Clinicopathologic Characteristics and Neoplasia Risk of Colorectal Inflammatory Polyposis in Inflammatory Bowel Disease.

CONTEXT.­: Inflammatory polyps (IPs) in inflammatory bowel disease may have been associated in the past with increased neoplasia risk. Additionally, colonic mucosa in filiform polyposis and giant inflammatory polyposis may be difficult to visualize during endoscopic surveillance, perhaps contributing to early colectomy in these patients. OBJECTIVE.­: To examine the clinicopathologic characteristics and significance of IPs and inflammatory polyposis in inflammatory bowel disease. DESIGN.­: We identified 336 resections from inflammatory bowel disease patients (212 [63.1%] male; mean age, 40.3 years; 175 [52.1%] with ulcerative colitis), including 78 with rare/few (<10) IPs, 141 with multiple (≥10) IPs, and 117 with inflammatory polyposis (including 30 with filiform polyposis/giant inflammatory polyposis) and compared them with 100 controls without IPs along various parameters, including overall and occult (unexpected) dysplasia. RESULTS.­: There was no increased neoplasia in resections with IPs compared with controls, given similar age, disease duration, degree of inflammation, anatomical extent of colitis, prevalence of primary sclerosing cholangitis, and tissue sampling. Increasing numbers of IPs and inflammatory polyposis were significantly associated in multivariate analysis with ulcerative and indeterminate colitis (P = .003) and shorter disease duration (P = .01), but also, and independently, with lower rates of dysplasia overall, including all grades (P = .001) and advanced neoplasia (P = .04). There were no instances of occult dysplasia (any grade) among inflammatory polyposis cases. CONCLUSIONS.­: These findings support the conclusion that the presence of IPs per se, and inflammatory polyposis in particular (including filiform polyposis and giant inflammatory polyposis), should not be considered an independent risk factor for the development of neoplasia in inflammatory bowel disease patients, outside the context of disease duration and inflammatory burden.

Protective Effect of Triphala against Oxidative Stress-Induced Neurotoxicity.

BACKGROUND: Oxidative stress is implicated in the progression of many neurological diseases, which could be induced by various chemicals, such as hydrogen peroxide (H2O2) and acrylamide. Triphala is a well-recognized Ayurvedic medicine that possesses different therapeutic properties (e.g., antihistamine, antioxidant, anticancer, anti-inflammatory, antibacterial, and anticariogenic effects). However, little information is available regarding the neuroprotective effect of Triphala on oxidative stress. MATERIALS AND METHODS: An in vitro H2O2-induced SH-SY5Y cell model and an in vivo acrylamide-induced zebrafish model were established. Cell viability, apoptosis, and proliferation were examined by MTT assay, ELISA, and flow cytometric analysis, respectively. The molecular mechanism underlying the antioxidant activity of Triphala against H2O2 was investigated dose dependently by Western blotting. The in vivo neuroprotective effect of Triphala on acrylamide-induced oxidative injury in Danio rerio was determined using immunofluorescence staining. RESULTS: The results indicated that Triphala plays a neuroprotective role against H2O2 toxicity in inhibiting cell apoptosis and promoting cell proliferation. Furthermore, Triphala pretreatment suppressed the phosphorylation of the mitogen-activated protein kinase (MARK) signal pathway (p-Erk1/2, p-JNK1/2, and p-p38), whereas it restored the activities of antioxidant enzymes (superoxide dismutase 1 (SOD1) and catalase) in the H2O2-treated SH-SY5Y cells. Consistently, similar protective effects of Triphala were observed in declining neuroapoptosis and scavenging free radicals in the zebrafish central neural system, possessing a critical neuroprotective property against acrylamide-induced oxidative stress. CONCLUSION: In summary, Triphala is a promising neuroprotective agent against oxidative stress in SH-SY5Y cells and zebrafishes with significant antiapoptosis and antioxidant activities.

The Genetic and Epigenetic Mechanisms Involved in Irreversible Pulp Neural Inflammation.

AIM: To identify the critical genetic and epigenetic biomarkers by constructing the long noncoding RNA- (lncRNA-) related competing endogenous RNA (ceRNA) network involved in irreversible pulp neural inflammation (pulpitis). MATERIALS AND METHODS: The public datasets regarding irreversible pulpitis were downloaded from the gene expression omnibus (GEO) database. The differential expression analysis was performed to identify the differentially expressed genes (DEGs) and DElncRNAs. Functional enrichment analysis was performed to explore the biological processes and signaling pathways enriched by DEGs. By performing a weighted gene coexpression network analysis (WGCNA), the significant gene modules in each dataset were identified. Most importantly, DElncRNA-DEmRNA regulatory network and DElncRNA-associated ceRNA network were constructed. A transcription factor- (TF-) DEmRNA network was built to identify the critical TFs involved in pulpitis. RESULT: Two datasets (GSE92681 and GSE77459) were selected for analysis. DEGs involved in pulpitis were significantly enriched in seven signaling pathways (i.e., NOD-like receptor (NLR), Toll-like receptor (TLR), NF-kappa B, tumor necrosis factor (TNF), cell adhesion molecules (CAMs), chemokine, and cytokine-cytokine receptor interaction pathways). The ceRNA regulatory relationships were established consisting of three genes (i.e., LCP1, EZH2, and NR4A1), five miRNAs (i.e., miR-340-5p, miR-4731-5p, miR-27a-3p, miR-34a-5p, and miR-766-5p), and three lncRNAs (i.e., XIST, MIR155HG, and LINC00630). Six transcription factors (i.e., GATA2, ETS1, FOXP3, STAT1, FOS, and JUN) were identified to play pivotal roles in pulpitis. CONCLUSION: This paper demonstrates the genetic and epigenetic mechanisms of irreversible pulpitis by revealing the ceRNA network. The biomarkers identified could provide research direction for the application of genetically modified stem cells in endodontic regeneration.

Novel dot-blot assay for detection of vascular Notch3 aggregates in patients with CADASIL.

To detect vascular Notch3 extracellular domain aggregates in CADASIL, we developed a novel dot-blot assay with both autopsy and biopsy skin samples. We obtained samples from 11 patients with CADASIL and 12 control patients, and we performed dot-blot analyses by using sequential biochemical tissue extractions with three different antibodies against specific regions of the Notch3 extracellular domain. We also analyzed clinical features and vascular accumulations of Notch3 by immunohistochemistry. Via the dot-blot assay with the antibody against the C-terminal region of the Notch3 extracellular domain, we successfully detected Notch3 extracellular domain aggregates in skin tissue homogenates obtained from patients with CADASIL. Our novel method may therefore aid the diagnosis of CADASIL.

A New Vision of Mitochondrial Unfolded Protein Response to the Sirtuin Family.

Mitochondrial damage is involved in many pathophysiological processes, such as tumor development, metabolism, and neurodegenerative diseases. The mitochondrial unfolded protein response (mtUPR) is the first stress-protective response initiated by mitochondrial damage, and it repairs or clears misfolded proteins to alleviate this damage. Studies have confirmed that the sirtuin family is essential for the mitochondrial stress response; in particular, SIRT1, SIRT3, and SIRT7 participate in the mtUPR in different axes. This article summarizes the associations of sirtuins with the mtUPR as well as specific molecular targets related to the mtUPR in different disease models, which will provide new inspiration for studies on mitochondrial stress, mitochondrial function protection, and mitochondria-related diseases, such as neurodegenerative diseases.

Reacquisition of E-cadherin expression in metastatic deposits of signet-ring cell carcinoma of the upper gastrointestinal system: a potential anchor for metastatic deposition.

AIMS: To examine the expression of E-cadherin in paired primary and metastatic signet-ring cell carcinomas (SRCC) of various organ systems in order to explore the potential role of the molecule in metastatic dissemination of this unique tumour type. METHODS: Thirty-seven consecutive cases of SRCC from various organs with paired primary and metastatic tumorous tissue available were retrieved. The intensity of membranous E-cadherin expression was semiquantitatively scored on a scale of 0-3+. RESULTS: Reduced E-cadherin expression was a distinct feature of primary SRCC and was observed in 78% of primary tumours. Interestingly, the E-cadherin reduction was less frequently seen in metastatic SRCC when compared with their primary counterparts, and was only found in 57% of tumours in lymph node metastases or at distant sites of relapse. Furthermore, the mean score of E-cadherin expression of primary SRCC was significantly lower than that of their metastatic counterparts (2.3 vs 1.8; p=0.008). When divided by organ systems, the reacquisition of E-cadherin expression in the metastatic deposits was most remarkable in the SRCC of upper gastrointestinal tract origin (2.3 vs 1.4; p=0.003), whereas no significant difference was observed in other organ systems. CONCLUSIONS: While the reduction of E-cadherin in primary SRCC supports its pivotal role in epithelial-mesenchymal transition, a process crucial in tumour progression and metastatic dissemination, the re-expression of this molecule in metastatic SRCC cells implies a reversal to their epithelial phenotype (thus mesenchymal-epithelial transition) which, in turn, theoretically helps tumour cells to anchor and form cohesive metastatic deposits.

Reduced E-Cadherin and Aberrant ß-Catenin Expression are Associated With Advanced Disease in Signet-Ring Cell Carcinomas.

Signet-ring cell carcinomas (SRCCs) tend to present at higher stages and thus are generally associated with a worse prognosis. It has been postulated that a deficiency of E-cadherin may be causal in the pathogenesis of SRCC in animal models. In this study, we systemically analyzed the expression of E-cadherin and ß-catenin, a key component of the cadherin complex, in 137 consecutive SRCCs of various organ systems to explore the significance of these molecules in the pathogenesis and progression of SRCCs. Seventy-six percent of SRCCs showed loss or reduced E-cadherin expression. Aberrant ß-catenin expression, defined as loss of membranous expression and nuclear/cytoplasmic subcellular localization, was observed in 60% of these cases, with the altered ß-catenin expression observed most commonly in the breast (93%) and least in the lung (38%) primaries. Further, the aberrant ß-catenin was significantly associated with pathologic nodal stage (P=0.002) and clinical stage (P=0.02). Our findings demonstrated that reduced membranous E-cadherin and aberrant ß-catenin expression were frequent events in SRCCs of various organs, and that the altered ß-catenin expression was significantly associated with advanced disease. The observations further support the importance of these molecules in the pathogenesis of SRCCs, and indicate the fundamental role of the Wnt/ß-catenin signaling pathway in the progression of these tumors. Further investigations of the downstream molecules in this cascade may provide potential novel therapeutic targets for this aggressive tumor type.

Synthesis of functional polyester for fabrication of nano-fibrous scaffolds and its effect on PC12 cells.

An ideal scaffold should mimic the advantageous characteristics of a natural extracellular matrix for cell attachment, proliferation, and differentiation. In this study, well-defined block copolymer with functional groups was synthesized. The structure of the block copolymer was characterized by nuclear magnetic resonance, gel permeation chromatography, and differential scanning calorimetry. Thermally induced phase separation was employed to fabricate nano-fibrous scaffolds based on the synthesized block copolymer. The scaffold, with fiber diameter ranging from 400 to 500 nm, was fabricated for in vitro culture of PC12 cells. The carboxyl groups on the side chain resulted in increased hydrophilicity of nano-fibrous scaffolds and enhanced cell proliferation. In addition, this scaffold structure was beneficial in directing the growth of regenerating axons in nerve tissue engineering. Results of 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay and scanning electron microscopy confirmed that the nano-fibrous scaffolds with functional groups were suitable for PC12 cells growth. Moreover, the carboxyl groups were suitable for coupling with biological signals. Thus, the nano-fibrous scaffolds have potential applications in tissue engineering.

Solitary, adult-onset, intraosseous myofibroma of the finger: report of a case and review of literature.

Myofibroma is a rare benign neoplasm of myofibroblastic origin. It typically occurs in the skin and subcutaneous tissues of the head and neck in infants and young children as multicentric lesions known as infantile myofibromatosis. Intraosseous myofibromas are very rare and are typically destructive lesions that predominantly affect craniofacial bones in the setting of myofibromatosis. Solitary, intraosseous myofibromas in adults are exceedingly rare. Herein, we report a myofibroma involving the middle phalanx of the right index finger in a 58-year-old man who presented with a pathologic fracture. Twelve other cases of adult-onset, intraosseous myofibroma were compiled from the English language literature and integrated with this report.

Necdin, a negative growth regulator, is a novel STAT3 target gene down-regulated in human cancer.

Cytokine and growth factor signaling pathways involving STAT3 are frequently constitutively activated in many human primary tumors, and are known for the transcriptional role they play in controlling cell growth and cell cycle progression. However, the extent of STAT3's reach on transcriptional control of the genome as a whole remains an important question. We predicted that this persistent STAT3 signaling affects a wide variety of cellular functions, many of which still remain to be characterized. We took a broad approach to identify novel STAT3 regulated genes by examining changes in the genome-wide gene expression profile by microarray, using cells expressing constitutively-activated STAT3. Using computational analysis, we were able to define the gene expression profiles of cells containing activated STAT3 and identify candidate target genes with a wide range of biological functions. Among these genes we identified Necdin, a negative growth regulator, as a novel STAT3 target gene, whose expression is down-regulated at the mRNA and protein levels when STAT3 is constitutively active. This repression is STAT3 dependent, since inhibition of STAT3 using siRNA restores Necdin expression. A STAT3 DNA-binding site was identified in the Necdin promoter and both EMSA and chromatin immunoprecipitation confirm binding of STAT3 to this region. Necdin expression has previously been shown to be down-regulated in a melanoma and a drug-resistant ovarian cancer cell line. Further analysis of Necdin expression demonstrated repression in a STAT3-dependent manner in human melanoma, prostate and breast cancer cell lines. These results suggest that STAT3 coordinates expression of genes involved in multiple metabolic and biosynthetic pathways, integrating signals that lead to global transcriptional changes and oncogenesis. STAT3 may exert its oncogenic effect by up-regulating transcription of genes involved in promoting growth and proliferation, but also by down-regulating expression of negative regulators of the same cellular processes, such as Necdin.

Histone deacetylase inhibitors downregulate checkpoint kinase 1 expression to induce cell death in non-small cell lung cancer cells.

BACKGROUND: Histone deacetylase inhibitors (HDACis) are promising anticancer drugs; however, the molecular mechanisms leading to HDACi-induced cell death have not been well understood and no clear mechanism of resistance has been elucidated to explain limited efficacy of HDACis in clinical trials. METHODS AND FINDINGS: Here, we show that protein levels of checkpoint kinase 1 (Chk1), which has a major role in G(2) cell cycle checkpoint regulation, was markedly reduced at the protein and transcriptional levels in lung cancer cells treated with pan-and selective HDACis LBH589, scriptaid, valproic acid, apicidin, and MS-275. In HDACi treated cells Chk1 function was impaired as determined by decreased inhibitory phosphorylation of cdc25c and its downstream target cdc2 and increased expression of cdc25A and phosphorylated histone H3, a marker of mitotic entry. In time course experiments, Chk1 downregulation occurred after HDACi treatment, preceding apoptosis. Ectopic expression of Chk1 overcame HDACi-induced cell death, and pretreating cells with the cdc2 inhibitor purvalanol A blocked entry into mitosis and prevented cell death by HDACis. Finally, pharmacological inhibition of Chk1 showed strong synergistic effect with LBH589 in lung cancer cells. CONCLUSIONS: These results define a pathway through which Chk1 inhibition can mediate HDACi-induced mitotic entry and cell death and suggest that Chk1 could be an early pharmacodynamic marker to assess HDACi efficacy in clinical samples.

CDKN1C negatively regulates RNA polymerase II C-terminal domain phosphorylation in an E2F1-dependent manner.

CDKN1C is a cyclin-dependent kinase inhibitor and is a candidate tumor suppressor gene. We previously found that the CDKN1C protein represses E2F1-driven transcription in an apparent negative feedback loop. Herein, we explore the mechanism by which CDKN1C represses transcription. We find that adenoviral-mediated overexpression of CDKN1C leads to a dramatic reduction in phosphorylation of the RNA polymerase II (pol II) C-terminal domain (CTD). RNA interference studies demonstrate that this activity is not an artifact of CDKN1C overexpression, because endogenous CDKN1C mediates an inhibition of RNA pol II CTD phosphorylation in HeLa cells upon treatment with dexamethasone. Surprisingly, we find that CDKN1C-mediated repression of RNA pol II phosphorylation is E2F1-dependent, suggesting that E2F1 may direct CDKN1C to chromatin. Chromatin immunoprecipitation assays demonstrate that CDKN1C is associated with E2F1-regulated promoters in vivo and that this association can dramatically reduce the level of RNA pol II CTD phosphorylation at both Ser-2 and Ser-5 of the C-terminal domain repeat. In addition, we show that CDKN1C interacts with both CDK7 and CDK9 (putative RNA pol II CTD kinases) and that CDKN1C blocks their ability to phosphorylate a glutathione S-transferase-CTD fusion protein in vitro. E2F1 and CDKN1C are found to form stable complexes both in vivo and in vitro. Molecular studies demonstrate that the E2F1-CDKN1C interaction is mediated by two E2F domains. A central E2F1 domain interacts directly with CDKN1C, whereas a C-terminal E2F1 domain interacts with CDKN1C via interaction with Rb. The results presented in this report highlight a novel mechanism of tumor suppression by CDKN1C.

Identification of Aurora-A as a direct target of E2F3 during G2/M cell cycle progression.

Aurora-A is a centrosome kinase and plays a pivotal role in G(2)/M cell cycle progression. Expression of Aurora-A is cell cycle-dependent. Levels of Aurora-A mRNA and protein are low in G(1)/S, accumulate during G(2)/M, and decrease rapidly after mitosis. Previous studies have shown regulation of the Aurora-A protein level during the cell cycle through the ubiquitin-proteasome pathway. However, the mechanism of transcriptional regulation of Aurora-A remains largely unknown. Here, we demonstrated that E2F3 modulates Aurora-A mRNA expression during the cell cycle. Ectopic expression of E2F3 induces Aurora-A expression. Stable knockdown of E2F3 decreases mRNA and protein levels of Aurora-A and delays G(2)/M entry. Further, E2F3 directly binds to Aurora-A promoter and stimulates the promoter activity. Deletion and mutation analyses of the Aurora-A promoter revealed that a region located 96-bp upstream of the transcription initiation site is critical for the activation of the promoter by E2F3. In addition, expression of E2F3 positively correlates with the protein level of Aurora-A in human ovarian cancer examined. These results indicate for the first time that Aurora-A is transcriptionally regulated by E2F3 during the cell cycle and that E2F3 is a causal factor for up-regulation of Aurora-A in a subset of human ovarian cancer. Thus, the E2F3-Aurora-A axis could be an important target for cancer intervention.

A small-molecule E2F inhibitor blocks growth in a melanoma culture model.

HLM006474 was identified using a computer-based virtual screen and the known crystal structure of the DNA-bound E2F4/DP2 heterodimer. Treatment of multiple cell lines with HLM006474 resulted in the loss of intracellular E2F4 DNA-binding activity as measured by electrophoretic mobility shift assay within hours. Overnight exposure to HLM006474 resulted in down-regulation of total E2F4 protein as well as known E2F targets. The effects of HLM006474 treatment on different cell lines varied but included a reduction in cell proliferation and an increase in apoptosis. HLM006474 induced apoptosis in a manner distinct from cisplatin and doxorubicin. E2F4-null mouse embryonic fibroblasts were less sensitive than wild-type counterparts to the apoptosis-inducing activity of the compound, revealing its biological specificity. A375 cells were extremely sensitive to the apoptosis-inducing activity of the compound in two-dimensional culture, and HLM006474 was a potent inhibitor of melanocytes proliferation and subsequent invasion in a three-dimensional tissue culture model system. Together, these results suggest that interference with E2F activity using small molecules may have clinical application in cancer therapy.

Signal transducer and activator of transcription 3 is required for hypoxia-inducible factor-1alpha RNA expression in both tumor cells and tumor-associated myeloid cells.

Hypoxia-inducible factor 1 (HIF-1) is a potent tumorigenic factor. Its alpha subunit (HIF-1alpha), which is tightly regulated in normal tissues, is elevated in tumors due to hypoxia and overactive growth signaling pathways. Although much is known about HIF-1alpha regulation in cancer cells, crucial molecular targets that affect HIF-1alpha levels modulated by both hypoxia and oncogenic signaling pathways remain to be identified. Additionally, whether and how the tumor microenvironment contributes to HIF-1alpha accumulation is unclear. This study shows a novel mechanism by which HIF-1alpha availability is regulated in both cancer cells and in myeloid cells in the tumor microenvironment. We show a requirement of signal transducer and activator of transcription 3 (Stat3) for HIF-1alpha RNA expression under both hypoxia and growth signaling conditions. Furthermore, tumor-derived myeloid cells express elevated levels of HIF-1alpha mRNA relative to their counterparts from normal tissues in a Stat3-dependent manner. Additionally, Stat3 activity in the nontransformed cells in the tumor milieu affects HIF-1alpha RNA expression of the entire growing tumor. Consistent with a role of Stat3 in regulating HIF-1alpha RNA transcription, elevated Stat3 activity increases HIF-1alpha promoter activity, and Stat3 protein binds to the HIF-1alpha promoter in both transformed cells and in growing tumors. Taken together, these findings show a novel mode by which HIF-1alpha is regulated not only in cancer cells but also in the tumor-associated inflammatory cells, suggesting Stat3 as an important molecular target for inhibiting the oncogenic potential of HIF-1 induced by both hypoxia and overactive growth signaling pathways prevalent in cancer.

RhoBTB2 (DBC2) is a mitotic E2F1 target gene with a novel role in apoptosis.

We have identified the RhoBTB2 putative tumor suppressor gene as a direct target of the E2F1 transcription factor. Overexpression of E2F1 led to up-regulation of RhoBTB2 at the level of mRNA and protein. This also occurred during the induction of E2F1 activity in the presence of cycloheximide, thus indicating that RhoBTB2 is a direct target. RNAi-mediated knockdown of E2F1 resulted in decreased RhoBTB2 protein expression, demonstrating that RhoBTB2 is a physiological target of E2F1. Because E2F1 primarily serves to transcribe genes involved in cell cycle progression and apoptosis, we explored whether RhoBTB2 played roles in either of these processes. We found RhoBTB2 expression highly up-regulated during mitosis, which was partially dependent on the presence of E2F1. Furthermore, overexpression of RhoBTB2 induced a short term increase in cell cycle progression and proliferation, while long term expression had a negative effect on these processes. We similarly found RhoBTB2 up-regulated during drug-induced apoptosis, with this being primarily dependent on E2F1. Finally, we observed that knockdown of RhoBTB2 levels via siRNA delayed the onset of drug-induced apoptosis. Collectively, we describe RhoBTB2 as a novel direct target of E2F1 with roles in cell cycle and apoptosis.

Interactions between E2F1 and SirT1 regulate apoptotic response to DNA damage.

The nicotinamide adenine dinucleotide (NAD)-dependent deacetylase Sir2 (silent information regulator 2) regulates gene silencing in yeast and promotes lifespan extension during caloric restriction. The mammalian homologue of Sir2 (SirT1) regulates p53, NF-kappaB and Forkhead transcription factors, and is implicated in stress response. This report shows that the cell-cycle and apoptosis regulator E2F1 induces SirT1 expression at the transcriptional level. Furthermore, SirT1 binds to E2F1 and inhibits E2F1 activities, forming a negative feedback loop. Knockdown of SirT1 by small interference RNA (siRNA) increases E2F1 transcriptional and apoptotic functions. DNA damage by etoposide causes E2F1-dependent induction of SirT1 expression and knockdown of SirT1 increases sensitivity to etoposide. These results reveal a mutual regulation between E2F1 and SirT1 that affects cellular sensitivity to DNA damage.

Bok, Bcl-2-related Ovarian Killer, Is Cell Cycle-regulated and Sensitizes to Stress-induced Apoptosis.

Bok/Mtd (Bcl-2-related ovarian killer/Matador) is considered a pro-apoptotic member of the Bcl-2 family. Although identified in 1997, little is known about its biological role. We have previously demonstrated that Bok mRNA is up-regulated following E2F1 overexpression. In the current work, we demonstrate that Bok RNA is low in quiescent cells and rises upon serum stimulation. To determine the mechanism underlying this regulation, we cloned and characterized the mouse Bok promoter. We find that the mouse promoter contains a conserved E2F binding site (-43 to -49) and that a Bok promoter-driven luciferase reporter is activated by serum stimulation dependent on this site. Chromatin immunoprecipitation assays demonstrate that endogenous E2F1 and E2F3 associate with the Bok promoter in vivo. Surprisingly, we find that H1299 cells can stably express high levels of exogenous Bok protein. However, these cells are highly sensitive to chemotherapeutic drug treatment. Taken together these results demonstrate that Bok represents a cell cycle-regulated pro-apoptotic member of the Bcl-2 family, which may predispose growing cells to chemotherapeutic treatment.

Role of Stat3 in regulating p53 expression and function.

Loss of p53 function by mutation is common in cancer. However, most natural p53 mutations occur at a late stage in tumor development, and many clinically detectable cancers have reduced p53 expression but no p53 mutations. It remains to be fully determined what mechanisms disable p53 during malignant initiation and in cancers without mutations that directly affect p53. We show here that oncogenic signaling pathways inhibit the p53 gene transcription rate through a mechanism involving Stat3, which binds to the p53 promoter in vitro and in vivo. Site-specific mutation of a Stat3 DNA-binding site in the p53 promoter partially abrogates Stat3-induced inhibition. Stat3 activity also influences p53 response genes and affects UV-induced cell growth arrest in normal cells. Furthermore, blocking Stat3 in cancer cells up-regulates expression of p53, leading to p53-mediated tumor cell apoptosis. As a point of convergence for many oncogenic signaling pathways, Stat3 is constitutively activated at high frequency in a wide diversity of cancers and is a promising molecular target for cancer therapy. Thus, repression of p53 expression by Stat3 is likely to have an important role in development of tumors, and targeting Stat3 represents a novel therapeutic approach for p53 reactivation in many cancers lacking p53 mutations.