MacKenzie Farrell, Duriez Patrick, Wong Fred, Noseda Michela, Karsan Aly
Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia V6T 2B5, Canada.
J Biol Chem. 2004 Mar 19;279(12):11657-63. doi: 10.1074/jbc.M312102200. Epub 2003 Dec 29.
Notch4, a member of the Notch family of transmembrane receptors, is expressed primarily on endothelial cells. Activation of Notch in various cell systems has been shown to regulate cell fate decisions, partly by regulating the propensity of cells to live or die. Various studies have demonstrated a role for Notch1 in modulating apoptosis, either in a positive or negative manner. In this study, we determined that constitutively active Notch4 (Notch4 intracellular domain) inhibited endothelial apoptosis triggered by lipopolysaccharide. Notch signals are transmitted by derepression and coactivation of the transcriptional repressor, RBP-Jkappa, as well as by less well defined mechanisms that are independent of RBP-Jkappa. A Notch mutant lacking the N-terminal RAM domain showed only partial antiapoptotic activity relative to Notch4 intracellular domain but stimulated equivalent RBP-Jkappa-dependent transcriptional activity. Similarly, constitutively active RBP-Jkappa activated a full transcriptional response but only demonstrated partial antiapoptotic activity. Additional studies suggest that Notch4 provides endothelial protection in two ways: inhibition of the JNK-dependent proapoptotic pathway in an RBP-Jkappa-dependent manner and induction of an antiapoptotic pathway through an RBP-Jkappa-independent up-regulation of Bcl-2. Our findings demonstrate that Notch4 activation inhibits apoptosis through multiple pathways and provides one mechanism to explain the remarkable capacity of endothelial cells to withstand apoptosis.
Notch4是跨膜受体Notch家族的成员之一，主要在内皮细胞上表达。在各种细胞系统中，Notch的激活已被证明可调节细胞命运决定，部分是通过调节细胞存活或死亡的倾向来实现的。多项研究表明，Notch1在以正向或负向方式调节细胞凋亡中发挥作用。在本研究中，我们确定组成型活性Notch4（Notch4细胞内结构域）可抑制脂多糖触发的内皮细胞凋亡。Notch信号通过转录抑制因子RBP-Jκ的去抑制和共激活以及通过与RBP-Jκ无关的不太明确的机制进行传递。与Notch4细胞内结构域相比，缺乏N端RAM结构域的Notch突变体仅显示出部分抗凋亡活性，但刺激了等效的RBP-Jκ依赖性转录活性。同样，组成型活性RBP-Jκ激活了完全的转录反应，但仅显示出部分抗凋亡活性。进一步的研究表明，Notch4通过两种方式提供内皮保护：以RBP-Jκ依赖性方式抑制JNK依赖性促凋亡途径，并通过Bcl-2的RBP-Jκ非依赖性上调诱导抗凋亡途径。我们的研究结果表明，Notch4激活通过多种途径抑制细胞凋亡，并提供了一种机制来解释内皮细胞抵抗细胞凋亡的显著能力。
