Biomedical subjects

Kanaga Sabapathy

Publications and source records attributed to Kanaga Sabapathy.

At least 19 recordsLinked to original sources

PubMed2008

TAp73beta and DNp73beta activate the expression of the pro-survival caspase-2S.

p73, the p53 homologue, exists as a transactivation-domain-proficient TAp73 or deficient deltaN(DN)p73 form. Expectedly, the oncogenic DNp73 that is capable of inactivating both TAp73 and p53 function, is over-expressed in cancers. However, the role of TAp73, which exhibits tumour-suppressive properties in gain or loss of function models, in human cancers where it is hyper-expressed is unclear. We demonstrate here that both TAp73 and DNp73 are able to specifically transactivate the expression of the anti-apoptotic member of the caspase family, caspase-2(S). Neither p53 nor TAp63 has this property, and only the p73beta form, but not the p73alpha form, has this competency. Caspase-2 promoter analysis revealed that a non-canonical, 18 bp GC-rich Sp-1-binding site-containing region is essential for p73beta-mediated activation. However, mutating the Sp-1-binding site or silencing Sp-1 expression did not affect p73beta's transactivation ability. In vitro DNA binding and in vivo chromatin immunoprecipitation assays indicated that p73beta is capable of directly binding to this region, and consistently, DNA binding p73 mutant was unable to transactivate caspase-2(S). Finally, DNp73beta over-expression in neuroblastoma cells led to resistance to cell death, and concomitantly to elevated levels of caspase-2(S.) Silencing p73 expression in these cells led to reduction of caspase-2(S) expression and increased cell death. Together, the data identifies caspase-2(S) as a novel transcriptional target common to both TAp73 and DNp73, and raises the possibility that TAp73 may be over-expressed in cancers to promote survival.

Binding Sites↗

PubMed2006

The pro-inflammatory oxidant hypochlorous acid induces Bax-dependent mitochondrial permeabilisation and cell death through AIF-/EndoG-dependent pathways.

At sites of chronic inflammation, such as in the inflamed rheumatoid joint, activated neutrophils release hydrogen peroxide (H(2)O(2)) and the enzyme myeloperoxidase to catalyse the formation of hypochlorous acid (HOCl). 3-chlorotyrosine, a marker of HOCl in vivo, has been observed in synovial fluid proteins from rheumatoid arthritis patients. However the mechanisms of HOCl-induced cytotxicity are unknown. We determined the molecular mechanisms by which HOCl induced cell death in human mesenchymal progenitor cells (MPCs) differentiated into a chondrocytic phenotype as a model of human cartilage cells and show that HOCl induced rapid Bax conformational change, mitochondrial permeability and release of intra-mitochondrial pro-apoptotic proteins which resulted in nuclear translocation of AIF and EndoG. siRNA-mediated knockdown of Bax substantially prevented mitochondrial permeability, release of intra-mitochondrial pro-apoptotic proteins. Cell death was inhibited by siRNA-mediated knockdown of Bax, AIF or EndoG. Although we observed several biochemical markers of apoptosis, caspase activation was not detected either by western blotting, fluorescence activity assays or by using caspase inhibitors to inhibit cell death. This was further supported by findings that (1) in vitro exposure of recombinant human caspases to HOCl caused significant inhibition of caspase activity and (2) the addition of HOCl to staurosporine-treated MPCs inhibited the activity of cellular caspases. Our results show for the first time that HOCl induced Bax-dependent mitochondrial permeability which led to cell death without caspase activity by processes involving AIF/EndoG-dependent pathways. Our study provides a novel insight into the potential mechanisms of cell death in the inflamed human joint.

Apoptosis Inducing Factor↗

PubMed2006

A novel c-Jun-dependent signal transduction pathway necessary for the transcriptional activation of interferon gamma response genes.

The biological effects of interferon gamma (IFNgamma) are mediated by interferon-stimulated genes (ISGs), many of which are activated downstream of Janus kinase (JAK)/signal transducer and activator of transcription 1 (STAT1) signaling. Herein we have shown that IFNgamma rapidly activated AP-1 DNA binding that required c-Jun but was independent of JAK1 and STAT1. IFNgamma-induced c-Jun phosphorylation and AP-1 DNA binding required the MEK1/2 and ERK1/2 signaling pathways, whereas the JNK1/2 and p38 mitogen-activated protein kinase pathways were dispensable. The induction of several ISGs, including ifi-205 and iNOS, was impaired in IFNgamma-treated c-Jun-/- cells, but others, such as IP-10 and SOCS3, were unaffected, and chromatin immunoprecipitation demonstrated that c-Jun binds to the iNOS promoter following treatment with IFNgamma. Thus, IFNgamma induced JAK1- and STAT1-independent activation of the ERK mitogen-activated protein kinase pathway, phosphorylation of c-Jun, and activation of AP-1 DNA binding, which are important for the induction of a subset of ISGs. This represents a novel signal transduction pathway induced by IFNgamma that proceeds in parallel with conventional JAK/STAT signaling to activate ISGs.

Animals↗

PubMed2006

Aflatoxin-B exposure does not lead to p53 mutations but results in enhanced liver cancer of Hupki (human p53 knock-in) mice.

Hepatocellular carcinoma (HCC) is a common human malignancy that is often associated with risk factors such as aflatoxin-B1 (AFB1) exposure and Hepatitis-B virus infection in developing countries. There is a strong correlation between these risk factors and mutation of the tumor-suppressor gene p53 at codon 249. In vitro experiments have also shown that treatment of human liver cells with AFB1 results in p53 mutations. A tumor-promoting role for mutant p53 was demonstrated using transgenic mice models, in which HCC development was accelerated upon AFB1-exposure. However, wild-type mice in which AFB1 alone was used to induce liver cancers have failed to recapitulate p53 mutations, raising the possibility that mouse DNA context may not be appropriate for the generation of AFB1-induced p53 mutations. We have now tested this hypothesis using the Hupki mice (human p53 knock-in) in which the mouse DNA-binding domain has been replaced by the homologous human p53 segment. Mice were followed for 80 weeks after AFB1 injection for survival and HCC formation. Hupki mice were found to be more susceptible to AFB1 than wild-type mice. Moreover, only 19% of wild-type mice developed HCCs compared to 44% in Hupki mice. However, none of the liver tumors and normal tissues from Hupki mice contained any mutations in the DNA-binding domain of p53. These findings suggest that the human DNA context of the p53 gene alone may not be the sole determinant of AFB1-induced mutagenesis. Furthermore, humanized p53 appears not to be as effective as murine p53 in the mouse cellular environment in preventing malignant transformation.

Aflatoxin B1↗

PubMed2006

Two distinct steps of Bak regulation during apoptotic stress signaling: different roles of MEKK1 and JNK1.

Stress-activated protein (SAP) kinases and the mitochondrial pro-apoptotic Bcl-2 protein Bak are important regulators of apoptosis. Reduced expression of Bak increases cellular resistance to the anticancer agent cisplatin, and we report here that mouse embryo fibroblasts deficient in the SAP kinase jnk1 are highly resistant to apoptosis induced by cisplatin. When human melanoma cells were treated with cisplatin, Bak function was found to be regulated in two distinct steps by two SAP kinases, MEKK1 and JNK1. The first of these steps involves MEKK1-controlled conformational activation of Bak. The second step leads to formation of 80-170 kDa Bak complexes correlating with apoptosis, and is controlled by JNK1. Inhibition of MEKK1 blocked the initial Bak conformational activation but did not block JNK1 activation, and deficiency in, or inhibition of, JNK1 did not prevent conformational activation of Bak. Furthermore, inducible expression of a constitutively active form of MEKK1 led to Bak conformational activation, but not to 80-170 kDa complexes. Consequently, apoptosis was delayed unless JNK was exogenously stimulated, indicating that Bak conformational activation is not necessarily an apoptotic marker. The two-step regulation of Bak revealed here may be important for tight control of mitochondrial factor release and apoptosis.

Animals↗

PubMed2005

Evaluation of the combined effect of p53 codon 72 polymorphism and hotspot mutations in response to anticancer drugs.

Mutations in p53 are common events during carcinogenesis and have been suggested to affect sensitivity to chemotherapy. Recently, the common polymorphism at codon 72, resulting in either an arginine (72R) or proline (72P) residue, was shown to differentially affect the response to anticancer drugs. Here, we have generated isogenic lung cancer cell lines to evaluate the effect of six p53 hotspot mutations (R175H, G245S, R248W, R249S, R273H, and R282W) in conjunction with the codon 72 polymorphism, for their response to a variety of anticancer drugs, either alone or in combination. The data indicate that 72R mutations do not confer general resistance to cisplatin, etoposide, gemcitabine, vinblastine, and taxol. For doxorubicin, cells expressing 249-72R were more resistant than the 249-72P cells. Combined treatment with cisplatin + etoposide resulted in an additive effect in cells expressing most 72R and 72P mutations, except for the 175-72R cells which were refractory to combined treatment. However, combined treatment with cisplatin + gemcitabine resulted in the absence of an additive effect in cells expressing the 273-72R and 282-72R mutants, unlike their 72P counterparts. Nonetheless, all p53 mutants (72R or 72P) equally inhibited p73-mediated transcriptional activity in lung cancer cells, suggesting that the selective resistance conferred by some 72R mutants to certain drugs is probably due to other p73-independent effects of these mutants. Together, the data show that the status of codon 72 polymorphism and p53 mutations can be used as a means for prediction of treatment response, although variables for each cancer type requires detailed evaluation.

Antineoplastic Agents↗

PubMed2005

ERK phosphorylates p66shcA on Ser36 and subsequently regulates p27kip1 expression via the Akt-FOXO3a pathway: implication of p27kip1 in cell response to oxidative stress.

Mice deficient for p66shcA represent an animal model to link oxidative stress and aging. p66shcA is implicated in oxidative stress response and mitogenic signaling. Phosphorylation of p66shcA on Ser36 is critical for its function in oxidative stress response. Here we report the identification of ERK as the kinase phosphorylating p66shcA on Ser36. Activation of ERKs was necessary and sufficient for Ser36 phosphorylation. p66shcA interacted with ERK and was demonstrated to be a substrate for ERK, with Ser36 being the major phosphorylation site. Furthermore, in response to H2O2, inhibition of ERK activation repressed p66shcA-dependent phosphorylation of FOXO3a and the down-regulation of its target gene p27kip1. Down-regulation of p27 might promote cell survival, as p27 played a proapoptotic role in oxidative stress response. As a feedback regulation, Ser36 phosphorylated p66shcA attenuated H2O2-induced ERK activation, whereas p52/46shcA facilitated ERK activation, which required tyrosine phosphorylation of CH1 domain. p66shcA formed a complex with p52/46ShcA, which may provide a platform for efficient signal propagation. Taken together, the data suggest there exists an interplay between ERK and ShcA proteins, which modulates the expression of p27 and cell response to oxidative stress.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Transactivation-dependent and -independent regulation of p73 stability.

The tumor suppressor p53 regulates its own stability by transcriptionally activating Mdm2, Pirh2, and COP1, which target p53 for degradation. However, whether such a negative feedback mechanism exists to regulate the stability of p73, the structural and functional homologue of p53, is unclear. Unlike p53, p73 is not mutated in cancers, but its expression is significantly elevated. Thus, we have investigated the regulation of p73 turnover. Our data suggest the existence of a negative feedback mechanism for p73 degradation. p73 mutants with compromised transactivation activity are generally more stable than the full-length TAp73 form. TAp73 appears to promote its own turnover as well as that of other p73 forms, including the DeltaNp73 that lacks the amino-terminal transactivation domain, in a transactivation-dependent manner. This degradation-inducing property of TAp73 was inhibited only by p73 mutants that also inhibit the transactivation activity TAp73 but not by mutant p53, highlighting the specificity in the regulation of p73 stability. Moreover, regions in the amino and carboxyl termini of p73 confer both stabilizing and destabilizing effects on the protein, independent of its transactivation ability. Finally, we have identified the regions between amino acids 56 and 248 of p73 as being the region required for p73-mediated and for ubiquitin-mediated degradation. Taken together, the data suggest that p73 turnover is tightly regulated in a transactivation-dependent and -independent manner, resulting in the controlled expression of the various p73 forms.

Base Sequence↗

PubMed2005

Relief of p53-mediated telomerase suppression by p73.

Reactivation of telomerase is a feature in many cancer cells. Telomerase activation inhibits telomere shortening, thereby preventing cell cycle arrest and apoptosis activated by shortened telomeres or chromosomal rearrangements. The tumor-suppressor gene product, p53, was previously shown to transcriptionally suppress the activation of the catalytic subunit of telomerase (hTERT). Here we have evaluated the role of p73 in hTERT regulation. We found that ectoptic expression of p73beta, in contrast to p73alpha or p53, in p53 null H1299 cells does not lead to suppression of hTERT transcription. However co-expression of p73alpha or p73beta together with p53 abolished p53-mediated hTERT suppression. This phenomenon was found to be dependent on the DNA binding ability of p73. We also show that p53-mediated suppression of hTERT transcription requires a minimum threshold level of p53, and p73 abrogates p53-mediated suppression by reducing p53 levels through the activation of HDM2. Moreover, p53-mediated hTERT suppression was not relieved by p73beta in cells depleted of HDM2 through small interfering RNA-mediated gene silencing. In addition, knockdown of HDM2 in MCF7 cells, which express moderately high levels of p73 and p53, resulted in the reduction of endogenous hTERT levels. Finally, knockdown of p73 in MCF7 cells resulted in increased p53 protein levels and a concomitant decrease in hTERT levels. Together, our data indicate a plausible way by which p73, through HDM2, can oppose p53 tumor suppressor function, thereby possibly contributing to tumorigenesis.

Catalytic Domain↗

PubMed2005

Ectopic mTERT expression in mouse embryonic stem cells does not affect differentiation but confers resistance to differentiation- and stress-induced p53-dependent apoptosis.

The fundamental role of telomerase is to protect telomere ends and to maintain telomere length during replication; hence, telomerase expression is high in stem cells but reduced upon differentiation. Recent studies indicate that telomerase might play other roles besides telomere maintenance. We have investigated the role of telomerase in cellular differentiation and death. Here, we show that ectopic expression of mouse telomerase catalytic subunit (mTERT) does not affect embryonic stem (ES) cell proliferation or differentiation in vitro, but protects ES cells against cell death during differentiation. Ectopic mTERT expression also confers resistance to apoptosis induced by oxidative stress and other genotoxic insults. This resistance depends on the catalytic activity of mTERT. Stress-signal-induced p53 accumulation and consequent p53-dependent apoptotic target gene expression was not affected by mTERT overexpression. However, although chemical inhibition of p53 by alpha-pifithrin reduced stress-induced apoptosis in vector-expressing cells, it did not significantly affect apoptosis in mTERT-expressing cells. Moreover, overexpression of mTERT in p53-/- ES cells did not confer further resistance to genotoxic insults, suggesting that mTERT might exert its protective effect by antagonizing the p53 pathway. Altogether, our findings indicate that ectopic mTERT expression in ES cells does not affect differentiation but confers resistance to apoptosis, and suggest that this strategy might be used in improving the efficiency of stem-cell therapies.

Animals↗

PubMed2005

Impaired long-term potentiation in c-Jun N-terminal kinase 2-deficient mice.

c-Jun N-terminal kinases (JNKs) are thought to be involved in regulating synaptic plasticity. We therefore investigated the specific role of JNK2 in modulating long-term potentiation (LTP) in hippocampus during development, using JNK2-deficient mice. The morphological structure and the numbers of both NeuN, a specific neuronal marker, and GABA-positive neurons in the hippocampal areas were similar in wild-type and Jnk2(-/-) mice. Western blot analysis revealed that JNK2 expression was higher and stable at 1 and 3 months of age, but JNK1 levels were lower at 1 month of age and almost undetectable in 3-month-old wild-type mice. In contrast to wild-type mice, there was a significant increase in JNK1 expression in JNK2 mutant mice, especially at 1 month of age. Electrophysiological studies demonstrated that LTP was impaired in both the CA1 and CA3 regions in 1-month-old, but not in adult, Jnk2(-/-) mice, probably owing to decreased presynaptic neurotransmitter release. Moreover, late-phase LTP, but not early-phase LTP, was impaired in the Jnk2(-/-) adult mice, suggesting that JNK2 plays a role in transforming early LTP to late LTP. Together, the data highlight the specific role of JNK2 in hippocampal synaptic plasticity during development.

Animals↗

PubMed2005

Evidence for selective expression of the p53 codon 72 polymorphs: implications in cancer development.

Polymorphism at codon 72 of p53 results in either the arginine or proline form of p53, whose functional significance in carcinogenesis is controversial. We have investigated if the expression of these p53 polymorphs is selectively regulated, using mRNA from peripheral blood of healthy Asian (Chinese) and the Caucasian (Polish) arginine/proline (arg/pro) heterozygote subjects. Asians were found to preferentially express the pro allele whereas the Caucasians preferentially express the arg allele. On the contrary, about 75% of the heterozygote Chinese breast cancer patients preferentially expressed the arg allele, which rarely contained any somatic mutations. Moreover, histologically normal tissues from Chinese heterozygote breast cancer patients showed selective expression of the arg allele, in contrast to the preferential expression of the pro allele in heterozygote healthy normal breast tissues. Together, the data suggest that the expression of the different p53 polymorphs is selectively regulated in different ethnic populations, and that the arg allele is activated during cancer development in Asians. Thus, the expression status of the p53 polymorphs, rather than the genotypic status, might be a useful indicator for cancer susceptibility.

Breast Neoplasms↗

PubMed2004

JNK2: a negative regulator of cellular proliferation.

The three different c-Jun N-terminal kinases (JNKs) are activated in multiple cell types by both apoptotic and mitogenic signals, and in turn regulate the activity of transcription factors such as c-Jun. Being highly homologous and ubiquitously expressed, the JNK1 and JNK2 proteins have been thought to perform redundant functions in many physiological process. However, our data from Jnk1-/- or Jnk2-/- cells and mice suggest that both JNK isozymes perform distinct functions in regulating cellular proliferation via differential regulation of c-Jun, which is a critical regulator of cell-cycle progression. Absence of JNK1, the positive regulator of c-Jun, leads to decreased fibroblast proliferation. In contrast, JNK2 deficiency leads to reduced c-Jun degradation, thereby augmenting c-Jun levels and cellular proliferation. Various cell types including fibroblasts, erythroblasts and hepatocytes from Jnk2-/- mice exhibit increased proliferation rates compared to their wild-type counterparts. These data therefore suggests that JNK2, in contrast to JNK1, is a negative regulator of cellular proliferation in multiple cell types.

Animals↗

PubMed2004

Distinct roles for JNK1 and JNK2 in regulating JNK activity and c-Jun-dependent cell proliferation.

Different c-Jun N-terminal kinases (JNKs) are activated by a plethora of signals and phosphorylate substrates such as c-Jun, which is required for efficient cell cycle progression. Although JNK1 and JNK2 were shown to differentially regulate fibroblast proliferation, the underlying mechanistic basis remains unclear. We found that Jnk2-/- fibroblasts exit G1 and enter S phase earlier than wild-type counterparts, while Jnk1-/- cells show the inverse phenotype. Moreover, Jnk2-/- erythroblasts also exhibit a proliferative advantage. JNK2 deficiency results in elevated c-Jun phosphorylation and stability, whereas the absence of JNK1 reduces c-Jun phosphorylation and stability. Re-expression of JNK2 in Jnk2-/- cells reverses the JNK2 null phenotype, whereas ectopic expression of JNK1 augments it. JNK2 is preferentially bound to c-Jun in unstimulated cells, thereby contributing to c-Jun degradation. In contrast, JNK1 becomes the major c-Jun interacting kinase after cell stimulation. These data provide mechanistic insights into the distinct roles of different JNK isoforms.

3T3 Cells↗

PubMed2004

c-Jun regulates the stability and activity of the p53 homologue, p73.

Chemotherapeutic drugs and stress signals activate p73, the structural and functional homologue of p53, both by transcriptional activation and post-translational modifications. However, cisplatin, a DNA damage-inducing chemotherapeutic agent, is thought to regulate p73 only by affecting its stability through mechanisms involving the MLH-1/c-Abl signaling cascade. Here we show that c-Jun, a component of the AP-1 family of transcription factors, contributes to p73 induction by cisplatin. c-jun(-/-) cells are defective in p73 induction, and ectopic c-Jun expression augments p73 levels. c-Jun-mediated accumulation of p73 requires the transactivation activity of c-Jun and occurs in a c-Abl- and Mdm2-independent manner. c-Jun expression increases p73 half-life by preventing it from proteasome-mediated degradation, resulting in the potentiation of p73-mediated transcriptional activity. Moreover, mouse fibroblasts lacking c-Jun are resistant to cisplatin-induced apoptosis, and reintroduction of c-Jun restores p73 activation and sensitivity to cisplatin. Furthermore, p73-mediated apoptosis is abrogated in c-jun(-/-) cells. Together, these findings demonstrate a possible role for c-Jun in regulating p73 function and highlight the importance of the cooperativity between transcription factors in potentiating apoptosis.

Animals↗

PubMed2003

An apoptotic signaling pathway in the interferon antiviral response mediated by RNase L and c-Jun NH2-terminal kinase.

Cellular stress responses induced during viral infections are critical to the health and survival of organisms. In higher vertebrates, interferons (IFNs) mediate the innate antiviral response in part through the action of RNase L, a uniquely regulated enzyme. RNase L is activated by 5'-phosphorylated, 2'-5' oligoadenylates (2-5A) produced from IFN-inducible and double stranded RNA-dependent synthetases. We show that viral activation of the c-Jun NH2-terminal kinases (JNK) family of MAP kinases and viral induction of apoptosis are both deficient in mouse cells lacking RNase L. Also, JNK phosphorylation in response to 2-5A was greatly reduced in RNase L-/- mouse cells. In addition, 2-5A treatment of the human ovarian carcinoma cell line, Hey1b, resulted in specific ribosomal RNA cleavage products coinciding with JNK activation. Furthermore, suppression of JNK activity with the chemical inhibitor, SP600125, prevented apoptosis induced by 2-5A. In contrast, inhibition of alternative MAP kinases, p38 and ERK, failed to prevent 2-5A-mediated apoptosis. Short interfering RNA to JNK1/JNK2 mRNAs resulted in JNK ablation while also suppressing 2-5A-mediated apoptosis. Moreover, Jnk1-/- Jnk2-/- cells were highly resistant to the apoptotic effects of IFN and 2-5A. These findings suggest that JNK and RNase L function in an integrated signaling pathway during the IFN response that leads to elimination of virus-infected cells through apoptosis.

Animals↗

PubMed2002

JNK1 modulates osteoclastogenesis through both c-Jun phosphorylation-dependent and -independent mechanisms.

Phosphorylation of the N-terminal domain of Jun by the Jun kinases (JNKs) modulates the transcriptional activity of AP-1, a dimeric transcription factor typically composed of c-Jun and c-Fos, the latter being essential for osteoclast differentiation. Using mice lacking JNK1 or JNK2, we demonstrate that JNK1, but not JNK2, is specifically activated by the osteoclast-differentiating factor RANKL. Activation of JNK1, but not JNK2, is required for efficient osteoclastogenesis from bone marrow monocytes (BMMs). JNK1 protects BMMs from RANKL-induced apoptosis during differentiation. In addition, BMMs from mice carrying a mutant of c-Jun phosphorylation sites (JunAA/JunAA), as well as cells lacking either c-Jun or JunD, which is another JNK substrate, revealed that c-Jun phosphorylation and c-Jun itself, but not JunD, are essential for efficient osteoclastogenesis. Moreover, JNK1-dependent c-Jun phosphorylation in response to RANKL is not involved in the anti-apoptotic function of JNK1. Thus, these data provide genetic evidence that JNK1 activation modulates osteoclastogenesis through both c-Jun-phosphorylation-dependent and -independent mechanisms.

Animals↗

PubMed2002

Differential effects of JNK1 and JNK2 on signal specific induction of apoptosis.

The c-Jun N-terminal kinases (JNKs) are activated by a variety of stress inducing agents and are thought to regulate apoptosis in a cell type and signal-specific manner. We have used fibroblasts lacking JNK1 or JNK2 to define their roles in response to different stress signals. Lack of JNK1 results in reduced c-Jun phosphorylation and resistance to UV-induced cell death. JNK2 deficient cells show increased sensitivity to UV irradiation which correlates with elevated and sustained phosphorylation of JNK1 and c-Jun. On the contrary, both Jnk1-/- and Jnk2-/- cells were more sensitive to tumor necrosis factor - alpha (TNF-alpha) and sorbitol-induced cell death. Treatment of Jnk1-/- cells with these reagents resulted in reduced JNK activity and a concomitant reduction of c-Jun phosphorylation, suggesting that phosphorylation of c-Jun does not influence TNF-alpha and sorbitol-induced apoptosis in fibroblasts. Moreover, both JNK1 and JNK2 appear to negatively regulate apoptosis independent of c-Jun phosphorylation. These data provide genetic evidence that although the JNK pathway is activated by a plethora of signals, it is required only for the induction of UV-induced cell death in a c-Jun phosphorylation-dependent manner, but not for TNF-alpha and sorbitol-induced apoptosis.

Animals↗