ZBP-89-induced apoptosis is p53-independent and requires JNK

Abstract

ZBP-89 induces apoptosis in human gastrointestinal cancer cells through a p53-independent mechanism. To understand the apoptotic pathway regulated by ZBP-89, we identified downstream signal transduction targets. Ectopic expression of ZBP-89 induced apoptosis through the mitochondrial pathway and was accompanied by activation of all three MAP kinase subfamilies: JNK1/2, ERK1/2 and p38 MAP kinase. ZBP-89-induced apoptosis was markedly enhanced by ERK inhibition with U0126. In contrast, inhibiting JNK with a JNK1-specific peptide inhibitor or dominant-negative JNK2 expression abrogated ZBP-89-mediated apoptosis. The p38 inhibitor SB202190 had no effect on ZBP-89-induced cell death. Protein dephosphorylation assays revealed that ZBP-89 activates JNK via repression of JNK dephosphorylation. Oligonucleotide microarray analyses revealed that ectopic expression of ZBP-89 downregulated expression of the dual-specificity phosphatase MKP6. Overexpression of MKP6 blocked ZBP-89-induced JNK phosphorylation and PARP cleavage. In addition, ectopic expression of ZBP-89 repressed Bcl-xL and Mcl-1 expression, but had no effect on Bcl-2. Silencing ZBP-89 with small interfering RNA enhanced both Bcl-xL and Mcl-1 expression. Taken together, ZBP-89-mediated apoptosis occurs via a p53-independent mechanism that requires JNK activation.

Silibinin Up-regulates DNA-Protein Kinase-dependent p53 Activation to Enhance UVB-induced Apoptosis in Mouse Epithelial JB6 Cells

“…Although Akt activation is known as a survival and anti-apoptotic response, in the present study, we found that silibinin enhances UVB-induced Akt activation, which appears to be a stress response consistent with recent reports showing that Akt is one of the substrates of DNA-PK, a genotoxic stress response gene (44). To further support this notion and to identify the pathway(s) regulating Akt activation in JB6 cells under our study conditions, we used LY294002, which in addition to its inhibitory activity toward PI 3-kinase, is also known as a potent and selective inhibitor of DNA-PK (39), which belongs to the PI 3-kinase-like kinase having a PI 3-kinase homology domain (10,39). Pre-treatment of cells with LY294002 completely abolished the silibinin-caused increase in Akt-Ser 473 phosphorylation as well as p53-Ser 15 phosphorylation and accumulation by UVB irradiation.…”

The genetic depletion or the triptolide inhibition of TFIIH in p53 deficient cells induce a JNK-dependent cell death in Drosophila

“…The overexpression of the tumour suppressor LKB1 or the ZBP-89 protein generates an apoptotic cell death that is p53-independent but JNKdependent, suggesting that this kinase may be an apoptosis instigator (Bai et al, 2004;Lee et al, 2006). Furthermore, it has been demonstrated that sirtuins can induce apoptosis mediated by JNK signalling independent of Dp53 (Griswold et al, 2008).…”

Neuronal insulin receptor substrate 2 (IRS2) expression is regulated by ZBP89 and SP1 binding to the IRS2 promoter

“…Direct binding of ZBP89 to p53, which causes growth arrest via p53 retention in the nucleus (Bai & Merchant 2001), has been described as well. Interestingly, ZBP89 induces apoptosis in a JNK-dependent, but p53-independent manner (Bai et al 2004). In summary, ZBP89 inhibits cell proliferation (Remington et al 1997), induces apoptosis, and cooperates or competes with SP1 promoter binding sites, for example, in the STAT1 (Bai & Merchant 2003) and the vimentin promoter (Zhang et al 2003).…”

“…We cloned two sequences into the pSuppressor Neo vector. One sequence is active in suppressing ZBP89 transcripts (5 0 -AAGATCGAAGTATGCCTCACCTT-3 0 ), and for control we used the same sequence mutated in five bps (5 0 -AAGATCGAACGTGTCCTCACCTT-3 0 ) which is ineffective in ZBP89 suppression (Bai et al 2004). The constructs were linearized and transfected into SHSY5Y cells.…”