Erxi Wu

PDGFRs are critical for PI3K/Akt activation and negatively regulated by mTOR

The receptor tyrosine kinase/PI3K/Akt/mammalian target of rapamycin (RTK/PI3K/Akt/mTOR) pathway is frequently altered in tumors. Inactivating mutations of either the TSC1 or the TSC2 tumor-suppressor genes cause tuberous sclerosis complex (TSC), a benign tumor syndrome in which there is both hyperactivation of mTOR and inhibition of RTK/PI3K/Akt signaling, partially due to reduced PDGFR expression. We report here that activation of PI3K or Akt, or deletion of phosphatase and tensin homolog (PTEN) in mouse embryonic fibroblasts (MEFs) also suppresses PDGFR expression. This was a direct effect of mTOR activation, since rapamycin restored PDGFR expression and PDGF-sensitive Akt activation in Tsc1-/- and Tsc2-/- cells. Akt activation in response to EGF in Tsc2-/- cells was also reduced. Furthermore, Akt activation in response to each of EGF, IGF, and PMA was reduced in cells lacking both PDGFRalpha and PDGFRbeta, implying a role for PDGFR in transmission of growth signals downstream of these stimuli. Consistent with the reduction in PI3K/Akt signaling, in a nude mouse model both Tsc1-/- and Tsc2-/- cells had reduced tumorigenic potential in comparison to control cells, which was enhanced by expression of either active Akt or PDGFRbeta. In conclusion, PDGFR is a major target of negative feedback regulation in cells with activated mTOR, which limits the growth potential of TSC tumors.

Mammalian target of rapamycin regulates murine and human cell differentiation through STAT3/p63/Jagged/Notch cascade

The receptor tyrosine kinase/PI3K/AKT/mammalian target of rapamycin (RTK/PI3K/AKT/mTOR) pathway is frequently altered in cancer, but the underlying mechanism leading to tumorigenesis by activated mTOR remains less clear. Here we show that mTOR is a positive regulator of Notch signaling in mouse and human cells, acting through induction of the STAT3/p63/Jagged signaling cascade. Furthermore, in response to differential cues from mTOR, we found that Notch served as a molecular switch to shift the balance between cell proliferation and differentiation. We determined that hyperactive mTOR signaling impaired cell differentiation of murine embryonic fibroblasts via potentiation of Notch signaling. Elevated mTOR signaling strongly correlated with enhanced Notch signaling in poorly differentiated but not in well-differentiated human breast cancers. Both human lung lymphangioleiomyomatosis (LAM) and mouse kidney tumors with hyperactive mTOR due to tumor suppressor TSC1 or TSC2 deficiency exhibited enhanced STAT3/p63/Notch signaling. Furthermore, tumorigenic potential of cells with uncontrolled mTOR signaling was suppressed by Notch inhibition. Our data therefore suggest that perturbation of cell differentiation by augmented Notch signaling might be responsible for the underdifferentiated phenotype displayed by certain tumors with an aberrantly activated RTK/PI3K/AKT/mTOR pathway. Additionally, the STAT3/p63/Notch axis may be a useful target for the treatment of cancers exhibiting hyperactive mTOR signaling.

SDF-1/CXCR4 signaling induces pancreatic cancer cell invasion and epithelial–mesenchymal transition in vitro through non-canonical activation of Hedgehog pathway

In our previous study, we found that blockade of SDF-1/CXCR4 signaling inhibits pancreatic cancer cell migration and invasion in vitro. However, the mechanism governing the downstream regulation of SDF-1/CXCR4-mediated invasion remains unclear. Here we report the role of SDF-1/CXCR4 in pancreatic cancer and the possible mechanism of SDF-1/CXCR4-mediated pancreatic cancer invasion. We show that there is a cross-talk between SDF-1/CXCR4 axis and non-canonical Hedgehog (Hh) pathway in pancreatic cancer. Furthermore, our data demonstrate that the ligand of CXCR4, SDF-1 induces CXCR4-positive pancreatic cancer invasion, epithelial-mesenchymal transition (EMT) process and activates the non-canonical Hh pathway. Moreover, we also demonstrate that the invasion of a pancreatic cancer and EMT resulting from the activation of SDF-1/CXCR4 axis is effectively inhibited by Smoothened (SMO) inhibitor cyclopamine and siRNA specific to Gli-1. Collectively, these data demonstrate that SDF-1/CXCR4 modulates the non-canonical Hh pathway by increasing the transcription of SMO in a ligand-independent manner. Taken together, SDF-1/CXCR4 axis may represent a promising therapeutic target to prevent pancreatic cancer progression.

Xanthones from Mangosteen Extracts as Natural Chemopreventive Agents: Potential Anticancer Drugs

Despite decades of research, the treatment and management of malignant tumors still remain a formidable challenge for public health. New strategies for cancer treatment are being developed, and one of the most promising treatment strategies involves the application of chemopreventive agents. The search for novel and effective cancer chemopreventive agents has led to the identification of various naturally occurring compounds. Xanthones, from the pericarp, whole fruit, heartwood, and leaf of mangosteen (Garcinia mangostana Linn., GML), are known to possess a wide spectrum of pharmacologic properties, including antioxidant, anti- tumor, anti-allergic, anti-inflammatory, anti-bacterial, anti-fungal, and anti-viral activities. The potential chemopreventive and chemotherapeutic activities of xanthones have been demonstrated in different stages of carcinogenesis (initiation, promotion, and progression) and are known to control cell division and growth, apoptosis, inflammation, and metastasis. Multiple lines of evidence from numerous in vitro and in vivo studies have confirmed that xanthones inhibit proliferation of a wide range of human tumor cell types by modulating various targets and signaling transduction pathways. Here we provide a concise and comprehensive review of preclinical data and assess the observed anticancer effects of xanthones, supporting its remarkable potential as an anticancer agent.

Anti-Cancer Activities of Tea Epigallocatechin-3-Gallate in Breast Cancer Patients under Radiotherapy

The purpose of this study was to test the hypothesis that administration of epigallocatechin-3-gallate (EGCG), a polyphenol present in abundance in widely consumed tea, inhibits cell proliferation, invasion, and angiogenesis in breast cancer patients. EGCG in 400 mg capsules was orally administered three times daily to breast cancer patients undergoing treatment with radiotherapy. Parameters related to cell proliferation, invasion, and angiogenesis were analyzed while blood samples were collected at different time points to determine efficacy of the EGCG treatment. Compared to patients who received radiotherapy alone, those given radiotherapy plus EGCG for an extended time period (two to eight weeks) showed significantly lower serum levels of vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), and reduced activation of metalloproteinase-9 and metalloproteinase-2 (MMP9/MMP2). Addition of sera obtained from patients treated with combination of radiotherapy and EGCG feeding for 2-8 weeks to in vitro cultures of highly-metastatic human MDA-MB-231 breast cancer cells resulted in the following significant changes: (1) suppression of cell proliferation and invasion; (2) arrest of cell cycles at the G0/G1 phase; (3) reduction of activation of MMP9/MMP2, expressions of Bcl-2/Bax, c-Met receptor, NF-κB, and the phosphorylation of Akt. MDA-MB-231 cells exposed to 5-10 μM EGCG also showed significant augmentation of the apoptosis inducing effects of γ-radiation, concomitant with reduced NF-κB protein level and AKT phosphorylation. These results provide hitherto unreported evidence that EGCG potentiated efficacy of radiotherapy in breast cancer patients, and raise the possibility that this tea polyphenol has potential to be a therapeutic adjuvant against human metastatic breast cancer.

Hedgehog signaling regulates hypoxia induced epithelial to mesenchymal transition and invasion in pancreatic cancer cells via a ligand-independent manner

BackgroundHypoxia plays a vital role in cancer epithelial to mesenchymal transition (EMT) and invasion. However, it is not quite clear how hypoxia may contribute to these events. Here we investigate the role of Hedgehog (Hh) signaling in hypoxia induced pancreatic cancer EMT and invasion.MethodsPancreatic cancer cells were cultured under controlled hypoxia conditions (3% O2) or normoxic conditions. HIF-1α siRNA, cyclopamine (a SMO antagonist) and GLI1 siRNA were used to inhibit HIF-1α transcription or Hh signaling activation. The effect of hypoxia and Hh signaling on cancer cell EMT and invasion were evaluated by Quantitative real-time PCR analysis, Western blot analysis and invasion assay.ResultsHere, we show that non-canonical Hh signaling is required as an important role to switch on hypoxia-induced EMT and invasion in pancreatic cancer cells. Moreover, our data demonstrate hypoxia induces EMT process as well as invasion, and activates the non-canonical Hh pathway without affecting sonic hedgehog homolog (SHH) expression. Moreover, these effects are reversible upon HIF-1α siRNA interference with unchanged SHH and patched1 (PTCH1) level. Furthermore, our data demonstrate that hypoxia induced invasion and EMT process are effectively inhibited by Smoothened (SMO) antagonist cyclopamine and GLI1 siRNA. In addition, GLI1 interference inhibited EMT progress with significantly suppressed vimentin expression, whereas inhibition of SMO through cyclopamine could not reduce vimentin level. This data indicate that hypoxia could trigger other factors (such as TGF-β, KRAS or RTK) bypassing SMO to activate GLI1 directly.ConclusionsOur findings suggest that Hh signaling modulates hypoxia induced pancreatic cancer EMT and invasion in a ligand-independent manner. Thus, Hh signaling may represent a promising therapeutic target for preventing pancreatic cancer progression.

High Glucose Promotes Pancreatic Cancer Cell Proliferation via the Induction of EGF Expression and Transactivation of EGFR

Multiple lines of evidence suggest that a large portion of pancreatic cancer patients suffer from either hyperglycemia or diabetes, both of which are characterized by high blood glucose level. However, the underlying biological mechanism of this phenomenon is largely unknown. In the present study, we demonstrated that the proliferative ability of two human pancreatic cancer cell lines, BxPC-3 and Panc-1, was upregulated by high glucose in a concentration-dependent manner. Furthermore, the promoting effect of high glucose levels on EGF transcription and secretion but not its receptors in these PC cell lines was detected by using an EGF-neutralizing antibody and RT-PCR. In addition, the EGFR transactivation is induced by high glucose levels in concentration- and time-dependent manners in PC cells in the presence of the EGF-neutralizing antibody. These results suggest that high glucose promotes pancreatic cancer cell proliferation via the induction of EGF expression and transactivation of EGFR. Our findings may provide new insight on the links between high glucose level and PC in terms of the molecular mechanism and reveal a novel therapeutic strategy for PC patients who simultaneously suffer from either diabetes or hyperglycemia.

Comprehensive Dissection of PDGF-PDGFR Signaling Pathways in PDGFR Genetically Defined Cells

Despite the growing understanding of PDGF signaling, studies of PDGF function have encountered two major obstacles: the functional redundancy of PDGFRα and PDGFRβ in vitro and their distinct roles in vivo. Here we used wild-type mouse embryonic fibroblasts (MEF), MEF null for either PDGFRα, β, or both to dissect PDGF-PDGFR signaling pathways. These four PDGFR genetically defined cells provided us a platform to study the relative contributions of the pathways triggered by the two PDGF receptors. They were treated with PDGF-BB and analyzed for differential gene expression, in vitro proliferation and differential response to pharmacological effects. No genes were differentially expressed in the double null cells, suggesting minimal receptor-independent signaling. Protean differentiation and proliferation pathways are commonly regulated by PDGFRα, PDGFRβ and PDGFRα/β while each receptor is also responsible for regulating unique signaling pathways. Furthermore, some signaling is solely modulated through heterodimeric PDGFRα/β.

Stromelysin‐3 suppresses tumor cell apoptosis in a murine model

Stromelysin‐3 (STR‐3) is a matrix metalloproteinase with a unique pattern of expression and substrate specificity. During embryogenesis and remodeling of normal adult tissues, STR‐3 is produced by stromal cells in direct contact with epithelial cells undergoing regional apoptosis and selective cell survival. STR‐3 is also overexpressed by interdigitating stromal cells in primary epithelial malignancies. Although STR‐3 does not degrade classic extracellular matrix components, the enzyme promotes the establishment of local tumors in nude mice by as yet undefined mechanisms. STR‐3 is induced when malignant epithelial cells come into contact with surrounding stromal elements; the active stromal cell‐derived 45 kDa enzyme is subsequently processed to a 35 kDa protein without enzymatic activity. We have generated MCF‐7 transfectants expressing wild type or catalytically inactive 45 kDa STR‐3 (STR‐3wt and STR‐3cat‐) or secreted 35 kDa STR‐3 (35 kDa STR‐3sec) and evaluated their implantation and survival in nude mice. Tumors developed significantly more rapidly in animals receiving STR‐3wt, rather than vector‐only, STR‐3cat‐ or 35 kDa STR‐3sec transfectants. Most importantly, STR‐3wt tumors had a significantly lower percentage of apoptotic cells than tumors derived from vector‐only, STR‐3cat‐ or 35 kDa STR‐3sec transfectants. Taken together, these studies suggest that the active STR‐3 enzyme may increase tumor take by suppressing tumor cell apoptosis and that 45 kDa to 35 kDa STR‐3 processing limits STR‐3 activity at the tumor/stromal interface. Because STR‐3 is secreted as an active enzyme rather than a proform, subsequent 45 kDa to 35 kDa STR‐3 processing may represent a novel mechanism for regulating enzymatic activity. J. Cell. Biochem. 82: 549–555, 2001.

Alterations of TP53 are associated with a poor outcome for patients with hepatocellular carcinoma: evidence from a systematic review and meta-analysis.

BACKGROUND The prognostic significance of p53 aberration in hepatocellular carcinoma (HCC) remains inconclusive. This systematic review and meta-analysis aimed to provide comprehensive evidence on the association of p53 alterations with recurrence-free survival (RFS) and overall survival (OS) in HCC patients. METHODS Systematic literature searches were conducted until July 2010. Meta-analysis was performed to estimate prognostic effects of p53 alterations on patient outcomes in HCC. Sensitivity and subgroup analyses were also conducted in the meta-analysis. RESULTS Thirty-seven studies (7 tumour p53 mutation, 23 tumour p53 expression and 7 serum anti-p53 antibodies) were included in the systematic review and meta-analysis. The average percentages of p53 mutation, p53 expression upregulation and anti-p53 antibody level elevation in HCC patients were 31.5%, 35.0% and 23.8%, respectively. Tumour p53 alterations were associated significantly with poor patient outcomes in HCC: the summary hazard ratio (HR) of mutant p53 versus wild type p53 phenotype was 2.58 [95% confidence interval (CI): 1.96-3.41] for OS and 3.19 [95% CI: 2.21-4.60] for RFS, respectively; and the summary HR of upregulated p53 expression versus low/undetectable p53 expression was 1.68 [95% CI: 1.49-1.90] for OS and 1.89 [95% CI: 1.34-2.66] for RFS, respectively. However, elevated serum anti-p53 antibody was only associated with poor OS in HCC group with a high proportion of (≥ 50%) of hepatitis C virus (HCV) infection [HR: 1.92; 95% CI: 1.30-2.85]. Moreover, sensitivity analyses showed that the results of meta-analyses were not altered. CONCLUSION HCC patients with p53 mutation and upregulated expression in tumour tissue have a shorter OS and RFS than patients with wild type p53 and low/undetectable p53 expression. However, the prognostic value of serum anti-p53 antibody is required to be further examined.