Chemosensitization of head and neck cancer cells by PUMA

ΔNp63 Regulates Radioresistance in Human Head and Neck Squamous Carcinoma Cells

Radiation therapy is commonly used to treat head and neck squamous cell carcinoma (HNSCC); however, recurrence results from the development of radioresistant cancer cells. Therefore, it is necessary to identify the underlying mechanisms of radioresistance in HNSCC. Previously, we showed that the inhibition of karyopherin-β1 (KPNB1), a factor in the nuclear transport system, enhances radiation-induced cytotoxicity, specifically in HNSCC cells, and decreases the localization of SCC-specific transcription factor ΔNp63. This suggests that ΔNp63 may be a KPNB1-carrying nucleoprotein that regulates radioresistance in HNSCC. Here, we determined whether ΔNp63 is involved in the radioresistance of HNSCC cells. Cell survival was measured by a colony formation assay. Apoptosis was assessed by annexin V staining and cleaved caspase-3 expression. The results indicate that ΔNp63 knockdown decreased the survival of irradiated HNSCC cells, increased radiation-induced annexin V+ cells, and cleaved caspase-3 expression. These results show that ΔNp63 is involved in the radioresistance of HNSCC cells. We further investigated which specific karyopherin-α (KPNA) molecules, partners of KPNB1 for nuclear transport, are involved in nuclear ΔNp63 expression. The analysis of nuclear ΔNp63 protein expression suggests that KPNA1 is involved in nuclear ΔNp63 expression. Taken together, our results suggest that ΔNp63 is a KPNB1-carrying nucleoprotein that regulates radioresistance in HNSCC.

PUMA overexpression dissociates thioredoxin from ASK1 to activate the JNK/BCL-2/BCL-XL pathway augmenting apoptosis in ovarian cancer

ASK1-JNK signaling promotes mitochondrial dysfunction-mediated apoptosis, but the bridge between JNK and apoptosis is not fully understood. PUMA induces apoptosis through BAX/BAK. Our previous study suggests a therapeutic potential of PUMA for ovarian cancer. However, whether and how PUMA activates ASK1 remains unclear. Here, we found for the first time that PUMA activated ASK1 by dissociating thioredoxin (TRX) from ASK1, however, it neither interacted with ASK1 nor TRX. Furthermore, PUMA overexpression caused ROS release from mitochondrial. H₂O₂ significantly impaired the interaction of ASK1 with TRX, whereas ROS scavenger NAC effectively abrogated the H₂O₂ effect, partly rescued PUMA-interfered interaction of ASK1 with TRX, and also abolished ASK1 phosphorylation. Interestingly, PUMA could not impair the association of ASK1 with TRX-C32S or TRX-C35S, two TRX mutants which are no longer oxidized in response to ROS. We further showed that PUMA activated ASK1-JNK axis to phosphorylate BCL-2 and BCL-XL, further augmenting apoptosis of ovarian cancer cells. In vivo, PUMA adenovirus combined with paclitaxel significantly inhibited intrinsically cisplatin-resistant ovarian cancer growth, and caused phosphorylation of BCL-2 and BCL-XL. Our results from human ovarian cancer TMA chips also revealed a positive correlation between PUMA expression and the phosphorylation of BCL-2 and BCL-XL. More importantly, all patients had no distal metastasis, implying a possibly clinical significance. Collectively, our results reveal a new pro-apoptotic signal amplification mechanism for PUMA by which PUMA overexpression first induces ROS-mediated dissociation of TRX from ASK1, and then causes JNK activation-triggering BCL-2/BCL-XL phosphorylation, ultimately augmenting apoptosis in ovarian cancer.

Mutant p53 Gain-of-Function: Role in Cancer Development, Progression, and Therapeutic Approaches

Frequent p53 mutations (mutp53) not only abolish tumor suppressor capacities but confer various gain-of-function (GOF) activities that impacts molecules and pathways now regarded as central for tumor development and progression. Although the complete impact of GOF is still far from being fully understood, the effects on proliferation, migration, metabolic reprogramming, and immune evasion, among others, certainly constitute major driving forces for human tumors harboring them. In this review we discuss major molecular mechanisms driven by mutp53 GOF. We present novel mechanistic insights on their effects over key functional molecules and processes involved in cancer. We analyze new mechanistic insights impacting processes such as immune system evasion, metabolic reprogramming, and stemness. In particular, the increased lipogenic activity through the mevalonate pathway (MVA) and the alteration of metabolic homeostasis due to interactions between mutp53 and AMP-activated protein kinase (AMPK) and Sterol regulatory element-binding protein 1 (SREBP1) that impact anabolic pathways and favor metabolic reprograming. We address, in detail, the impact of mutp53 over metabolic reprogramming and the Warburg effect observed in cancer cells as a consequence, not only of loss-of-function of p53, but rather as an effect of GOF that is crucial for the imbalance between glycolysis and oxidative phosphorylation. Additionally, transcriptional activation of new targets, resulting from interaction of mutp53 with NF-kB, HIF-1α, or SREBP1, are presented and discussed. Finally, we discuss perspectives for targeting molecules and pathways involved in chemo-resistance of tumor cells resulting from mutp53 GOF. We discuss and stress the fact that the status of p53 currently constitutes one of the most relevant criteria to understand the role of autophagy as a survival mechanism in cancer, and propose new therapeutic approaches that could promote the reduction of GOF effects exercised by mutp53 in cancer.

Gilteritinib induces PUMA-dependent apoptotic cell death via AKT/GSK-3β/NF-κB pathway in colorectal cancer cells

As a highly potent and highly selective oral inhibitor of FLT3/AXL, gilteritinib showed activity against FLT3D835 and FLT3‐ITD mutations in pre‐clinical testing, although its role on colorectal cancer (CRC) cells is not yet fully elucidated. We examined the activity of gilteritinib in suppressing growth of CRC and its enhancing effect on other drugs used in chemotherapy. In this study, we observed that, regardless of p53 status, treatment using gilteritinib induces PUMA in CRC cells via the NF‐κB pathway after inhibition of AKT and activation of glycogen synthase kinase 3β (GSK‐3β). PUMA was observed to be vital for apoptosis in CRC cells through treatment of gilteritinib. Moreover, enhancing induction of PUMA through different pathways could mediate chemosensitization by using gilteritinib. Furthermore, PUMA deficiency revoked the antitumour role of gilteritinib in vivo. Thus, our results indicate that PUMA mediates the antitumour activity of gilteritinib in CRC cells. These observations are critical for the therapeutic role of gilteritinib in CRC.

MEK inhibitors induce apoptosis via FoxO3a-dependent PUMA induction in colorectal cancer cells

Mutations in BRAF are common to many cancers, including CRC. The MEK inhibitors are being investigated in BRAF-mutant CRC. In this study, we aimed to investigate how MEK inhibitor suppresses growth of BRAF-mutated CRC cells as well as its potential mechanisms. Our findings indicated that MEK inhibitor promote PUMA expression via ERK/FoxO3a signaling pathway. In addition, PUMA induction is essential for MEK inhibitor-induced apoptosis. Moreover, PUMA induction is required for MEK inhibitors to induced apoptosis in combination with cisplatin, dabrafenib, or Gefitinib. Knockdown of PUMA suppressed the anticancer effect of the MEK inhibitor in vivo. Our findings indicate a novel role for PUMA as a regulator of the antitumor effects of MEK inhibitor, suggesting that PUMA induction may modulate MEK inhibitor sensitivity.

Effect of taurine on cell proliferation and apoptosis human lung cancer A549 cells

To investigate the effects of taurine on cell proliferation and apoptosis, the human lung cancer A549 cell line and xenograft tumors in nude mice were used. The effects of taurine on cell proliferation and apoptosis were observed at time points of 24, 48 and 72 h after treatment using an MTT assay to detect the survival rate, and flow cytometry to detect the apoptotic rate. Western blot analysis was performed to examine the levels of p53 upregulated modulator of apoptosis (PUMA), BCL2, apoptosis regulator (Bcl-2) and BCL2-associated X, apoptosis regulator (Bax) in A549 cells. The level of PUMA, Bax and Bcl-2 proteins in the mouse xenograft tumors treated with taurine and/or exogenous PUMA were assessed by immunohistochemistry, with taurine suppressing the proliferation of the human lung cancer A549 cell line in a concentration-dependent manner, and it significantly enhanced the apoptosis rate at all concentrations. Taurine induced the significant upregulation of PUMA and Bax, but led to downregulation of Bcl-2. In comparison to the control group, taurine treatment markedly reduced the volume and weight of A549-derived xenograft tumors in nude mice. Expression of PUMA and Bax were upregulated in the xenograft tumors following taurine treatment, whereas Bcl-2 was downregulated. In addition, the inhibitory effect of taurine and exogenous PUMA on tumor growth was significantly higher than that of a single treatment of taurine or exogenous PUMA. It can therefore be concluded that taurine can inhibit cell proliferation of the human lung cancer A549 cell line and the growth of the xenograft tumors, whereas PUMA serves an important role in taurine-induced growth suppression.

Targeting p53-dependent stem cell loss for intestinal chemoprotection

The gastrointestinal (GI) epithelium is the fastest renewing adult tissue and is maintained by tissue-specific stem cells. Treatment-induced GI side effects are a major dose-limiting factor for chemotherapy and abdominal radiotherapy and can decrease the quality of life in cancer patients and survivors. p53 is a key regulator of the DNA damage response, and its activation results in stimulus- and cell type-specific outcomes via distinct effectors. We demonstrate that p53-dependent PUMA induction mediates chemotherapy-induced intestinal injury in mice. Genetic ablation of Puma, but not of p53, protects against chemotherapy-induced lethal GI injury. Blocking chemotherapy-induced loss of LGR5+ stem cells by Puma KO or a small-molecule PUMA inhibitor (PUMAi) prevents perturbation of the stem cell niche, rapid activation of WNT and NOTCH signaling, and stem cell exhaustion during repeated exposures. PUMAi also protects human and mouse colonic organoids against chemotherapy-induced apoptosis and damage but does not protect cancer cells in vitro or in vivo. Therefore, targeting PUMA is a promising strategy for normal intestinal chemoprotection because it selectively blocks p53-dependent stem cell loss but leaves p53-dependent protective effects intact.

The role of ROS and subsequent DNA-damage response in PUMA-induced apoptosis of ovarian cancer cells

PUMA is a member of the "BH3-only" branch of the BCL-2 family. Our previous study suggests a therapeutic potential of PUMA in treating ovarian cancer, however, the action mechanism of PUMA remains elusive. In this work, we found that in PUMA adenovirus-infected A2780s ovarian cancer cells, exogenous PUMA was partially accumulated in the cytosol and mainly located to the mitochondria. We further showed that PUMA induces mitochondrial dysfunction-mediated apoptosis and ROS generation through functional BAX in a ROS generating enzyme- and caspase-independent manner irrespective of their p53 status, and results in activation of Nrf2/HO-1 pathway. Furthermore, PUMA induces DNA breaks in γ-H2AX staining, and causes activation of DNA damage-related kinases including ATM, ATR, DNA-PKcs, Chk1 and Chk2, which are correlated with the apoptosis. PUMA also results in ROS-triggered JNK activation. Intriguingly, JNK plays a dual role in both DNA damage response and apoptosis, and has an additional contribution to apoptosis. Taken together, we have provided new insight into the action mechanism by which elevated PUMA first induces ROS generation then results in DNA damage response and JNK activation, ultimately contributing to apoptosis in ovarian cancer cells.

Effect of Ginsenoside Rh-2 via Activation of Caspase-3 and Bcl-2-Insensitive Pathway in Ovarian Cancer Cells

Ginsenoside has been reported to have therapeutic effects for some types of cancer, but its effect on ovarian cancer cells has not been evaluated. In this study, we monitored the effects of ginsenoside-Rh2 (Rh2) on the inhibition of cell proliferation and the apoptotic process in the ovarian cancer cell line SKOV3 using an MTT assay and TUNEL assay. We found that Rh2 inhibited cell proliferation and significantly induced apoptosis. We confirmed the apoptotic effects of Rh2 using western blot analysis of apoptosis-related proteins. Specifically, the levels of cleaved poly ADP ribose polymerase (PARP) and cleaved caspase-3 significantly increased in SKOV3 cells treated with Rh2. Therefore, Rh2 clearly suppressed the growth of SKOV3 cells in vitro, which was associated with induction of the apoptosis pathway. Moreover, the migration assay showed that Rh2 inhibited the invasive ability of SKOV3 cells. Taken together, our results suggest that Rh2 has anticancer effects in SKOV3 cells through inhibition of cell proliferation and induction of apoptosis. Considering the therapeutic potential of Rh2, more studies should be carried out to facilitate the future application of this natural product as a potential anti-cancer agent.

BRAFV600E-dependent Mcl-1 stabilization leads to everolimus resistance in colon cancer cells

mTOR activation is commonly caused by oncogenic mutations in RAS/RAF/MAPK and PI3K/AKT pathways, and promotes cancer progression and therapeutic resistance. However, mTOR inhibitors show limited single agent efficacy in patients. mTOR inhibitors suppress tumor cell growth and angiogenesis, and have recently been shown to induce death receptor/FADD-dependent apoptosis in colon cancers. Using a panel of BRAF V600E and WT colorectal cancer cell lines and in vitro selected resistant culture, and xenograft models, we demonstrate here that BRAFV600E confers resistance to mTOR inhibitors. Everolimus treatment disrupts the S6K1-IRS-2/PI3K negative feedback loop, leading to BRAF V600E-dependent activation of ERK and Mcl-1 stabilization in colon cancer cells, which in turn blocks the crosstalk from the death receptor to mitochondria. Co-treatment with inhibitors to Mcl-1, PI3K, RAF or MEK restores mTOR inhibitor-induced apoptosis by antagonizing Mcl-1 or abrogating ERK activation in BRAFV600E cells. Our findings provide a rationale for genotype-guided patient stratification and potential drug combinations to prevent or mitigate undesired activation of survival pathways induced by mTOR inhibitors.

Exogenous p53 upregulated modulator of apoptosis (PUMA) decreases growth of lung cancer A549 cells

PURPOSE

To investigate the influence of exogenous p53 upregulated modulator of apoptosis (PUMA) expression on cell proliferation and apoptosis in human non-small cell lung cancer A549 cells and transplanted tumor cell growth in nude mice.

MATERIALS AND METHODS

A549 cells were divided into the following groups: control, non- carrier (NC), PUMA (transfected with pCEP4- (HA) 2-PUMA plasmid), DDP (10 μg/mL cisplatin treatment) and PUMA+DDP (transfected with pCEP4-(HA)2-PUMA plasmid and 10 μg/mL cisplatin treatment). The MTT method was used to detect the cell survival rate. Cell apoptosis rates were measured by flow cytometry, and PUMA, Bax and Bcl-2 protein expression levels were measured by Western blotting.

RESULTS

Compared to the control group, the PUMA, DDP and PUMA+DDP groups all had significantly decreased A549 cell proliferation (p<0.01), with the largest reduction in the PUMA+DDP group. Conversely, the apoptosis rates of the three groups were significantly increased (P<0.01), and the PUMA and DDP treatments were synergistic. Moreover, Bax protein levels significantly increased (p<0.01), while Bcl-2 protein levels significantly decreased (p<0.01). Finally, both the volume and the weights of transplanted tumors were significantly reduced (p<0.01), and the inhibition ratio of the PUMA+DDP group was significantly higher than in the single DDP or PUMA groups.

CONCLUSIONS

Exogenous PUMA effectively inhibited lung cancer A549 cell proliferation and transplanted tumor growth by increasing Bax protein levels and reducing Bcl-2 protein levels.

mTOR inhibitors induce apoptosis in colon cancer cells via CHOP-dependent DR5 induction on 4E-BP1 dephosphorylation

The mammalian target of rapamycin (mTOR) is commonly activated in colon cancer. mTOR complex 1 (mTORC1) is a major downstream target of the PI3K/ATK pathway and activates protein synthesis by phosphorylating key regulators of mRNA translation and ribosome synthesis. Rapamycin analogs Everolimus and Temsirolimus are non-ATP-competitive mTORC1 inhibitors, and suppress proliferation and tumor angiogenesis and invasion. We now show that apoptosis plays a key role in their anti-tumor activities in colon cancer cells and xenografts through the DR5, FADD and caspase-8 axis, and is strongly enhanced by TRAIL and 5-fluorouracil. The induction of DR5 by rapalogs is mediated by the ER stress regulator and transcription factor CHOP, but not the tumor suppressor p53, upon rapid and sustained inhibition of 4E-BP1 phosphorylation, and attenuated by eIF4E expression. ATP-competitive mTOR/PI3K inhibitors also promote DR5 induction and FADD-dependent apoptosis in colon cancer cells. These results establish activation of ER stress and the death receptor pathway as a novel anticancer mechanism of mTOR inhibitors.

Gene therapy of pancreatic cancer targeting the K-Ras oncogene

Ras mutations are present in ∼95% of pancreatic cancer (PC) cases leading to increased proliferation and apoptosis resistance. The aim of this study is to selectively kill Ras-transformed cells by overexpressing the pro-apoptotic protein, p53 upregulated modulator of apoptosis (PUMA) under a Ras-responsive promoter. Colo357, Panc1 and MiaPaca, PC cell lines harboring K-Ras mutations, normal rat IEC18 enterocytes, and their K-Ras transformed R1 counterparts, were tested. We constructed adenoviral vectors containing the PUMA gene downstream to: (1) Four or five repetitive Ras-responsive elements (Ad-PY4/PY5-PUMA) and (2) a negative control (Ad-SV40-PUMA). Cell viability was estimated by 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and apoptosis was evaluated by FACS. In vivo potency of the adenoviruses was evaluated in athymic nude mice. Infection with Ad-PY4/PY5-PUMA markedly inhibited cell growth (∼40-50%), and apoptosis was detected in all cells with high Ras activity, whereas IEC18 cells remained unaffected. The control vector, Ad-SV40-PUMA, did not induce any cell death. Selective and high expression of PUMA was detected in Ad-PY4-PUMA-infected cells. In vivo, Ad-PY4-PUMA inhibited by ∼35% the growth of established tumors compared with the Ad-SV40-PUMA. Selective overexpression of PUMA efficiently inhibits the growth of Ras-transformed cells while sparing the normal ones. This treatment modality may become a useful, effective and safe approach to selectively target Ras-mutated tumor cells.

AKT serine/threonine protein kinase modulates bufalin-triggered intrinsic pathway of apoptosis in CAL 27 human oral cancer cells

Bufalin has been reported to induce apoptosis in a variety of cancers but little is demonstrated in oral squamous cell carcinoma (OSCC) cells. The present study investigated the inhibition of proliferation, cell cycle arrest and apoptotic effects of bufalin in CAL 27 human oral cancer cells. Bufalin inhibited the growth of CAL 27 cells in a concentration-dependent manner and an IC50 value of bufalin was about 125 nM for 24 h treatment using the MTT assay. Moreover, the cell cycle distribution was arrested at the G0/G1 phase in CAL 27 cells after bufalin exposure. Upon bufalin stimulation, the expression of Bcl-2 was significantly decreased while that of cytochrome c, Apaf-1 and AIF was increased compared to the control group by western blot analysis. An increase in the expression of the active form of caspases was found in bufalin-treated cells, and the caspase activities were also elevated. Bufalin-triggered apoptosis was blocked by specific inhibitors of caspase-9 (z-LEHD-fmk) and caspase-3 (z-DEVD-fmk), respectively. In contrast, CAL 27 cells overexpressing constitutively active AKT (CAL 27/CA-AKT) were exposed to bufalin at different concentrations, and cell growth remained unchanged. Bufalin exhibited minimal apoptotic effects on CAL 27/CA-AKT cells. Taken together, bufalin induced G0/G1 phase arrest and provoked the intrinsic apoptotic pathway via AKT activation in CAL 27 cells. Our data suggest that bufalin could be potentially efficacious in the treatment of oral cancer in the future.

A feasibility study on gene therapy of pancreatic carcinoma with Ad-PUMA

Pancreatic cancer is one of the most malignant tumors with high mortality and poor prognosis even with the aggressive conventional therapies. Biotherapy based on the understanding of tumorigenesis mechanism is ongoing to improve the outcomes of cancer patients. We sought here to evaluate the therapeutic potential of a proapoptotic gene, PUMA, in pancreatic cancer. We found that PUMA was differently expressed in a series of pancreatic ductal adenocarcinoma cancer cell lines, and adenovirus-mediated expression of PUMA (Ad-PUMA) in these cells resulted in massive apoptosis. PUMA was more potent than p53 in suppressing growth of cancer cells. RT-PCR and Western Blot revealed that exogenous PUMA was expressed 6 h after Ad-PUMA infection. Furthermore, we assessed the efficacy of Ad-PUMA combining anticancer drugs (5-fluorouracil, cisplatin, gemcitabine hydrochloride, respectively) in these pancreatic cancer cell lines. Data revealed that PUMA significantly sensitized pancreatic carcinoma cell lines to chemotherapeutics, which may be resulted from abundant apoptosis induction. In nude mice with PANC-1 xenografts, Ad-PUMA treatment significantly inhibited the tumor growth. These results suggest that PUMA is a potent molecular tool in suppressing tumor growth sensitizing pancreatic carcinoma cells to chemical drugs. PUMA plays roles in negatively regulating cancer cell growth and may be a promising tool for cancer biotherapy, with or without combination with chemotherapeutic agents.

The multi-targeted kinase inhibitor sunitinib induces apoptosis in colon cancer cells via PUMA

Constitutive activation of pro-survival kinases has become a promising target of small molecules with an increasing interest in developing multi-targeted agents. The mechanisms underlying the responsiveness to most agents targeting cancer specific survival pathways are still poorly understood but critical for their clinical application. In this study, we found that sunitinib, a small molecule inhibitor of multiple tyrosine kinases including VEGFRs and PDGFRs induces apoptosis and inhibits cell growth in colon cancer cells in cell culture and xenograft models via the BH3-only protein PUMA. Sunitinib treatment induced PUMA transcription via the AKT/FoxO3a axis. PUMA, BH3 mimetics, or 5-Flurourical sensitized colon cancer cells to sunitinib-induced apoptosis. Furthermore, PUMA was induced by sunitinib treatment in xenograft tumors, and deficiency in PUMA significantly suppressed the anti-tumor effects of sunitinib. Our study suggests that PUMA-mediated apoptosis is important for the therapeutic responses to sunitinib, and activation of the mitochondrial pathway by BH3 mimetics or PUMA manipulation may be useful for improving the antitumor activity of sunitinib. Modulation of PUMA and selective Bcl-2 family members might be potential biomarkers for predicting sunitinib responses.

Genetic variants of a BH3-only pro-apoptotic gene, PUMA, and risk of HPV16-associated squamous cell carcinoma of the head and neck

P53 up-regulated modulator of apoptosis (PUMA) is a critical factor in the intrinsic apoptotic pathway. Through PUMA-dependent mechanisms, human papillomavirus 16 (HPV16) oncoprotein may affect apoptosis by E6-mediated p53 degradation. To examine whether the PUMA variants modify the association between HPV16 serology and risk of squamous cell carcinoma of the head and neck (SCCHN), we genotyped two polymorphisms in the PUMA promoter (rs3810294 and rs2032809) in 380 cases and 335 cancer-free controls of non-Hispanic Whites, who were frequency-matched by age (±5 yr), sex, smoking, and drinking status. We found that each individual polymorphism had only a modest impact on risk of SCCHN, particularly in oropharyngeal cancer for rs3810294 and non-oropharyngeal cancer for rs2032809. After we stratified the individuals by HPV16 serology, and used those with the corresponding common homozygous genotype and HPV16 seronegativity as the reference group, for each polymorphism we found that the risk of SCCHN associated with HPV16 seropositivity was higher among those with variant genotypes than those with the corresponding common homozygous genotype. Notably, this effect modification was particularly pronounced in several subgroups including never smokers, never drinkers, younger patients, and patients with oropharyngeal cancer. Furthermore, we also characterized the functional relevance of the two polymorphisms to explore the genotype-phenotype correlation. Our results suggested that the PUMA promoter polymorphisms may be a biomarker for risk of HPV16-associated SCCHN, particularly in never smokers, never drinkers, younger patients, and patients with oropharyngeal cancer. Larger studies are needed to validate our findings.

PUMA-mediated apoptosis drives chemical hepatocarcinogenesis in mice

Hepatocyte death and proliferation contribute to hepatocellular carcinoma development after carcinogen exposure or chronic liver inflammation. However, the role and the molecular targets of hepatocyte death in relation to compensatory proliferation have not been fully characterized. In this study, we investigated the role of p53 up-regulated modulator of apoptosis (PUMA), a BH3-only protein important for both p53-dependent and -independent apoptosis, in a diethylnitrosamine (DEN)-induced liver carcinogenesis model. PUMA deficiency significantly decreased the multiplicity and size of liver tumors. DEN treatment induced p53-independent PUMA expression, PUMA-dependent hepatocyte death, and compensatory proliferation. Furthermore, inhibition or deletion of c-jun N-terminal kinase 1 (JNK1) abrogated PUMA induction, hepatocyte death, and compensatory proliferation.

CONCLUSION

These results provide direct evidence that JNK1/PUMA-dependent apoptosis promotes chemical hepatocarcinogenesis through compensatory proliferation, and suggest apoptotic inducers as potential therapeutic targets in liver injury and cancer.

Smac modulates chemosensitivity in head and neck cancer cells through the mitochondrial apoptotic pathway

PURPOSE

Overexpression of inhibitors of apoptosis proteins (IAP) contributes to therapeutic resistance. Second mitochondria-derived activator of caspase (Smac) promotes caspase activation by binding to IAPs upon release from the mitochondria. IAP antagonists, also called SMAC mimetics, are promising anticancer agents modeled after this mechanism. We investigated the role and mechanisms of Smac- and Smac mimetic-mediated chemosensitization in head and neck squamous cell carcinoma (HNSCC) cells.

EXPERIMENTAL DESIGN

The effects of SMAC knockdown, SMAC overexpression, and a small molecule Smac mimetic on the chemosensitivities of HNSCC cells were determined. The mechanisms of Smac- and Smac mimetic-mediated chemosensitization were investigated by analyzing growth suppression, the mitochondrial apoptotic pathway, caspase activation, and IAP proteins. The therapeutic responses of HNSCC cells with different levels of Smac were compared in xenograft models.

RESULTS

We found that Smac mediates apoptosis induced by several classes of therapeutic agents through the mitochondrial pathway. SMAC knockdown led to impaired caspase activation, mitochondrial membrane depolarization, and release of cytochrome c. A small molecule Smac mimetic, at nanomolar concentrations, significantly sensitized HNSCC cells to gemcitabine-induced apoptosis and restored gemcitabine sensitivity in SMAC knockdown cells, through caspase activation, X-linked IAP dissociation, and mitochondria-associated events, but not the TNF-α pathway. Furthermore, Smac levels modulated the therapeutic response of HNSCC cells to gemcitabine in xenograft models.

CONCLUSIONS

Our results establish a critical role of Smac in mediating therapeutic responses of HNSCC cells and provide a strong rationale for combining Smac mimetics with other anticancer agents to treat HNSCC.

RNA interference targeting slug increases cholangiocarcinoma cell sensitivity to cisplatin via upregulating PUMA

Slug is an E-cadherin repressor and a suppressor of PUMA (p53 upregulated modulator of apoptosis) and it has recently been demonstrated that Slug plays an important role in controlling apoptosis. In this study, we examined whether Slug's ability to silence expression suppresses the growth of cholangiocarcinoma cells and/or sensitizes cholangiocarcinoma cells to chemotherapeutic agents through induction of apoptosis. We targeted the Slug gene using siRNA (Slug siRNA) via full Slug cDNA plasmid (Slug cDNA) transfection of cholangiocarcinoma cells. Slug siRNA, cisplatin, or Slug siRNA in combination with cisplatin, were used to treat cholangiocarcinoma cells in vitro. Western blot was used to detect the expression of Slug, PUMA, and E-cadherin protein. TUNEL, Annexin V Staining, and cell cycle analysis were used to detect apoptosis. A nude mice subcutaneous xenograft model of QBC939 cells was used to assess the effect of Slug silencing and/or cisplatin on tumor growth. Immunohistochemical staining was used to analyze the expression of Slug and PUMA. TUNEL was used to detect apoptosis in vivo. The results showed that PUMA and E-cadherin expression in cholangiocarcinoma cells is Slug dependent. We demonstrated that Slug silencing and cisplatin both promote apoptosis by upregulation of PUMA, not by upregulation of E-cadherin. Slug silencing significantly sensitized cholangiocarcinoma cells to cisplatin through upregulation of PUMA. Finally, we showed that Slug silencing suppressed the growth of QBC939 xenograft tumors and sensitized the tumor cells to cisplatin through PUMA upregulation and induction of apoptosis. Our findings indicate that Slug is an important modulator of the therapeutic response of cholangiocarcinoma cells and is potentially useful as a sensitizer in cholangiocarcinoma therapy. One of the mechanisms is the regulation of PUMA by Slug.

Development of small-molecule PUMA inhibitors for mitigating radiation-induced cell death

PUMA (p53 upregulated modulator of apoptosis) is a Bcl-2 homology 3 (BH3)-only Bcl-2 family member and a key mediator of apoptosis induced by a wide variety of stimuli. PUMA is particularly important in initiating radiation-induced apoptosis and damage in the gastrointestinal and hematopoietic systems. Unlike most BH3-only proteins, PUMA neutralizes all five known antiapoptotic Bcl-2 members though high affinity interactions with its BH3 domain to initiate mitochondria-dependent cell death. Using structural data on the conserved interactions of PUMA with Bcl-2-like proteins, we developed a pharmacophore model that mimics these interactions. In silico screening of the ZINC 8.0 database with this pharmacophore model yielded 142 compounds that could potentially disrupt these interactions. Thirteen structurally diverse compounds with favorable in silico ADME/Toxicity profiles have been retrieved from this set. Extensive testing of these compounds using cell-based and cell-free systems identified lead compounds that confer considerable protection against PUMA-dependent and radiation-induced apoptosis, and inhibit the interaction between PUMA and Bcl-xL.

The p53 upregulated modulator of apoptosis (PUMA) chemosensitizes intrinsically resistant ovarian cancer cells to cisplatin by lowering the threshold set by Bcl-x(L) and Mcl-1

Ovarian cancer is the number one cause of death from gynecologic malignancy. A defective p53 pathway is a hallmark of ovarian carcinoma. The p53 mutation correlates significantly with resistance to platinum-based chemotherapy, early relapse and shortened overall survival in ovarian cancer patients. PUMA (p53 upregulated modulator of apoptosis), a BH3-only Bcl-2 family protein, was recently identified as a transcriptional target of p53 and a potent apoptosis inducer in various cancer cells. In this study, we showed that the induction of PUMA by cisplatin was abolished in p53-deficient SKOV3 cells. Elevated expression of PUMA-induced apoptosis and sensitized A2780s and SKOV3 ovarian cancer cells to cisplatin, and the combination of PUMA and low-dose cisplatin, significantly suppressed xenograft tumor growth in vivo through enhanced induction of apoptosis compared with treatment with PUMA or cisplatin alone. The effects of PUMA were mediated by enhanced caspase activation and release of cytochrome c and Smac (second mitochondria-derived activator of caspase) into the cytosol. Furthermore, PUMA chemosensitized intrinsically resistant SKOV3 cells to cisplatin through downregulation of B-cell lymphoma-extra large (Bcl-x(L)) and myeloid cell leukemia sequence 1 (Mcl-1). PUMA-mediated Bcl-x(L) downregulation mainly happened at the transcription level, whereas PUMA-induced Mcl-1 down-regulation was associated with caspase-dependent cleavage and proteasome-mediated degradation. To our knowledge, these data suggest a new mechanism by which overexpression of PUMA enhances sensitivity of SKOV3 cells to cisplatin by lowering the threshold set simultaneously by Bcl-x(L) and Mcl-1. Taken together, our findings indicate that PUMA is an important modulator of therapeutic responses of ovarian cancer cells and is potentially useful as a chemosensitizer in ovarian cancer therapy.

Reactive oxygen species-mediated apoptosis contributes to chemosensitization effect of saikosaponins on cisplatin-induced cytotoxicity in cancer cells

Background

Saikosaponin-a and -d, two naturally occurring compounds derived from Bupleurum radix, have been shown to exert anti-cancer activity in several cancer cell lines. However, the effect of combination of saikosaponins with chemotherapeutic drugs has never been addressed. Thus, we investigated whether these two saikosaponins have chemosensitization effect on cisplatin-induced cancer cell cytotoxicity.

Methods

Two cervical cancer cell lines, HeLa and Siha, an ovarian cancer cell line, SKOV3, and a non-small cell lung cancer cell line, A549, were treated with saikosaponins or cisplatin individually or in combination. Cell death was quantitatively detected by the release of lactate dehydrogenase (LDH) using a cytotoxicity detection kit. Cellular ROS was analyzed by flow cytometry. Apoptosis was evaluated by AO/EB staining, flow cytometry after Anexin V and PI staining, and Western blot for caspase activation. ROS scavengers and caspase inhibitor were used to determine the roles of ROS and apoptosis in the effects of saikosaponins on cisplatin-induced cell death.

Results

Both saikosaponin-a and -d sensitized cancer cells to cisplatin-induced cell death in a dose-dependent manner, which was accompanied with induction of reactive oxygen species (ROS) accumulation. The dead cells showed typical apoptotic morphologies. Both early apoptotic and late apoptotic cells detected by flow cytometry were increased in saikosaponins and cisplatin cotreated cells, accompanied by activation of the caspase pathway. The pan-caspase inhibitor z-VAD and ROS scanvengers butylated hydroxyanisole (BHA) and N-acetyl-L-cysteine (NAC) dramatically suppressed the potentiated cytotoxicity achieved by combination of saikosaponin-a or -d and cisplatin.

Conclusions

These results suggest that saikosaponins sensitize cancer cells to cisplatin through ROS-mediated apoptosis, and the combination of saikosaponins with cisplatin could be an effective therapeutic strategy.

Expression of Bcl-2 family proteins and association with clinicopathological characteristics of oral squamous cell carcinoma

AIMS

To characterize the expression of proteins that inhibit (Bcl-2, Bcl-x, Bcl-xL, Bcl-2-related protein A1, BAG-1) or promote (Bak, Bax, Bim/Bod, Bim-Long, Bad, Bid, PUMA) apoptosis and determine possible correlations between the expression of these proteins and clinicopathological features of oral squamous cell carcinoma (OSCC).

METHODS AND RESULTS

Two-hundred and twenty-nine cases of OSCC, arranged in a tissue microarray, were immunohistochemically analysed. The results demonstrated that the absence of vascular invasion was associated with increased expression of Bak, Bax, Bcl-xL, Bcl-2-related protein and PUMA. Increased expression of Bim/Bod and BAG-1 was associated with the presence of perineural infiltration. An increase in Bid and Bim-Long expression was associated with moderately to well-differentiated tumours. Increased expression of the Bcl-2-related protein and PUMA was associated with tumours occurring in the floor of mouth and increased expression of PUMA was also associated with recurrence of the tumour. Multivariate Cox analysis demonstrated that PUMA and Bim-Long were independent factors in prognosis of OSCC.

CONCLUSIONS

Our results showed the involvement of the Bcl-2 family of proteins in OSCC tumorigenesis and suggest that the expression of apoptotic molecules might be used as a prognostic indicator for OSCC.

microRNA-21 negatively regulates Cdc25A and cell cycle progression in colon cancer cells

microRNAs (miRNA) are small noncoding RNAs that participate in diverse biological processes by suppressing target gene expression. Altered expression of miR-21 has been reported in cancer. To gain insights into its potential role in tumorigenesis, we generated miR-21 knockout colon cancer cells through gene targeting. Unbiased microarray analysis combined with bioinformatics identified cell cycle regulator Cdc25A as a miR-21 target. miR-21 suppressed Cdc25A expression through a defined sequence in its 3'-untranslated region. We found that miR-21 is induced by serum starvation and DNA damage, negatively regulates G(1)-S transition, and participates in DNA damage-induced G(2)-M checkpoint through down-regulation of Cdc25A. In contrast, miR-21 deficiency did not affect apoptosis induced by a variety of commonly used anticancer agents or cell proliferation under normal cell culture conditions. Furthermore, miR-21 was found to be underexpressed in a subset of Cdc25A-overexpressing colon cancers. Our data show a role of miR-21 in modulating cell cycle progression following stress, providing a novel mechanism of Cdc25A regulation and a potential explanation of miR-21 in tumorigenesis.

PUMA Kills Stem Cells to Stall Cancer?

Apoptosis evasion is a hallmark of human cancer. PUMA is a BH3-only Bcl-2 family protein that mediates both p53-dependent and independent apoptosis. However, its role in tumor suppression had not been well established. Our recent work provides direct evidence that PUMA plays an important role in suppressing intestinal tumorigenesis in two mouse models including (i) the azoxymethane (AOM)/dextran sulfate sodium salt (DSS)-treated mice and (ii) APC(Min/+) mice. The activities of PUMA appeared to be in the intestinal stem cells, and involve both p53-dependent response to DNA damage, and p53-independent mechanisms triggered by inflammation. Our data suggest that the interplay between different apoptotic pathways in intestinal stem cells underlie the initiation of intestinal carcinogenesis, and should be considered in the context of cancer prevention and therapy.

PUMA mediates EGFR tyrosine kinase inhibitor-induced apoptosis in head and neck cancer cells

Overexpression of epidermal growth factor receptor (EGFR) is found in over 80% of head and neck squamous cell carcinomas (HNSCC) and associated with poor clinical outcomes. EFGR selective tyrosine kinase inhibitors (TKIs) or antibodies have recently emerged as promising treatments for solid tumors, including HNSCC, though the response rate to these agents is low. p53 upregulated modulator of apoptosis (PUMA), a BH3-only Bcl-2 family protein, is required for apoptosis induced by p53 and various chemotherapeutic agents. In this study, we show that PUMA induction is correlated with EGFR-TKI sensitivity, and is mediated through the p53 family protein p73beta and inhibition of the PI3K/AKT pathway. In some HNSCC cells, the gefitinib-induced degradation of oncogenic Delta Np63 seems to facilitate p73-mediated PUMA transcription. Inhibiting PUMA expression by small hairpin RNA (shRNA) impairs gefitinib-induced apoptosis. Furthermore, PUMA or BH3 mimetics sensitize HNSCC cells to gefitinib-induced apoptosis. Our results suggest that PUMA induction through p73 represents a new mechanism of EGFR inhibitor-induced apoptosis, and provide potential ways for enhancing and predicting the sensitivity to EGFR-targeted therapies in HNSCC.

PUMA suppresses intestinal tumorigenesis in mice

Defective apoptosis contributes to tumorigenesis, although the critical molecular targets remain to be fully characterized. PUMA, a BH3-only protein essential for p53-dependent apoptosis, has been shown to suppress lymphomagenesis. In this study, we investigated the role of PUMA in intestinal tumorigenesis using two animal models. In the azoxymethane (AOM)/dextran sulfate sodium salt model, PUMA deficiency increased the multiplicity and size of colon tumors but reduced the frequency of beta-catenin hotspot mutations. The absence of PUMA led to a significantly elevated incidence of precursor lesions induced by AOM. AOM was found to induce p53-dependent PUMA expression and PUMA-dependent apoptosis in the colonic crypts and stem cell compartment. Furthermore, PUMA deficiency significantly enhanced the formation of spontaneous macroadenomas and microadenomas in the distal small intestine and colon of APC(Min/+) mice. These results show an essential role of PUMA-mediated apoptosis in suppressing intestinal tumorigenesis in mice.

PUMA, a potent killer with or without p53

PUMA (p53 upregulated modulator of apoptosis) is a Bcl-2 homology 3 (BH3)-only Bcl-2 family member and a critical mediator of p53-dependent and -independent apoptosis induced by a wide variety of stimuli, including genotoxic stress, deregulated oncogene expression, toxins, altered redox status, growth factor/cytokine withdrawal and infection. It serves as a proximal signaling molecule whose expression is regulated by transcription factors in response to these stimuli. PUMA transduces death signals primarily to the mitochondria, where it acts indirectly on the Bcl-2 family members Bax and/or Bak by relieving the inhibition imposed by antiapoptotic members. It directly binds and antagonizes all known antiapoptotic Bcl-2 family members to induce mitochondrial dysfunction and caspase activation. PUMA ablation or inhibition leads to apoptosis deficiency underlying increased risks for cancer development and therapeutic resistance. Although elevated PUMA expression elicits profound chemo- and radiosensitization in cancer cells, inhibition of PUMA expression may be useful for curbing excessive cell death associated with tissue injury and degenerative diseases. Therefore, PUMA is a general sensor of cell death stimuli and a promising drug target for cancer therapy and tissue damage.

Sp1 and p73 activate PUMA following serum starvation

p53-upregulated modulator of apoptosis (PUMA) plays an essential role in p53-dependent apoptosis following DNA damage. PUMA also mediates apoptosis independent of p53. In this study, we investigated the role and mechanism of PUMA induction in response to serum starvation in p53-deficient cancer cells. Following serum starvation, the binding of Sp1 to the PUMA promoter significantly increased, whereas inhibition of Sp1 completely abrogated PUMA induction. p73 was found to be upregulated by serum starvation and mediate PUMA induction through the p53-binding sites in the PUMA promoter. Sp1 and p73beta appeared to cooperatively activate PUMA transcription, which is inhibited by the phosphoinsitide 3-kinase (PI3K)-protein kinase B (AKT) pathway. Furthermore, knockdown of PUMA suppressed serum starvation-induced apoptosis in leukemia cells. Our results suggest that transcription factors Sp1 and p73 mediate p53-independent induction of PUMA following serum starvation to trigger apoptosis in human cancer cells.

Regulation of pro-apoptotic BH3-only proteins and its contribution to cancer progression and chemoresistance

The BH3-only members of the Bcl-2 protein family function as damage sensors in the cell and initiate the apoptotic cascade. Apoptosis is the primary mechanism by which the body gets rid of genetically defective cells and is critical for preventing the accumulation of cells with tumorigenic potential. BH3-only proteins have evolved to respond to distinct forms of cellular stress or DNA damage by inactivating the protective function of the prosurvival members of the Bcl-2 family. Therefore, a downregulated expression or activity of these proteins may favour tumor development. Moreover, the pro-apoptotic proteins are required for the success of most cancer treatments, including chemotherapy. Resistance to chemotherapy, a common feature of cancer, often reflects an inability of tumor cells to undergo apoptosis. Deciphering the regulation and activity of the BH3-only proteins may provide the basis for novel therapeutic strategies aimed at promoting tumor cell death or enhancing susceptibility to chemotherapeutic agents. This review summarizes the current knowledge of BH3-only proteins and their contribution to tumorigenesis and chemoresistance.