Aberrant FoxM1B expression increases matrix metalloproteinase-2 transcription and enhances the invasion of glioma cells

We recently showed that FoxM1 is overexpressed in human glioblastomas and that forced FoxM1B expression in anaplastic astrocytoma cells leads to the formation of highly invasive glioblastoma multiforme (GBM) in nude mice. However, the molecular mechanisms by which FoxM1 enhances glioma invasion are unknown. In this study, we found that FoxM1 overexpression increased matrix metalloproteinase (MMP)-2 expression in glioma cells, whereas blockade of FoxM1 expression suppressed MMP-2 expression. Transfection of FoxM1 into glioma cells directly activated the MMP-2 promoter, whereas inhibition of FoxM1 expression by FoxM1-siRNA suppressed its activation. We identified a FoxM1-binding site in the MMP-2 promoter and demonstrated that FoxM1 protein bound directly to it. Mutation of this FoxM1-binding site significantly attenuated MMP-2 promoter activity. Furthermore, FoxM1 overexpression increased the invasiveness of glioma cells, whereas inhibition of FoxM1 expression suppressed the invasiveness of GBM cells. Inhibition of MMP-2 by a specific MMP-2 inhibitor reversed the invasive phenotype of glioma cells overexpressing FoxM1. Finally, immunohistochemical analysis of 45 human GBM specimens showed a significant correlation between FoxM1 overexpression and elevated MMP-2 expression. Collectively, these findings provide evidence that FoxM1 contributes to glioma progression by enhancing MMP-2 gene transcription and thus tumor-cell invasion.

Regulation of androgen receptor activity by tyrosine phosphorylation

The androgen receptor (AR) is essential for the growth of prostate cancer cells. Here, we report that tyrosine phosphorylation of AR is induced by growth factors and elevated in hormone-refractory prostate tumors. Mutation of the major tyrosine phosphorylation site in AR significantly inhibits the growth of prostate cancer cells under androgen-depleted conditions. The Src tyrosine kinase appears to be responsible for phosphorylating AR, and there is a positive correlation of AR tyrosine phosphorylation with Src tyrosine kinase activity in human prostate tumors. Our data collectively suggest that growth factors and their downstream tyrosine kinases, which are elevated during hormone-ablation therapy, can induce tyrosine phosphorylation of AR and such modification may be important for prostate tumor growth under androgen-depleted conditions.

The 44 kDa Pim-1 kinase directly interacts with tyrosine kinase Etk/BMX and protects human prostate cancer cells from apoptosis induced by chemotherapeutic drugs

Protein kinase Pim-1 has been implicated in the development of hematopoietic and prostatic malignancies. Here, we present the evidence that two isoforms, the 44 and 33 kDa Pim-1, are expressed in all human prostate cancer cell lines examined. The subcellular localization of human 44 kDa Pim-1 is primarily on the plasma membrane, while the 33 kDa isoform is present in both the cytosol and nucleus in PCA cells. The 44 kDa Pim-1 contains the proline-rich motif at the N-terminus and directly binds to the SH3 domain of tyrosine kinase Etk. Such interaction leads to the activation of Etk kinase activity possibly by competing with the tumor suppressor p53. This is corroborated by the fact that overexpression of the 44 kDa Pim-1 in prostate cancer cells confers the resistance to chemotherapeutic drugs. Our results suggest that these two isoforms of Pim-1 kinase may regulate distinct substrates and the 44 kDa Pim-1 may play a more prominent role in drug resistance in prostate cancer cells.

Novel gastrin receptors mediate mitogenic effects of gastrin and processing intermediates of gastrin on Swiss 3T3 fibroblasts. Absence of detectable cholecystokinin (CCK)-A and CCK-B receptors

We have reported previously mitogenic effects of gastrin on several immortalized and neoplastic cell lines, including Swiss 3T3 fibroblasts. Receptor subtypes, cholecystokinin (CCK)-A and CCK-B, for a closely related peptide, cholecystokinin, were recently cloned. These studies were undertaken to investigate if CCK-A- and CCK-B receptors were perhaps mediating the mitogenic effects of gastrin on Swiss 3T3 cells. Receptor antagonists that inhibit the biological effects and binding of peptides to the CCK-A (L-364,718 (L18)) and CCK-B (L-365,260 (L60)) receptors were ineffective toward inhibiting the binding and proliferative effects of gastrin on Swiss 3T3 cells. Radiolabeled L18 and L60 demonstrated no binding to the cells, indicating that CCK-A and CCK-B receptors may be absent on Swiss 3T3 cells. Radiolabeled CCK-8, gastrin, L18, and L60, on the other hand, demonstrated specific binding to a pancreatic cancer cell line (AR42J cells) (used as a positive control). In cross-linking studies the molecular mass of the major band of gastrin receptors (GR) on Swiss 3T3 cells was determined to be approximately 45 kDa. The mitogenic potency of 0.1-1.0 nM gastrin-like peptides on Swiss 3T3 cells was in the order of G1-17 > or = G1-17-Gly > G5-17 > or = G5-17-Gly > G2-17 > CCK-8-Gly > or = G1-17-Lys > or = CCK-8. The relative binding affinity of the peptides (based on the dose-dependent inhibition of binding of 125I-G1-17 to Swiss 3T3 cells) was similar to the relative mitogenic potency of the peptides as given above. Furthermore, G1-17-Gly was equally effective as G1-17 in displacing the binding of 125I-G1-17 to the 45-kDa GR from the Swiss 3T3 cells. Based on these studies it became evident that the novel gastrin preferring GR, expressed by Swiss 3T3 cells, binds and mediates the mitogenic effects of not only the mature (amidated) forms of gastrin-like peptides but also binds and mediates the mitogenic effects of glycine-extended forms of gastrin-like peptides. Possible mRNA expression of CCK-A and CCK-B receptor subtypes by gastrin-responsive rodent intestinal and fibroblast cell lines (Swiss 3T3, IEC-6, CA) was measured by the methods of Northern blot analysis and reverse transcriptase-polymerase chain reaction. mRNA from rat pancreas, AR42J cells, and rat antrum served as positive controls.(ABSTRACT TRUNCATED AT 400 WORDS)

Autocrine gastrins in colon cancer cells Up-regulate cytochrome c oxidase Vb and down-regulate efflux of cytochrome c and activation of caspase-3

Suppression of the gastrin gene in human colon cancer cells by stably expressing antisense (AS) gastrin RNA results in significant growth suppression of AS cells. To understand mechanisms mediating the growth effects of autocrine gastrins, differential expression of transcripts by AS and control (C) clones of a representative cell line (HCT-116) was analyzed to identify target genes of autocrine gastrins. Six differentially expressed transcripts were confirmed and sequenced. Of these, the RNA and protein levels of cytochrome c oxidase (COX) Vb were significantly higher in C versus AS cells. The expression of COX Vb by colon cancer cells was proportional to the expression of gastrin. Higher levels of COX Vb coprecipitated with cytochrome c in the mitochondria of C versus AS cells. Treatment of mitochondria with digitonin resulted in a 2-fold higher release of cytochrome c from AS versus C mitochondria. As a corollary, the cytosolic levels of cytochrome c were significantly higher in AS versus C cells, which correlated with approximately 2- and approximately 3-fold higher activation of caspase-9 and -3, respectively, in AS versus C cells in response to camptothecin. Thus, autocrine gastrins may support growth/survival of cells by up-regulating COX Vb, which may decrease the sensitivity of the cancer cells to apoptotic stimuli by increasing retention of cytochrome c in mitochondria.

Tyrosine kinase Etk/BMX is up-regulated in human prostate cancer and its overexpression induces prostate intraepithelial neoplasia in mouse

The nonreceptor tyrosine kinase Etk/BMX was originally identified from the human prostate xenograft CWR22. Here, we report that Etk is up-regulated in human prostate tumor specimens surveyed. Knocking down Etk expression by a specific small interfering RNA (siRNA) in prostate cancer cells attenuates cell proliferation, suggesting an essential role of Etk for prostate cancer cell survival and growth. Targeted expression of Etk in mouse prostate epithelium results in pathologic changes resembling human prostatic intraepithelial neoplasia, indicating that up-regulation of Etk may contribute to prostate cancer development. A marked increase of luminal epithelial cell proliferation was observed in the Etk transgenic prostate, which may be attributed in part to the elevated activity of Akt and signal transducers and activators of transcription 3 (STAT3). More interestingly, the expression level of acetyltransferase cyclic AMP-responsive element binding protein-binding protein (CBP) is also increased in the Etk transgenic prostate as well as in a prostate cancer cell line overexpressing Etk, concomitant with elevated histone 3 acetylation at lysine 18 (H3K18Ac). Down-modulation of Etk expression by a specific siRNA leads to a decrease of H3 acetylation in prostate cancer cell lines. Our data suggest that Etk may also modulate chromatin remodeling by regulating the activity of acetyltransferases, such as CBP. Given that Etk may exert its effects in prostate through modulation of multiple signaling pathways altered in human prostate cancer, the Etk transgenic mouse model may be a useful tool for studying the functions of Etk and identification of new molecular markers and drug targets relevant to human diseases.

Proliferation and differentiation of a human colon cancer cell line (CaCo2) is associated with significant changes in the expression and secretion of insulin-like growth factor (IGF) IGF-II and IGF binding protein-4: role of IGF-II

The extent to which the insulin-like growth factor (IGF) system contributes to the initiation and progression of colon cancer remains poorly defined. We recently reported that a majority of human colon cancers express and secrete the potent mitogen IGF-II and at least two inhibitory binding proteins, IGFBP-2 and IGFBP-4. In the present study we measured the expression and secretion of IGF-II, IGFBP-2, and IGFBP-4 in relation to growth and differentiation of CaCo2 human colon cancer cells, which undergo spontaneous enterocytic differentiation in culture. Under the conditions of the present study, CaCo2 cells demonstrated an initial rapid phase of growth between Day 2 through days 7-9 of culture, followed by a significant retardation in the growth between days 9-13. Alkaline phosphatase (ALP) activity, a marker of enterocytic differentiation, progressively increased between Days 7-13 in culture, temporally correlating with post-confluent phase of negligible growth. These changes in growth and differentiation were accompanied by > 80% decline in the relative concentration of IGF-II messenger RNA (mRNA) between Days 2-13. In contrast, the relative mRNA concentrations of inhibitory binding proteins (IGFBP-2 and IGFBP-4) increased rapidly to 200% of Day 2 values by Days 5-7 before returning to baseline levels by Day 13. The relative protein concentrations of the three factors measured in the conditioned media of the cells followed a pattern very similar to that measured for the mRNA levels. While the changes in the relative protein concentrations and mRNA levels of IGF-II and IGFBP-4 were statistically significant, the changes measured in the RNA and protein levels of IGFBP-2 were not, as a result of large inter experimental variations. Thus these results suggested that CaCo2 cell differentiation may require an attenuation of IGF-II effects. To confirm the latter possibility, additional studies were conducted with a specific neutralizing antibody against IGF-II. Incubation of CaCo2 cells with anti-IGF-II antibodies from Day 0 through Day 7 significantly retarded the growth of the cells and was accompanied by a significant increase in the concentration of Alkaline phosphatase activity per 10(6) cells. Recently, we reported a potent inhibitory role of IGFBP-4 in the growth of colon cancer cells. In the present studies, a possible important role of IGF-II is illustrated not only in the growth but also in the differentiation of colonic cells. Our studies thus suggest that differential expression of IGF-II and IGFBPs may be playing a critical role in both proliferation and differentiation of colonocytes.

Compensatory upregulation of tyrosine kinase Etk/BMX in response to androgen deprivation promotes castration-resistant growth of prostate cancer cells

We previously showed that targeted expression of non-receptor tyrosine kinase Etk/BMX in mouse prostate induces prostate intraepithelial neoplasia, implying a possible causal role of Etk in prostate cancer development and progression. Here, we report that Etk is upregulated in both human and mouse prostates in response to androgen ablation. Etk expression seems to be differentially regulated by androgen and interleukin 6 (IL-6), which is possibly mediated by the androgen receptor (AR) in prostate cancer cells. Our immunohistochemical analysis of tissue microarrays containing 112 human prostate tumor samples revealed that Etk expression is elevated in hormone-resistant prostate cancer and positively correlated with tyrosine phosphorylation of AR (Pearson correlation coefficient rho = 0.71, P < 0.0001). AR tyrosine phosphorylation is increased in Etk-overexpressing cells, suggesting that Etk may be another tyrosine kinase, in addition to Src and Ack-1, which can phosphorylate AR. We also showed that Etk can directly interact with AR through its Src homology 2 domain, and such interaction may prevent the association of AR with Mdm2, leading to stabilization of AR under androgen-depleted conditions. Overexpression of Etk in androgen-sensitive LNCaP cells promotes tumor growth while knocking down Etk expression in hormone-insensitive prostate cancer cells by a specific shRNA that inhibits tumor growth under androgen-depleted conditions. Taken together, our data suggest that Etk may be a component of the adaptive compensatory mechanism activated by androgen ablation in prostate and may play a role in hormone resistance, at least in part, through direct modulation of the AR signaling pathway.

MicroRNA-214-3p: A link between autophagy and endothelial cell dysfunction in atherosclerosis

AIM

Endothelial cell injury assumes a fundamental part in the pathogenesis of atherosclerosis, and endothelial cell autophagy has protective effects on the development of atherosclerosis, although the underlying molecular regulation mechanism is indistinct. This study aimed to investigate whether microRNA-214-3p (miR-214-3p) is involved in the endothelial cell autophagy regulation of atherosclerosis.

METHODS

We utilized ApoE^-/- mice provided with a high-fat diet (HFD) as atherosclerosis model. We analysed the level of miR-214-3p and the levels of autophagy-related protein 5 (ATG5) and autophagy-related protein 12 (ATG12) in the purified CD31⁺ endothelial cells from mouse aorta. Bioinformatics analysis and a dual-luciferase reporter assay were performed to confirm the binding target of miR-214-3p. In vitro study, human umbilical vein endothelial cells (HUVECs) were transfected with miR-214-3p mimics/inhibitor and stimulated with 100 μg/mL oxidized low-density lipoprotein (ox-LDL) for 12 hours to initiate a stress-repairing autophagic process.

RESULTS

In mouse models, we identified an inverse correlation between miR-214-3p, ATG5 and ATG12. We observed that in young HUVECs, ox-LDL-initiated autophagy was repressed by miR-214-3p overexpression, as evaluated by autophagic protein analysis, microtubule-associated protein 1 light chain 3B-II (LC3B-II) immunofluorescence assay and transmission electron microscopy (TEM). Also, miR-214-3p promoted ox-LDL accumulation in HUVECs and THP-1 monocyte adhesion. Conversely, in old HUVECs, suppression of miR-214-3p preserved the ability to initiate a protective autophagy reaction to the ox-LDL stimulation.

CONCLUSION

miR-214-3p regulates ox-LDL-initiated autophagy in HUVECs by directly targeting the 3'UTR of ATG5 and may have a suitable role in the pathogenesis of atherosclerosis.

Functional and molecular interactions between ERK and CHK2 in diffuse large B-cell lymphoma

Distinct oncogenic signalling cascades have been associated with non-Hodgkin lymphoma. ERK1/2 signalling elicits both transcriptional and post-transcriptional effects through phosphorylation of numerous substrates. Here we report a novel molecular relationship between ERK1/2 and CHK2, a protein kinase that is a key mediator of the DNA damage checkpoint that responds to DNA double-strand breaks. Our studies are the first to demonstrate the co-localization and overexpression of ERK1/2 and CHK2 in diffuse large B-cell lymphoma (DLBCL). The physical interaction between ERK and CHK2 was highly dependent on phosphorylated Thr 68 of CHK2. Concurrent administration of an ERK inhibitor enhances the antitumour activity of CHK2 inhibition in both a human DLBCL xenograft model as well as primary human DLBCL cells. Our data suggest a functional interaction between ERK and CHK2 and support the potential combined therapeutic targeting of ERK and CHK2 in human DLBCL.

Chk2 is a kinase that is a potential chemotherapeutic target. Here, Chk2 and the kinase ERK are shown to functionally interact, and are elevated in expression in human diffuse B-cell lymphomas. Combinatorial inhibition of the kinases was also shown to block tumour growth in an in vivo mouse model.

Extracellular lumican augments cytotoxicity of chemotherapy in pancreatic ductal adenocarcinoma cells via autophagy inhibition

Lumican, an extracellular matrix proteoglycan overexpressed by pancreatic stellate cells (PSCs) and pancreatic ductal adenocarcinoma cells (PDACs), drives the formation of a tumor-specific microenvironment. We recently showed that extracellular lumican inhibits pancreatic cancer cell growth and is associated with prolonged survival after surgery. Here we investigated the role of extracellular lumican in chemotherapy-mediated cancer therapy. Lumican secretion was increased by chemotherapeutic agents in PDAC, and especially in PSCs, and appeared to be linked to the extent of cells' response to chemotherapy-induced growth inhibition. In multiple PDAC models, including cell lines, patient-derived xenografts and lumican knockout mice, lumican significantly increased antitumor effect of chemotherapy. This effect was associated with DNA damage, apoptosis and inhibition of cell viability, glucose consumption, lactate production and vascular endothelial growth factor secretion. In PDAC cells, chemotherapeutic agents triggered autophagosome formation and increased LC3 expression through the reactive oxygen species-mediated AMP-activated kinase (AMPK) signaling pathway. Inhibition of gemcitabine-induced autophagy in cancer cells by treatment with AMPK inhibitor compound C, lysosomal inhibitor chloroquine or autophagy inhibitor 3MA enhanced gemcitabine-induced apoptosis, suggesting that autophagy is a protective cellular response to gemcitabine treatment. Importantly, lumican dramatically decreased AMPK activity, inhibiting chemotherapy-induced autophagy in both in vitro and in vivo PDAC models. Co-treatment of PDAC cells with lumican and gemcitabine increased mitochondrial damage, reactive oxygen species (ROS) production and cytochrome c release, indicating that lumican-induced disruption of mitochondrial function may be the mechanism of sensitization to gemcitabine. Together, our findings demonstrate that extracellular lumican augments cytotoxicity of chemotherapy in PDAC cells through inhibition of chemotherapeutic agent-induced autophagy.

Identification of transformation-related pathways in a breast epithelial cell model using a ribonomics approach

The aberrant expression of many genes is a common feature in the malignant transformation of cells. In mammalian cells, posttranscriptional gene regulatory processes are emerging as critical determinants controlling gene expression both in physiologic and pathologic conditions. These regulatory mechanisms are directed primarily by the interaction of mRNAs with specific RNA-binding proteins (RBP). There is an emerging body of data demonstrating that two RBPs, AUF1 and HuR, can antagonistically affect the posttranscriptional fate of target mRNAs, as well as concurrently bind to common target transcripts. Employing MCT-1 oncogene-mediated transformation of immortalized breast epithelial MCF10A cells, we characterized the largely reciprocal association of these two RBPs with target mRNAs and their influence on protein expression vis-a-vis cellular transformation. Using a ribonomics approach, we identified mRNAs from cancer-related pathways whose association with AUF1 and/or HuR were altered when comparing immortalized with transformed MCF10A cells. Significantly, we were able to show that knockdown of HuR expression using RNA interference reduced anchorage-independent growth capacity in transformed MCF10A cells and decreased protein expression of a number of validated target genes. Our data show that the global alterations in binding of HuR and AUF1 with target transcripts have a critical role in posttranscriptional regulation of genes encoding proteins involved in breast epithelial cell transformation. These findings further support the feasibility of using a ribonomics approach for the identification of cancer-related pathways.

Down-regulation of eIF4GII by miR-520c-3p represses diffuse large B cell lymphoma development

Deregulation of the translational machinery is emerging as a critical contributor to cancer development. The contribution of microRNAs in translational gene control has been established however; the role of microRNAs in disrupting the cap-dependent translation regulation complex has not been previously described. Here, we established that elevated miR-520c-3p represses global translation, cell proliferation and initiates premature senescence in HeLa and DLBCL cells. Moreover, we demonstrate that miR-520c-3p directly targets translation initiation factor, eIF4GII mRNA and negatively regulates eIF4GII protein synthesis. miR-520c-3p overexpression diminishes cells colony formation and reduces tumor growth in a human xenograft mouse model. Consequently, downregulation of eIF4GII by siRNA decreases translation, cell proliferation and ability to form colonies, as well as induces cellular senescence. In vitro and in vivo findings were further validated in patient samples; DLBCL primary cells demonstrated low miR-520c-3p levels with reciprocally up-regulated eIF4GII protein expression. Our results provide evidence that the tumor suppressor effect of miR-520c-3p is mediated through repression of translation while inducing senescence and that eIF4GII is a key effector of this anti-tumor activity.

Control of gene expression on the translational level is critical for proper function of major cellular processes and deregulation of translation can promote cellular transformation. Emerging actors in this post-transcriptional gene regulation are small non-coding RNAs referred to as microRNAs (miRNAs). We established that miR-520c-3p represses tumor growth through the repression of eIF4GII, a major structural component of the translation initiation complex. Since translation of most cellular mRNAs is primarily regulated at the level of initiation, this node is becoming a potential target for therapeutic intervention. Identified in this study, tumor suppressor function of miR-520c-3p is mediated through the inhibition of translational factor eIF4GII, resulting in the repression of global translational machinery and induction of senescence in tumor cells. While aging and senescence has been shown to be associated with reduced translation the linkage between translational deregulation and senescence in malignant cells has not been previously described. Lending further clinical significance to our findings, we were able to demonstrate that primary DLBCL samples had elevated levels of eIF4GII while having reciprocally low miR-520c-3p expression.

Overexpression of the DMP1 C-terminal fragment stimulates FGF23 and exacerbates the hypophosphatemic rickets phenotype in Hyp mice

Dentin matrix protein-1 (DMP1) or phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) inactivation results in elevation of the phosphaturic hormone fibroblast growth factor (FGF)-23, leading to hypophosphatemia, aberrant vitamin D metabolism, and rickets/osteomalacia. Compound mutant Phex-deficient Hyp and Dmp1(ko) mice exhibit nonadditive phenotypes, suggesting that DMP1 and PHEX may have interdependent effects to regulate FGF23 and bone mineralization. To determine the relative importance of DMP1 and PHEX in regulating FGF23 and mineralization, we tested whether the transgenic expression of full-length [Dmp1(Tg(full-length))] or C-terminal Dmp1 [Dmp1(Tg(57kDa))] could rescue the phenotype of Hyp mice. We found that Dmp1(ko) and Hyp mice have similar phenotypes characterized by decreased cortical bone mineral density (-35% vs. wild type, P < 0.05) and increased serum FGF23 levels (~12-fold vs. wild type, P < 0.05). This was significantly corrected by the overexpression of either the full-length or the C-terminal transgene in Dmp1(ko) mice. However, neither of the transgenes rescued the Hyp mice phenotype. Hyp/Dmp1(Tg(full-length)) and Hyp mice were similar, but Hyp/Dmp1(Tg(57 kDa)) mice exhibited worsening of osteomalacia (-20% cortical bone mineral density) in association with increased serum FGF23 levels (+2-fold) compared with Hyp mice. Bone FGF23 mRNA expression was decreased and a 2-fold increase in the ratio of the full-length/degraded circulating FGF23 was observed, indicating that degradation of FGF23 was impaired in Hyp/Dmp1(Tg(57 kDa)) mice. The paradoxical effects of the C-terminal Dmp1 transgene were observed in Hyp/Dmp1(Tg(57 kDa)) but not in Dmp1(Tg(57 kDa)) mice expressing a functional PHEX. These findings indicate a functional interaction between PHEX and DMP1 to regulate bone mineralization and circulating FGF23 levels and for the first time demonstrate effects of the C-terminal DMP1 to regulate FGF23 degradation.

ATM regulates a DNA damage response posttranscriptional RNA operon in lymphocytes

Maintenance of genomic stability depends on the DNA damage response, a biologic barrier in early stages of cancer development. Failure of this response results in genomic instability and high predisposition toward lymphoma, as seen in patients with ataxia-telangiectasia mutated (ATM) dysfunction. ATM activates multiple cell-cycle checkpoints and DNA repair after DNA damage, but its influence on posttranscriptional gene expression has not been examined on a global level. We show that ionizing radiation modulates the dynamic association of the RNA-binding protein HuR with target mRNAs in an ATM-dependent manner, potentially coordinating the genotoxic response as an RNA operon. Pharmacologic ATM inhibition and use of ATM-null cells revealed a critical role for ATM in this process. Numerous mRNAs encoding cancer-related proteins were differentially associated with HuR depending on the functional state of ATM, in turn affecting expression of encoded proteins. The findings presented here reveal a previously unidentified role of ATM in controlling gene expression posttranscriptionally. Dysregulation of this DNA damage response RNA operon is probably relevant to lymphoma development in ataxia-telangiectasia persons. These novel RNA regulatory modules and genetic networks provide critical insight into the function of ATM in oncogenesis.

Bi-directional Regulation between Tyrosine Kinase Etk/BMX and Tumor Suppressor p53 in Response to DNA Damage

Etk/Bmx, a member of the Tec family of nonreceptor tyrosine kinases, has been implicated in the regulation of various cellular processes including proliferation, differentiation, motility, and apoptosis. Here, we report the identification of Tec family kinases as the potential interacting proteins of the tumor suppressor p53 by an Src homology 3 domain array screening. Etk is physically associated with p53 through its Src homology 3 domain and the proline-rich domain of p53. Induction of p53 expression by DNA damage inhibits Etk activity in several cell types. Down-regulation of Etk expression by a specific small interfering RNA sensitizes prostate cancer cells to doxorubicin-induced apoptosis, suggesting that inhibition of Etk activity is required for apoptosis in response to DNA damage. We also show that Etk primarily interacts with p53 in the cytoplasm and that such interaction leads to bidirectional inhibition of the activities of both proteins. Overexpression of Etk in prostate cancer cells results in inhibition of p53 transcriptional activity and its interaction with the mitochondrial protein BAK and confers the resistance to doxorubicin. Therefore, we propose that the stoichiometry between p53 and the Tec family kinases in a given cell type may determine its sensitivity to chemotherapeutic drugs.

Prolonged exposure to extracellular lumican restrains pancreatic adenocarcinoma growth

We previously demonstrated that pancreatic stellate cells within pancreatic ductal adenocarcinoma (PDAC) stroma secrete lumican and its presence is associated with prolonged survival of patients with localized PDAC. Here, we observed that extracellular lumican decreases PDAC tumour cell growth in xenograft and syngeneic orthotopic animal models, and induces growth inhibition of low-passage human PDAC cells in a species-specific manner. PDAC cells grown in variant culture conditions and exposed to extracellular lumican display typical characterizations of cancer cell in a quiescent state, such as growth inhibition, apoptosis, G0/G1 arrest and chemoresistance. Importantly, extracellular lumican is associated with diminished ERK1/2 phosphorylation and increased p38 phosphorylation within PDAC cells. We further demonstrated that extracellular lumican physically binds with EGFR to trigger EGFR internalization and downregulation of EGFR and its downstream signal molecule ERK. Lumican enhances casitas B-lineage lymphoma expression, which stabilized the TGFβ Type II receptor sensitizing PDAC cells to TGFβ-mediated activation of p38 and SMAD signals. These provide a mechanism for the shift in signalling and phenotypic changes we observed after prolonged exposure to lumican. Together, our findings demonstrate that stromal lumican restrains PDAC cell growth through mediating cell entry into a quiescent state.

Hepatitis C virus upregulates B-cell receptor signaling: a novel mechanism for HCV-associated B-cell lymphoproliferative disorders

B-cell receptor (BCR) signaling is essential for the development of B cells and has a critical role in B-cell neoplasia. Increasing evidence indicates an association between chronic hepatitis C virus (HCV) infection and B-cell lymphoma, however, the mechanisms by which HCV causes B-cell lymphoproliferative disorder are still unclear. Herein, we demonstrate the expression of HCV viral proteins in B cells of HCV-infected patients and show that HCV upregulates BCR signaling in human primary B cells. HCV nonstructural protein NS3/4A interacts with CHK2 and downregulates its activity, modulating HuR posttranscriptional regulation of a network of target mRNAs associated with B-cell lymphoproliferative disorders. Interestingly, the BCR signaling pathway was found to have the largest number of transcripts with increased association with HuR and was upregulated by NS3/4A. Our study reveals a previously unidentified role of NS3/4A in regulation of host BCR signaling during HCV infection, contributing to a better understanding of the molecular mechanisms underlying HCV-associated B-cell lymphoproliferative disorders.

Antitumor activity of fucoidan against diffuse large B cell lymphoma in vitro and in vivo

Fucoidan is one of the major sulfated polysaccharides isolated from brown seaweeds. In this study, we determined the anti-cancer activity of fucoidan on diffuse large B cell lymphoma (DLBCL) cells both in vitro and in vivo. Fucoidan inhibited the growth of DLBCL cells in a dose- and time-dependent manner, and fucoidan treatment provoked G0/G1 cell cycle arrest, which was accompanied by p21 up-regulation and cyclin D1, Cdk4, and Cdk6 down-regulation. Fucoidan also induced caspase-dependent cell apoptosis in DLBCL cell lines and primary DLBCL cell. In addition, fucoidan treatment caused the loss of mitochondrial membrane potential and the release of cytochrome c and apoptosis-inducing factor from the mitochondria into the cytosol. Fucoidan also potentiated the activities of carfilzomib in killing DLBCL cells. Oral administration of fucoidan effectively inhibited tumor growth in xenograft mouse models. Our findings reveal the novel function of fucoidan as an anti-DLBCL agent, which can be used in the clinical treatment of DLBCL.

Bacillus licheniformis, a potential probiotic, inhibits obesity by modulating colonic microflora in C57BL/6J mice model

AIMS

This study evaluated the effects of a potential probiotic, Bacillus sp., on the growth, serum and hepatic triglyceride, histological features of liver tissues and colonic microflora in high-fat diet-induced obese mice.

METHODS AND RESULTS

Sixty male C57BL/6J mice were randomly divided into five groups: mice fed a low-fat diet (Cont), mice fed a high-fat diet (Hf), Hf and orally challenged with Bacillus subtilis (Bs), B. licheniformis (Bl) and a mixture of B. subtilis and B. licheniformis (Bls). Gavage feeding was provided at week 9 and the experiment was continued for 8 weeks. Treatment with B. licheniformis and a mixture of Bacillus sp. attenuated body weight gain at the end of study and enhanced glucose tolerance by sensitizing insulin action in the Hf-fed mice. Lower serum and hepatic triglyceride and epididymal fat weight were observed in Bl and Bls groups than that of Hf group. Lesser hepatic fat deposition was observed in the Bl and Bls groups than in the Hf group. High-throughput sequencing showed that Bacillus sp. supplementation dramatically changed the colonic bacterial community in obese mice.

CONCLUSIONS

Bacillus licheniformis reduced body weight and improved glucose tolerance, obesity and insulin resistance in Hf-fed mice by changing colonic microbiota composition.

SIGNIFICANCE AND IMPACT OF THE STUDY

Orally administration of Bacillus licheniformis may reduce body weight and decrease fat deposition by modulating colonic bacterial community in Hf model.

STAT1 modulates tissue wasting or overgrowth downstream from PDGFRβ

In this study, He et al. investigated how gain-of-function PDGFRβ mutations cause human disease, specifically whether PDGFRB mutations alone are responsible for genetic diseases characterized by musculoskeletal wasting or overgrowth. Using a genetic approach, their findings suggest a molecular mechanism by which STAT1 suppresses PDGFRβ-driven fibrosis and bone growth.

Platelet-derived growth factor (PDGF) acts through two conserved receptor tyrosine kinases: PDGFRα and PDGFRβ. Gain-of-function mutations in human PDGFRB have been linked recently to genetic diseases characterized by connective tissue wasting (Penttinen syndrome) or overgrowth (Kosaki overgrowth syndrome), but it is unclear whether PDGFRB mutations alone are responsible. Mice with constitutive PDGFRβ signaling caused by a kinase domain mutation (D849V) develop lethal autoinflammation. Here we used a genetic approach to investigate the mechanism of autoinflammation in Pdgfrb^+/D849V mice and test the hypothesis that signal transducer and activator of transcription 1 (STAT1) mediates this phenotype. We show that Pdgfrb^+/D849V mice with Stat1 knockout (Stat1^−/−Pdgfrb^+/D849V) are rescued from autoinflammation and have improved life span compared with Stat1^+/−Pdgfrb^+/D849V mice. Furthermore, PDGFRβ–STAT1 signaling suppresses PDGFRβ itself. Thus, Stat1^−/−Pdgfrb^+/D849V fibroblasts exhibit increased PDGFRβ signaling, and mice develop progressive overgrowth, a distinct phenotype from the wasting seen in Stat1^+/−Pdgfrb^+/D849V mice. Deletion of interferon receptors (Ifnar1 or Ifngr1) does not rescue wasting in Pdgfrb^+/D849V mice, indicating that interferons are not required for autoinflammation. These results provide functional evidence that elevated PDGFRβ signaling causes tissue wasting or overgrowth reminiscent of human genetic syndromes and that the STAT1 pathway is a crucial modulator of this phenotypic spectrum.