Resistance to Fas-mediated apoptosis: activation of caspase 3 is regulated by cell cycle regulator p21WAF1 and IAP gene family ILP

Survivin initiates cell cycle entry by the competitive interaction with Cdk4/p16(INK4a) and Cdk2/cyclin E complex activation

Survivin is observed uniquely in tumor cells and developmental cells, which undergo either inappropriate or programmed cell growth. In the current study, we investigated the influence of Survivin on cell cycle. Overexpression of Survivin resulted in accelerated S phase shift, resistance to G1 arrest, and activated Cdk2/Cyclin E complex leading Rb phosphorylation. In addition, nuclear translocation of Survivin followed by an interaction with Cdk4 was detected. Interestingly, Survivin nuclear translocation coincided with S phase shift, and prevention of nuclear transport suppressed Survivin nuclear translocation and S phase shift. Further, we also observed that Survivin competitively interacted with the Cdk4/p16(INK4a) complex in a cell free system and in vivo. These results suggest that Survivin initiates the cell cycle entry as a result of nuclear translocation followed by an interaction with Cdk4.

Inhibition of Fas-mediated fulminant hepatitis in CrmA gene-transfected mice

Hyperimmune response via Fas/Fas-ligand and perforin/granzyme pathways may be essential in pathogenesis of virus-induced fulminant hepatitis. CrmA inhibits activation of caspases and granzyme B, suggesting it may block these pathways. We investigated whether CrmA expression would inhibit Fas-associated lethal hepatitis in mice. We successfully generated AxCALNLCrmA, a recombinant adenovirus expressing CrmA gene with a Cre-mediated switching cassette. We increased CrmA expression level in the liver transfected with AxCALNLCrmA (10(9) pfu) by increasing administration dose (10(7)-10(9) pfu) of AxCANCre, a recombinant, adenovirus-expressing Cre gene. Injection of anti-Fas antibody into the control mice rapidly led to animal death due to massive liver apoptosis, while the apoptosis was dramatically reduced in the CrmA-expressed mice. The animal survival increased with an increase of CrmA expression. The formation of active caspase-3 was markedly inhibited in the crmA-transfected hepatocytes in vitro. These results suggest that crmA is an effective gene that can inhibit immune-related liver apoptosis.

Analysis of in vivo patterns of caspase 3 gene expression in primary hepatocellular carcinoma and its relationship to p21WAF1 expression and hepatic apoptosis

AIM: To detect the expression of caspase 3 gene in primary huma n hepatocellular carcinoma (HCC) and investigate its relationship to p21^WAF1 gene expression and HCC apoptosis.

METHODS: In situ hybridization was employed to determine caspase 3 and p21^WAF1 expression in HCC. In situ end-labeling was used to detect hepatocytic apoptosis in HCC.

RESULTS: Twenty-one of 39 (53.8%) cases of HCC were found to express caspase 3 transcripts, while 46.2% of HCC failed to express caspase 3. Non-cancerous adjacent liver tissues showed more positive caspase 3 (87.5%, 7/8) as compared with HCC (P < 0.05). The expression of caspase 3 is correlated with HCC differentiation, 72.2% (13/18) of moderately to highly differentiated HCC showed caspase 3 transcripts positive, while only 38.1% of poorly differentiated HCC harbored caspase 3 transcripts (P < 0.05). No relationship was found between caspase 3 expression and tumor size or grade or metastasis, although 62.5% (5/8) of HCC with metastasis were caspase 3 positive and a little higher than that with no metastasis (51.6%, P > 0.05). Expression of caspase 3 alone did not affect the apoptosis index (AI) of HCC. The AI was 7.12‰ in caspase 3-positive tumors (n = 21), while in caspase 3-negative cases (n = 18) 6.59‰ (P > 0.05). Expression of caspase 3 clearly segregated with p21^WAF1 positive tumors as compared with p21^WAF1 negative cases (16 of 23, 69.6% vs 5 of 16, 31.3%) with statistical significance(P = 0.017). In the cases with positive caspase 3 and negative p21^WAF1, the AI was found slightly higher, but with no statistical significance, than that with expression of p21^WAF1 and caspase 3 (7.21‰vs 6.98‰, P > 0.05).

CONCLUSION: Loss of caspase 3 expression may contribute to HCC carcinogenesis, although the expression of caspase 3 does not correlate well with cell apoptosis in HCC. p21^WAF1 may be merely one of the inhibitors which can reduce caspase 3 mediated cell apoptosis in HCCs.

Apoptosis-inducing levels of UV radiation and proteasome inhibitors produce opposite effects on p21(WAF1) in human melanoma cells

The stability of p21(WAF1) and p53 is increased by UV radiation or proteasome inhibitors in normal and some tumor cells. However, p21(WAF1) can either stimulate in vitro assembly of active cyclin-kinase complexes at low concentrations or inhibit this activity at high concentrations. Also, ectopic p21(WAF1) over-expression has been reported to promote or suppress apoptosis, depending on the target cells. We have investigated changes in p21(WAF1) expression as a result of exposure to either 25 J/m(2) UV or 10 microM MG-115 proteasome inhibitor, both of which cause apoptosis in human C8161 melanoma cells. p21(WAF1) mRNA increased in response to UV irradiation but failed to accumulate at the protein level because of its early UV-activated degradation counteracted by proteasome inhibition. UV-mediated loss of p21(WAF1) protein preceding induction of p53 and cell death was greater in non-metastatic than in metastatic C8161 melanoma cells. No loss in p21(WAF1) occurred with apoptosis induced by 10 microM proteasome inhibitors MG-115 or lactacystin, mediated by over-expression of p21(WAF1). Our results suggest that conditions causing prolonged or permanent changes in basal levels of p21(WAF1) may impair its reversible cell-cycle checkpoint function, leading to irreversible growth arrest or cell death.

Survivin promotes cell proliferation in human hepatocellular carcinoma

Survivin is a recently described inhibitor of apoptosis. Because suppression of apoptosis is important for carcinogenesis and tumor growth, we investigated the expression and function of survivin in human hepatocellular carcinomas (HCCs). We have shown that 4 HCC cell lines and 7 out of 8 human HCC tissues expressed survivin messenger RNA (mRNA), whereas expression of survivin mRNA was not detected in normal liver and nontumor areas of these tissues using the reverse transcription polymerase chain reaction. Survivin was detected primarily in the nucleus by immunofluorescence staining of HCC cells. In addition, 14 of 20 (70%) HCC tissues showed positive nuclear staining for survivin, whereas nontumor tissues showed little detectable staining by immunohistochemistry. Survivin expression strongly correlated with the proliferation index but not significantly with the apoptosis index in HCC tissues. Therefore, we performed cell cycle analysis after survivin transfection and showed that overexpression of survivin resulted in a decrease in the G(0)/G(1) phase and an increase in the S phase in all 4 HCC cell lines. Furthermore, we have found that survivin interacted with cyclin-dependent kinase 4 (Cdk4) and overexpression of survivin released p21(WAF1/Cip1) (p21) from Cdk4. From these results, we conclude that survivin promotes cell proliferation by interacting with Cdk4 and releasing p21 from Cdk4. This may play an important role in carcinogenesis and progression of human HCCs.

p21(WAF1/CIP1) inhibits initiator caspase cleavage by TRAIL death receptor DR4

Death receptors of the Tumor Necrosis Factor (TNF) family form membrane-bound self-activating signaling complexes that initiate apoptosis through cleavage of proximal caspases including CASP8 and 10. Here we show that overexpression of the cytoplasmic domain (CD) of the DR4 TRAIL receptor (TNFRSF10A, TRAIL R1) in human breast, lung, and colon cancer cell lines, using an adenovirus vector (Ad-DR4-CD), leads to p53-independent apoptotic cell death involving cleavage of CASP8 and 10 proximally and CASP3, 6, and 7 distally. DR4-CD overexpression also leads to cleavage of poly(ADP-ribose) polymerase (PARP) and the DNA fragmentation factor (DFF45; ICAD). Importantly, normal lung fibroblasts are resistant to DR4-CD overexpression and show no evidence of PARP-, CASP8- or CASP3-cleavage despite similar levels of adenovirus-delivered DR4-CD protein as the cancer cells. These results suggest that DR4 may signal death through known caspases and that further studies are required to evaluate Ad-DR4-CD as a novel anti-cancer agent. Finally, we show that overexpression of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1) (CDKN1A), or its N-terminal 91 amino acids containing cell cycle-inhibitory activity, inhibits DR4-CD-dependent proximal caspase cleavage. The blockage of initiator caspase activation provides a novel insight into how p21 may suppress apoptosis and enhance cell survival.

Survivin initiates procaspase 3/p21 complex formation as a result of interaction with Cdk4 to resist Fas-mediated cell death

Caspase 3 is an essential death factor for the Fas-mediated cell death, and its inactivation in cells is initiated by an interaction with p21 on mitochondria or with IAP family member ILP. Survivin is also a member of IAP family and is specifically expressed during embryogenesis and in tumor cells and suppresses cell death signaling. In our current study, we demonstrated that Survivin translocation into the nucleus is dependent on Fas stimulation and cell proliferation. Survivin also interacts with the cell cycle regulator Cdk4, leading to Cdk2/Cyclin E activation and Rb phosphorylation. As a result of Survivin/Cdk4 complex formation, p21 is released from its complex with Cdk4 and interacts with mitochondrial procaspase 3 to suppress Fas-mediated cell death. Here, we propose that Survivin supports procaspase 3/p21 complex formation as a result of interaction with Cdk4 resulting in suppression of cell death signaling.

Ki-ras activation in vitro affects G1 and G2M cell-cycle transit times and apoptosis

Mutant ras genes occur frequently in human neoplasia and, in particular, in pancreatic, colorectal, and lung adenocarcinomas. Recent evidence suggests that G-->T and G-->C transversions of the Ki-ras gene in codon 12 may lead to biological effects in vitro and in vivo that may be associated with an abnormal cell cycle and increased tumour aggressiveness. The role of Ki-ras activation (a G-->C transversion in codon 12, arginine for glycine) in the cell cycle and apoptosis was investigated using control and permanently transfected NIH3T3 mouse fibroblasts. Flow cytometry was used to evaluate the G1-, S- and G2M-phase transit times, the potential doubling time, the growth fraction, and the cell loss factor during asynchronous exponential growth. Apoptosis was induced in both cell lines by absence of growth factors for an extended period of time (72 h) and quantitatively evaluated using the TUNEL method coupled with flow cytometry. It was found that codon 12 G-->C Ki-ras transfected cells compared with controls, had a significant prolongation of G1 by about 50%, a reduction of the G2M transit time by 30%, and a decrease of the cell loss factor by about 90%. Apoptotic cells were about 10% in control and less than 0.5% in Ki-ras transfected cells after 72 h starvation-confluency. These data suggest that codon 12 G-->C Ki-ras activation in mouse NIH3T3 fibroblasts is associated with deregulation of checkpoint controls in the G1 and G2M phases of the cell cycle and inhibition of apoptosis. It appears plausible that these cell mechanisms are related to a proliferative advantage and that they may also be important in the progression of human tumours characterized by specific Ki-ras mutations.

Fas and Fas ligand in gut and liver

Apoptosis (programmed cell death) has been shown to play a major role in development and in the pathogenesis of numerous diseases. A principal mechanism of apoptosis is molecular interaction between surface molecules known as the "death receptors" and their ligands. Perhaps the best-studied death receptor and ligand system is the Fas/Fas ligand (FasL) system, in which FasL, a member of the tumor necrosis factor (TNF) family of death-inducing ligands, signals death through the death receptor Fas, thereby resulting in the apoptotic death of the cell. Numerous cells in the liver and gastrointestinal tract have been shown to express Fas/FasL, and there is a growing body of evidence that the Fas/FasL system plays a major role in the pathogenesis of many liver and gastrointestinal diseases, such as inflammatory bowel disease, graft vs. host disease, and hepatitis. Here we review the Fas/FasL system and the evidence that it is involved in the pathogenesis of liver and gastrointestinal diseases.

Induction of p21Waf1/Cip1 by TNFalpha requires NF-kappaB activity and antagonizes apoptosis in Ewing tumor cells

The Ewing family of tumors is characterized by recurrent reciprocal translocations that generate chimeric proteins, either EWS - FLI-1 or EWS - ERG. These proteins are potent transcriptional activators and are responsible for maintaining the oncogenic properties of tumor cells. Since apoptosis appears to be the main mechanism whereby chemotherapy and radiation kill tumor cells, identification of events that can antagonize apoptosis in Ewing tumors is essential for improving their response to conventional therapies. Here, we report that the transcriptional factor NF-kappaB is a survival factor for Ewing tumor-derived cells. In fact, inhibition of NF-kappaB activation as a consequence of the overexpression of a degradation-resistant form of IkappaBalpha, IkappaBalpha (A32/36), sensitized these cells to TNFalpha-induced killing. Although treatment with TNFalpha did not modify the cellular expression of Bcl-2, c-IAP1, c-IAP2, p53 and EWS - FLI-1 proteins, it increased p21Waf1/Cip1 levels. This induction required NF-kappaB activation since it was not observed in the IkappaBalpha (A32/36) expressing cells. Moreover, overexpression of p21Waf1/Cip1 in these IkappaBalpha (A32/36)-expressing cells, in which NF-kappaB and consequently p21Waf1/Cip1 are no longer inducible by TNFalpha, decreased their susceptibility to TNFalpha-induced killing. Our results therefore identify p21Waf1/Cip1 as a mediator of the antiapoptotic effect of TNFalpha-induced NF-kappaB in Ewing tumor cells.

Properties of the hepatitis C virus core protein: a structural protein that modulates cellular processes

The core protein of hepatitis C virus (HCV) is believed to form the capsid shell of virus particles. Maturation of the protein is achieved through cleavage by host cell proteases to give a product of 21 000 MW, which is found in tissue culture systems and sera from infected individuals. However, efficient propagation of the virus is not possible at present in tissue culture. Hence, studies have focused on the properties of the core protein and its possible role in pathologies associated with HCV infection. This review describes key features of the polypeptide and the status of current knowledge on its ability to influence several cellular processes.

Mitochondrial role in life and death of the cell

Mitochondria are the major ATP producer of the mammalian cell. Moreover, mitochondria are also the main intracellular source and target of reactive oxygen species (ROS) that are continually generated as by-products of aerobic metabolism in human cells. A low level of ROS generated from the respiratory chain was recently proposed to take part in the signaling from mitochondria to the nucleus. Several structural characteristics of mitochondria and the mitochondrial genome enable them to sense and respond to extracellular and intracellular signals or stresses in order to sustain the life of the cell. It has been established that mitochondrial respiratory function declines with age, and that defects in the respiratory chain increase the production of ROS and free radicals in mitochondria. Within a certain concentration range, ROS may induce stress responses of the cell by altering the expression of a number of genes in order to uphold energy metabolism to rescue the cell. However, beyond this threshold, ROS may elicit apoptosis by induction of mitochondrial membrane permeability transition and release of cytochrome c. Intensive research in the past few years has established that mitochondria play a pivotal role in the early phase of apoptosis in mammalian cells. In this article, the role of mitochondria in the determination of life and death of the cell is reviewed on the basis of recent findings gathered from this and other laboratories.

Role of NF-kappaB in the apoptotic-resistant phenotype of keratinocytes

Several studies point to a role for NF-kappaB in modulating epidermal thickness and apoptotic susceptibility of keratinocytes. When phorbol esters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) are topically applied, prominent epidermal thickening occurs, and exposure to interferon (IFN)-gamma promotes increased epidermal thickness producing psoriatic lesions. While keratinocytes derived from psoriatic plaque resist apoptosis, and combination of TPA and IFN-gamma activates NF-kappaB, the molecular mechanism linking NF-kappaB activation and keratinocyte apoptosis resistance was unknown. Therefore, we examined the ability of IFN-gamma plus TPA to influence NF-kappaB activity, gene expression, and response to UV light-induced apoptosis. These responses in normal keratinocytes were compared with immortalized keratinocytes (HaCaT cells). Exposure of normal keratinocytes to IFN-gamma plus TPA produced a synergistic activation of NF-kappaB, compared with when each reagent was used individually. Normal keratinocytes when exposed to IFN-gamma plus TPA acquired a resistance to UV light-induced apoptosis, which was dependent on NF-kappaB because expression of a dominant negative form of IkappaBalpha overcame the resistance. Compared with normal keratinocytes, HaCaT cells have a dysfunctional constitutive NF-kappaB signaling pathway not induced by IFN-gamma and TPA, rendering HaCaT cells highly susceptible to UV-induced apoptosis. Thus, immortalized HaCaT cells have an abnormal constitutive and dysfunctional NF-kappaB signaling system. These results provide evidence that activation and proper regulation of NF-kappaB is essential for acquisition of an apoptotic-resistant phenotype for epidermal-derived keratinocytes.

Cell proliferation and apoptosis

Cell proliferation and cell death are essential yet opposing cellular processes. Crosstalk between these processes promotes a balance between proliferation and death, and it limits the growth and survival of cells with oncogenic mutations. New insights into the mechanisms by which strong signals to proliferate and activation of cyclin-dependent kinases promote apoptosis have recently been published, and a novel cell cycle regulated caspase inhibitor, Survivin, has been described.

Apoptosis in proliferating, senescent, and immortalized keratinocytes

Skin provides an attractive organ system for exploring coordinated regulation of keratinocyte (KC) proliferation, differentiation, senescence, and apoptosis. Our main objective was to determine whether various types of cell cycle arrest confer resistance to apoptosis. We postulated that KC cell cycle and cell death programs are tightly regulated to ensure epidermal homeostasis. In this report, simultaneous expression of cyclin-dependent kinase inhibitors (p15, p16, p21, and p27), a marker of early differentiation (keratin 1), mediators of apoptosis (caspases 3 and 8), and NF-kappaB were analyzed in three types of KCs. By comparing the response of proliferating, senescent, and immortalized KCs (HaCaT cells) to antiproliferative agents followed by UV exposure, we observed: 1) Normal KCs follow different pathways to abrupt cell cycle arrest; 2) KCs undergoing spontaneous replicative senescence or confluency predominantly express p16; 3) Abruptly induced growth arrest, confluency, and senescence pathways are associated with resistance to apoptosis; 4) The death-defying phenotype of KCs does not require early differentiation; 5) NF-kappaB is one regulator of resistance to apoptosis; and 6) HaCaT cells have undetectable p16 protein (hypermethylation of the promoter), dysfunctional NF-kappaB, and diminished capacity to respond to antiproliferative treatments, and they remain highly sensitive to apoptosis with cleavage of caspases 3 and 8. These data indicate that KCs (but not HaCaT cells) undergoing abruptly induced cell cycle arrest or senescence become resistant to apoptosis requiring properly regulated activation of NF-kappaB but not early differentiation.

Cancer dormancy and cell signaling: induction of p21(waf1) initiated by membrane IgM engagement increases survival of B lymphoma cells

The p21(WAF1) (p21) cyclin-dependent kinase inhibitor plays a major role in regulating cell cycle arrest. It was recently reported that the p53-independent elevation of p21 protein levels is essential in mediating the G(1) arrest resulting from signal transduction events initiated by the crosslinking of membrane IgM on Daudi Burkitt lymphoma cells. Although the role of p21 in cell cycle regulation is well documented, there is little information concerning its role in antibody-mediated apoptosis. In the present study, we examined the involvement of p21 in the regulation of apoptosis by suppressing its induction in anti-IgM-treated Daudi cells through a p21 antisense expression construct approach. Reduction in induced p21 protein levels resulted in diminished G(1) arrest and increased apoptosis. The increased susceptibility to anti-IgM-mediated apoptosis was associated with increased caspase-3-like activity and poly-(ADP)ribose polymerase cleavage. These data suggest that p21 may directly interfere with the caspase cascade, thus playing a dual role in regulating both cell cycle progression and apoptosis.

Relationship between expression of p21WAF1/CIP1 and radioresistance in human gliomas

The role of p21WAF1/CIP1 (p21) in DNA repair and apoptosis following gamma-irradiation remains controversial. In this study the influence of p21 on the radiosensitivity of human brain tumors was investigated. Resected tumors were stained immunohistochemically for p21. Expression of p21 in astrocytic tumors was high, but it was low in medulloblastomas, germinomas, and primary malignant lymphomas. Glioma and medulloblastoma cell lines were transfected with pcDNA/p21 to cause p21 overexpression, then tumor-cell colony formation and apoptosis were assessed following gamma-irradiation of the transfected and nontransfected cells. Overexpression of p21 enhanced clonogenic survival and suppressed apoptosis after gamma-irradiation in human brain tumor cell lines with or without p53 protein deficiency. Radioresistance was acquired when p21 was overproduced in the glioma cell lines irrespective of p53 status.

Mitochondrial regulation of cell death: mitochondria are essential for procaspase 3-p21 complex formation to resist Fas-mediated cell death

Death receptor Fas transduces cell death signaling upon stimulation by Fas ligand, and this death signaling is mediated by caspase. Recently, we reported that the cell cycle regulator p21 interacts with procaspase 3 to resist Fas-mediated cell death. In the present study, the molecular characterization and functional region of the procaspase 3-p21 complex was further investigated. We observed the p21 expression in the mitochondrial fraction of HepG2 cells and detected Fas-mediated cell death only in the presence of actinomycin D. However, mitochondrial-DNA-lacking HepG2 (MDLH) cells showed this effect even in the absence of actinomycin D. Both p21 and procaspase 3 were expressed in MDLH cells, but the procaspase 3-p21 complex formation was not observed. Interestingly, the resistance to Fas-mediated cell death in the MDLH cells without actinomycin D was recovered after microinjection of HepG2-derived mitochondria into the MDLH cells. We conclude that mitochondria are necessary for procaspase 3-p21 complex formation and propose that the mitochondrial role during cell death is not only death induction but also death suppression.