Systematic genetic dissection of p14ARF-mediated mitochondrial cell death signaling reveals a key role for p21CDKN1 and the BH3-only protein Puma/bbc3

Overexpression of CCDC69 activates p14ARF/MDM2/p53 pathway and confers cisplatin sensitivity

OBJECTIVES

The aim of the study is to explore the relationship between CCDC69 expression and resistance of ovarian cancer cells to cisplatin and reveal the underlying mechanism.

METHODS

One hundred thirty five ovarian cancer patients with intact chemo-response information from The Cancer Genome Atlas (TCGA) database were included and analyzed. Stable CCDC69 overexpressing 293 and ovarian cancer A2780 cell lines were established and subjected to examine cell apoptosis and cell cycle distribution using CCK-8 assay and flow cytometry. Cell cycle and apoptosis pathway were evaluated by immunoblots. Stability of p14^ARF/MDM2/p53 pathway related proteins were determined by half-life analysis and ubiquitination experiments.

RESULTS

We found that CCDC69 expression was significantly higher in chemo-sensitive groups compared with chemo-resistant groups from TCGA database. High CCDC69 expression was associated longer survival. CCDC69 overexpressing 293 and A2780 cells with wildtype p53 and contributes to cisplatin sensitivity following treatment with cisplatin. We further found over-expression of CCDC69 activated p14^ARF/MDM2/p53 pathway. Importantly, we also demonstrated that CCDC69 expression extended p53 and p14^ARF protein half-life and shortened MDM2 protein half-life. Ubiquitination assay revealing a decrease in p14 ubiquitination in CCDC69 over-expression cells comparing to cells expressing empty vector.

CONCLUSIONS

It is tempting to conclude that targeting CCDC69 may play a role in cisplatin resistance.

The determination of stage in nonmuscle urothelial carcinoma: Staining pattern of caspase-8

Context

Urothelial carcinoma (UC) is one of the most frequent epithelial tumors worldwide.

Aims

We aimed to investigate the protein expressions of caspase-8, p53, murine double minute 2 (mdm2), and p14^ARF in nonmuscle UCs and to correlate the findings with clinicopathological characteristics.

Settings and Design:

A total of 50 patients who had pTa and pT1 tumors were analyzed.

Subjects and Methods

The protein expressions of caspase-8, p53, mdm2, and p14^ARF were analyzed by immunohistochemistry.

Statistical Analysis Used

Chi-square test was done using SPSS version 16.0 (SPSS, Inc., Chicago, IL, USA).

Results

Cytoplasmic caspase-8 expression was significantly higher in pT1 UCs while nuclear caspase-8 expression was significantly higher in pTa UCs (P = 0.005 and P = 0.011, respectively). Cytoplasmic caspase-8 expression was also higher in high-grade UCs (P = 0.035). The expression of p53, mdm2, and p14^ARF was not also related with pathological stage or grade (P > 0.05 for all). The p14^ARF expression was related with nuclear caspase-8 expression in most of the patients. Complete agreement among nonmuscle UCs for immunohistochemical expression of p14 and nuclear caspase-8 was seen in 41 cases, and the pairwise kappa agreement value was substantial (κ =0.614). The patients who had recurrence were positive for both p53 and mdm2 or either p53 or mdm2 (P = 0.025).

Conclusions

These results suggested that the staining pattern of caspase-8 might be helpful for determining of the stages in nonmuscle UC. It was also showed that the expression status of p53 and mdm2 were related with the recurrence.

Bax/Bak-independent mitochondrial depolarization and reactive oxygen species induction by sorafenib overcome resistance to apoptosis in renal cell carcinoma

Renal cell carcinoma (RCC) is polyresistant to chemo- and radiotherapy and biologicals, including TNF-related apoptosis-inducing ligand (TRAIL). Sorafenib, a multikinase inhibitor approved for the treatment of RCC, has been shown to sensitize cancer cells to TRAIL-induced apoptosis, in particular by down-regulation of the Bak-inhibitory Bcl-2 family protein Mcl-1. Here we demonstrate that sorafenib overcomes TRAIL resistance in RCC by a mechanism that does not rely on Mcl-1 down-regulation. Instead, sorafenib induces rapid dissipation of the mitochondrial membrane potential (ΔΨ_m) that is accompanied by the accumulation of reactive oxygen species (ROS). Loss of ΔΨ_m and ROS production induced by sorafenib are independent of caspase activities and do not depend on the presence of the proapoptotic Bcl-2 family proteins Bax or Bak, indicating that both events are functionally upstream of the mitochondrial apoptosis signaling cascade. More intriguingly, we find that it is sorafenib-induced ROS accumulation that enables TRAIL to activate caspase-8 in RCC. This leads to apoptosis that involves activation of an amplification loop via the mitochondrial apoptosis pathway. Thus, our mechanistic data indicate that sorafenib bypasses central resistance mechanisms through a direct induction of ΔΨ_m breakdown and ROS production. Activation of this pathway might represent a useful strategy to overcome the cell-inherent resistance to cancer therapeutics, including TRAIL, in multiresistant cancers such as RCC.

p14ARF induces apoptosis via an entirely caspase-3-dependent mitochondrial amplification loop

The p14(ARF) tumor suppressor triggers cell death or cell cycle arrest upon oncogenic stress. In MCF-7 breast carcinoma cells, expression of the tumor suppressor gene p14(ARF) fails to trigger apoptosis but induces an arrest in the G1 and, to a lesser extent, in the G2 phase in the cell division cycle. Here, inhibition of cell cycle arrest resulted in apoptosis induction in caspase-3 proficient MCF-7 cells upon expression of p14(ARF) . This occurred in the absence of S-phase progression or mitotic entry. In contrast, syngeneic, caspase-3-deficient MCF-7 cells remained entirely resistant to p14(ARF) -induced apoptosis. Thus, cell cycle checkpoint abrogation overcomes resistance to p14(ARF) -induced cell death and promotes cell death via a caspase-3-dependent pathway. Cell death coincided with dissipation of the mitochondrial membrane potential, release of cytochrome c, and was inhibitable by pan-caspase inhibitors and the caspase-3/7 inhibitor zDEVD-fmk. Of note, mitochondrial events of apoptosis execution depended entirely on caspase-3 proficiency indicating that caspase-3 either acts "up-stream" of the mitochondria in a "non-canonical" pathway or mediates a mitochondrial feedback loop to amplify the apoptotic caspase signal in p14(ARF) -induced stress signaling.

p14(ARF)-induced apoptosis in p53 protein-deficient cells is mediated by BH3-only protein-independent derepression of Bak protein through down-regulation of Mcl-1 and Bcl-xL proteins

The p14(ARF) tumor suppressor plays a central role in regulating cell cycle arrest and apoptosis. We reported previously that p14(ARF) is capable of triggering apoptosis in a p53-independent manner. However, the mechanism remained unclear. Here we demonstrate that the p53-independent activation of the mitochondrial apoptosis pathway by p14(ARF) is primarily mediated by the pro-apoptotic Bax-homolog Bak. Expression of p14(ARF) exclusively triggers a N-terminal conformational switch of Bak, but not Bax, which allows for mitochondrial permeability shift, release of cytochrome c, activation of caspases, and subsequent fragmentation of genomic DNA. Although forced expression of Bak markedly sensitizes toward p14(ARF)-induced apoptosis, re-expression of Bax has no effect. Vice versa, knockdown of Bak by RNA interference attenuates p14(ARF)-induced apoptosis, whereas down-regulation of Bax has no effect. Bak activation coincides with a prominent, caspase-independent deprivation of the endogenous Bak inhibitors Mcl-1 and Bcl-x(L). In turn, mitochondrial apoptosis is fully blocked by overexpression of either Mcl-1 or Bcl-x(L). Taken together, these data indicate that in the absence of functional p53 and Bax, p14(ARF) triggers mitochondrial apoptosis signaling by activating Bak, which is facilitated by down-regulating anti-apoptotic Mcl-1 and Bcl-x(L). Moreover, our data suggest that the simultaneous inhibition of two central endogenous Bak inhibitors, i.e. Mcl-1 and Bcl-x(L), may be sufficient to activate mitochondrial apoptosis in the absence of BH3-only protein regulation.

Modeling of miRNA and drug action in the EGFR signaling pathway

MicroRNAs have gained significant interest due to their widespread occurrence and diverse functions as regulatory molecules, which are essential for cell division, growth, development and apoptosis in eukaryotes. The epidermal growth factor receptor (EGFR) signaling pathway is one of the best investigated cellular signaling pathways regulating important cellular processes and its deregulation is associated with severe diseases, such as cancer. In this study, we introduce a systems biological model of the EGFR signaling pathway integrating validated miRNA-target information according to diverse studies, in order to demonstrate essential roles of miRNA within this pathway. The model consists of 1241 reactions and contains 241 miRNAs. We analyze the impact of 100 specific miRNA inhibitors (anit-miRNAs) on this pathway and propose that the embedded miRNA-network can help to identify new drug targets of the EGFR signaling pathway and thereby support the development of new therapeutic strategies against cancer.