilical vein endothelial cells (HUVEC). Its described function is to block TNF-induced apoptosis in fibroblasts and B lymphocytes, but more recently it has also been shown to play a role in lymphoid cell maturation. The mechanism of action of A20 is unknown. The aim of our study was to assess the effect of A20 upon endothelial cell activation. By transfecting bovine aortic endothelial cells (BAEC) with A20 as well as reporter constructs consisting of the promoters of genes known to be up-regulated during endothelial cell activation, i.e. E-selectin, interleukin (IL)-8, tissue factor (TF), and inhibitor of nuclear factor kappaBalpha (IkappaBalpha), we demonstrate that A20 expression inhibits gene up-regulation associated with TNF, lipopolysaccharide (LPS), phorbol 12-myristate 13-acetate (PMA), and hydrogen peroxide (H2O2)-induced endothelial cell (EC) activation. The mechanism of action of A20 is in part, or totally, due to the blockade of nuclear factor kappaB (NF-kappaB), as shown by its ability to suppress the activity of a NF-kappaB reporter. This effect is specific, as A20 does not block a noninducible, constitutively expressed reporter, Rous sarcoma virus-luciferase (RSV-LUC); nor does it block the c-Tat-inducible, NF-kappaB-independent reporter, human immunodeficiency virus-chloramphenicol acetyltransferase (HIV-CAT). How A20 blocks NF-kappaB is unclear, although we demonstrate that it does not affect p65 (RelA)-mediated gene transactivation. The inhibition of endothelial cell activation by A20 is a novel function for A20.
A20基因产物是一种新型锌指蛋白，最初被描述为人类脐静脉内皮细胞（HUVEC）中肿瘤坏死因子α（TNF）诱导的早期反应基因。其所述功能是阻断TNF诱导的成纤维细胞和B淋巴细胞凋亡，但最近也已表明它在淋巴细胞成熟中发挥作用。A20的作用机制尚不清楚。我们研究的目的是评估A20对内皮细胞活化的影响。通过用A20以及由已知在内皮细胞活化期间上调的基因启动子组成的报告构建体转染牛主动脉内皮细胞（BAEC），即E-选择素、白细胞介素（IL）-8、组织因子（TF）和核因子κBα（IkappaBα）抑制剂，我们证明A20表达抑制与TNF、脂多糖（LPS）、佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）和过氧化氢（H2O2）诱导的内皮细胞（EC）活化相关的基因上调。如A20抑制NF-κB报告基因活性所示，A20的作用机制部分或完全归因于对核因子κB（NF-κB）的阻断。这种作用是特异性的，因为A20不阻断非诱导性、组成性表达的报告基因劳斯肉瘤病毒-荧光素酶（RSV-LUC）；它也不阻断c-Tat诱导的、NF-κB非依赖性报告基因人类免疫缺陷病毒-氯霉素乙酰转移酶（HIV-CAT）。尽管我们证明A20不影响p65（RelA）介导的基因反式激活，但A20如何阻断NF-κB尚不清楚。A20对内皮细胞活化的抑制是A20的一种新功能。
