C-Fos is not essential for apoptosis

Impact of Complex Apoptotic Signaling Pathways on Cancer Cell Sensitivity to Therapy

Anticancer drugs induce apoptotic and non-apoptotic cell death in various cancer types. The signaling pathways for anticancer drug-induced apoptotic cell death have been shown to differ between drug-sensitive and drug-resistant cells. In atypical multidrug-resistant leukemia cells, the c-Jun/activator protein 1 (AP-1)/p53 signaling pathway leading to apoptotic death is altered. Cancer cells treated with anticancer drugs undergo c-Jun/AP-1-mediated apoptotic death and are involved in c-Jun N-terminal kinase activation and growth arrest- and DNA damage-inducible gene 153 (Gadd153)/CCAAT/enhancer-binding protein homologous protein pathway induction, regardless of the p53 genotype. Gadd153 induction is associated with mitochondrial membrane permeabilization after anticancer drug treatment and involves a coupled endoplasmic reticulum stress response. The induction of apoptosis by anticancer drugs is mediated by the intrinsic pathway (cytochrome c, Cyt c) and subsequent activation of the caspase cascade via proapoptotic genes (e.g., Bax and Bcl-xS) and their interactions. Anticancer drug-induced apoptosis involves caspase-dependent and caspase-independent pathways and occurs via intrinsic and extrinsic pathways. The targeting of antiapoptotic genes such as Bcl-2 enhances anticancer drug efficacy. The modulation of apoptotic signaling by Bcl-xS transduction increases the sensitivity of multidrug resistance-related protein-overexpressing epidermoid carcinoma cells to anticancer drugs. The significance of autophagy in cancer therapy remains to be elucidated. In this review, we summarize current knowledge of cancer cell death-related signaling pathways and their alterations during anticancer drug treatment and discuss potential strategies to enhance treatment efficacy.

Comprehensive Identification of Key Genes Involved in Development of Diabetes Mellitus-Related Atherogenesis Using Weighted Gene Correlation Network Analysis

Coronary heart disease (CHD) is common in patients with diabetes mellitus (DM), however, the relevant mechanism remains elusive. The whole blood gene expression profiles of healthy control, patients with DM, patients with DM and CHD (DMCHD) were used to performed weight gene correlation network analysis (WGCNA) to identify the gene modules associated with DM-related atherogenesis. The candidate module was significantly involved in immune- and T cell activity-related biological process. GSEA results suggested that lysosome and apoptosis were enriched in DM and DMCHD samples. The protein-protein-KEGG pathway network may reveal the potential transcriptional regulatory network involving in DM-related atherosclerosis. Nineteen genes (RTKN, DCP1B, PDZD4, CACNA2D2, TSEN54, PVRIG, PLEKHF1, NKG7, ZAP70, NUDCD3, SLAMF6, CCDC107, NAG6, ZDHHC14, EOMES, VIL2, WDR54, DMAP1, and PMPCA) were considered as DM-related atherogenesis genes (DRAGs). The Gene Set Variation Analysis (GSVA) score of the DRAG set gradually increased in the control, DM and DMCHD. ROC curve analysis showed that ZAP70, TSEN54, and PLEKHF1 may be potential blood circulation biomarkers for DMCHD in patients with DM. In conclusion, we identified nineteen hallmark genes involving in DM-related atherogenesis and constructed a potential transcriptional regulatory network involving in DM-related atherosclerosis.

Global transcriptional regulation of STAT3- and MYC-mediated sepsis-induced ARDS

Background:

In recent years, sepsis-induced acute respiratory distress syndrome (ARDS) has remained a major clinical challenge for patients in intensive care units. While some progress has been reported over the years, the pathogenesis of ARDS still needs to be further expounded.

Methods:

In the present study, gene set enrichment analysis, differentially expressed genes analysis, short time-series expression miner, protein–protein interaction (PPI) networks, module analysis, hypergeometric test, and functional enrichment analysis were performed in whole blood gene expression profiles of sepsis and induced-sepsis ARDS to explore the molecular mechanism of sepsis-induced ARDS.

Results:

Further dysregulated genes in the process evolving from healthy control through sepsis to sepsis-induced ARDS were identified and organized into 10 functional modules based on their PPI networks. These functional modules were significantly involved in cell cycle, ubiquitin mediated proteolysis, spliceosome, and other pathways. MYC, STAT3, LEF1, and BRCA1 were potential transcription factors (TFs) regulating these modules. A TF-module-pathway global regulation network was constructed. In particular, our findings suggest that MYC and STAT3 may be the key regulatory genes in the underlying dysfunction of sepsis-induced ARDS. Receiver operating characteristic curve analysis showed the core genes in the global regulation network may be biomarkers for sepsis or sepsis-induced ARDS.

Conclusions:

We found that MYC and STAT3 may be the key regulatory genes in the underlying dysfunction of sepsis-induced ARDS.

The reviews of this paper are available via the supplementary material section.

Differential effects of selective frankincense (Ru Xiang) essential oil versus non-selective sandalwood (Tan Xiang) essential oil on cultured bladder cancer cells: a microarray and bioinformatics study

BACKGROUND

Frankincense (Boswellia carterii, known as Ru Xiang in Chinese) and sandalwood (Santalum album, known as Tan Xiang in Chinese) are cancer preventive and therapeutic agents in Chinese medicine. Their biologically active ingredients are usually extracted from frankincense by hydrodistillation and sandalwood by distillation. This study aims to investigate the anti-proliferative and pro-apoptotic activities of frankincense and sandalwood essential oils in cultured human bladder cancer cells.

METHODS

The effects of frankincense (1,400-600 dilutions) (v/v) and sandalwood (16,000-7,000 dilutions) (v/v) essential oils on cell viability were studied in established human bladder cancer J82 cells and immortalized normal human bladder urothelial UROtsa cells using a colorimetric XTT cell viability assay. Genes that responded to essential oil treatments in human bladder cancer J82 cells were identified using the Illumina Expression BeadChip platform and analyzed for enriched functions and pathways. The chemical compositions of the essential oils were determined by gas chromatography-mass spectrometry.

RESULTS

Human bladder cancer J82 cells were more sensitive to the pro-apoptotic effects of frankincense essential oil than the immortalized normal bladder UROtsa cells. In contrast, sandalwood essential oil exhibited a similar potency in suppressing the viability of both J82 and UROtsa cells. Although frankincense and sandalwood essential oils activated common pathways such as inflammatory interleukins (IL-6 signaling), each essential oil had a unique molecular action on the bladder cancer cells. Heat shock proteins and histone core proteins were activated by frankincense essential oil, whereas negative regulation of protein kinase activity and G protein-coupled receptors were activated by sandalwood essential oil treatment.

CONCLUSION

The effects of frankincense and sandalwood essential oils on J82 cells and UROtsa cells involved different mechanisms leading to cancer cell death. While frankincense essential oil elicited selective cancer cell death via NRF-2-mediated oxidative stress, sandalwood essential oil induced non-selective cell death via DNA damage and cell cycle arrest.

(-)-Xanthatin induces the prolonged expression of c-Fos through an N-acetyl-L-cysteine (NAC)-sensitive mechanism in human breast cancer MDA-MB-231 cells

We reported that (-)-xanthatin, a xanthanolide sesquiterpene lactone present in the Cocklebur plant, exhibited potent anti-proliferative effects on human breast cancer cells, in which GADD45γ, a novel tumor suppressor gene, was induced. Mechanistically, topoisomerase IIα (Topo IIα) inhibition by (-)-xanthatin was shown to be the upstream trigger that stimulated the expression of GADD45γ mRNA and concomitantly produced reactive oxygen species (ROS) to maintain this expression. Since the anti-cancer drug etoposide, a selective Topo IIα inhibitor, has also been shown to induce intracellular ROS, (-)-xanthatin may exert its anti-proliferative effects on cancer cells in a similar manner to those of etoposide. In the present study, to generalize its applicability to cancer therapy, we further investigated the biological activities of (-)-xanthatin by comparing its activities to those of the established anti-cancer drug etoposide. After the exposure of breast cancer cells to (-)-xanthatin or etoposide, a prolonged and marked up-regulation in the expression of c-fos, a proapoptotic molecule, was detected together with GADD45γ; and the expression of these molecules was stabilized by ROS and abrogated by the pretreatment with N-acetyl-L-cysteine (NAC), a potent ROS scavenger. (-)-Xanthatin in particular exhibited stronger anti-proliferative potential than that of etoposide, which underlies the marked induction of c-fos/GADD45γ and ROS production.

Anandamide inhibits cholangiocyte hyperplastic proliferation via activation of thioredoxin 1/redox factor 1 and AP-1 activation

The endocannabinoid system regulates various aspects of hepatic fibrosis; however, nothing is known about its role in regulating cholangiocyte proliferation and function. We evaluated the effects of anandamide (AEA) on cholangiocyte proliferation and explored the effects of AEA on the thioredoxin 1 (TRX1)/redox factor 1 (Ref1)/activator protein-1 (AP-1) pathway. Mice underwent bile duct ligation (BDL) and were infused with AEA for 3 days postsurgery. Proliferation and apoptosis were evaluated in liver sections. Effects of in vitro AEA treatment on cholangiocyte proliferation and apoptosis were studied in purified cholangiocytes. The relative expression of cannabinoid receptors was also assessed in liver sections and cholangiocytes. mRNA expression of the cannabinoid receptors Cb1 and VR1 was decreased after BDL, whereas there was an upregulation of Cb2 mRNA. AEA decreased cholangiocyte growth and induced accumulation of reactive oxygen species, upregulation of TRX1, Ref1, c-Fos, and c-Jun expression, increased nuclear localization of TRX1, and increased AP-1 transcriptional activity. Specific knockdown of TRX1 or Ref1 expression ablated the AP-1 transcriptional activity and AEA-induced cell death but not expression of c-Fos and c-Jun. Knockdown of c-Fos and c-Jun expression also ablated AEA-induced apoptosis. We conclude that AEA suppresses cholangiocyte proliferation during cholestasis via a Cb2-dependent mechanism. Modulation of the endocannabinoid system may be important in the treatment of cholangiopathies.

Abnormal activator protein 1 transcription factor expression in CD30-positive cutaneous large-cell lymphomas

BACKGROUND

CD30+ cutaneous large-cell lymphomas (CLCL) represent a heterogeneous subgroup of skin lymphomas including primary cutaneous CD30+ anaplastic large-cell lymphoma (C-ALCL), lymphomatoid papulosis (LyP), transformed mycosis fungoides (T-MF) and Hodgkin's lymphoma (HL) with cutaneous involvement. The activator protein 1 (AP-1) transcription factor consists of JUN, FOS and other protein families. Recent studies have revealed upregulation of JUNB in both MF and C-ALCL and overexpression of JUNB and CD30 in systemic HL and ALCL.

OBJECTIVES

To assess systematically the expression pattern of AP-1 transcription factors in CLCL.

METHODS

We analysed paraffin tissue sections from 27 patients with LyP, 10 with C-ALCL, eight with T-MF and two with cutaneous HL by immunohistochemistry with antibodies against c-JUN, JUNB, JUND, c-FOS and RAF-1. We also stained samples from 10 patients with C-ALCL, seven with Sézary syndrome (SS), six with T-MF, three with cutaneous HL, two with LyP and control samples with total and phosphorylated mitogen-activated protein kinase (MAPK) antibodies. Results Positive staining for JUND (++) was observed in 13 cases of LyP (48%), 10 C-ALCL, six T-MF (75%) and two cutaneous HL cases. Positive JUNB protein expression was present in four cases of T-MF (50%), four C-ALCL (44%), three LyP (11%) and two cutaneous HL. Expression of total (p44/42) MAP kinase and phosphorylated p44/42 MAP kinase were detected in nine cases of C-ALCL (90%), seven SS (88%), five T-MF (89%) and three cutaneous HL. Most of these samples also showed positive staining for JUNB.

CONCLUSION

These results suggest the presence of abnormal AP-1 protein expression in CLCL, which may be relevant to CLCL.

PTEN down regulates AP-1 and targets c-fos in human glioma cells via PI3-kinase/Akt pathway

The continual activation of signaling cascades results in dramatic consequences that include loss of cellular growth control and neoplastic transformation. We show here that phosphoinositide 3-kinase and its mediator Akt was constitutively activated in glioma and that this might be due to the aberrant expression of their natural antagonist PTEN. The PTEN (phosphatase and tensin homologue deleted on chromosome ten) tumor suppressor gene modulates cell growth and survival through mechanisms that are incompletely understood. In this study, we investigated the possibility that PTEN mediates its effects through modulation of transcription factor AP-1, which is in part due to decrease in c-fos expression which was dependent on PI3kinase activity. Consistent with a reduction in the c-fos levels, an AP-1 dependent reporter gene was poorly induced in the PTEN expressing cell lines. In contrast to its effect on c-fos, PTEN did not affect the expression of c-Jun and other fos family members. We also show that the effect of PTEN on c-fos expression was due to its ability to antagonize PI3-kinase and could be mimicked by the expression of dominant negative Akt mutant. Taken together, these data indicate that the aberrant expression of PTEN contributes to the activation of the PI3kinase/Akt pathway and its transcription factor mediators in glioma. We conclude that the ectopic expression of PTEN down regulates the proliferation of glioma cells through the suppression of AP-1 and that this target might be essential for its central role in the growth and survival of glioma cancer cells.

cFos is critical for MCF-7 breast cancer cell growth

The activating protein-1 (AP-1) transcription factor is a converging point of multiple signal transduction pathways in many cells. We have previously demonstrated that overexpressing Tam67, a dominant-negative (DN) form of cJun, blocks AP-1 activity and inhibits breast cancer cell growth. We hypothesized that Tam67 forms dimers with other AP-1 proteins to suppress the growth of breast cancer cells. In the present study, we used immunoprecipitation-Western blotting to demonstrate that Tam67 binds all Jun and Fos proteins in breast cancer cells. In addition, we used two variants of the Tam67 mutant to investigate whether Jun or Fos protein was required for breast cancer cell growth. We created a Tam/Fos mutant in which the cJun dimerization domain was replaced by the cFos dimerization domain, and a Tam/Squelcher mutant in which the cJun dimerization domain was deleted. We then isolated MCF-7 cell lines that stably expressed these cJun-DN mutants under the control of an inducible promoter. Using AP-1-dependent reporter assays, we observed that Tam67 and Tam/Fos mutants inhibited AP-1 transcriptional activity, while the Tam/Squelcher mutant did not. We then determined whether Tam/Fos or Tam/Squelcher inhibited breast cell growth as well as Tam67. We found that while Tam67 repressed cell growth, neither Tam/Fos nor Tam/Squelcher mutant affected cell growth. These results indicate that Tam67 likely inactivates Fos family member proteins to suppress breast cancer cell growth. Finally, we performed antisense experiments to knock down the expression of individual family members (cJun or cFos). Our results demonstrated that antisense cFos inhibited breast cancer cell proliferation and colony formation, while antisense cJun did not. These results suggest that Tam67 suppresses breast cancer cell growth by interacting with Fos family members, specifically with cFos, to produce an inactive AP-1 complex.

AP-1 in mouse development and tumorigenesis

Genetically modified mice have provided important insights into the biological functions of the dimeric transcription factor complex AP-1. Extensive analyses of mice and cells with genetically modified Fos or Jun proteins provide novel insights into the physiological functions of AP-1 proteins. Using knock-out strategies it was found that some components, such as c-Fos, FosB and JunD are dispensable, whereas others, like c-Jun, JunB and Fra-1 are essential in embryonic development and/or in the adult organism. Besides the specific roles of AP-1 proteins in developmental processes, we are beginning to obtain a better molecular understanding of the cell-context dependent function of AP-1 in cell proliferation and apoptosis, in bone biology as well as in multistep tumorigenesis.

The mammalian Jun proteins: redundancy and specificity

The AP-1 transcription factor is composed of a mixture of homo- and hetero-dimers formed between Jun and Fos proteins. The different Jun and Fos family members vary significantly in their relative abundance and their interactions with additional proteins generating a complex network of transcriptional regulators. Thus, the functional activity of AP-1 in any given cell depends on the relative amount of specific Jun/Fos proteins which are expressed, as well as other potential interacting proteins. This diversity of AP-1 components has complicated our understanding of AP-1 function and resulted in a paucity of information about the precise role of individual AP-1 members in distinct cellular processes. We shall discuss recent studies which suggest that different Jun and Fos family members may have both opposite and overlapping functions in cellular proliferation and cell fate.

The role of AP-1 in glucocorticoid resistance in leukaemia

Glucocorticoids are used in the treatment of acute lymphoblastic leukaemia (ALL) and chronic lymphocytic leukaemia (CLL) but many patients develop glucocorticoid resistance on relapse. The ligand-activated glucocorticoid receptor inhibits activity of the AP-1 transcription factor and the purpose of this study was to test the hypothesis that up-regulation or overexpression of AP1-binding activity may be an important mechanism of glucocorticoid resistance in ALL and CLL. In vitro sensitivity of patient blasts to prednisolone was measured using th

Apoptosis: A Current Molecular Analysis

Apoptosis is a cell suicide program characterized by distinct morphological (cell shrinkage, membrane blebbing, pyknosis, chromatin margination, denser cytoplasmic images) and biochemical (e.g., DNA fragmentation into distinct ladders; degradation of apoptotic markers such as PARP and nuclear lamins) features. It is involved in multiple physiological processes examplified by involution of mammary tissues, embryonic development, homeostatic maintenance of tissues and organs, and maturation of the immune system, as well as in many pathological conditions represented by neurologic degeneration (Alzeimer's disease), autoimmune and inflammatory diseases, etiology of atherosclerosis, AIDS, and oncogenesis and tumor progression. Numerous molecular entities have been shown to regulate the apoptotic process. This review provides a concise summary of the recent data on the role of oncogenes/tumor suppressor genes, cytokines and growth factors/growth factor receptors, intracellular signal transducers, cell cycle regulators, reactive oxygen species or other free radicals, extracellular matrix regulators/cell adhesion molecules, and specific endonucleases and cytoplasmic proteases (the ICE family proteins) in regulating cell survival and apoptosis. Elucidation of the molecular mechanisms regulating apoptosis bears tremendous impact on enhancing our understanding of many diseases inflicting the human beings and undoubtedly brings us hope for the cure of these diseases.

Molecular mechanisms implicated in galectin-1-induced apoptosis: activation of the AP-1 transcription factor and downregulation of Bcl-2

Galectins are emerging as a new class of bioactive molecules with specific immunomodulatory properties. Galectin-1 (Gal-1), a member of this family, has been shown to induce apoptosis of mature T cells and immature thymocytes. To gain insight into the intracellular signals transduced by Gal-1 upon binding to mature T cells, we investigated whether this protein triggered activation of the dimeric AP-1 transcription factor. A marked increase in the binding of nuclear extracts to synthetic oligonucleotides containing the AP-1 consensus sequence, could be detected by an electrophoretic mobility shift assay, when T cells were cultured for 30 min in the presence of Gal-1. This DNA-binding activity was preceded by a rapid increase in the levels of c-Jun mRNA, as determined by Northern blot analysis. Requirement of AP-1 for Gal-1-induced apoptosis was confirmed by the dose-dependent reduction on the level of DNA fragmentation observed when cells were pre-treated with curcumin (an inhibitor of AP-1 activation) before exposure to Gal-1. Finally, evidence is also provided by Western blot analysis, showing that Gal-1 inhibits Concanavalin A (Con A) induction of Bcl-2 protein. Results presented in this study provide the first experimental evidence regarding AP-1 and Bcl-2 as targets of the signal transduction pathway triggered by Gal-1 and set the basis for a more in depth understanding of the molecular mechanisms of T-cell death regulation.

c-fos controls the "private pathway" of light-induced apoptosis of retinal photoreceptors

White light (5 klux for 2 hr) induces apoptosis of rod photoreceptors in wild-type mice (c-fos(+/+)) within 24 hr, whereas rods of c-fos knock-out mice (c-fos(-/-)) are protected (). The range of this protection was tested by analyzing retinas of c-fos(+/+) and c-fos(-/-) mice up to 10 d after exposure to threefold increased light intensities (15 klux for 2 hr). In c-fos(-/-) mice, rods were unaffected, whereas they were destroyed in c-fos(+/+) mice. After light exposure, mitochondrial damage in rods was observed exclusively in c-fos(+/+) mice. Electroretinograms recorded 48 hr after exposure revealed a decrease of all components in c-fos(+/+) mice but indicated no light-induced loss of function in c-fos(-/-) mice. Thus, in c-fos(-/-) mice, light-induced apoptosis is blocked or its threshold is elevated more than threefold. Increased activity of the transcription factor activator protein-1 (AP-1) in retinas of light-exposed c-fos(+/+) mice indicated an acute contribution of AP-1 to apoptosis induction. AP-1 activity increased already during exposure and peaked approximately 6 hr thereafter, coinciding with the appearance of major morphological signs of apoptosis. Activated AP-1 mainly consisted of c-Fos/Jun heterodimers. In c-fos(-/-) mice, AP-1 activity remained unchanged, indicating that no other Jun- or Fos-family member could substitute for c-Fos. Like damaging light, N-methyl-N-nitrosourea (MNU) induced AP-1 containing c-Fos in c-fos(+/+) mice and did not induce AP-1 in c-fos(-/-) mice. In contrast to light, however, MNU induced apoptosis in rods of c-fos(-/-) mice. Thus, c-Fos is essential for a specific premitochondrial "private apoptotic pathway" induced by light but not for the execution of apoptosis induced by other stimuli.

Changes of the trans-activating potential of AP-1 transcription factor during cyclosporin A-induced apoptosis of glioma cells are mediated by phosphorylation and alterations of AP-1 composition

Although the AP-1 transcription factor is known to play a role in cell proliferation and activation, it is also involved in apoptosis of cells in response to stress, DNA-damaging agents, or lack of survival signals. To understand how AP-1 might contribute to distinct biological processes, we tested a hypothesis that changes in AP-1 composition or phosphorylation state modulate its transcriptional activity during cyclosporin A-induced apoptosis of glioma cells. The induction of AP-1 DNA binding activity composed of c-Jun, JunB, JunD, and ATF-2 proteins preceded apoptosis. The compositional changes of AP-1 were associated with an elevation of c-Jun and JunB protein levels and the appearance of phosphorylated c-Jun and ATF-2 at 15-40 h posttreatment. Immunocytochemistry and staining with Hoechst 33258 revealed an accumulation of phosphorylated c-Jun protein in apoptotic cells. Because c-Jun expression and transcriptional activity are stimulated by phosphorylation at Ser63/73 by c-Jun N-terminal kinase (JNK), we measured JNK activities. We found prolonged induction of JNK activity in extracts from cyclosporin-treated cells, which suggests an involvement of persistent JNK activation in the initiation of glioma cell apoptosis. We provided evidence that variations in AP-1 composition and phosphorylation resulted in modification of trans-activating potential toward different promoters. Whereas collagenase AP-1/TRE-dependent transcription was down-regulated during apoptosis, Fas ligand promoter became activated.

Is Fos protein expressed by dying striatal neurons after immature hypoxic-ischemic brain injury?

The transient induction of mRNA for the immediate-early gene c-fos has been reported following hypoxic-ischemic brain injury in the immature brain. However, no studies have examined the temporal expression of Fos protein, which is the functionally relevant product of c-fos gene expression. Increased expression of Fos protein has been linked to cell death. We therefore examined whether Fos protein is expressed by dying neurons after immature hypoxic-ischemic brain injury. A well characterized immature rat model of hypoxic-ischemic injury at postnatal day (PN) 7 was used. Three hypoxic-ischemic and three normoxic control pups were studied per time point (i.e., 0, 2, 12, 24, 48, and 72 h posttreatment). Expression of Fos within striatal and other neurons was detected immunocytochemically. Fos protein was expressed within dying striatal neurons at 0-12 h after hypoxia-ischemia. However, detection was only seen in 2 of 17 hypoxic-ischemic pups. These 2 pups had >/=80% of their striatal neurons dying within their right, hypoxic-ischemic-exposed hemisphere. Fos protein expression after severe injury may, therefore, be a response to extraordinary or extreme stress. The absence of Fos protein expression in the majority of hypoxic-ischemic pups, which all exhibited striatal neuronal death, suggests that Fos expression is not necessary for cell death to occur. Therapies directed against Fos protein expression may therefore have limited usefulness in immature hypoxic-ischemic brain injury.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Apoptosis in developing retinal tissue

The mechanisms of apoptosis are strongly dependent on cell-cell interactions typical of organized tissues. Experimental studies of apoptosis using a histotypical preparation of retinal explants are reported in the present article. We found that various characteristics of apoptosis are selectively associated with retinal cell death depending on cell type, stage of maturation, and means of induction of apoptosis. Among these were: (1) the requirements of protein synthesis; (2) the role of cAMP; (3) the expression of certain apoptosis-associated proteins; and (4) the sensitivity to excitotoxicity, modulation of protein phosphatases and calcium mobilization. Dividing cells undergo apoptosis in response to several inducers in specific phases of the cell cycle, and in distinct regions within their pathway of interkinetic nuclear migration. Recent post-mitotic cells are selectively sensitive to apoptosis induced by blockade of protein synthesis, while both proliferating and differentiated cells are more resistant. We also studied the association of several proteins, some of which play critical roles in the cell cycle, with both differentiation and apoptosis in the retinal tissue. Detection of cell cycle markers did not support the hypothesis that retinal cells re-enter the cell cycle on their pathway to apoptosis, although some proteins associated with cell proliferation re-appeared in degenerating cells. The transcription factors c-Jun, c-Fos and c-Myc were found associated with apoptosis in retinal cells, but their sub-cellular location in apoptotic bodies is not consistent with their canonical functions in the control of gene expression. The bifunctional redox factor/AP endonuclease Ref-1 and the transcription factor Max are associated with progressive cell differentiation, and both are down-regulated during cell death in the retina. The data suggest that Ref-1 and Max may normally function as negative modulators of retinal apoptosis. The results indicate that nuclear exclusion of transcription factors and other important control proteins is a hallmark of retinal apoptosis. Histotypical explants may be a choice preparation for the experimental analysis of the mechanisms of apoptosis, in the context both of cell-cell interactions and of the dynamic behavior of developing cells within the organized retinal tissue.

Regulation of MCL1 through a serum response factor/Elk-1-mediated mechanism links expression of a viability-promoting member of the BCL2 family to the induction of hematopoietic cell differentiation

Proliferation, differentiation, and apoptosis are tightly regulated during hematopoiesis, allowing amplification along specific lineages while preventing excessive proliferation of immature cells. The MCL1 member of the BCL2 family is up-regulated during the induction of monocytic differentiation (approximately 10-fold with 12-O-tetradecanoylphorbol 13-acetate (TPA)). MCL1 has effects similar to those of BCL2, up-regulation promoting viability, but differs from BCL2 in its rapid inducibility and its pattern of expression. Nuclear factors that regulate MCL1 transcription have now been identified, extending the previous demonstration of signal transduction through mitogen-activated protein kinase. A 162-base pair segment of the human MCL1 5'-flank was found to direct luciferase reporter activity, allowing approximately 10-fold induction with TPA that was suppressible upon inhibition of the extracellular signal-regulated kinase (ERK) pathway. Serum response factor (SRF), Elk-1, and Sp1 bound to cognate sites within this segment, SRF and Elk-1 acting coordinately to affect both basal activity and TPA inducibility, whereas Sp1 affected basal activity only. Thus, the mechanism of the TPA-induced increase in MCL1 expression seen in myelomonocytic cells at early stages of differentiation involves signal transduction through ERKs and transcriptional activation through SRF/Elk-1. This finding provides a parallel to early response genes (e.g. c-FOS and EGR1) that affect maturation commitment in these cells and therefore suggests a means through which enhancement of cell viability may be linked to the induction of differentiation.

Apoptotic cell death in retinal degenerations

Apoptosis is a regulated mode of single cell death that involves gene expression in many instances and occurs under physiological and pathological conditions in a large variety of systems. We briefly summarize major features of apoptosis in general and describe the occurrence of apoptosis in the retina in different situations that comprise animal models of retinitis pigmentosa, light-induced lesions, histogenesis during development, and others. Apoptosis can be separated into several phases: the induction by a multitude of stimuli, the effector phase in which the apoptotic signal is transmitted to the cellular death machinery, the excecution period when proteolytic cascades are activated, and the phagocytic removal of cellular remnants. Control mechanisms for retinal apoptosis are only beginning to be clarified. Potential apoptotic signal transducers were investigated in our laboratory, including metabolites of arachidonic acid and downstream mediators of signaling molecules such as transcription factors. Work in our laboratory revealed an essential role of the immediate-early gene product c-Fos in light-induced apoptosis. c-Fos is a member of the AP-1 family of transcription factors and, together with other members of this family, it may regulate apoptosis in the central nervous system. Expression of the c-fos gene in the retina can be evoked by light exposure and follows a diurnal rhythm. Future studies will have to clarify how light can control the expression of specific genes, and specifically, the role of c-fos and other genes of retinal apoptosis including potential target genes and signaling pathways.

AP1 regulation of proliferation and initiation of apoptosis in erythropoietin-dependent erythroid cells

The transcription factor AP1 has been implicated in the induction of apoptosis in cells in response to stress factors and growth factor withdrawal. We report here that AP1 is necessary for the induction of apoptosis following hormone withdrawal in the erythropoietin (EPO)-dependent erythroid cell line HCD57. AP1 DNA binding activity increased upon withdrawal of HCD57 cells from EPO. A dominant negative AP1 mutant rendered these cells resistant to apoptosis induced by EPO withdrawal and blocked the downregulation of Bcl-XL. JunB is a major binding protein in the AP1 complex observed upon EPO withdrawal; JunB but not c-Jun was present in the AP1 complex 3 h after EPO withdrawal in HCD57 cells, with a concurrent increase in junB message and protein. Furthermore, analysis of AP1 DNA binding activity in an apoptosis-resistant subclone of HCD57 revealed a lack of induction in AP1 DNA binding activity and no change in junB mRNA levels upon EPO withdrawal. In addition, we determined that c-Jun and AP1 activities correlated with EPO-induced proliferation and/or protection from apoptosis. AP1 DNA binding activity increased over the first 3 h following EPO stimulation of HCD57 cells, and suppression of AP1 activity partially inhibited EPO-induced proliferation. c-Jun but not JunB was present in the AP1 complex 3 h after EPO addition. These results implicate AP1 in the regulation of proliferation and survival of erythroid cells and suggest that different AP1 factors may play distinct roles in both triggering apoptosis (JunB) and protecting erythroid cells from apoptosis (c-Jun).

Involvement of c-Jun NH2-terminal kinase activation and c-Jun in the induction of apoptosis by the ether phospholipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine

The ether phospholipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3; edelfosine) is a potent inducer of apoptosis in human tumor cells. We show that ET-18-OCH3-induced apoptosis is associated with activation of the c-Jun NH2-terminal kinase (JNK) signaling. The addition of ET-18-OCH3 to distinct human leukemic cells (HL-60, U937, and Jurkat), which undergo rapid apoptosis on treatment with ET-18-OCH3, induced a dramatic and sustained increase in the of c-jun mRNA level that was associated with activation of activator protein-1 transcription factor. We found that ET-18-OCH3 induced a persistent activation of JNK in HL-60 cells that was detected before the onset of apoptosis, the latter being assessed by DNA fragmentation and by the appearance of phosphatidylserine on the external leaflet of the plasma membrane. The inductions of JNK after HL-60 monocyte/macrophage differentiation and ET-18-OCH3-mediated apoptosis were distinguished by the different activation patterns, transient versus persistent, respectively. ET-18-OCH3 analogues unable to induce apoptosis failed to activate JNK. ET-18-OCH3-dependent JNK activation was not detected in K562 cells, which did not undergo apoptosis on treatment with ET-18-OCH3. Phorbol myristate acetate inhibited both ET-18-OCH3-induced apoptosis and sustained JNK activation; thus, persistent JNK activation by ET-18-OCH3 is associated with the capacity of this ether phospholipid to induce apoptosis. Furthermore, antisense oligonucleotides directed against c-jun blocked ET-18-OCH3-induced apoptosis, indicating a role for c-Jun in this apoptotic response. These data indicate that JNK activation and c-Jun are involved in the induction of apoptosis by ET-18-OCH3.

The roles of mitotic arrest and protein synthesis in induction of apoptosis and differentiation in neuroblastoma cells in culture

Studies of the response of neural crest tumor cells to the DNA cleaving antimitotic agent, neocarzinostatin, have left unanswered the question of whether the DNA cleavage per se or the antimitotic effect is responsible for this response. Furthermore, they do not define the timeframe within which a cell commits to its fate. Using the reversible microtubule-active agent, vinblastine, we now demonstrate that mitotic arrest, even without DNA cleavage, results in the same cellular changes as those seen with neocarzinostatin treatment. The commitment of the cell to its fate occurs within a 15 min treatment with vinblastine, and requires new protein synthesis. The immediate early gene products, c-Fos and c-Jun, appear not to be determinants of this process.

Biochemical and molecular mechanisms regulating apoptosis

In eukaryotes, the regulation of tissue cell numbers is a critical homeostatic objective that is achieved through tight control of apoptosis, mitosis and differentiation. While much is known about the genetic regulation of cell growth and differentiation, the molecular basis of apoptosis is less well understood. Genes involved in both cell proliferation and apoptosis reflect the role of some stimuli in both of these processes, the cell response depending on the overall cellular milieu. Recent research has given fascinating insights into the complex genetic and molecular mechanisms regulating apoptosis. A picture is emerging of the initiation in certain cells, after an apoptotic trigger, of sequential gene expression and specific signal transduction cascades that guide cells along the cell death pathway. Changes in gene expression precede the better known biochemical and morphological changes of apoptosis. It seems possible that, as a result of increased understanding of the cellular events preceding cell death, apoptosis may become more amenable to manipulation by appropriate drug- and gene-based therapies.

Zinc metabolism in the brain: relevance to human neurodegenerative disorders

Zinc is an important trace element in biology. An important pool of zinc in the brain is the one present in synaptic vesicles in a subgroup of glutamatergic neurons. In this form it can be released by electrical stimulation and may serve to modulate responses at receptors for a number of different neurotransmitters. These include both excitatory and inhibitory receptors, particularly the NMDA and GABA(A) receptors. This pool of zinc is the only form of zinc readily stained histochemically (the chelatable zinc pool), but constitutes only about 8% of the total zinc content in the brain. The remainder of the zinc is more or less tightly bound to proteins where it acts either as a component of the catalytic site of enzymes or in a structural capacity. The metabolism of zinc in the brain is regulated by a number of transport proteins, some of which have been recently characterized by gene cloning techniques. The intracellular concentration may be mediated both by efflux from the cell by the zinc transporter ZrT1 and by complexing with apothionein to form metallothlonein. Metallothionein may serve as the source of zinc for incorporation into proteins, including a number of DNA transcription factors. However, zinc is readily released from metallothionein by disulfides, increasing concentrations of which are formed under oxidative stress. Metallothionein is a very good scavenger of free radicals, and zinc itself can also reduce oxidative stress by binding to thiol groups, decreasing their oxidation. Zinc is also a very potent inhibitor of nitric oxide synthase. Increased levels of chelatable zinc have been shown to be present in cell cultures of immune cells undergoing apoptosis. This is very reminiscent of the zinc staining of neuronal perikarya dying after an episode of ischemia or seizure activity. Thus a possible role of zinc in causing neuronal death in the brain needs to be fully investigated. intraventricular injections of calcium EDTA have already been shown to reduce neuronal death after a period of ischemia. Pharmacological doses of zinc cause neuronal death, and some estimates indicate that extracellular concentrations of zinc could reach neurotoxic levels under pathological conditions. Zinc is released in high concentrations from the hippocampus during seizures. Unfortunately, there are contrasting observations as to whether this zinc serves to potentiate or decrease seizure activity. Zinc may have an additional role in causing death in at least some neurons damaged by seizure activity and be involved in the sprouting phenomenon which may give rise to recurrent seizure propagation in the hippocampus. In Alzheimer's disease, zinc has been shown to aggregate beta-amyloid, a form which is potentially neurotoxic. The zinc-dependent transcription factors NF-kappa B and Sp1 bind to the promoter region of the amyloid precursor protein (APP) gene. Zinc also inhibits enzymes which degrade APP to nonamyloidogenic peptides and which degrade the soluble form of beta-amyloid. The changes in zinc metabolism which occur during oxidative stress may be important in neurological diseases where oxidative stress is implicated, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS). Zinc is a structural component of superoxide dismutase 1, mutations in which give rise to one form of familiar ALS. After HIV infection, zinc deficiency is found which may be secondary to immune-induced cytokine synthesis. Zinc is involved in the replication of the HIV virus at a number of sites. These observations should stimulate further research into the role of zinc in neuropathology.

Expression of Fos, Jun, and Krox family proteins in Alzheimer's disease

Apoptosis is an active process of cell death characterized by distinct morphological features and is often the end result of a genetic program of events, i.e., programmed cell death (PCD). There is growing evidence supporting a role for apoptosis and/or PCD in Alzheimer's disease (AD), based on DNA fragmentation studies and recent findings of increased levels of inducible transcription factors (ITFs) such as c-Jun in AD brains. We have characterized the expression of a large range of ITFs (c-Fos, Fos B, Fos-related antigens, c-Jun, Jun B, Jun D, Krox20, and Krox24) using multiple antisera in AD postmortem hippocampi and compared this with human control hippocampi as well as Huntington's disease hippocampi and human epilepsy biopsy tissue. We found little evidence of nuclear expression of any ITF except c-Jun in the human postmortem tissue, compared with nuclear staining in biopsy tissue. We found some evidence for increased levels of c-Jun and Krox24 protein and krox24 mRNA in the CA1 region of AD hippocampi, suggesting that PCD may be involved in the pathogenesis of AD. In general, staining characteristics of ITFs varied with different antisera directed against the same protein, indicating the need for caution when interpreting results.

AP-1 function and regulation

AP-1 (activating protein-1) is a collective term referring to dimeric transcription factors composed of Jun, Fos or ATF (activating transcription factor) subunits that bind to a common DNA site, the AP-1-binding site. As the complexity of our knowledge of AP-1 factors has increased, our understanding of their physiological function has decreased. This trend, however, is beginning to be reversed due to the recent studies of gene-knockout mice and cell lines deficient in specific AP-1 components. Such studies suggest that different AP-1 factors may regulate different target genes and thus execute distinct biological functions. Also, the involvement of AP-1 factors in functions such as cell proliferation and survival has been made somewhat clearer as a result of such studies. In addition, there has been considerable progress in understanding some of the mechanisms and signaling pathways involved in the regulation of AP-1 activity. In addition to regulation by heterodimerization between Jun, Fos and ATF proteins, AP-1 activity is regulated through interactions with specific protein kinases and a variety of transcriptional coactivators.

Cryptic brain cell injury caused by fetal nicotine exposure is associated with persistent elevations of c-fos protooncogene expression

Neurobehavioral teratogenesis caused by prenatal nicotine exposure is associated with deficiencies in brain cell numbers that reflect, in part, effects on cell replication but that also involve delayed cell loss. In the current study, pregnant rats were given nicotine by implanted minipump infusion either from gestational days 4-12 or 4-21 and fetal and neonatal brain regions were examined for expression of the mRNA encoding c-fos, a nuclear transcription factor that becomes chronically elevated when cell injury or apoptosis are occurring. Fetuses exposed to nicotine on gestational days 4-12 did not show elevations of c-fos mRNA on gestational day 18 whereas animals undergoing exposure through day 21 did. In the latter group, elevated c-fos expression was still present on postnatal day 2 despite the cessation of nicotine exposure on gestational day 21. In contrast to the elevation of c-fos seen with prenatal nicotine, postnatal nicotine injections given to 2-day-old rats did not cause acute stimulation of c-fos expression. The ability of injected nicotine to evoke acute rises in c-fos emerged by postnatal day 8 and initially displayed regional specificity paralleling the concentration of nicotinic cholinergic receptors. With increasing maturity, regional selectivity of the c-fos response to acute nicotine was lost, consistent with indirect actions that could be mediated through nicotine-induced hypoxia/ischemia. These results indicate that prenatal nicotine exposure causes chronic elevations of c-fos expression in fetal and neonatal brain that are distinguishable from the later onset of the ability of acute nicotine to cause short-term stimulation of c-fos. The critical period and dose threshold for these effects correspond to those of subsequent cell damage and cell loss identified in previous studies with fetal nicotine exposure. Given that chronic elevations of c-fos are known to be associated with cell injury and to evoke apoptosis in otherwise healthy cells, these results suggest that prenatal nicotine exposure evokes delayed neurotoxicity by altering the program of neural cell differentiation, and that elevated c-fos expression provides an early marker of the eventual deficits.