Notch2 Signaling Sensitizes Endothelial Cells to Apoptosis by Negatively Regulating the Key Protective Molecule Survivin

Abstract

BackgroundNotch signaling pathway controls key functions in vascular and endothelial cells (ECs) where Notch4 plays a major role. However, little is known about the contribution of other Notch receptors. This study investigated regulation of Notch2 and further examined its implication in EC dysfunction.Methodology/Principal FindingsHere, we provide evidence for a novel link between Notch and TNF signaling, where Notch2 is upregulated and activated in response to TNF. Forced expression of Notch2 intracellular domain in cultured ECs promotes apoptosis and allows the significant downregulation of several cell-death-related transcripts in a dose-dependent manner. In particular, activation of Notch2 led to a rapid decrease in survivin mRNA and protein expression, while survivin upregulation was obtained by the selective knockdown of Notch2 in ECs, indicating that survivin expression is controlled at the Notch level. Moreover, Notch2 silencing and ectopic expression of survivin, but not XIAP or Bcl2, rescued ECs from TNF and Notch2-mediated apoptosis, respectively.Conclusions/SignificanceIn conclusion, TNF signaling activates Notch2 that sensitizes ECs to apoptosis via modulation of the key apoptosis regulator survivin. Overall, our findings also indicate that specific Notch receptors control distinct functions in vascular cells and inflammatory cytokines contribute to this specificity.

Signaling of endothelial cytoprotection in transplantation

“…Consistently, loss of Notch4 and Hes1 signaling by siRNA in primary ECs elicited apoptosis [88]. In contrast, Notch2 NICD transduction in ECs promoted EC apoptosis, notably by inhibiting the expression of survivin [90]. It is therefore likely that Notch expression pattern modulation induced by inflammatory cytokines as TNF, characterized by a decrease in Notch4 expression and an increase in Notch2, can act as an important event that contributes to endothelial dysfunction-associated apoptosis [87].…”

Insights into the Regulation of Survivin Expression in Tumors

“…If p21/ CDKN1A gene is deleted, p53-mediated repression is abolished [51]. Unlike Notch1, Notch2 inhibited survivin transcription [52]. Further, Egr-1 (early growth response 1 transcription factor) is also a negative regulator of survivin transcription.…”

A Switch in Akt Isoforms Is Required for Notch-Induced Snail1 Expression and Protection from Cell Death

“…In particular, our results demonstrate that Notch protects endothelial cells from oxidative stress-induced cell death. Although the Notch effect might be isoform dependent (67), the majority of published data suggest a role for most Notch family members in apoptosis protection. For instance, constitutively active Notch4 inhibits endothelial cell apoptosis induced by lipopolysaccharide by a dual mechanism that requires JNK activation and Bcl-2 upregulation (68).…”