Spatiotemporal activation of caspase‐dependent and ‐independent pathways in staurosporine‐induced apoptosis of p53wt and p53mt human cervical carcinoma cells

Background information. Caspase‐dependent and ‐independent death mechanisms are involved in apoptosis in a variety of human carcinoma cells treated with antineoplastic compounds. Our laboratory has reported that p53 is a key contributor of mitochondrial apoptosis in cervical carcinoma cells after staurosporine exposure. However, higher mitochondrial membrane potential dissipation and greater DNA fragmentation were observed in p53^wt (wild‐type p53) HeLa cells compared with p53^mt (mutated p53) C‐33A cells. Here, we have studied events linked to the mitochondrial apoptotic pathway. Results. Staurosporine can induce death of HeLa cells via a cytochrome c/caspase‐9/caspase‐3 mitochondrial‐dependent apoptotic pathway and via a delayed caspase‐independent pathway. In contrast with p53^wt cells, p53^mt C‐33A cells exhibit firstly caspase‐8 activation leading to caspase‐3 activation and Bid cleavage followed by cytochrome c release. Attenuation of PARP‐1 [poly(ADP‐ribose) polymerase‐1] cleavage as well as oligonucleosomal DNA fragmentation in the presence of z‐VAD‐fmk points toward a major involvement of a caspase‐dependent pathway in staurosporine‐induced apoptosis in p53^wt HeLa cells, which is not the case in p53^mt C‐33A cells. Meanwhile, the use of 3‐aminobenzamide, a PARP‐1 inhibitor known to prevent AIF (apoptosis‐inducing factor) release, significantly decreases staurosporine‐induced death in these p53^mt carcinoma cells, suggesting a preferential implication of caspase‐independent apoptosis. On the other hand, we show that p53, whose activity is modulated by pifithrin‐α, isolated as a suppressor of p53‐mediated transactivation, or by PRIMA‐1 (p53 reactivation and induction of massive apoptosis), that reactivates mutant p53, causes cytochrome c release as well as mitochondrio—nuclear AIF translocation in staurosporine‐induced apoptosis of cervical carcinoma cells. Conclusions. The present paper highlights that staurosporine engages the intrinsic mitochondrial apoptotic pathway via caspase‐8 or caspase‐9 signalling cascades and via caspase‐independent cell death, as well as through p53 activity.     

BCL-2 antisense and cisplatin combination treatment of MCF-7 breast cancer cells with or without functional p53

Summary Chemotherapy has been used for treatment of breast cancer but with limited success. We characterized the effects of bcl-2 antisense and cisplatin combination therapy in two human isogenic breast carcinoma cells p53(+)MCF-7 and p53(−)MCF-7/E6. The transferrin-facilitated lipofection strategy we have developed yielded same transfection efficiency in both cells. Bcl-2 antisense delivered with this strategy significantly induced more cell death, apoptosis, and cytochrome c release in MCF-7/E6 than in MCF-7, but did not affect Fas level in both cells and activated caspase-8 equally. Cisplatin exerted same effects on cell viability and apoptosis in both cells, but released smaller amounts of cytochrome c while activated more caspase-8 in MCF-7/E6. The combination treatment yielded greater effects on cell viability, apoptosis, cytochrome c release, and caspase-8 activation than individual treatments in both cells although p53(−) cells were more sensitive. The potentiated activation of caspase-8 in the combination treatment suggested that caspase-8-mediated (but cytochrome c-independent) apoptotic pathway is the major contributor of the enhanced cell killing. Thus, bcl-2 antisense delivered with transferrin-facilitated lipofection can achieve the efficacy of killing breast cancer cells and sensitizing them to chemotherapy. Bcl-2 antisense and cisplatin combination treatment is a potentially useful therapeutic strategy for breast cancer irrespective of p53 status. Hesham Basma and Hesham El-Refaey contributed equally     

Arsenite-Induced Apoptosis Is Prevented by Selenite in A375 Cell Line

Arsenic trioxide induces apoptosis and clinical remission in patients diagnosed with acute promyelocytic leukemia. The human malignant melanoma A375 cells were treated with NaAsO₂ (0.1–130 μM) and also treated with combined 10 μM NaAsO₂ and 10 μM Na₂SeO₃. NaAsO₂ arrested cell growth in the G1 phase and induced apoptosis in a concentration- and time-dependent manner. In contrast, administration of Na₂SeO₃ antagonized the cell growth inhibition and apoptosis induced by NaAsO₂. The NaAsO₂ treatment resulted in a marked increase in p53 protein as early as 4 h and in Bcl-2 protein level by 12 h. In addition, p53 downregulation accompanied the combined treatment of NaAsO₂ and Na₂SeO₃. Thus, our results indicate upregulation of p53 and Bcl-2 play a crucial role in the NaAsO₂-induced G1 arrest and apoptosis of A375 cells and that downregulation p53 appears to contribute to the inhibition by Na₂SeO₃ of the effects induced by NaAsO₂.     

L-ascorbic acid (vitamin C) induces the apoptosis of B16 murine melanoma cells via a caspase-8-independent pathway

l-Ascorbic acid (vitamin C) has been reported to play a role in the treatment and prevention of cancer. However, its specific mechanistic pathways remain obscure. This study was carried out to identify the sodium ascorbate–induced apoptotic pathway in B16F10 murine melanoma cells. Sodium ascorbate was found to induce the apoptosis of B16F10 murine melanoma in a time- and dose-dependent manner, and this was prevented by pretreatment with N-acetyl-l-cysteine (NAC), a well-known antioxidant. In fact, sodium ascorbate–treated B16F10 melanoma cells showed increased intracellular reactive oxygen species generation (ROS) levels. These results indicate that sodium ascorbate induced apoptosis in B16F10 murine melanoma cells by acting as a prooxidant. We examined the involvement of caspase-8 using a specific caspase-8 inhibitor (z-IETD-fmk) on the sodium ascorbate–induced apoptotic pathway. Cell death was found not to be inhibited by z-IETD-fmk treatment, indicating that sodium ascorbate–induced apoptosis is not mediated by caspase-8. In addition, we detected a reduction in the mitochondrial membrane potential during apoptosis and confirmed cytochrome-c release from mitochondria by immunoblotting. Taken together, it appears that the induction of a prooxidant state by sodium ascorbate and a subsequent reduction in mitochondrial membrane potential are involved in the apoptotic pathway of B16F10 murine melanoma cells, and that this occurs in a caspase-8–independent manner.Abbreviations NAC N-acetyl-l-cysteine - ROS reactive oxygen species - _m mitochondrial membrane potentialJae Seung Kang and Daeho Cho contributed equally to this work.     

Trifolin acetate-induced cell death in human leukemia cells is dependent on caspase-6 and activates the MAPK pathway

In the present study we demonstrated that the flavonoid derivative trifolin acetate (TA), obtained by acetylation of naturally occurring trifolin, induces apoptosis. Associated downstream signaling events were also investigated. TA-induced cell death was prevented by the non-specific caspase inhibitor z-VAD-fmk and reduced by the presence of the selective caspase inhibitors z-LEHD-fmk (caspase-9), z-DEVD-fmk (caspase-3) and z-VEID-fmk (caspase-6). The apoptotic effect of TA was associated with (i) the release of cytochrome c from mitochondria which was not accompanied by dissipation of the mitochondrial membrane potential (ΔΨ_m), (ii) the activation of the mitogen-activated protein kinases (MAPKs) pathway and (iii) abrogated by the over-expression of Bcl-2 or Bcl-x_L. TA-induced cell death was attenuated by inhibition of extracellular signal-regulated kinases (ERK) 1/2 with U0126 and inhibition of p38^MAPK with SB203580. In contrast, inhibition of c-Jun NH₂-terminal kinase (JNK) by SP600125 significantly enhanced apoptosis. Although reactive oxygen species (ROS) increased in response to TA, this did not seem to play a pivotal role in the apoptotic process since different anti-oxidants were unable to provide cell protection. The present study demonstrates that TA-induced cell death is mediated by an intrinsic-dependent apoptotic event involving mitochondria and MAPK, and through a mechanism independent of ROS generation.     

<Emphasis Type="Italic">Clostridium difficile</Emphasis> toxin A-induced apoptosis is p53-independent but depends on glucosylation of Rho GTPases

Clostridium difficile toxin A (TcdA) is one of two homologous glucosyltransferases that mono-glucosylate Rho GTPases. HT29 cells were challenged with wild-type and mutant TcdA to investigate the mechanism by which apoptosis is induced. The TcdA-induced re-organization of the actin cytoskeleton led to an increased number of cells within the G2/M phase. Depolymerization of the actin filaments with subsequent G2/M arrest, however, was not causative for apoptosis, as shown in a comparative study using latrunculin B. The activation of caspase-3, -8, and -9 strictly depended on the glucosylation of Rho GTPases. Apoptosis measured by flow cytometry was completely abolished by a pan-caspase inhibitor (z-VAD-fmk). Interestingly, cleavage of procaspase-3 and Bid was not inhibited by z-VAD-fmk, but was inhibited by the calpain/cathepsin inhibitor ALLM. Cleavage of procaspase-8 was susceptible to inhibition by z-VAD-fmk and to the caspase-3 inhibitor Ac-DMQD-CHO, indicating a contribution to the activation of caspase-3 in an amplifying manner. Although TcdA induced mitochondrial damage and cytochrome c release, p53 was not activated or up-regulated. A p53-independent apoptotic effect was also checked by treatment of HCT 116 p53^−/− cells. In summary, TcdA-induced apoptosis in HT29 cells depends on glucosylation of Rho GTPases leading to activation of cathepsins and caspase-3.     

Association of the ERK1/2 and p38 kinase pathways with nitric oxide-induced apoptosis and cell cycle arrest in colon cancer cells

To investigate the mechanism by which nitric oxide (NO) induces cell death in colon cancer cells, we compared two types of colon cancer cells with different p53 status: HCT116 (p53 wild-type) cells and SW620 (p53-deficient) cells. We found that S-nitrosoglutathione (GSNO), the NO donor, induced apoptosis in both types of colon cancer cells. However, SW620 cells were much more susceptible than HCT116 cells to apoptotic death by NO. We investigated the role of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 kinase on NO-induced apoptosis in both types of colon cancer cells. GSNO treatment effectively stimulated activation of the ERK1/2 and p38 kinase in both types of cells. In HCT116 cells, pretreatment with PD98059, an inhibitor of ERK1/2, or SB203580, an inhibitor of p38 kinase, had no marked effect on GSNO-induced apoptosis. However, in SW620 cells, SB203580 significantly reduced the NO-induced apoptosis, whereas PD098059 increases NO-induced apoptosis. Furthermore, we found evidence of cell cycle arrest of the G₀/G₁ phase in SW620 cells but not in HCT116 cells. Inhibition of ERK1/2 with PD098059, or of p38 kinase with SB203580, reduced the GSNO-induced cell cycle arrest of the G₀/G₁ phase in SW620 cells. We therefore conclude that NO-induced apoptosis in colon cancer cells is mediated by a p53-independent mechanism and that the pathways of ERK1/2 and p38 kinase are important in NO-induced apoptosis and in the cell cycle arrest of the G₀/G₁ phase.     

The ruthenium(II)–arene compound RAPTA-C induces apoptosis in EAC cells through mitochondrial and p53–JNK pathways

An investigation of the molecular mechanism of the anticancer activity demonstrated by the ruthenium(II)–arene compound [Ru(η⁶-p-cymene)Cl₂(pta)] (pta is 1,3,5-triaza-7-phosphaadamantane), termed “RAPTA-C”, in Ehrlich ascites carcinoma (EAC) bearing mice is described. RAPTA-C exhibits effective cell growth inhibition by triggering G₂/M phase arrest and apoptosis in cancer cells. Cell cycle arrest is associated with increased levels of p21 and reduced amounts of cyclin E. RAPTA-C treatment also enhances the levels of p53, and its treatment triggers the mitochondrial apoptotic pathway, as shown by the change in Bax to Bcl-2 ratios, resulting in cytochrome c release and caspase-9 activation. c-Jun NH₂-terminal kinase (JNK) is a critical mediator in RAPTA-C-induced cell growth inhibition. Activation of JNK by RAPTA-C increases significantly during apoptosis. Overall, these results suggest a critical role for JNK and p53 in RAPTA-C-induced G₂/M arrest and apoptosis of EAC-bearing mice. Consequently, RAPTA-C treatment results in a significant inhibition in the progression of cancer in an animal model, which emulates the human disease, and does so with remarkably low general toxicity; hence, RAPTA-C has potential for clinical application.     

Distinct apoptotic phenotypes induced by radiation and ceramide in both p53-wild-type and p53-mutated lymphoblastoid cells

The tumour suppressor gene p53 and the intracellular signalling molecule ceramide have both been shown to play crucial roles in the induction of apoptosis by ionising radiation. In this study we examined whether p53 and ceramide are involved in independent signal pathways, inducing different types of apoptosis. TK6 (p53^wt/wt) and WTK1 (p53^mut/mut) lymphoblastoid cells were treated with ionising radiation or N-acetyl-d-sphingosine (C₂-ceramide). Flow cytometry and fluorescence microscopy studies were performed to characterise the time kinetics and morphological features of induced apoptosis. Ceramide- and radiation-induced apoptotic cells display characteristic differences in morphology and DNA staining and ceramide-induced apoptosis is expressed much faster than radiation-induced apoptosis. Radiation-induced apoptosis is p53-dependent and ceramide-induced apoptosis is p53-independent. The p53 pathway and the ceramide pathway are two independent signal pathways leading to distinct types of apoptosis. Since p53 is very often dysfunctional in tumour cells, modifying the ceramide pathway is a promising strategy to increase tumour sensitivity to radiation and other anticancer agents. Received: 19 April 2001 / Accepted: 15 October 2001     

Kaempferol induces apoptosis in human HCT116 colon cancer cells via the Ataxia-Telangiectasia Mutated-p53 pathway with the involvement of p53 Upregulated Modulator of Apoptosis

Dietary flavonols have been found to possess preventive and therapeutic potential against several kinds of cancers. This study is conducted to investigate the anti-proliferation effects of kaempferol, a major component of food flavonols, against colon cancer cells. In the human HCT116 colon cancer cell line, kaempferol induced p53-dependent growth inhibition and apoptosis. Furthermore, kaempferol was found to induce cytochrome c release from mitochondria and activate caspase-3 cleavage. The Bcl-2 family proteins including PUMA were involved in this process. Kaempferol also induced ATM and H2AX phosphorylation in HCT116 cells, inhibition of ATM by a chemical inhibitor resulted in abrogation of the downstream apoptotic cascades. These findings suggest kaempferol could be a potent candidate for colorectal cancer management.     

p38 MAP kinase regulates benzo(a)pyrene-induced apoptosis through the regulation of p53 activation

Polycyclic aromatic hydrocarbons, such as benzo(a)pyrene (BaP), are widespread in the environment and cause untoward effects, including carcinogenesis, in mammalian cells. However, the molecular mechanism of apoptosis by BaP is remained to be elusive. Pharmacological inhibition of p38 kinase markedly inhibited the BaP-induced cytotoxicity, which was proven as apoptosis characterized by an increase in sub-G(0)/G(1) fraction of DNA content, ladder-pattern fragmentation of genomic DNA, and catalytic activation of caspase-3 with PARP cleavage. Our data also demonstrated that activation of caspase-3 was accompanied with activation of caspase-9 and mitochondrial dysfunction, which was also apparently suppressed by pretreatment with p38 kinase inhibitors. Also, pharmacological inhibition of p38 markedly inhibited the phosphorylation, accumulated expression, and transactivation activity of p53 in BaP-treated cells. Adenoviral overexpression of human p53 (wild-type) further augmented in increase of PARP cleavage and the sub-G(0)/G(1) fraction of DNA content. Furthermore, p53 mediated apoptotic activity in BaP-treated cells was inhibited by p38 kinase inhibitor. The current data collectively indicate that BaP induces apoptosis of Hepa1c1c7 cells via activation of p53-related signaling, which was, in part, regulated by p38 kinase.     

DNA‐PK suppresses a p53‐independent apoptotic response to DNA damage

p53 is required for DNA damage‐induced apoptosis, which is central to its function as a tumour suppressor. Here, we show that the apoptotic defect of p53‐deficient cells is nearly completely rescued by inactivation of any of the three subunits of the DNA repair holoenzyme DNA‐dependent protein kinase (DNA‐PK). Intestinal crypt cells from p53 nullizygous mice were resistant to radiation‐induced apoptosis, whereas apoptosis in DNA‐PK_cs/p53, Ku80/p53 and Ku70/p53 double‐null mice was quantitatively equivalent to that seen in wild‐type mice. This p53‐independent apoptotic response was specific to the loss of DNA‐PK, as it was not seen in ligase IV (Lig4)/p53 or ataxia telangiectasia mutated (Atm)/p53 double‐null mice. Furthermore, it was associated with an increase in phospho‐checkpoint kinase 2 (CHK2), and cleaved caspases 3 and 9, the latter indicating engagement of the intrinsic apoptotic pathway. This shows that there are two separate, but equally effective, apoptotic responses to DNA damage: one is p53 dependent and the other, engaged in the absence of DNA‐PK, does not require p53.     

Expression of the p53 Gene and Activation of p53-Dependent Transcription in Melanoma Cell Lines

Malignant melanoma has poor prognosis because of its high metastatic potential and resistance to chemotherapy. A possible approach to more effective therapy is induction of p53-dependent apoptosis. This approach is promising, since the wild-type _p53 is expressed in most melanomas. An attempt was made to estimate the functional activity of p53 in several malignant melanoma cell lines. Most lines were characterized by a high protein level and nuclear localization of p53. All cell lines expressing the wild-type p53 showed stabilization of p53, its translocation into the nucleus, and activation of several target genes in response to DNA-damaging agents, suggesting that p53 was functionally active. A high-molecular-weight protein localized in the cytoplasm and mimicking a p53 epitope was found in several cell lines. It was shown that the DO-1 epitope is not derived from p53, ruling out cytoplasmic retention of p53 in melanoma cell lines. A mechanism of camptothecin-induced stabilization of p53 by decreasing the level of the HDM2 mRNA was described for melanoma cells but not for normal melanocytes, suggesting a differential effect of camptothecin on tumor-derived and primary cells.__________Translated from Molekulyarnaya Biologiya, Vol. 39, No. 3, 2005, pp. 445–456.Original Russian Text Copyright © 2005 by Razorenova, Agapova, Chumakov.     

Transfection of mutant p53 gene depresses X-ray- or CDDP-induced apoptosis in a human squamous cell carcinoma of the head and neck

The present study examined whether X-ray- and CDDP-sensitivities depend on p53 gene status in human squamous cell carcinoma of the head and neck (SAS cells) showing dominant negative nature of mutant p53 protein. SAS cells were transfected with a vector carrying a mutant p53 gene (SAS/Trp248 cells) or neomycin resistant gene control vector (SAS/neo cells). Sensitivities of the transfected cells to X-ray or CDDP were measured with colony formation assay. The incidence of apoptosis by X-ray or CDDP was analyzed with Hoechst staining or DNA ladder formation assay. The activation of caspase-3 was estimated as an indicator of apoptosis by the detection of fragmentation of caspase-3 or poly (ADP ribose) polymerase (PARP) with Western blot. SAS/Trp248 cells showed X-ray- and CDDP-resistance due to the dominant negative nature of mutant p53, compared with SAS/neo cells. The incidence of DNA ladders and apoptotic bodies increased markedly in SAS/neo cells after X-ray irradiation or CDDP treatment, but increased only slightly in SAS/Trp248 cells. Fragmentation of caspase-3 and PARP was observed in SAS/neo cells, but almost no such fragmentation was observed in SAS/Trp248 cells after X-ray irradiation or CDDP treatment. The present results strongly suggest that the X-ray- and CDDP-sensitivities of human squamous cell carcinomas are p53-dependent, and that the sensitivities are tightly correlated with the induction of apoptosis through caspase-3 activation. The p53-dependent X-ray- or CDDP-sensitivity was supported by results from p53-null human lung cancer H1299 cells which were transfected with wild-type or mutant p53 gene.     

Caspase-2 activation in neural stem cells undergoing oxidative stress-induced apoptosis

Oxidative stress occurs as a consequence of disturbance in the balance between the generation of reactive oxygen species (ROS) and the antioxidant defence mechanisms. The interaction of ROS with DNA can cause single-, or double-strand breaks that subsequently can lead to the activation of p53, which is central for the regulation of cellular response, e.g. apoptosis, to a range of environmental and intracellular stresses. Previous reports have suggested a regulatory role of p53 in the early activation of caspase-2, upstream of mitochondrial apoptotic signaling. Here we show that excessive ROS formation, induced by 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) exposure, induces apoptosis in primary cultured neural stem cells (NSCs) from cortices of E15 rat embryos. Following DMNQ exposure cells exhibited apoptotic hallmarks such as Bax oligomerization and activation, cytochrome c release, caspase activation and chromatin condensation. Additionally, we could show early p53 accumulation and a subsequent activation of caspase-2. The attenuation of caspase-2 activity with selective inhibitors could antagonize the mitochondrial signaling pathway and cell death. Overall, our results strongly suggest that DMNQ-induced oxidative stress causes p53 accumulation and consequently caspase-2 activation, which in turn initiates apoptotic cell death via the mitochondria-mediated caspase-dependent pathway in NSCs.     

Repression of apurinic/apyrimidinic endonuclease by p53-dependent apoptosis in hydronephrosis-induced rat kidney

Abstract

p53 plays a major role in apoptosis through activation of pro-apoptotic gene Bax. It also regulates apurinic/apyrimidinic endonuclease (APE) expression in the base excision repair pathway against oxidative DNA damages. This study investigated whether p53-dependent apoptosis is correlated with APE using an experimental rat model of hydronephrosis. Hydronephrosis was induced by partial ligation of the right ureter. Animals were sacrificed on scheduled time after unilateral ureteral obstruction and the expression of 8-OHdG, γ-H2AX, apoptotic proteins and APE was determined. The accumulated p53 activated Bax and caspase-3 7 days after hydronephrosis induction and the resulting high levels of p53-dependent apoptotic proteins and γ-H2AX tended to decrease APE. The intensities of 8-OHdG and caspase-3 immunolocalization significantly increased in obstructed kidneys than in sham-operated kidneys, although APE immunoreactivity increased after hydronephrosis induction. These results suggest that oxidative DNA damages in obstructed kidneys may trigger p53-dependent apoptosis through repression of APE.     

Protective Role of Taurine against Arsenic-Induced Mitochondria-Dependent Hepatic Apoptosis via the Inhibition of PKCδ-JNK Pathway

Background

Oxidative stress-mediated hepatotoxic effect of arsenic (As) is mainly due to the depletion of glutathione (GSH) in liver. Taurine, on the other hand, enhances intracellular production of GSH. Little is known about the mechanism of the beneficial role of taurine in As-induced hepatic pathophysiology. Therefore, in the present study we investigated its beneficial role in As-induced hepatic cell death via mitochondria-mediated pathway.

Methodology/Principal Findings

Rats were exposed to NaAsO₂ (2 mg/kg body weight for 6 months) and the hepatic tissue was used for oxidative stress measurements. In addition, the pathophysiologic effect of NaAsO₂ (10 µM) on hepatocytes was evaluated by determining cell viability, mitochondrial membrane potential and ROS generation. As caused mitochondrial injury by increased oxidative stress and reciprocal regulation of Bcl-2, Bcl-xL/Bad, Bax, Bim in association with increased level of Apaf-1, activation of caspase 9/3, cleavage of PARP protein and ultimately led to apoptotic cell death. In addition, As markedly increased JNK and p38 phosphorylation with minimal disturbance of ERK. Pre-exposure of hepatocytes to a JNK inhibitor SP600125 prevented As-induced caspase-3 activation, ROS production and loss in cell viability. Pre-exposure of hepatocytes to a p38 inhibitor SB2035, on the other hand, had practically no effect on these events. Besides, As activated PKCδ and pre-treatment of hepatocytes with its inhibitor, rottlerin, suppressed the activation of JNK indicating that PKCδ is involved in As-induced JNK activation and mitochondrial dependent apoptosis. Oral administration of taurine (50 mg/kg body weight for 2 weeks) both pre and post to NaAsO₂ exposure or incubation of the hepatocytes with taurine (25 mM) were found to be effective in counteracting As-induced oxidative stress and apoptosis.

Conclusions/Significance

Results indicate that taurine treatment improved As-induced hepatic damages by inhibiting PKCδ-JNK signalling pathways. Therefore taurine supplementation could provide a new approach for the reduction of hepatic complication due to arsenic poisoning.     

p38/p53-Mediated Bax induction contributes to neurons degeneration in rotenone-induced cellular and rat models of Parkinson’s disease

Rotenone is an environmental neurotoxin that induces degeneration of dopaminergic (DA) neurons in substantia nigra pars compacta (SNpc), which ultimately results in parkinsonism, but the molecular mechanisms of selective degeneration of nigral DA neurons are not fully understood. In the present study, we investigated the induction of p38^MAPK/p53 and Bax in SNpc of Lewis rats after chronic treatment with rotenone and the contribution of Bax to rotenone-induced apoptotic commitment of differentiated PC12 cells. Lewis rats were subcutaneously treated with rotenone (1.5 mg/kg) twice a day for 50 days and the loss of tyrosine hydroxylase (THase), motor function impairment, and expression of p38^MAPK, P-p38^MAPK, p53, and Bax were assessed. After differentiated PC cells were treated with rotenone (500 nM) for 6–36 h, protein levels of p38^MAPK and P-p38^MAPK, p53 nuclear translocation, Bax induction and cell death were measured. The results showed that rotenone administration significantly reduced motor activity and caused a loss of THase immunoreactivity in SNpc of Lewis rats. The degeneration of nigral DA neurons was accompanied by the increases in p38^MAPK, P-p38^MAPK, p53, and Bax protein levels. In cultured PC12 cells, rotenone also induced an upregulation of p38^MAPK, P-p38^MAPK, p53 and Bax. Pharmacological inhibition of p38^MAPK with SB203580 (25 μM) blunted rotenone-induced cell apoptosis. Treatment with SB203580 prevented the p53 nuclear translocation and upregulation of Bax. Inhibition of p53 with pifthrin-alpha or Bax with siRNAs significantly reduced rotenone-induced Bax induction and apoptotic cell death. These results suggest that the p38^MAPK/p53-dependent induction of Bax contributes to rotenone’s neurotoxicity in PD models.