Ultraviolet B exposure activates Stat3 signaling via phosphorylation at tyrosine705 in skin of SKH1 hairless mouse: a target for the management of skin cancer?

Analysis of Radiation Toxicity in Mammalian Cells Stably Transduced with Mitochondrial Stat3

A coordinated action between nuclear and mitochondrial activities is essential for a proper cellular response to genotoxic stress. Several nuclear transcription factors, including STAT3, translocate to mitochondria to exert mitochondrial function regulation; however, the role of mitochondrial STAT3 (mitoSTAT3) under stressed conditions is still poorly understood. In this study, we examined whether the stable expression of mitoSTAT3 wild-type or mutated at the conserved serine residue (Ser727), which is involved in the mitochondrial function of STAT3, can affect the DNA damage response to UVC radiation. To address this issue, we generated mammalian cells (NIH-3T3 and HCT-116 cells) stably transduced to express the mitochondrial-targeted Stat3 gene in its wild-type or Ser727 mutated forms. Our results show that cell proliferation is enhanced in mitoStat3-transduced cells under both non-stressed and stressed conditions. Once irradiated with UVC, cells expressing wild-type mitoSTAT3 showed the highest cell survival, which was associated with a significant decrease in cell death. Low levels of oxidative stress were detected in UVC-irradiated NIH-3T3 cells expressing mitoSTAT3 wild-type or serine-related dominant active form (Ser727D), confirming a role of mitochondrial STAT3 in minimizing oxidant cellular stress that provides an advantage for cell survival.

miR-124-3p Delivered Using Exosomes Attenuates the Keratinocyte Response to IL-17A Stimulation in Psoriasis

Methods

NHEKs, HaCaT cells, and HEK 293T cells were treated with IL-17A. CCK-8 assays were performed to detect cell activity, and immunofluorescence staining and Western blotting were performed to detect the protein expression of STAT3. After isolation of exosomes via ultracentrifugation, the contents of miR-124-3p and oxidative stress markers such as superoxide dismutase (SOD), malondialdehyde (MDA), and glutathione peroxidase (GSH-Px) in keratinocytes were measured. Subsequently, transcriptomic analysis was performed using RNA-seq. Data were analysed by using the “edgeR” package within R. After verifying the abnormally expressed genes stimulated by IL-17A, a dual luciferase reporter assay was used to determine the interaction between miR-124-3p and STAT3. Finally, BALB/c mice were used to establish a psoriasis model for analysis. The effect of elevated miR-124-3p on the psoriasis mouse model was determined by exosomal delivery of miR-124-3p.

Results

IL-17 intervention enhanced the cell activity of keratinocytes (P < 0.05). miR-124-3p was identified by RNA-seq as one of the differentially expressed miRNAs stimulated by IL-17A. miR-124-3p overexpression induced decreased STAT3 and MDA levels, increased SOD and GSH-Px levels in keratinocytes, and alleviated emergency responses of sclerosis damage (P < 0.05). The dual luciferase reporter assay results confirmed that STAT3 was regulated by miR-124-3p in a targeted manner (P < 0.05). Finally, miR-124-3p delivered by exosomes effectively alleviated the pathological manifestations and oxidative stress responses of psoriatic mice.

Conclusions

miR-124-3p regulates keratinocyte activity via STAT3 in response to IL-17A stimulation. The ectopic expression of miR-124-3p in psoriatic skin reduces IL-17A-induced inflammation and inhibits the STAT3 pathway, thus alleviating the symptoms of psoriasis. The findings of this study suggest that exosomes can be used to therapeutically deliver miR-124-3p to keratinocytes and psoriatic lesions, which may provide novel insight for psoriasis treatment.

STAT3 Activation in Psoriasis and Cancers

Activation of signal transducer and activator of transcription (STAT)3 has been reported in many cancers. It is also well known that STAT3 is activated in skin lesions of psoriasis, a chronic skin disease. In this study, to ascertain whether patients with psoriasis have a predisposition to STAT3 activation, we examined phosphorylated STAT3 in cancer cells of psoriasis patients via immunohistochemistry. We selected patients with psoriasis who visited the Department of Dermatology, Jichi Medical University Hospital, from January 2000 to May 2015, and had a history of cancer. We performed immunostaining for phosphorylated STAT3 in tumor cells of five, four, and six cases of gastric, lung, and head and neck cancer, respectively. The results showed that there was no significant difference in STAT3 activation in any of the three cancer types between the psoriasis and control groups. Although this study presents limitations in its sample size and inconsistency in the histology and differentiation of the cancers, results suggest that psoriasis patients do not have a predisposition to STAT3 activation. Instead, STAT3 activation is intricately regulated by each disorder or cellular microenvironment in both cancer and psoriasis.

A topical formulation containing quercetin-loaded microcapsules protects against oxidative and inflammatory skin alterations triggered by UVB irradiation: enhancement of activity by microencapsulation

Ultraviolet B (UVB) irradiation causes free radical production, increase inflammation and oxidative stress, thus, supporting the use of antioxidants by topical administration as therapeutic approaches. Quercetin (QC) is a flavonoid with antioxidant activity, however, high liposolubility makes it difficult to remain in the viable skin layer. Thus, this study evaluated whether microencapsulation of QC would enhance its activity in comparison with the same dose of free QC (non-active dose) and unloaded-microcapsules added in formulation for topical administration in a mouse model of UVB irradiation targeting the skin. Topical formulation containing Quercetin-loaded microcapsules (TFcQCMC) presents physico-chemical (colour, consistence, phase separation and pH) and functional antioxidant stability at 4 °C, room temperature and 40 °C for 6 months. TFcQCMC inhibited the UVB-triggered depletion of antioxidants observed by GSH (reduced glutathione), ability to reduce iron, ability to scavenge 2,2'-azinobis radical and catalase activity. TFcQCMC also inhibited markers of oxidation (lipid hydroperoxides and superoxide anion production). Concerning inflammation, TFcQCMC reduced the production of inflammatory cytokines, matrix metalloproteinase-9 activity, skin edoema, collagen fibre damage, myeloperoxidase activity/neutrophil recruitment, mast cell and sunburn cell counts. The pharmacological activity of TFcQCMC was not shared by the same pharmaceutical form containing the same dose of free QC or unloaded control microcapsules.

Targeting STAT-3 signaling pathway in cancer for development of novel drugs: Advancements and challenges

Signal transducers and activators of transcription 3 (STAT-3) is a transcription factor that regulates the gene expression of several target genes. These factors are activated by the binding of cytokines and growth factors with STAT-3 specific receptors on cell membrane. Few years ago, STAT-3 was considered an acute phase response element having several cellular functions such as inflammation, cell survival, invasion, metastasis and proliferation, genetic alteration, and angiogenesis. STAT-3 is activated by several types of inflammatory cytokines, carcinogens, viruses, growth factors, and oncogenes. Thus, the STAT3 pathway is a potential target for cancer therapeutics. Abnormal STAT-3 activity in tumor development and cellular transformation can be targeted by several genomic and pharmacological methodologies. An extensive review of the literature has been conducted to emphasize the role of STAT-3 as a unique cancer drug target. This review article discusses in detail the wide range of STAT-3 inhibitors that show antitumor effects both in vitro and in vivo. Thus, targeting constitutive STAT-3 signaling is a remarkable therapeutic methodology for tumor progression. Finally, current limitations, trials and future perspectives of STAT-3 inhibitors are also critically discussed.

Phytochemicals for the Prevention of Photocarcinogenesis

Ultraviolet (UV) exposure has an array of damaging effects and is the main cause of skin cancer in humans. Nonmelanoma skin cancer (NMSC), including basal cell carcinoma and squamous cell carcinoma, is the most common type of cancer. Incidence of NMSC has increased due to greater UV radiation, increased life expectancy and other changes in lifestyle; the annual cost of skin cancer treatment in the United States has increased concurrently to around eight billion dollars. Because of these trends, novel approaches to skin cancer prevention have become an important area of research to decrease skin cancer morbidity and defray the costs associated with treatment. Chemoprevention aims to prevent or delay the development of skin cancer through the use of phytochemicals. Use of phytochemicals as chemopreventive agents has gained attention due to their low toxicity and anticarcinogenic properties. Phytochemicals also exhibit antioxidant, anti-inflammatory and antiproliferative effects which support their use as chemopreventive agents, particularly for skin cancer. Preclinical and human studies have shown that phytochemicals decrease UV-induced skin damage and photocarcinogenesis. In this review article, we discuss the selected phytochemicals that may prevent or delay UV-induced carcinogenesis and highlight their potential use for skin protection.

A homolog of teleostean signal transducer and activator of transcription 3 (STAT3) from rock bream, Oplegnathus fasciatus: Structural insights, transcriptional modulation, and subcellular localization

Signal transducer and activator of transcription 3 (STAT3) is one of the crucial transcription factors in the Janus kinase (JAK)/STAT signaling pathway, and it was previously considered as acute phase response factor. A number of interleukins (ILs) such as IL-5, IL-6, IL-9, IL-10, IL-12, and IL-22 are known to be involved in activation of STAT3. In addition, various growth factors and pathogenic or oxidative stresses mediate the activation of a wide range of functions via STAT3. In this study, a STAT3 homolog was identified and functionally characterized from rock bream (RbSTAT3), Oplegnathus fasciatus. In silico characterization revealed that the RbSTAT3 amino acid sequence shares highly conserved common domain architectural features including N-terminal domain, coiled coil domain, DNA binding domain, linker domain, and Src homology 2 (SH2) domains. In addition, a fairly conserved transcriptional activation domain (TAD) was located at the C-terminus. Comparison of RbSTAT3 with other counterparts revealed higher identities (>90%) with fish orthologs. The genomic sequence of RbSTAT3 was obtained from a bacterial artificial chromosome (BAC) library, and was identified as a multi-exonic gene (24 exons), as found in other vertebrates. Genomic structural comparison and phylogenetic studies have showed that the evolutionary routes of teleostean and non-teleostean vertebrates were distinct. Quantitative real time PCR (qPCR) analysis revealed that the spatial distribution of RbSTAT3 mRNA expression was ubiquitous and highly detectable in blood, heart, and liver tissues. Transcriptional modulation of RbSTAT3 was examined in blood and liver tissues after challenges with bacteria (Edwardsiella tarda and Streptococcus iniae), rock bream irido virus (RBIV), and immune stimulants (LPS and poly (I:C)). Significant changes in RbSTAT3 transcription were also observed in response to tissue injury. In addition, the transcriptional up-regulation of RbSTAT3 was detected in rock bream heart cells upon recombinant rock bream IL-10 (rRbIL-10) treatment. Subcellular localization and nuclear translocation of rock bream STAT3 following poly (I:C) treatment were also demonstrated. Taken together, the results of the current study provide important evidence for potential roles of rock bream STAT3 in the immune system and wound healing processes.

Differential activation of signaling pathways by UVA and UVB radiation in normal human epidermal keratinocytes

Ultraviolet (UV) radiation from the solar spectrum is a major etiological factor for many cutaneous pathologies including cancer. By understanding changes in cell signaling pathways induced by UVA and UVB, novel strategies for prevention and treatment of UV-related pathologies could be developed. However, much of the information in the literature from various laboratories cannot cross talk because of difficulties associated with the use of ill-defined light sources and physiologically irrelevant light dosimetry. Herein, we have assessed the effect of exposure of normal human epidermal keratinocytes (NHEK) to UVA (2 and 4 J cm(-2)) or UVB (20 and 40 mJ cm(-2)) radiation. Employing western blot analysis, we found that exposure of NHEK to UVB, but not UVA, phosphorylates JNK1/2 at Th(183)/Tyr(185), STAT3 at Ser(727) , AKT at Ser(473) and increases c-Fos expression, whereas exposure to UVA, but not UVB, phosphorylates AKT at Thr(308). UVB as well as UVA exposure leads to increased phosphorylation of (1) ERK1/2 at Th(202)/Tyr(204); (2) p38 at Th(180)/Tyr(204); (3) STAT3 at Tyr(705); (4) mTOR at Thr(2448); and (v) p70S6k at Thr(421) /Ser(424); enhanced expression of PI3K (p85) and c-jun; and nuclear translocation of NFκB proteins. These findings could be considered as a beginning for understanding the differential effects of UVA and UVB in the human skin and may have implications both with respect to risk assessment from exposure to solar UV radiation, and to target interventions against signaling events mediated by UVA and UVB.

Growth factor signaling pathways as targets for prevention of epithelial carcinogenesis

Growth factor receptor (GFR) signaling controls epithelial cell growth by responding to various endogenous or exogenous stimuli and subsequently activating downstream signaling pathways including Stat3, PI3K/Akt/mTOR, MAPK, and c-Src. Environmental chemical toxicants and UVB irradiation cause enhanced and prolonged activation of GFR signaling and downstream pathways that contributes to epithelial cancer development including skin cancer. Recent studies, especially those with tissue-specific transgenic mouse models, have demonstrated that GFRs and their downstream signaling pathways contribute to all three stages of epithelial carcinogenesis by regulating a wide variety of biological functions including proliferation, apoptosis, angiogenesis, cell adhesion, and migration. Inhibiting these signaling pathways early in the carcinogenic process results in reduced cell proliferation and survival, leading to decreased tumor formation. Collectively, these studies suggest that GFR signaling and subsequent downstream signaling pathways are potential targets for the prevention of epithelial cancers including skin cancer.

Guidelines for the welfare and use of animals in cancer research

Animal experiments remain essential to understand the fundamental mechanisms underpinning malignancy and to discover improved methods to prevent, diagnose and treat cancer. Excellent standards of animal care are fully consistent with the conduct of high quality cancer research. Here we provide updated guidelines on the welfare and use of animals in cancer research. All experiments should incorporate the 3Rs: replacement, reduction and refinement. Focusing on animal welfare, we present recommendations on all aspects of cancer research, including: study design, statistics and pilot studies; choice of tumour models (e.g., genetically engineered, orthotopic and metastatic); therapy (including drugs and radiation); imaging (covering techniques, anaesthesia and restraint); humane endpoints (including tumour burden and site); and publication of best practice.

A single UVB exposure increases the expression of functional KIT in human melanocytes by up-regulating MITF expression through the phosphorylation of p38/CREB

KIT is an essential receptor that modulates melanocyte function and whose function is disrupted in several pigmentary disorders. However, little is known about the effects of a single UVB exposure on the expression of KIT and two important regulatory transcription factors, MITF and AP-2 alpha, in human melanocytes. We found that a single UVB exposure of human melanocytes induces an early decrease and a subsequent increase in functional KIT expression in concert with up-regulated MITF expression. The increased MITF expression was accompanied by a markedly stimulated and prolonged phosphorylation of p38/CREB. The UVB-stimulated expression of KIT could be completely abolished by a p38 inhibitor, concomitant with a reduced phosphorylation of CREB and a down-regulation of MITF expression. Interestingly, in non-UVB exposed human melanocytes, a MEK inhibitor stimulated the phosphorylation of p38/CREB which was associated with an increased production of MITF and KIT in a pattern similar to that induced by UVB. These findings indicate that UVB stimulates functional KIT expression in human melanocytes via the up-regulation of MITF which is, in turn, due to the activation of p38 and CREB.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Constitutive activation and targeted disruption of signal transducer and activator of transcription 3 (Stat3) in mouse epidermis reveal its critical role in UVB-induced skin carcinogenesis

In this study, the potential role of Stat3 in UVB-induced skin carcinogenesis was examined using skin-specific gain and loss of function transgenic mice, i.e., K5.Stat3C and K5Cre.Stat3^fl/fl mice, respectively. The epidermis of Stat3-deficient mice was highly sensitive to UVB-induced apoptosis, whereas the epidermis of K5.Stat3C mice was more resistant to UVB-induced apoptosis. In particular, the status of Stat3 influenced the survival of UV-photoproduct cells, including those located in the bulge region of hair follicles. K5.Stat3C mice exhibited significantly increased epidermal proliferation and hyperplasia in response to UVB irradiation, whereas Stat3-deficient mice showed reduced epidermal proliferation and hyperplasia. Expression of target genes regulated by Stat3, such as cyclin D1 and Bcl-x_L, was increased in epidermis of both control and UVB-irradiated K5.Stat3C mice, and downregulated in epidermis of both control and UVB-irradiated K5Cre.Stat3^fl/fl mice. Following UVB irradiation, the formation of skin tumors in K5.Stat3C mice was accelerated and both the incidence and multiplicity of skin tumors was significantly greater than wild-type controls. In contrast, Stat3-deficient mice were resistant to UVB skin carcinogenesis. These results demonstrate that Stat3 plays an important role in the development of UVB-induced skin tumors through its effects on both survival and proliferation of keratinocytes during carcinogenesis.

Molecular biology of basal and squamous cell carcinomas

Basal cell carcinomas and Squamous cell carcinomas are the two most common human cancers. The incidence of these two types of cancer is estimated to double within 20 years. Identification of the key molecular events is critical in helping us design novel strategies to treat and to prevent these cancers. For example, identification of hedgehog signaling activation has opened up many opportunities for targeted therapy and prevention of basal cell carcinomas. Significant progress has also been made in our understanding of squamous cell carcinomas of the skin. In this chapter, we will focus on major recent developments in our understanding of basal cell carcinomas and squamous cell carcinomas at the molecular levels and their clinical implications.

Ultraviolet radiation (UVR) activates p38 MAP kinase and induces post-transcriptional stabilization of the C/EBPδ mRNA in G0 growth arrested mammary epithelial cells

The G(0) growth arrest (quiescent) state is highly conserved in evolution to promote survival under adverse environmental conditions. To maintain viability, G(0) growth arrested cells limit gene expression to essential growth control and pro-survival genes. CCAAT enhancer binding protein delta (C/EBPdelta), a member of the C/EBP family of nuclear proteins, is highly expressed in G(0) growth arrested mammary epithelial cells (MECs). Although C/EBPdelta gene transcription is elevated during G(0) growth arrest, C/EBPdelta mRNA and protein are relatively short lived, suggesting tight control of the cellular C/EBPdelta content in unstressed, quiescent cells. Treatment of G(0) growth arrested MECs with ultraviolet radiation (UVR) dramatically increases the C/EBPdelta mRNA half-life (approximately 4-fold) and protein content (approximately 3-fold). The mRNA stabilizing effects of UVR treatment are mediated by the C/EBPdelta mRNA 3'untranslated region, which contains an AU rich element. UVR increased p38 MAP kinase (MAPK) activation and SB203580, a p38 MAPK inhibitor, blocked UVR-induced C/EBPdelta mRNA stabilization. UVR increased the nuclear to cytoplasmic translocation of HuR, an ARE-binding protein that functions in mRNA stabilization. Finally, HuR siRNA treatment blocked UVR-induced stabilization of the C/EBPdelta and C/EBPbeta mRNAs but had no effect on C/EBPzeta (CHOP) mRNA stability. In summary, G(0) growth arrested MECs respond to UVR treatment by activating p38 MAPK, increasing HuR translocation and HuR/C/EBPdelta mRNA binding and stabilizing the C/EBPdelta mRNA. These results identify post-transcriptional stabilization of the C/EBPdelta mRNA as a mechanism to increase C/EBPdelta levels in the stress response of quiescent cells to UVR.

Signal transducer and activator of transcription 3 (Stat3) in epithelial carcinogenesis

Signal transducer and activator of transcription 3 (Stat3) is one of a family of cytoplasmic proteins that participate in normal cellular responses to cytokines and growth factors as transcription factors. Stat3 modulates various physiological functions including cell survival, cell-cycle regulation, and angiogenesis through regulation of gene expression, and its constitutive activation is associated with a number of human epithelial cancers. Recent studies with skin-specific gain and loss of Stat3 function transgenic mice have shown that Stat3 plays critical roles in skin carcinogenesis. Multistage skin carcinogenesis bioassays performed with these transgenic mice clearly demonstrate that Stat3 is required for both tumor initiation and promotion through regulation of genes involved in survival and proliferation, respectively. Stat3 also plays a role in malignant progression of skin tumors by regulating genes that are involved in angiogenesis and invasion. Further studies have revealed that Stat3 plays a critical role in epidermal cell proliferation and survival following exposure to ultraviolet B (UVB) irradiation. In addition, Stat3 is constitutively active in UVB-induced skin tumors from both mice and humans. Collectively, these studies suggest that Stat3 may be a potential target for both the prevention and treatment of human epithelial cancers including skin cancer.

Silibinin Inhibits Inflammatory and Angiogenic Attributes in Photocarcinogenesis in SKH-1 Hairless Mice

Sunscreens partially filter UVB and, therefore, could partially prevent skin cancer; however, efficient approaches are desired to effectively prevent photocarcinogenesis. It is hypothesized that nontoxic pharmacologically active natural compounds can increase photoprotective effects. Our completed studies suggest that silibinin, a bioactive phytochemical, strongly prevents photocarcinogenesis; however, its mechanism is not fully understood. Herein, for the first time, we used a clinically relevant UVB dose (30 mJ/cm(2)/day) to examine the photoprotective effect and associated mechanisms of silibinin in SKH1 hairless mice. Topical or dietary silibinin treatment caused a strong protection against photocarcinogenesis in terms of delay in tumor appearance, multiplicity, and volume. Analyses of normal skin, uninvolved skin from tumor-bearing mice, and skin tumors showed a statistically significant decrease (P < 0.05-0.001) in inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2) levels by silibinin. Concomitantly, phospho-signal transducers and activators of transcription 3 (Tyr(705)) and phospho-p65(Ser(536)) were also decreased by silibinin, which are potential up-stream regulators of iNOS and COX-2. Simultaneously, silibinin also decreased UVB-caused increase in cell proliferation and microvessel density. In tumors, hypoxia-inducible factor 1alpha (HIF-1alpha) and vascular endothelial growth factor protein levels were decreased by silibinin. Further analysis showed that silibinin inhibited UVB-caused phosphorylation and nuclear translocation of STAT3 and p65, as well as nuclear factor kappaB (NF-kappaB) DNA binding activity. Together, these results suggest that silibinin causes a strong protective effect against photocarcinogenesis via down-regulation of inflammatory and angiogenic responses, involving HIF-1alpha, STAT3, and NF-kappaB transcription factors, as well as COX2 and iNOS.

Targeting signal-transducer-and-activator-of-transcription-3 for prevention and therapy of cancer: modern target but ancient solution

Recent evidence indicates a convergence of molecular targets for both prevention and therapy of cancer. Signal-transducer-and-activator-of-transcription-3 (STAT3), a member of a family of six different transcription factors, is closely linked with tumorigenesis. Its role in cancer is indicated by numerous avenues of evidence, including the following: STAT3 is constitutively active in tumor cells; STAT3 is activated by growth factors (e.g., EGF, TGF-alpha, IL-6, hepatocyte growth factor) and oncogenic kinases (e.g., Src); STAT3 regulates the expression of genes that mediate proliferation (e.g., c-myc and cyclin D1), suppress apoptosis (e.g., Bcl-x(L) and survivin), or promote angiogenesis (e.g, VEGF); STAT3 activation has been linked with chemoresistance and radioresistance; and chemopreventive agents have been shown to suppress STAT3 activation. Thus inhibitors of STAT3 activation have potential for both prevention and therapy of cancer. Besides small peptides and oligonucleotides, numerous small molecules have been identified as blockers of STAT3 activation, including synthetic molecules (e.g., AG 490, decoy peptides, and oligonucleotides) and plant polyphenols (e.g., curcumin, resveratrol, flavopiridol, indirubin, magnolol, piceatannol, parthenolide, EGCG, and cucurbitacin). This article discusses these aspects of STAT3 in more detail.