Ultraviolet-induced junD activation and apoptosis in myeloblastic leukemia ML-1 cells

Krüppel-Like Factor 4 and Its Activator APTO-253 Induce NOXA-Mediated, p53-Independent Apoptosis in Triple-Negative Breast Cancer Cells

Inducing apoptosis is an effective treatment for cancer. Conventional cytotoxic anticancer agents induce apoptosis primarily through activation of tumor suppressor p53 by causing DNA damage and the resulting regulation of B-cell leukemia/lymphoma-2 (BCL-2) family proteins. Therefore, the effects of these agents are limited in cancers where p53 loss-of-function mutations are common, such as triple-negative breast cancer (TNBC). Here, we demonstrate that ultraviolet (UV) light-induced p53-independent transcriptional activation of NOXA, a proapoptotic factor in the BCL-2 family, results in apoptosis induction. This UV light-induced NOXA expression was triggered by extracellular signal-regulated kinase (ERK) activity. Moreover, we identified the specific UV light-inducible DNA element of the NOXA promoter and found that this sequence is responsible for transcription factor Krüppel-like factor 4 (KLF4)-mediated induction. In p53-mutated TNBC cells, inhibition of KLF4 by RNA interference reduced NOXA expression. Furthermore, treatment of TNBC cells with a KLF4-inducing small compound, APTO-253, resulted in the induction of NOXA expression and NOXA-mediated apoptosis. Therefore, our results help to clarify the molecular mechanism of DNA damage-induced apoptosis and provide support for a possible treatment method for p53-mutated cancers.

IER5 as a promising predictive marker promotes irradiation-induced apoptosis in cervical cancer tissues from patients undergoing chemoradiotherapy

Purpose

To define the role of immediate-early 5 (IER5) gene as a promising biomarker in predicting the radiosensitivity and prognosis of cervical cancer patients receiving cisplatin-based concurrent chemoradiotherapy (DDP-CCRT).

Results

Our investigations found that IER5 level was markedly elevated in cervical cancer patients after being treated with irradiation, which indicated IER5 was closely dose induced. By contrast, the correlation between IER5 and radiosensitivity cannot be confirmed by the present study. The up-regulation of IER5 expression effectively increased cell apoptosis after administration of irradiation (P < 0.05). Using an ANOVA model for repeated-measures, we found significant association between the IER5 level and tumor size (P < 0.05).

Materials and Methods

Forty-three cervical cancer patients stage II_b-III_b received DDP-CCRT were registered. Biopsy tissues were obtained after administration of irradiation dose of 0 Gy, 2~6 Gy, 10 Gy, 20 Gy, 30 Gy, respectively. The IER5 protein and mRNA levels were measured by immunohistochemistry, western blot and quantitative polymerase chain reaction, respectively; besides, the apoptosis rate was assessed by transferase-mediated dUTP nick end labeling.

Conclusions

Mechanistically, we confirmed that IER5 induced by radiation dose enhanced apoptosis of cervical cancer, was inversely associated with tumor size. In conclusion, our studies indicate target IER5 is improved to be a potential radiosensitizer for developing effective therapeutic strategies against cervical cancer to radiotherapy and a predictive biomarker for radiosensitivity.

LILRB1 polymorphisms influence posttransplant HCMV susceptibility and ligand interactions

UL18 is a human CMV (HCMV) MHC class I (MHCI) homolog that efficiently inhibits leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1)+ NK cells. We found an association of LILRB1 polymorphisms in the regulatory regions and ligand-binding domains with control of HCMV in transplant patients. Naturally occurring LILRB1 variants expressed in model NK cells showed functional differences with UL18 and classical MHCI, but not with HLA-G. The altered functional recognition was recapitulated in binding assays with the binding domains of LILRB1. Each of 4 nonsynonymous substitutions in the first 2 LILRB1 immunoglobulin domains contributed to binding with UL18, classical MHCI, and HLA-G. One of the polymorphisms controlled addition of an N-linked glycan, and that mutation of the glycosylation site altered binding to all ligands tested, including enhancing binding to UL18. Together, these findings indicate that specific LILRB1 alleles that allow for superior immune evasion by HCMV are restricted by mutations that limit LILRB1 expression selectively on NK cells. The polymorphisms also maintained an appropriate interaction with HLA-G, fitting with a principal role of LILRB1 in fetal tolerance.

UVB induces apoptosis via downregulation of CALML3-dependent JNK1/2 and ERK1/2 pathways in cataract

The aim of the current study was to understand the mechanisms of apoptosis occurring in cultured human lens epithelial cells (HLECs) following ultraviolet B (UVB) irradiation. The investigations intended to confirm the presence of apoptosis and to reveal the roles of oxidative stress, calcium (Ca2+), c‑Jun NH2‑terminal kinase (JNK)1/2, and extracellular signal‑regulated kinase (ERK)1/2 signaling pathway in these progresses. Cell apoptosis, ROS generation and intracellular Ca2+ concentration was measured by flow cytometry. The expression of CALML3, caspase-3, Bax, Bcl-2, p-JNK1/2, JNK1/2, p-ERK1/2 and ERK1/2 was measured by RT-qPCR and western blot analysis. Annexin V‑fluorescein isothiocyanate/propidium iodide staining demonstrated that UVB irradiation increased the apoptotic rate, reactive oxygen species (ROS) production and intracellular Ca2+ concentration of HLECs in dose‑ and time‑dependent manners. Overexpression of calmodulin like 3 (CALML3) reversed the effects of UVB irradiation on apoptosis, ROS production and Ca2+ concentration of HLECs, and decreased expressions of caspase‑3 and Bax, with increased expressions of Bcl‑2. Notably, silencing of CALML3 had similar effects to UVB irradiation and inhibited the activation JNK1/2 and ERK1/2 pathways. Nimodipine, a Ca2+‑channel antagonist, significantly attenuated the damages induced by CALML3 downregulation. In conclusion, UVB irradiation induced increase in apoptosis, ROS production and Ca2+ concentration of HLECs, in part, by downregulating the expression of CALML3 and involved oxidative stress, Ca2+, JNK1/2 and ERK1/2 signaling pathways, suggesting that investigating CALML3 may useful for developing cataract treatment.

Derivation of marker gene signatures from human skin and their use in the interpretation of the transcriptional changes associated with dermatological disorders

Numerous studies have explored the altered transcriptional landscape associated with skin diseases to understand the nature of these disorders. However, data interpretation represents a significant challenge due to a lack of good maker sets for many of the specialized cell types that make up this tissue, whose composition may fundamentally alter during disease. Here we have sought to derive expression signatures that define the various cell types and structures that make up human skin, and demonstrate how they can be used to aid the interpretation of transcriptomic data derived from this organ. Two large normal skin transcriptomic datasets were identified, one RNA-seq (n = 578), the other microarray (n = 165), quality controlled and subjected separately to network-based analyses to identify clusters of robustly co-expressed genes. The biological significance of these clusters was then assigned using a combination of bioinformatics analyses, literature, and expert review. After cross comparison between analyses, 20 gene signatures were defined. These included expression signatures for hair follicles, glands (sebaceous, sweat, apocrine), keratinocytes, melanocytes, endothelia, muscle, adipocytes, immune cells, and a number of pathway systems. Collectively, we have named this resource SkinSig. SkinSig was then used in the analysis of transcriptomic datasets for 18 skin conditions, providing in-context interpretation of these data. For instance, conventional analysis has shown there to be a decrease in keratinization and fatty metabolism with age; we more accurately define these changes to be due to loss of hair follicles and sebaceous glands. SkinSig also highlighted the over-/under-representation of various cell types in skin diseases, reflecting an influx in immune cells in inflammatory disorders and a relative reduction in other cell types. Overall, our analyses demonstrate the value of this new resource in defining the functional profile of skin cell types and appendages, and in improving the interpretation of disease data. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Repurposing L-Menthol for Systems Medicine and Cancer Therapeutics? L-Menthol Induces Apoptosis through Caspase 10 and by Suppressing HSP90

The objective of the present study was to repurpose L-menthol, which is frequently used in oral health and topical formulations, for cancer therapeutics. In this article, we argue that monoterpenes such as L-menthol might offer veritable potentials in systems medicine, for example, as cheaper anti-cancer compounds. Other monoterpenes such as limonene, perillyl alcohol, and geraniol have been shown to induce apoptosis in various cancer cell lines, but their mechanisms of action are yet to be completely elucidated. Earlier, we showed that L-menthol modulates tubulin polymerization and apoptosis to inhibit cancer cell proliferation. In the present report, we used an apoptosis-related gene microarray in conjunction with proteomics analyses, as well as in silico interpretations, to study gene expression modulation in human adenocarcinoma Caco-2 cell line in response to L-menthol treatment. The microarray analysis identified caspase 10 as the important initiator caspase, instead of caspase 8. The proteomics analyses showed downregulation of HSP90 protein (also corroborated by its low transcript abundance), which in turn indicated inhibition of AKT-mediated survival pathway, release of pro-apoptotic factor BAD from BAD and BCLxL complex, besides regulation of other factors related to apoptosis. Based on the combined microarray, proteomics, and in silico data, a signaling pathway for L-menthol-induced apoptosis is being presented for the first time here. These data and literature analysis have significant implications for "repurposing" L-menthol beyond oral medicine, and in understanding the mode of action of plant-derived monoterpenes towards development of cheaper anticancer drugs in future.

Gene expression profile analysis of SUDHL6 cells with siRNA-mediated BCL11A downregulation

Our previous study has shown that downregulation of B-cell chronic lymphocytic leukemia (CLL)/lymphoma11A (BCL11A) gene by small interfering RNA (siRNA) resulted in the growth inhibition and apoptosis of B cell lymphoma cell line SUDHL6. To gain further insight into the molecular mechanisms of this process and identify the differentially expressed genes in SUDHL6 cells after BCL11A downregulation, the global gene expression profile was identified and analyzed using the Affymetrix HG-U133 Plus 2.0 array. Twenty-one differentially expressed genes were validated and analyzed from the BCL11A siRNA-treated SUDHL6 cells. There was a significant dysregulation in the global gene expression of the BCL11A-suppressed SUDHL6 cells. There were 1903 genes differentially expressed with >2-fold changes between the BCL11A siRNA- and negative control-transfected cells. Of these, there were 916 upregulated genes and 987 downregulated genes. The differential genes are involved in various molecular functions and signaling pathways. QRT-PCR validation of the selected differentially expressed genes demonstrated there was a good correlation with the microarray analysis. There was a significant deregulation of expression in the apoptosis-related genes such as BCL-2, BCL2L11 and involved in TGFβ, MAPK, WNT signaling pathways after BCL11A was downregulated in SUDHL6 cells. Our results show that the suppression of BCL11A by RNA interference altered gene expression profile of SUDHL6 cells. The apoptosis-related genes BCL-2, BCL2L11 and the gene alterations in TGFβ, MAPK, WNT signaling pathways might be important in BCL11A siRNA-induced apoptosis of SUDHL6 cells, suggesting BCL11A is involved in gene networks associated with apoptosis.

Epidermal growth factor (EGF)-induced corneal epithelial wound healing through nuclear factor κB subtype-regulated CCCTC binding factor (CTCF) activation

Epidermal growth factor (EGF) plays an important role in corneal epithelial migration and proliferation to improve the wound healing process. This study aimed to understand the role of NFκB in EGF-induced corneal epithelial wound healing through regulation of CTCF activity, which plays important roles in cell motility and migration to promote wound healing. The effect of NFκB p50 on corneal epithelial wound healing was investigated by comparing the eyes of wild-type and p50 knockout mice. We found that there was a significant retardation in corneal epithelial wound healing in the corneas of p50 knockout mice. Wound closure rates were measured in human corneal epithelial cells transfected with an NFκB activation-sensitive CTCF expression construct to demonstrate the effect of human CTCF expression under the control of EGF-induced NFκB activation on wound healing. EGF stimulation activated NFκB, which directly triggered the expression of the exogenous human CTCF in transfected cells and, subsequently, promoted human corneal epithelial cell motility, migration, and wound healing. Overexpression of CTCF in corneal epithelial cells and mouse corneas significantly enhanced the wound healing process. Furthermore, the effect of overexpressing NFκB p50 in corneal epithelial cells on the promotion of wound healing was abolished by knockdown of CTCF with CTCF-specific shRNA. Thus, a direct regulatory relationship between EGF-induced NFκB p50 and CTCF activation affecting corneal epithelial wound healing has been established, indicating that CTCF is, indeed, a NFκB p50-targeted and effective gene product in the core transcriptional network downstream from the growth factor-induced NFκB signaling pathway.

Inactivation of DNA-dependent protein kinase promotes heat-induced apoptosis independently of heat-shock protein induction in human cancer cell lines

The inhibition of DNA damage response pathway seems to be an attractive strategy for cancer therapy. It was previously reported that in rodent cells exposed to heat stress, cell growth was promoted by the activity of DNA-dependent protein kinase (DNA-PK), an enzyme involved in DNA non-homologous end joining (NHEJ) required for double-strand break repair. The absence of a functioning DNA-PK was associated with down regulation of heat shock protein 70 (HSP70). The objective of this study is thus to investigate the role of DNA-PK inhibition in heat-induced apoptosis in human cell lines. The inhibitors of phosphorylation of the DNA-PK catalytic subunit (DNA-PKcs) at Ser2056, such as NU7026 and NU7441, were utilized. Furthermore, knock down of DNA-PKcs was carried out using small interfering RNA (siDNA-PKcs). For heat exposure, cells were placed in water bath at 44°C for 60 min. Apoptosis was evaluated after 24 h incubation flow cytometrically. Proteins were extracted after 24 h and analyzed for HSP70 and HSP40 expression by Western blotting. Total RNA was extracted 6 h after treatment and analyzed using a GeneChip® microarray system to identify and select the up-regulated genes (≥1.5 fold). The results showed an enhancement in heat-induced apoptosis in absence of functioning DNA-PKcs. Interestingly, the expression levels of HSP70 and HSP40 were elevated in the absence of DNA-PKcs under heat stress. The results of genetic network analysis showed that HSPs and JUN genes were up-regulated independently of DNA-PKcs in exposed parent and knock out cells. In the presence of functioning DNA-PKcs, there was an observed up-regulation of anti-apoptotic genes, such as NR1D1, whereas in the absence of DNA-PKcs the pro-apoptotic genes, such as EGR2, were preferentially up-regulated. From these findings, we concluded that in human cells, the inactivation of DNA-PKcs can promote heat-induced apoptosis independently of heat-shock proteins.

Overexpression of RNA-binding protein CELF1 prevents apoptosis and destabilizes pro-apoptotic mRNAs in oral cancer cells

CELF1 RNA-binding protein, otherwise called CUGBP1, associates and coordinates the degradation of GU-rich element (GRE) containing mRNA’s encoding factors important for cell growth, migration and apoptosis. Although many substrates of CELF1 have been identified, the biological significance of CELF1-mediated mRNA decay remains unclear. As the processes modulated by CELF1 are frequently disrupted in cancer, we investigated the expression and role of CELF1 in oral squamous cancer cells (OSCCs). We determined that CELF1 is reproducibly overexpressed in OSCC tissues and cell lines. Moreover, depletion of CELF1 reduced proliferation and increased apoptosis in OSCCs, but had negligible effect in non-transformed cells. We found that CELF1 associates directly with the 3′UTR of mRNAs encoding the pro-apoptotic factors BAD, BAX and JunD and mediates their rapid decay. Specifically, 3′UTR fragment analysis of JunD revealed that the GRE region is critical for binding with CELF1 and expression of JunD in oral cancer cells. In addition, silencing of CELF1 rendered BAD, BAX and JunD mRNAs stable and increased their protein expression in oral cancer cells. Taken together, these results support a critical role for CELF1 in modulating apoptosis and implicate this RNA-binding protein as a cancer marker and potential therapeutic target.

Anti-proliferative and pro-apoptotic effects of 3,3'-diindolylmethane in human cervical cancer cells

The antitumor effects of Indo-3-carbinol (I3C) have been proven in many human carcinoma cells. However, the roles of 3,3-diindolylmethane (DIM), an important polymer converted from I3C under pH 5.0-7.0, on the growth and proliferation of cervical cancer HeLa and SiHa cells still remain unrevealed. In the present study, we investigated the potential anti-proliferative and pro-apoptotic effects of DIM on HeLa and SiHa cells. Cell proliferation was detected by Cell Counting kit-8 and apoptosis was analyzed by flow cytometry. In addition, morphological changes accompanying cell apoptosis were observed using an inverted microscope after Hoechst 33258 staining. In addition, expression changes of proteins involved in the MAPK and PI3K pathways were determined by western blotting. DIM treatment inhibited the proliferation and induced apoptosis of HeLa and SiHa cells significantly in a time- and dose-dependent manner. Moreover, SiHa cells were more sensitive to DIM treatment than HeLa cells (P<0.05). In addition, the expression of ERK, p38 and p-p38, which are involved in the MAPK pathway, was downregulated by DIM treatment. Another protein involved in the MAPK pathway, JNK, was upregulated. Furthermore, DIM treatment significantly suppressed the expression of Akt, p-Akt, PI3K p110α, PI3K p110β, PI3K class III, GSK3-β, p-PDK1 and p-c-Raf which are involved in the PI3K pathway. These results demonstrate that DIM exerts antitumor effects on HeLa and SiHa cells through its anti-proliferative and pro-apoptotic roles, especially for SiHa cells. The molecular mechanism for these effects may be related to its regulatory effects on MAPK and PI3K pathway and apoptosis proteins. DIM may be a preventive and therapeutic agent against cervical cancer.

Role of CTCF in EGF-induced migration of immortalized human corneal epithelial cells

PURPOSE

EGF-induced activation of the epigenetic CCCTC binding factor (CTCF) plays an important role in corneal epithelial cell proliferation by suppressing the Pax6 gene. The present study focused on further understanding the role of CTCF in mediating EGF-induced migration of immortalized human corneal epithelial cells.

METHODS

CTCF activities in human corneal epithelial cells immortalized by telomerase (HTCE cells) and SV-40 (HCE cells) transformation were suppressed and enhanced by CTCF mRNA knockdown and by overexpressing CTCF cDNA, respectively. EGF-induced cell migration was evaluated by linear scratch wound healing, a cell migration assay, and live cell motility GFP-tracking with a fluorescence microscope. Immunochemical analysis was performed for detecting focal adhesion changes in EGF-induced and CTCF activity-altered cells.

RESULTS

EGF-induced wound closure and cell migration rates of human corneal epithelial cells were significantly suppressed and enhanced by CTCF mRNA knockdown and by overexpression of CTCF, respectively. CTCF mRNA knockdown also markedly suppressed cell motility, determined by using a live-cell-tracking system in GFP-tag-expressed HTCE cells. Finally, alterations of EGF-stimulated focal adhesion were observed in CTCF knockdown HTCE cells by immunostaining of F-actin and vinculin in cytoskeleton reorganization.

CONCLUSIONS

CTCF, an epigenetic regulator and transcription factor, involves EGF-induced increases in cell motility and migration. CTCF plays an essential role in growth factor-regulated human corneal epithelial cell wound healing.

Repression of the RHOH gene by JunD

RhoH is a member of the Rho family of small GTP-binding proteins that lacks GTPase activity. Since RhoH is constantly bound by GTP, it is thought to be constitutively active and controlled predominantly by changes in quantitative expression. RhoH is produced specifically in haematopoietic cells and aberrant expression has been linked to various forms of leukaemia. Transcription of the RHOH gene is the first level at which the quantitative levels of the RhoH protein are regulated. Previous studies have demonstrated that RHOH gene transcription is initiated by three distinct promoter regions designated P1, P2 and P3 that define the 5' end of exons 1, 2 and 4 respectively. In the present study we report that the P3 promoter is largely responsible for RHOH gene transcription in the B-lymphocytic cell line Raji. The P3 promoter contains a minimal promoter region and a repressor region extending from -236 to +67 and +68 to +245 respectively, relative to the 5' end of exon 4. Chromatin immunoprecipitation demonstrated that two AP1 (activator protein 1) sites in the minimal promoter region bind JunD. When JUND is overexpressed, the endogenous RHOH gene is repressed; however, when JUND is inhibited, expression of endogenous RHOH is induced both in the Raji cell line and AML (acute myeloid leukaemia) cells. In the HCL (hairy cell leukaemia) cell line JOK-1, induction of RHOH increases expression of the α isoform of protein kinase C. This downstream target of RHOH is also induced in AML cells by JUND inhibition. Collectively, these data indicate that JunD is an inhibitor of RHOH gene expression.

NF-kappaB subtypes regulate CCCTC binding factor affecting corneal epithelial cell fate

CCCTC binding factor (CTCF) controls DNA imprinting, insulates important gene expression, and mediates growth factor- and stress-induced cell fate. However, regulatory mechanisms involved in intracellular CTCF activity are largely unknown. In this study, we show that epidermal growth factor (EGF)-induced increase and UV stress-induced decrease in CTCF activities mediate human corneal epithelial cell proliferation and apoptosis, respectively. CTCF is regulated by activation of different NF-kappaB subtypes via stimulation by EGF and UV stress. EGF-induced formation of a p65/p50 heterodimer activated CTCF transcription to promote cellular proliferation. This was accomplished by the heterodimer binding to a kappaB site in the promoter region of CTCF gene. In contrast, UV stress induced formation of a p50/p50 homodimer, which suppressed CTCF expression leading to apoptosis. Thus, CTCF by itself plays a central role in mediating the dichotomous effects of growth factor- and stress-stimulated NF-kappaB activation on cell survival and death. These results suggest that CTCF is a downstream component of the NF-kappaB pathway involved in the core transcriptional network of cell fate.

Transcription factor AP-1 in esophageal squamous cell carcinoma: alterations in activity and expression during human Papillomavirus infection

Background

Esophageal squamous cell carcinoma (ESCC) is a leading cause of cancer-related deaths in Jammu and Kashmir (J&K) region of India. A substantial proportion of esophageal carcinoma is associated with infection of high-risk HPV type 16 and HPV18, the oncogenic expression of which is controlled by host cell transcription factor Activator Protein-1 (AP-1). We, therefore, have investigated the role of DNA binding and expression pattern of AP-1 in esophageal cancer with or without HPV infection.

Methods

Seventy five histopathologically-confirmed esophageal cancer and an equal number of corresponding adjacent normal tissue biopsies from Kashmir were analyzed for HPV infection, DNA binding activity and expression of AP-1 family of proteins by PCR, gel shift assay and immunoblotting respectively.

Results

A high DNA binding activity and elevated expression of AP-1 proteins were observed in esophageal cancer, which differed between HPV positive (19%) and HPV negative (81%) carcinomas. While JunB, c-Fos and Fra-1 were the major contributors to AP-1 binding activity in HPV negative cases, Fra-1 was completely absent in HPV16 positive cancers. Comparison of AP-1 family proteins demonstrated high expression of JunD and c-Fos in HPV positive tumors, but interestingly, Fra-1 expression was extremely low or nil in these tumor tissues.

Conclusion

Differential AP-1 binding activity and expression of its specific proteins between HPV - positive and HPV - negative cases indicate that AP-1 may play an important role during HPV-induced esophageal carcinogenesis.

Opposing roles of c-Jun NH2-terminal kinase and p38 mitogen-activated protein kinase in the cellular response to ionizing radiation in human cervical cancer cells

Exposure of cells to ionizing radiation induces activation of multiple signaling pathways that play critical roles in determining cell fate. However, the molecular basis for cell death or survival signaling in response to radiation is unclear at present. Here, we show opposing roles of the c-jun NH(2)-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) pathways in the mitochondrial cell death in response to ionizing radiation in human cervical cancer cells. Ionizing radiation triggered Bax and Bak activation, Bcl-2 down-regulation, and subsequent mitochondrial cell death. Inhibition of JNK completely suppressed radiation-induced Bax and Bak activation and Bcl-2 down-regulation. Dominant-negative forms of stress-activated protein kinase/extracellular signal-regulated kinase kinase 1 (SEK-1)/mitogen-activated protein kinase kinase-4 (MKK-4) inhibited JNK activation. Radiation also induced phosphoinositide 3-kinase (PI3K) activation. Interestingly, inhibition of PI3K effectively attenuated radiation-induced mitochondrial cell death and increased clonogenic survival. Inhibition of PI3K also suppressed SEK-1/MKK-4 and JNK activation, Bax and Bak activation, and Bcl-2 down-regulation. In contrast, inhibition of p38 MAPK led to enhanced Bax and Bak activation and mitochondrial cell death. RacN17, a dominant-negative form of Rac1, inhibited p38 MAPK activation and increased Bax and Bak activation. Exposure of cells to radiation also induced selective activation of c-Src among Src family kinases. Inhibition of c-Src by pretreatment with Src family kinase inhibitor PP2 or small interfering RNA targeting of c-Src attenuated radiation-induced p38 MAPK and Rac1 activation and enhanced Bax and Bak activation and cell death. Our results support the notion that the PI3K-SEK-1/MKK-4-JNK pathway is required for the mitochondrial cell death in response to radiation, whereas the c-Src-Rac1-p38 MAPK pathway plays a cytoprotective role against mitochondrial cell death.

c-Src-p38 mitogen-activated protein kinase signaling is required for Akt activation in response to ionizing radiation

The Akt and mitogen-activated protein kinase (MAPK) pathways have been implicated in tumor cell survival and contribute to radiation resistance. However, the molecular basis for link between MAPK and Akt in cell survival response to radiation is unclear. Here, we show that c-Src-Rac1-p38 MAPK pathway signals Akt activation and cell survival in response to radiation. Ionizing radiation triggered Thr(308) and Ser(473) phosphorylation of Akt. Exposure of cells to radiation also induced p38 MAPK and c-Jun NH(2)-terminal kinase activations. Inhibition of c-Jun NH(2)-terminal kinase suppressed radiation-induced cell death, whereas inhibition of p38 MAPK effectively increased sensitivity to radiation. Interestingly, inhibition of p38 MAPK completely attenuated radiation-induced Ser(473) phosphorylation of Akt but did not affect Thr(308) phosphorylation. Conversely, overexpression of p38 MAPK enhanced Ser(473) phosphorylation of Akt in response to radiation. In addition, inhibition of p38 MAPK failed to alter phosphoinositide 3-kinase and phosphoinositide-dependent protein kinase activities. Ectopic expression of RacN17, dominant-negative form of Rac1, inhibited p38 MAPK activation and Ser(473) phosphorylation of Akt. Following exposure to radiation, c-Src was selectively activated among Src family tyrosine kinases. Inhibition of c-Src attenuated Rac1 and p38 MAPK activations and Ser(473) phosphorylation of Akt. Our results support the notion that the c-Src-Rac1-p38 MAPK pathway is required for activation of Akt in response to radiation and plays a cytoprotective role against radiation in human cancer cells.

Cellular effects of long wavelength UV light (UVA) in mammalian cells

UVA should receive significant consideration as a human health risk as it is a large proportion of the solar spectrum that reaches the earth's surface and because of its ability to penetrate human skin. It is only relatively recently that this has been recognized and this previously under-researched part of the UV spectrum is becoming increasingly well characterized at doses that are quite low in relation to those experienced by humans. Absorption of UVA in a cell leads to the production of reactive oxygen and nitrogen species that can damage major biomolecules including DNA and membrane lipids. Various types of damage induced in these molecules lead to significant biological effects including cytotoxicity, mutations and alterations in cell signalling pathways. Longer-term effects such as persistent genomic instability and bystander effects have also been observed following UVA treatment of mammalian cells and, as with ionizing radiation, this changes some of the fundamental thinking around tissue effects of irradiation. Antioxidants have been assessed extensively for their ability to protect against the biological effects of UVA and a number have been shown to be successful at least in-vitro, for example vitamin E and epigallocatechin-3-gallate. Other potential targets for protection are suggested through the increased understanding of some of the signalling mechanisms activated following treatment, for example the inhibition of NADPH oxidase is seen to reduce a bystander effect. The search for appropriate and successful photoprotective agents remains an important area of research.

Activation of Polo-like kinase 3 by hypoxic stresses

Hypoxia/reoxygenation stress induces the activation of specific signaling proteins and activator protein 1 (AP-1) to regulate cell cycle regression and apoptosis. In the present study, we report that hypoxia/reoxygenation stress activates AP-1 by increasing c-Jun phosphorylation and DNA binding activity through activation of Polo-like-kinase 3 (Plk3) resulting in apoptosis. The specific effect of hypoxia/reoxygenation stress on Plk3 activation resulting in c-Jun phosphorylation was the opposite of UV irradiation-induced responses that are meanly independent on activation of the stress-induced JNK signaling pathway in human corneal epithelial (HCE) cells. The effect of hypoxia/reoxygenation stress-induced Plk3 activation on increased c-Jun phosphorylation and apoptosis was also mimicked by exposure of cells to CoCl(2). Hypoxia/reoxygenation activated Plk3 in HCE cells to directly phosphorylate c-Jun proteins at phosphorylation sites Ser-63 and Ser-73, and to increase DNA binding activity of c-Jun, detected by EMSA. Further evidence demonstrated that Plk3 and phospho-c-Jun were immunocolocalized in the nuclear compartment of hypoxia/reoxygenation stress-induced cells. Increased Plk3 activity by overexpression of wild-type and dominantly positive Plk3 enhanced the effect of hypoxia/reoxygenation on c-Jun phosphorylation and cell death. In contrast, knocking-down Plk3 mRNA suppressed hypoxia-induced c-Jun phosphorylation. Our results provide a new mechanism indicating that hypoxia/reoxygenation induces Plk3 activation instead of the JNK effect to directly phosphorylate and activate c-Jun, subsequently contributing to apoptosis in HCE cells.

Multiple facets of junD gene expression are atypical among AP-1 family members

JunD is a versatile AP-1 transcription factor that can activate or repress a diverse collection of target genes. Precise control of junD expression and JunD protein-protein interactions modulate tumor angiogenesis, cellular differentiation, proliferation and apoptosis. Molecular and clinical knowledge of two decades has revealed that precise JunD activity is elaborated by interrelated layers of constitutive transcriptional control, complex post-transcriptional regulation and a collection of post-translational modifications and protein-protein interactions. The stakes are high, as inappropriate JunD activity contributes to neoplastic, metabolic and viral diseases. This article deconvolutes multiple layers of control that safeguard junD gene expression and functional activity. The activity of JunD in transcriptional activation and repression is integrated into a regulatory network by which JunD exerts a pivotal role in cellular growth control. Our discussion of the JunD regulatory network integrates important open issues and posits new therapeutic targets for the neoplastic, metabolic and viral diseases associated with JunD/AP-1 expression.

Stress-induced c-Jun activation mediated by Polo-like kinase 3 in corneal epithelial cells

Polo-like kinase 3 (Plk3) activation occurs after exposure to environmental or genotoxic stresses. Plk3 regulates cell fate through regulating cell cycle progression. UV irradiation is one of the major environmental stresses that affect corneal epithelial wound healing. In the present study, we report that UV irradiation activated Plk3 and that Plk3 interacts with AP-1 and c-Jun, which appears to be important to mediate corneal epithelial cell apoptosis after UV irradiation. Recombinant Plk3, as well as Plk3 immunoprecipitated from UV-irradiated cells, phosphorylated c-Jun in vitro. The phosphorylation of c-Jun by Plk3 immunoprecipitates was not altered by the pre-removal of JNK from the cell lysates. In addition, the effect of UV irradiation-induced phosphorylation of c-Jun and apoptosis were not significantly affected by knockdown of JNK mRNA. Co-immunoprecipitation reveals that Plk3 and c-Jun directly interacted with each other. Consistently, Plk3 co-localized with c-Jun to the nucleus after UV irradiation. Further, modulating Plk3 activities by overexpressing Plk3 or its mutants significantly affected UV irradiation-induced c-Jun activity and subsequent apoptosis. Our results thus provide for the first time that Plk3 mediates UV irradiation-induced c-Jun activation by phosphorylating c-Jun, suggesting that Plk3 plays an important role in mediating programmed cell death of corneal epithelial cells after UV irradiation.

Interferon-inducible Stat2 activation of JUND and CLDN4: mediators of IFN responses

Signal transducer and activator of transcription 2 (Stat2) is a critical signaling protein involved in mediating interferon-alpha/beta (IFN-alpha/beta) responses. Using site-directed mutagenesis in conjunction with gene microarray and biologic studies, we have previously demonstrated that in addition to Stat2 functioning as a transactivator of transcription of a subset of IFN-inducible genes (ISG), Stat2-DNA binding mediates the transcriptional activation of other ISGs required for IFN-inducible antiviral and growth inhibitory responses. Among these, two candidate genes identified were Jun-D (JUND) and claudin-4 (CLDN4). To further explore the role of JUND and CLDN4 in IFN responses, we conducted knockdown studies using siRNA specific for either JUND or CLDN4 in 2fTGH fibroblast cells, and consistent with cells expressing the DNA-binding mutant of Stat2 (U6A-2VV-II), siRNA-mediated knockdown resulted in cells that exhibited reduced antiproliferative and antiviral responses to IFN. Our data suggest that JUND and CLDN4 are critical mediators of the antiproliferative and antiviral effects of type I IFNs and further confirm the functional importance of the DNA-binding domain of Stat2.

Role of c-Fos/JunD in protecting stress-induced cell death

OBJECTIVE

The exposure of mammalian cells to extracellular stress induces the expression of immediate early genes such as c-fos and c-jun and activates transcription factor activator protein-1 (AP-1). The purpose of the current study was to investigate the role of c-Fos and JunD in stress-induced cell death.

MATERIALS AND METHODS

We exposed cultured primary mouse embryonic fibroblasts (MEF) to ultraviolet light (UV-C) or hydrogen peroxide (H(2)O(2)). Induction of c-Fos and JunD and activation of MAPK/ERK1/2 signalling in the presence or absence of a MAPK inhibitor were analyzed by western blotting. Activation of AP-1 transcription factors was detected by the electrophoretic mobility shift assay and immunoprecipitation. Cell death was measured by changes in caspase 3 activities and nuclear morphology. Effects of c-Fos and JunD expression on cell death were investigated by transfection.

RESULTS

We found that the exposure of cultured primary MEF cells to UV or H(2)O(2) caused a significant increase in c-Fos and JunD protein levels. In addition, these two proteins formed complexes with each other and contributed to activation of AP-1 transcription complexes. More importantly, under both stress conditions, overexpression of JunD alone or overexpression of both c-Fos and JunD reduced caspase 3 activity and cell death. At the same time, UV irradiation activated the MAPK/ERK1/2 signalling pathway. The suppression of MEK1/ERK1/2 activation inhibited UV-induced expression of c-Fos and JunD and increased caspase 3 activity and cell death.

CONCLUSION

Our results suggest that both UV and H(2)O(2 )induce the activation of c-Fos/JunD AP-1 complexes resulting in the prevention of cell death. Moreover, UV irradiation-induced increases in c-Fos/JunD expression in primary MEF cells are mediated through the activation of the MAPK/ERK1/2 signalling pathway.

Pax6 regulation in retinal cells by CCCTC binding factor

PURPOSE

A previous study demonstrated that CTCF (CCCTC binding factor) regulates homeobox Pax6 gene expression in early embryonic stages and plays a dominant role in eye development. The purpose of the present study was to explore further the mechanism of CTCF controlling Pax6 gene expression in human retinoblastoma (Rb) cells and in the development of chicken and mouse retinas.

METHODS

Northern and Western analyses were used to detect expressions of CTCF and Pax6 in Rb cells. Pax6 transcription reporter and deletion mutants were used to study the regulatory interaction between CTCF and Pax6 in Rb cells and in the retina of chicken embryos. CTCF transgenic chicken embryos and mice were established by lipofection and microinjection of linearized cytomegalovirus (CMV)-CTCF construct into fertilized eggs and mouse oocytes, respectively. Injected oocytes were implanted in the uterus of foster mothers through microinjection into the ovarian duct. The expression of CTCF and Pax6 was determined in embryo sections by immunochemistry.

RESULTS

Stimulation of Rb cells with 10% FBS resulted in an increase in CTCF expression and a decrease in Pax6 expression. To study the regulatory mechanism, the Pax6 reporter and its deletion mutant activities were determined in transfected Rb cells and chicken embryonic retinas, revealing that CTCF interacts with the Pax6 gene in Rb cells through transcription control in the 5'-flanking region upstream from the Pax6 P0 promoter. Overexpression of CTCF in Rb cells suppressed Pax6 reporter activity and downregulated endogenous Pax6 expression. In contrast, downregulation of CTCF expression by knockdown of CTCF mRNA using specific small interfering (si)RNA markedly enhanced Pax6 expression in Rb cells. Further study in CTCF transgenic mouse embryos verified that overexpression of CTCF suppressed Pax6 gene expression in the retina.

CONCLUSIONS

CTCF plays an important role in regulating Pax6 expression in Rb cells and in the developmental retina, and the regulation of Pax6 gene expression by CTCF in the retina is through transcriptional regulation.

Stress-induced corneal epithelial apoptosis mediated by K+ channel activation

One of the functional roles of the corneal epithelial layer is to protect the cornea, lens and other underlying ocular structures from damages caused by environmental insults. It is important for corneal epithelial cells to maintain this function by undergoing continuous renewal through a dynamic process of wound healing. Previous studies in corneal epithelial cells have provided substantial evidence showing that environmental insults, such as ultraviolet (UV) irradiation and other biohazards, can induce stress-related cellular responses resulting in apoptosis and thus interrupt the dynamic process of wound healing. We found that UV irradiation-induced apoptotic effects in corneal epithelial cells are started by the hyperactivation of K+ channels in the cell membrane resulting in a fast loss of intracellular K+ ions. Recent studies provide further evidence indicating that these complex responses in corneal epithelial cells are resulted from the activation of stress-related signaling pathways mediated by K+ channel activity. The effect of UV irradiation on corneal epithelial cell fate shares common signaling mechanisms involving the activation of intracellular responses that are often activated by the stimulation of various cytokines. One piece of evidence for making this distinction is that at early times UV irradiation activates a Kv3.4 channel in corneal epithelial cells to elicit activation of c-Jun N-terminal kinase cascades and p53 activation leading to cell cycle arrest and apoptosis. The hypothetic model is that UV-induced potassium channel hyperactivity as an early event initiates fast cell shrinkages due to the loss of intracellular potassium, resulting in the activation of scaffolding protein kinases and cytoskeleton reorganizations. This review article presents important control mechanisms that determine Kv channel activity-mediated cellular responses in corneal epithelial cells, involving activation of stress-induced signaling pathways, arrests of cell cycle progression and/or induction of apoptosis.

Gene expression profiling of noninvasive primary urothelial tumours using microarrays

At present, the mechanism leading to bladder cancer is still poorly understood, and our knowledge about early events in tumorigenesis is limited. This study describes the changes in gene expression occurring during the neoplastic transition from normal bladder urothelium to primary Ta tumours. Using DNA microarrays, we identified novel differentially expressed genes in Ta tumours compared to normal bladder, and genes that were altered in high-grade tumours. Among the mostly changed genes between normal bladder and Ta tumours, we found genes related to the cytoskeleton (keratin 7 and syndecan 1), and transcription (high mobility group AT-hook 1). Altered genes in high-grade tumours were related to cell cycle (cyclin-dependent kinase 4) and transcription (jun d proto-oncogene). Furthermore, we showed the presence of high keratin 7 transcript expression in bladder cancer, and Western blotting analysis revealed three major molecular isoforms of keratin 7 in the tissues. These could be detected in urine sediments from bladder tumour patients.

Selective role of intracellular chloride in the regulation of the intrinsic but not extrinsic pathway of apoptosis in Jurkat T-cells

Apoptosis is a genetic program for the removal of unwanted cells from an organism, which is distinct from necrosis by its characteristic volume loss or apoptotic volume decrease. This cell shrinkage is the result of ion redistribution that is crucial for both the activation and execution of apoptosis. Here we report that UV-C but not Fas ligand treatment results in a significant decrease in intracellular chloride that can be abolished by modulation of chloride flux using either the chloride channel inhibitor SITS or medium with a reduced chloride concentration. Accordingly, downstream events are diminished during UV-C-induced apoptosis following chloride flux modulation, whereas Fas ligand-induced apoptotic characteristics are not affected. Moreover, the activation of the mitogen-activated protein kinase signal transduction pathway early in the apoptotic signaling cascade was affected by chloride flux in Jurkat T-cells. Thus, an alteration of intracellular chloride plays an important role in the activation of signaling molecules upstream of the mitochondria, specifically impairing the intrinsic but not extrinsic apoptotic pathway.

12-O-Tetradecanoylphorbol-13-acetate (TPA)-induced dual-specificity phosphatase expression and AML cell survival

12-O-Tetradecanoylphorbol-13-acetate (TPA) is being developed as a therapeutic agent by virtue of its being a potent modulator of signal transduction in pre-clinical models of AML [Strair RK, Schaar D, Goodell L, Aisner J, Chin KV, Eid J, et al. Administration of a phorbol ester to patients with hematological malignancies: preliminary results from a phase I clinical trial of 12-O-tetradecanoylphorbol-13-acetate. Clin Cancer Res 2002;8:2512-8]. In this report, we identify a subset of primary AML samples that undergoes apoptosis after exposure to TPA and demonstrate that TPA-induced cytotoxicity is associated with modulation of the ERK signaling pathway. Analysis of mitogen-activated protein kinase (MAPK) dual-specificity phosphatases (DUSP), as potential regulators of AML cell signaling, indicates that these genes are coordinately regulated and rapidly induced by TPA in primary AML cells. Therefore, TPA-induced primary AML cytotoxicity is associated with modulation of ERK signaling which may be partially mediated by regulation of phosphatase expression.

Tumor necrosis factor-alpha induced the release of interleukin-6 from endometriotic stromal cells by the nuclear factor-kappaB and mitogen-activated protein kinase pathways

OBJECTIVE

To examine the involvement of nuclear factor-kappaB (NF-kappaB) and mitogen-activated protein kinase (MAPK) in the induction of interleukin-6 (IL-6) by tumor necrosis factor-alpha (TNF-alpha) in endometriotic stromal cells (ESC).

DESIGN

Prospective study.

SETTING

Department of Obstetrics and Gynecology, Tottori University Hospital, Yonago, Japan.

PATIENT(S)

Twelve patients who underwent laparoscopic surgery.

INTERVENTION(S)

Endometriotic stromal cells were obtained from chocolate cyst linings of the ovary.

MAIN OUTCOME MEASURE(S)

We determined the effect of TNF-alpha on the production of IL-6 and the effect of inhibitors for NF-kappaB and the MAPK pathway on IL-6 production using ELISA. Western blottings and electrophoretic mobility shift assays were used to detect activation of NF-kappaB and extracellular signal-regulated kinase 1/2 (ERK1/2).

RESULT(S)

The addition of TNF-alpha (0.1 ng/mL) significantly increased IL-6 protein in endometriotic stromal cells. Western blottings and electrophoretic mobility shift assays revealed that incubation with TNF-alpha induced degradation of inhibitor kappaB (I kappaB) and expression of phosphorylated ERK1/2. The NF-kappaB inhibitor (TPCK) and MAPK inhibitor (U0126) blocked the TNF-alpha-induced IL-6 expression. Electrophoretic mobility shift assay revealed that U0126 attenuated activator protein-1 (AP-1) activation induced by TNF-alpha.

CONCLUSION(S)

These findings demonstrate that NF-kappaB and AP-1 activation is critical for TNF-alpha-induced IL-6 expression in endometriotic stromal cells. Novel therapeutic modalities targeting these molecules may be possible in the near future.

K(+) channel activity and redox status are differentially required for JNK activation by UV and reactive oxygen species

Upon exposure to ultraviolet (UV) radiation, osmotic changes or the presence of reactive oxygen species (ROS) c-Jun N-terminal kinases (JNKs) are rapidly activated. Extensive studies have elucidated molecular components that mediate the activation of JNKs. However, it remains unclear whether activation of JNKs by various stress signals involves different pathways. Here we show that K(+) channel activity is involved in mediating apoptosis induced by UV but not by H(2)O(2) in myelocytic leukemic ML-1 cells. Specifically, JNKs were rapidly phosphorylated upon treatment of ML-1 cells with UV and H(2)O(2). UV-induced, but not H(2)O(2)-induced, JNK-1 phosphorylation was inhibited by pretreatment with 4-aminopyridine (4-AP), a K(+) channel blocker. 4-AP also blocked UV-induced increase in JNK activity as well as p38 phosphorylation. Immunofluorescent microscopy revealed that phosphorylated JNKs were concentrated at centrosomes in ML-1 cells and that these proteins underwent rapid subcellular translocation upon UV treatment. Consistently, the subcellular translocation of JNKs induced by UV was largely blocked by 4-AP. Furthermore, UV-induced JNK activation was blocked by NEM, a sulfhydryl alkylating agent also affecting K(+) current. Both UV- and H(2)O(2)-induced JNK activities were inhibited by glutathione, suggesting that the redox status does play an important role in the activation of JNKs. Taken together, our findings suggest that JNK activation by UV and H(2)O(2) is mediated by distinct yet overlapping pathways and that K(+) channel activity and redox status are differentially required for UV- and H(2)O(2)-induced activation of JNKs.

Proapoptotic function of protein kinase CK2alpha" is mediated by a JNK signaling cascade

Protein kinase CK2 (formerly casein kinase II) is a tetrameric enzyme constitutively expressed in all eurakyotic tissues that plays a significant role in the regulation of cell proliferation, malignant transformation, and apoptosis. The catalytic alpha-subunit of the enzyme is known to exist in three isoforms CK2alpha, CK2alpha' and CK2alpha". CK2alpha" is highly expressed in liver compared with other tissues and is required for the normal trafficking of several hepatocellular membrane proteins. Initial studies of dengue virus infection indicated that the CK2alpha"-deficient membrane trafficking mutant cell line (Trf1) was resistant to virus-induced cell death compared with the parental human hepatoma (HuH)-7 hepatoma line. Expression of recombinant CK2alpha" in Trf1 was capable of reverting this resistant phenotype. This study was extended to TNF-alpha in addition to other stimuli of cell death in an attempt to uncover common death pathways that might be modulated by CK2alpha". Evaluation of different pathways involved in death signaling suggest that the regulation of a critical proapoptotic step in HuH-7 cells by CK2alpha" is mediated by a JNK signaling cascade.

Gene expression profiling and subgroup identification of oligodendrogliomas

The histological diagnosis of low-grade astrocytomas and oligodendrogliomas (WHO grade II) is often challenging, particularly in cases that show both astrocytic and oligodendroglial differentiation. We carried out gene expression profiling on 17 oligodendrogliomas (93% with LOH 1p and/or 19q) and 15 low-grade astrocytomas (71% with a TP53 mutation), using a cDNA array containing 1176 cancer-related genes. In oligodendrogliomas, 40 genes showed on average higher expression (at least a two-fold increase) than in astrocytomas, including DES, TDGF1, TGF-beta, GABA-BR1A, Histone H4, CDKN1A, PCDH43, Rho7 and Jun-D, while 39 genes were expressed at lower levels (at least a two-fold decrease), including JNK2, ITGB4, JNK3A2, RhoC, IFI-56K, AAD14 and EGFR. Immunohistochemistry revealed nuclear staining of Jun-D in oligodendrogliomas, in contrast to the immunoreactivity of cytoplasm and cell processes in low-grade astrocytomas. Partial least-squares analysis of the 79 genes at least two-fold differentially expressed between oligodendrogliomas and low-grade astrocytomas demonstrated perfect separation of oligodendrogliomas from low-grade astrocytomas and normal cerebral white matter. Clustering analysis based on the entire gene set divided the 17 subjects with oligodendrogliomas into two subgroups with significantly different survival (log-rank test, P=0.0305; survival to 5-years, 80 vs 0%, P=0.048). These results demonstrate that oligodendrogliomas and low-grade astrocytomas differ in their gene expression profiles, and that there are subgroups of oligodendroglioma with distinct expression profiles related to clinical outcome.

Phosphorylation on Thr-55 by TAF1 mediates degradation of p53: a role for TAF1 in cell G1 progression

The largest subunit of TFIID, TAF1, possesses an intrinsic protein kinase activity and is important for cell G1 progression and apoptosis. Since p53 functions by inducing cell G1 arrest and apoptosis, we investigated the link between TAF1 and p53. We found that TAF1 induces G1 progression in a p53-dependent manner. TAF1 interacts with and phosphorylates p53 at Thr-55 in vivo. Substitution of Thr-55 with an alanine residue (T55A) stabilizes p53 and impairs the ability of TAF1 to induce G1 progression. Furthermore, both RNAi-mediated TAF1 ablation and apigenin-mediated inhibition of the kinase activity of TAF1 markedly reduced Thr-55 phosphorylation. Thus, phosphorylation and the resultant degradation of p53 provide a mechanism for regulation of the cell cycle by TAF1. Significantly, the Thr-55 phosphorylation was reduced following DNA damage, suggesting that this phosphorylation contributes to the stabilization of p53 in response to DNA damage.

Regulation of eye development by transcription control of CCCTC binding factor (CTCF)

CCCTC binding factor (CTCF), a transcriptional regulator, plays important roles in epigenetics and development. In the present study, we report that overexpression of CTCF in transgenic mice during embryonic development suppresses Pax6 gene expression. This effect causes defects in ocular development that result in microophthalmia. In eye-derived cells transfected with a tetracycline turn-on CTCF system, up-regulation of CTCF expression significantly suppressed Pax6 expression. In contrast, the knockdown of CTCF mRNA resulted in the down-regulation of CTCF protein expression, which in turn enhanced the Pax6 expression. CTCF controls Pax6 transcription by interacting with a repressor element located in the 5'-flanking region upstream of the Pax6 P0 promoter. This interaction suppressed Pax6 gene transcription by blocking the effect of an ectoderm enhancer located 3.5 kb upstream from the P0 promoter. We also found an 80-bp sequence in a region -1.2 kbp upstream from the P0 promoter that contained multiple CTCF binding sites and interacted with nuclear proteins obtained from eye-derived cells forming electrophoretic mobility shift assay complexes with CTCF. We conclude that a novel function of CTCF is to regulate Pax6 transcription by binding to the repressor element, which in turn blocks the effect of the ectoderm enhancer resulting in the inhibition of P0 promoter activity.

Phosphorylation of PML by mitogen-activated protein kinases plays a key role in arsenic trioxide-mediated apoptosis

The promyelocytic leukemia (PML) protein is a potent growth suppressor and proapototic factor, whereas aberrant fusions of PML and retinoic acid receptor (RAR)-alpha are causal agents in human acute promyelocytic leukemia. Arsenic trioxide (As(2)O(3)) treatment induces apoptosis in acute promyelocytic leukemia cells through an incompletely understood mechanism. We report here that As(2)O(3) treatment induces phosphorylation of the PML protein through a mitogen-activated protein (MAP) kinase pathway. Increased PML phosphorylation is associated with increased sumoylation of PML and increased PML-mediated apoptosis. Conversely, MAP kinase cascade inhibitors, or the introduction of phosphorylation or sumoylation-defective mutations of PML, impair As(2)O(3)-mediated apoptosis by PML. We conclude that phosphorylation by MAP kinase cascades potentiates the antiproliferative functions of PML and helps mediate the proapoptotic effects of As(2)O(3).

Rapid and preferential induction of ATF3 transcription in response to low doses of UVA light

Long-wavelength UV light (UVA) is known to induce transcription of various genes in the cell and to cause a variety of pathological or protective responses in the skin. To find additional UVA-responsive genes, human skin-derived fibroblasts were exposed to UVA under non- or partially lethal conditions, and the effects of UVA on the transcriptional profile were examined by using DNA microarray and RT-PCR. Transcription of several genes including those already known to be UVA-responsive was induced to a significant extent under 50% lethal conditions of exposure. Among those, ATF3 was the most sensitive and its transcription was increased 10-fold within 1h. Even at a non-lethal dose of UVA (8J/cm(2)), it was increased 8-fold, if cells were cultured for 3h post-exposure. Typical immediate-early genes such as c-fos and c-jun were not affected at this dose. We thus suggest that ATF3 could be a key regulator for a variety of cellular responses in the skin, particularly to low doses of UVA.

Suppression of Extracellular Signal-related Kinase and Activation of p38 MAPK Are Two Critical Events Leading to Caspase-8- and Mitochondria-mediated Cell Death in Phytosphingosine-treated Human Cancer Cells

We previously demonstrated that the phytosphingosine-induced apoptosis was accompanied by the concomitant induction of both the caspase-8-mediated and mitochondrial activation-mediated apoptosis pathways. In the present study, we investigated the role of mitogen-activated protein kinases (MAPKs) in the activation of these two distinct cell death pathways induced by phytosphingosine in human cancer cells. Phytosphingosine caused strong induction of caspase-8 activity and caspase-independent Bax translocation to the mitochondria. A rapid decrease of phosphorylated ERK1/2 and a marked increase of p38 MAPK phosphorylation were observed within 10 min after phytosphingosine treatment. Activation of ERK1/2 by pretreatment with phorbol 12-myristate 13-acetate or forced expression of ERK1/2 attenuated phytosphingosine-induced caspase-8 activation. However, Bax translocation and caspase-9 activation was unaffected, indicating that down-regulation of the ERK activity is specifically required for the phytosphingosine-induced caspase-8-dependent cell death pathway. On the other hand, treatment with SB203580, a p38 MAPK-specific inhibitor, or expression of a dominant negative form of p38 MAPK suppressed phytosphingosine-induced translocation of the proapoptotic protein, Bax, from the cytosol to mitochondria, cytochrome c release, and subsequent caspase-9 activation but did not affect caspase-8 activation, indicating that activation of p38 MAPK is involved in the mitochondrial activation-mediated cell death pathway. Our results suggest that phytosphingosine can utilize two different MAPK signaling pathways for amplifying the apoptosis cascade, enhancing the understanding of the molecular mechanisms utilized by naturally occurring metabolites to regulate cell death. Molecular dissection of the signaling pathways that activate the apoptotic cell death machinery is critical for both our understanding of cell death events and development of cancer therapeutic agents.