Refractory nature of normal human diploid fibroblasts with respect to oncogene-mediated transformation

Transcriptional Dynamics of Immortalized Human Mesenchymal Stem Cells during Transformation

Comprehensive analysis of alterations in gene expression along with neoplastic transformation in human cells provides valuable information about the molecular mechanisms underlying transformation. To further address these questions, we performed whole transcriptome analysis to the human mesenchymal stem cell line, UE6E7T-3, which was immortalized with hTERT and human papillomavirus type 16 E6/E7 genes, in association with progress of transformation in these cells. At early stages of culture, UE6E7T-3 cells preferentially lost one copy of chromosome 13, as previously described; in addition, tumor suppressor genes, DNA repair genes, and apoptosis-activating genes were overexpressed. After the loss of chromosome 13, additional aneuploidy and genetic alterations that drove progressive transformation, were observed. At this stage, the cell line expressed oncogenes as well as genes related to anti-apoptotic functions, cell-cycle progression, and chromosome instability (CIN); these pro-tumorigenic changes were concomitant with a decrease in tumor suppressor gene expression. At later stages after prolong culture, the cells exhibited chromosome translocations, acquired anchorage-independent growth and tumorigenicity in nude mice, (sarcoma) and exhibited increased expression of genes encoding growth factor and DNA repair genes, and decreased expression of adhesion genes. In particular, glypican-5 (GPC5), which encodes a cell-surface proteoglycan that might be a biomarker for sarcoma, was expressed at high levels in association with transformation. Patched (Ptc1), the cell surface receptor for hedgehog (Hh) signaling, was also significantly overexpressed and co-localized with GPC5. Knockdown of GPC5 expression decreased cell proliferation, suggesting that it plays a key role in growth in U3-DT cells (transformants derived from UE6E7T-3 cells) through the Hh signaling pathway. Thus, the UE6E7T-3 cell culture model is a useful tool for assessing the functional contribution of genes showed by expression profiling to the neoplastic transformation of human fibroblasts and human mesenchymal stem cells (hMSC).

mLST8 Promotes mTOR-Mediated Tumor Progression

The activity of the mechanistic target of rapamycin (mTOR) is elevated in various types of human cancers, implicating a role in tumor progression. However, the molecular mechanisms underlying mTOR upregulation remain unclear. In this study, we found that the expression of mLST8, a required subunit of both mTOR complex 1 (mTORC1) and complex 2 (mTORC2), was upregulated in several human colon and prostate cancer cell lines and tissues. Knockdown of mLST8 significantly suppressed mTORC1 and mTORC2 complex formation, and it also inhibited tumor growth and invasiveness in human colon carcinoma (HCT116) and prostate cancer (LNCaP) cells. Overexpression of mLST8 induced anchorage-independent cell growth in normal epithelial cells (HaCaT), although mLST8 knockdown had no effect on normal cell growth. mLST8 knockdown reduced mTORC2-mediated phosphorylation of AKT in both cancer and normal cells, whereas it potently inhibited mTORC1-mediated phosphorylation of 4E-BP1 specifically in cancer cells. These results suggest that mLST8 plays distinct roles in normal and cancer cells, depending upon its expression level, and that mLST8 upregulation may contribute to tumor progression by constitutively activating both the mTORC1 and mTORC2 pathways.

Fer tyrosine kinase oligomer mediates and amplifies Src-induced tumor progression

c-Src is upregulated in various human cancers, suggesting its role in malignant progression. However, the molecular circuits of c-Src oncogenic signaling remain elusive. Here we show that Fer tyrosine kinase oligomer mediates and amplifies Src-induced tumor progression. Previously, we showed that transformation of fibroblasts is promoted by the relocation of c-Src to non-raft membranes. In this study, we identified Fer and ezrin as non-raft c-Src targets. c-Src directly activated Fer by initiating its autophosphorylation, which was further amplified by Fer oligomerization. Fer interacted with active c-Src at focal adhesion membranes and activated Fer-phosphorylated ezrin to induce cell transformation. Fer was also crucial for cell transformation induced by v-Src or epidermal growth-factor receptor activation. Furthermore, Fer activation was required for tumorigenesis and invasiveness in some cancer cells in which c-Src is upregulated. We propose that the Src-Fer axis represents a new therapeutic target for treatment of a subset of human cancers.

mTORC1 upregulation via ERK-dependent gene expression change confers intrinsic resistance to MEK inhibitors in oncogenic KRas-mutant cancer cells

Cancer cells harboring oncogenic BRaf mutants, but not oncogenic KRas mutants, are sensitive to MEK inhibitors (MEKi). The mechanism underlying the intrinsic resistance to MEKi in KRas-mutant cells is under intensive investigation. Here, we pursued this mechanism by live imaging of extracellular signal-regulated kinases (ERK) and mammalian target of rapamycin complex 1 (mTORC1) activities in oncogenic KRas or BRaf-mutant cancer cells. We established eight cancer cell lines expressing Förster resonance energy transfer (FRET) biosensors for ERK activity and S6K activity, which was used as a surrogate marker for mTORC1 activity. Under increasing concentrations of MEKi, ERK activity correlated linearly with the cell growth rate in BRaf-mutant cancer cells, but not KRas-mutant cancer cells. The administration of PI3K inhibitors resulted in a linear correlation between ERK activity and cell growth rate in KRas-mutant cancer cells. Intriguingly, mTORC1 activity was correlated linearly with the cell growth rate in both BRaf-mutant cancer cells and KRas-mutant cancer cells. These observations suggested that mTORC1 activity had a pivotal role in cell growth and that the mTORC1 activity was maintained primarily by the ERK pathway in BRaf-mutant cancer cells and by both the ERK and PI3K pathways in KRas-mutant cancer cells. FRET imaging revealed that MEKi inhibited mTORC1 activity with slow kinetics, implying transcriptional control of mTORC1 activity by ERK. In agreement with this observation, MEKi induced the expression of negative regulators of mTORC1, including TSC1, TSC2 and Deptor, which occurred more significantly in BRaf-mutant cells than in KRas-mutant cells. These findings suggested that the suppression of mTORC1 activity and induction of negative regulators of mTORC1 in cancer cells treated for at least 1 day could be used as surrogate markers for the MEKi sensitivity of cancer cells.

Quantitative in vivo fluorescence cross-correlation analyses highlight the importance of competitive effects in the regulation of protein-protein interactions

Computer-assisted simulation is a promising approach for clarifying complicated signaling networks. However, this approach is currently limited by a deficiency of kinetic parameters determined in living cells. To overcome this problem, we applied fluorescence cross-correlation spectrometry (FCCS) to measure dissociation constant (Kd) values of signaling molecule complexes in living cells (in vivo Kd). Among the pairs of fluorescent molecules tested, that of monomerized enhanced green fluorescent protein (mEGFP) and HaloTag-tetramethylrhodamine was most suitable for the measurement of in vivo Kd by FCCS. Using this pair, we determined 22 in vivo Kd values of signaling molecule complexes comprising the epidermal growth factor receptor (EGFR)-Ras-extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase pathway. With these parameters, we developed a kinetic simulation model of the EGFR-Ras-ERK MAP kinase pathway and uncovered a potential role played by stoichiometry in Shc binding to EGFR during the peak activations of Ras, MEK, and ERK. Intriguingly, most of the in vivo Kd values determined in this study were higher than the in vitro Kd values reported previously, suggesting the significance of competitive bindings inside cells. These in vivo Kd values will provide a sound basis for the quantitative understanding of signal transduction.

A recurrent neomorphic mutation in MYOD1 defines a clinically aggressive subset of embryonal rhabdomyosarcoma associated with PI3K-AKT pathway mutations

Rhabdomyosarcoma, a cancer of skeletal muscle lineage, is the most common soft-tissue sarcoma in children. Major subtypes of rhabdomyosarcoma include alveolar (ARMS) and embryonal (ERMS) tumors. Whereas ARMS tumors typically contain translocations generating PAX3-FOXO1 or PAX7-FOXO1 fusions that block terminal myogenic differentiation, no functionally comparable genetic event has been found in ERMS tumors. Here we report the discovery, through whole-exome sequencing, of a recurrent somatic mutation encoding p.Leu122Arg in the myogenic transcription factor MYOD1 in a distinct subset of ERMS tumors with poor outcomes that also often contain mutations altering PI3K-AKT pathway components. Previous mutagenesis studies had shown that MYOD1 with a p.Leu122Arg substitution can block wild-type MYOD1 function and bind to MYC consensus sequences, suggesting a possible switch from differentiation to proliferation. Our functional data now confirm this prediction. Thus, MYOD1 p.Leu122Arg defines a subset of rhabdomyosarcomas eligible for high-risk protocols and the development of targeted therapeutics.

Induction of the CLOCK gene by E2-ERα signaling promotes the proliferation of breast cancer cells

Growing genetic and epidemiological evidence suggests a direct connection between the disruption of circadian rhythm and breast cancer. Moreover, the expression of several molecular components constituting the circadian clock machinery has been found to be modulated by estrogen-estrogen receptor α (E2-ERα) signaling in ERα-positive breast cancer cells. In this study, we investigated the regulation of CLOCK expression by ERα and its roles in cell proliferation. Immunohistochemical analysis of human breast tumor samples revealed high expression of CLOCK in ERα-positive breast tumor samples. Subsequent experiments using ERα-positive human breast cancer cell lines showed that both protein and mRNA levels of CLOCK were up-regulated by E2 and ERα. In these cells, E2 promoted the binding of ERα to the EREs (estrogen-response elements) of CLOCK promoter, thereby up-regulating the transcription of CLOCK. Knockdown of CLOCK attenuated cell proliferation in ERα-positive breast cancer cells. Taken together, these results demonstrated that CLOCK could be an important gene that mediates cell proliferation in breast cancer cells.

Development of a novel, single-cycle replicable rift valley Fever vaccine

Rift Valley fever virus (RVFV) (genus Phlebovirus, family Bunyaviridae) is an arbovirus that causes severe disease in humans and livestock in sub-Saharan African countries. Although the MP-12 strain of RVFV is a live attenuated vaccine candidate, neuroinvasiveness and neurovirulence of MP-12 in mice may be a concern when vaccinating certain individuals, especially those that are immunocompromised. We have developed a novel, single-cycle replicable MP-12 (scMP-12), which carries an L RNA, M RNA mutant encoding a mutant envelope protein lacking an endoplasmic reticulum retrieval signal and defective for membrane fusion function, and S RNA encoding N protein and green fluorescent protein. The scMP-12 underwent efficient amplification, then formed plaques and retained the introduced mutation after serial passages in a cell line stably expressing viral envelope proteins. However, inoculation of the scMP-12 into naïve cells resulted in a single round of viral replication, and production of low levels of noninfectious virus-like particles. Intracranial inoculation of scMP-12 into suckling mice did not cause clinical signs or death, a finding which demonstrated that the scMP-12 lacked neurovirulence. Mice immunized with a single dose of scMP-12 produced neutralizing antibodies, whose titers were higher than in mice immunized with replicon particles carrying L RNA and S RNA encoding N protein and green fluorescent protein. Moreover, 90% of the scMP-12-immunized mice were protected from wild-type RVFV challenge by efficiently suppressing viremia and replication of the challenge virus in the liver and the spleen. These data demonstrated that scMP-12 is a safe and immunogenic RVFV vaccine candidate.

The mTOR pathway controls cell proliferation by regulating the FoxO3a transcription factor via SGK1 kinase

The mechanistic target of rapamycin (mTOR) functions as a component of two large complexes, mTORC1 and mTORC2, which play crucial roles in regulating cell growth and homeostasis. However, the molecular mechanisms by which mTOR controls cell proliferation remain elusive. Here we show that the FoxO3a transcription factor is coordinately regulated by mTORC1 and mTORC2, and plays a crucial role in controlling cell proliferation. To dissect mTOR signaling, mTORC1 was specifically inactivated by depleting p18, an essential anchor of mTORC1 on lysosomes. mTORC1 inactivation caused a marked retardation of cell proliferation, which was associated with upregulation of cyclin-dependent kinase inhibitors (CDKIs). Although Akt was activated by mTORC1 inactivation, FoxO3a was upregulated via an epigenetic mechanism and hypophosphorylated at Ser314, which resulted in its nuclear accumulation. Consistently, mTORC1 inactivation induced downregulation of serum- and glucocorticoid-inducible kinase 1 (SGK1), the kinase responsible for Ser314 phosphorylation. Expression of FoxO3a mutated at Ser314 suppressed cell proliferation by inducing CDKI expression. SGK1 overexpression suppressed CDKI expression in p18-deficient cells, whereas SGK1 knockdown induced CDKI expression in wild-type cells, resulting in the suppression of cell proliferation. These results suggest that mTORC1, in coordination with mTORC2, controls cell proliferation by regulating FoxO3a gene expression and SGK1-mediated phosphorylation of FoxO3a at Ser314.

Cisplatin induces resistance by triggering differentiation of testicular embryonal carcinoma cells

Although testicular germ cell tumors are generally quite responsive to treatment with cisplatin, a small fraction of them acquire resistance during therapy. Even when cisplatin treatment is successful the patient is often left with a residual teratoma at the site of the primary tumor suggesting that cisplatin may trigger differentiation in some tumors. Using the human embryonal carcinoma cell line NTera2/D1, we confirmed that exposure to the differentiating agent retinoic acid produced a reduction in pluripotency markers NANOG and POU5F1 (Oct3/4) and an acute concentration-dependent increase in resistance to both cisplatin and paclitaxel that reached as high as 18-fold for cisplatin and 61-fold for paclitaxel within four days. A two day exposure to cisplatin also produced a concentration-dependent decrease in the expression of the NANOG and POU5F1 and increased expression of three markers whose levels increase with differentiation including Nestin, SCG10 and Fibronectin. In parallel, exposure to cisplatin induced up to 6.2-fold resistance to itself and 104-fold resistance to paclitaxel. Paclitaxel did not induce differentiation or resistance to either itself or cisplatin. Neither retinoic acid nor cisplatin induced resistance in cervical or prostate cancer cell lines or other germ cell tumor lines in which they failed to alter the expression of NANOG and POU5F1. Forced expression of NANOG prevented the induction of resistance to cisplatin by retinoic acid. We conclude that cisplatin can acutely induce resistance to itself and paclitaxel by triggering a differentiation response in pluripotent germ cell tumor cells.

C-ERC/mesothelin provokes lymphatic invasion of colorectal adenocarcinoma

BACKGROUND

Lymph node metastasis is a key event of colorectal cancer (CRC) progression. Mesothelin is expressed in various types of malignant tumor and associated with an unfavorable prognosis. The full-length mesothelin (Full-ERC) is cleaved by protease into membrane-bound C-ERC/mesothelin and N-ERC/mesothelin which is secreted into the blood. The aim of this study was to examine the biological role of mesothelin in CRC by clinicopathological analysis and in vitro lymphatic invasion assay.

METHODS

Ninety-one cases of CRC specimens were immunohistochemically examined and the localization of mesothelin in luminal membrane and/or cytoplasm was also evaluated. Lymphatic invasion assay was also performed using the human CRC cell line, WiDr, which was transfected with Full-, N- and C-ERC/mesothelin expression plasmids (Full-WiDr, N-WiDr and C-WiDr).

RESULTS

Immunohistochemically, "luminal membrane positive" of mesothelin was identified in 37.4 %, and correlated with lymphatic permeation and lymph node metastasis, but not with patients' prognosis. Interestingly, among the patients with lymph node metastasis (N = 38), "luminal membrane positive" of mesothelin significantly correlated with unfavorable patients' outcome. In addition, lymphatic invasion assay revealed that Full-WiDr and C-WiDr more significantly invaded human lymphatic endothelial cells than the Mock-WiDr (P < 0.01).

CONCLUSION

The luminal membrane expression of mesothelin was associated with unfavorable prognosis of CRC patients with lymph node metastasis. Moreover, this is the first report to prove the biological function of C-ERC/mesothelin associated with lymphatic invasion of cancer in vitro.

Effective embryoid body formation from induced pluripotent stem cells for regeneration of respiratory epithelium

OBJECTIVES/HYPOTHESIS

We have previously demonstrated the potential use of induced pluripotent stem (iPS) cells for regeneration of respiratory epithelium by culturing embryoid bodies (EBs). The aim of the present study was to determine the most effective conditions for EB formation from iPS cells for regeneration of respiratory epithelium.

STUDY DESIGN

Experimental study.

METHODS

iPS cells cultured on a gelatin-coated dish were seeded on low-attachment plates for generating EBs. Under several conditions including the air-liquid interface (ALI) method, with varying cell numbers and suspension times, EBs were transferred to a gelatin-coated dish supplemented with growth factors. The shape, size, aggregation, and adhesion of EBs for iPS cell differentiation were evaluated, and the cultured tissue was histologically examined.

RESULTS

EBs appropriate for differentiation were observed using 1,000 cells after 5 days of suspension culture. Respiratory epithelium-like tissue was histologically observed. The ciliary epithelium was confirmed immunohistologically.

CONCLUSIONS

Based on the varying suspension times and cell numbers with the ALI method, this study presented effective conditions for EB formation from iPS cells for regeneration of respiratory epithelium.

Nectin and junctional adhesion molecule are critical cell adhesion molecules for the apico-basal alignment of adherens and tight junctions in epithelial cells

Tight junctions (TJs) and adherens junctions (AJs) form an apical junctional complex at the apical side of the lateral membranes of epithelial cells, in which TJs are aligned at the apical side of AJs. Many cell adhesion molecules (CAMs) and cell polarity molecules (CPMs) cooperatively regulate the formation of the apical junctional complex, but the mechanism for the alignment of TJs at the apical side of AJs is not fully understood. We developed a cellular system with which epithelial-like TJs and AJs were reconstituted in fibroblasts and analyzed the cooperative roles of CAMs and CPMs. We exogenously expressed various combinations of CAMs and CPMs in fibroblasts that express negligible amounts of these molecules endogenously. In these cells, the nectin-based cell-cell adhesion was formed at the apical side of the junctional adhesion molecule (JAM)-based cell-cell adhesion, and cadherin and claudin were recruited to the nectin-3- and JAM-based cell-cell adhesion sites to form AJ-like and TJ-like domains, respectively. This inversed alignment of the AJ-like and TJ-like domains was reversed by complementary expression of CPMs Par-3, atypical protein kinase C, Par-6, Crb3, Pals1 and Patj. We describe the cooperative roles of these CAMs and CPMs in the apico-basal alignment of TJs and AJs in epithelial cells.

Binding between the junctional proteins afadin and PLEKHA7 and implication in the formation of adherens junction in epithelial cells

Adherens junction (AJ) is a specialized cell-cell junction structure that plays a role in mechanically connecting adjacent cells to resist strong contractile forces and to maintain tissue structure, particularly in the epithelium. AJ is mainly comprised of cell adhesion molecules cadherin and nectin and their associating cytoplasmic proteins including β-catenin, α-catenin, p120(ctn), and afadin. Our series of studies have revealed that nectin first forms cell-cell adhesion and then recruits cadherin to form AJ. The recruitment of cadherin by nectin is mediated by the binding of α-catenin and p120(ctn) to afadin. Recent studies showed that PLEKHA7 binds to p120(ctn), which is associated with E-cadherin, and maintains the integrity of AJ in epithelial cells. In this study, we showed that PLEKHA7 bound to afadin in addition to p120(ctn) and was recruited to the nectin-3α-based cell-cell adhesion site in a manner dependent on afadin, but not on p120(ctn). The binding of PLEKHA7 to afadin was required for the proper formation of AJ, but not for the formation of tight junction, in EpH4 mouse mammary gland epithelial cells. These results indicate that PLEKHA7 plays a cooperative role with nectin and afadin in the proper formation of AJ in epithelial cells.

CDK9-dependent transcriptional elongation in the innate interferon-stimulated gene response to respiratory syncytial virus infection in airway epithelial cells

Respiratory syncytial virus (RSV) is a negative-sense single-stranded RNA virus responsible for lower respiratory tract infections. During infection, the presence of double-stranded RNA (dsRNA) activates the interferon (IFN) regulatory factor 3 (IRF3) transcription factor, an event triggering expression of immediate early, IFN-stimulated genes (ISGs). We examine the role of transcriptional elongation in control of IRF3-dependent ISG expression. RSV infection induces ISG54, ISG56, and CIG5 gene expression in an IRF3-dependent manner demonstrated by IRF3 small interfering RNA (siRNA) silencing in both A549 epithelial cells and IRF3(-/-) MEFs. ISG expression was mediated by the recruitment of IRF3, CDK9, polymerase II (Pol II), and phospho-Ser(2) carboxy-terminal domain (CTD) Pol II to the IFN-stimulated response element (ISRE) binding sites of the IRF3-dependent ISG promoters in native chromatin. We find that RSV infection enhances the activated fraction of cyclin-dependent kinase 9 (CDK9) by promoting its association with bromodomain 4 (BRD4) and disrupting its association with the inhibitory 7SK small nuclear RNA. The requirement of CDK9 activity for ISG expression was shown by siRNA-mediated silencing of CDK9 and by a selective CDK9 inhibitor in A549 cells. In contrast, RSV-induced beta interferon (IFN-β) expression is not influenced by CDK9 inhibition. Using transcript-selective quantitative real-time reverse transcription-PCR (Q-RT-PCR) assays for the ISG54 gene, we observed that RSV induces transition from short to fully spliced mRNA transcripts and that this transition is blocked by CDK9 inhibition in both A549 and primary human small airway epithelial cells. These data indicate that transcription elongation plays a major role in RSV-induced ISG expression and is mediated by IRF3-dependent recruitment of activated CDK9. CDK9 activity may be a target for immunomodulation in RSV-induced lung disease.

Class A scavenger receptor 1 (MSR1) restricts hepatitis C virus replication by mediating toll-like receptor 3 recognition of viral RNAs produced in neighboring cells

Persistent infections with hepatitis C virus (HCV) may result in life-threatening liver disease, including cirrhosis and cancer, and impose an important burden on human health. Understanding how the virus is capable of achieving persistence in the majority of those infected is thus an important goal. Although HCV has evolved multiple mechanisms to disrupt and block cellular signaling pathways involved in the induction of interferon (IFN) responses, IFN-stimulated gene (ISG) expression is typically prominent in the HCV-infected liver. Here, we show that Toll-like receptor 3 (TLR3) expressed within uninfected hepatocytes is capable of sensing infection in adjacent cells, initiating a local antiviral response that partially restricts HCV replication. We demonstrate that this is dependent upon the expression of class A scavenger receptor type 1 (MSR1). MSR1 binds extracellular dsRNA, mediating its endocytosis and transport toward the endosome where it is engaged by TLR3, thereby triggering IFN responses in both infected and uninfected cells. RNAi-mediated knockdown of MSR1 expression blocks TLR3 sensing of HCV in infected hepatocyte cultures, leading to increased cellular permissiveness to virus infection. Exogenous expression of Myc-MSR1 restores TLR3 signaling in MSR1-depleted cells with subsequent induction of an antiviral state. A series of conserved basic residues within the carboxy-terminus of the collagen superfamily domain of MSR1 are required for binding and transport of dsRNA, and likely facilitate acidification-dependent release of dsRNA at the site of TLR3 expression in the endosome. Our findings reveal MSR1 to be a critical component of a TLR3-mediated pattern recognition receptor response that exerts an antiviral state in both infected and uninfected hepatocytes, thereby limiting the impact of HCV proteins that disrupt IFN signaling in infected cells and restricting the spread of HCV within the liver.

Persistent hepatitis C virus (HCV) infection is an important cause of fatal cirrhosis and liver cancer in humans. While viral disruption of interferon (IFN) signaling pathways may contribute to the persistence of HCV, IFN-stimulated gene (ISG) expression is often prominent within the infected liver. We show here that this is due, at least in part, to Toll-like receptor 3 sensing of HCV mediated by class A scavenger receptor type 1 (MSR1)-dependent endocytosis and transport of extracellular viral double-stranded RNA (dsRNA) allowing it to be engaged by TLR3 in the late endosome. TLR3 expressed within uninfected cells is capable of sensing HCV infection in neighboring infected cells in a process that is dependent upon the dsRNA-scavenging activity of MSR1, resulting in the induction of a localized functional antiviral response. This contributes to the ISG expression that typifies the chronically-infected liver, as it occurs within cells that do not express HCV proteins that disrupt IFN signaling. TLR3 signaling thus limits the spread of virus within the liver, potentially explaining why only a small fraction of hepatocytes are infected with HCV in vivo.

A novel function of novobiocin: disrupting the interaction of HIF 1α and p300/CBP through direct binding to the HIF1α C-terminal activation domain

Hypoxia-inducible factor 1α (HIF1α) is an important cellular survival protein under hypoxic conditions, regulating the cellular response to low oxygen tension via recruitment of a transcriptional co-activator, p300/CBP. p300/CBP induces expression of multiple genes involved in cell survival, proliferation, angiogenesis, and tumor development. Thus, a strategy to inhibit hypoxic responses in tumors may be to target the protein-protein interaction between HIF1α and p300/CBP. Here, we document, for the first time, that the aminocoumarin antibiotic, novobiocin, directly blocks the protein-protein interaction between the HIF1α C-terminal activation domain (CTAD) and the cysteine-histidine rich (CH1) region of p300/CBP. Also, novobiocin down-regulated HIF1α-controlled gene expression, specifically CA9, which is related to tumorigenesis. In a monolayer cell culture, novobiocin inhibited cell proliferation and colony formation in the MCF-7 human breast adenocarcinoma cell line and the A549 human lung cancer cell line. Rescue experiments revealed that the recombinant CTAD fragment of HIF1α partially reversed novobiocin’s inhibitory effects on cell proliferation and colony formation in MCF-7 cells. These findings suggest a novel mechanism of action for novobiocin which has the potential for innovative therapeutic use in tumor treatment.

Identification of a new interaction mode between the Src homology 2 domain of C-terminal Src kinase (Csk) and Csk-binding protein/phosphoprotein associated with glycosphingolipid microdomains

Proteins with Src homology 2 (SH2) domains play major roles in tyrosine kinase signaling. Structures of many SH2 domains have been studied, and the regions involved in their interactions with ligands have been elucidated. However, these analyses have been performed using short peptides consisting of phosphotyrosine followed by a few amino acids, which are described as the canonical recognition sites. Here, we report the solution structure of the SH2 domain of C-terminal Src kinase (Csk) in complex with a longer phosphopeptide from the Csk-binding protein (Cbp). This structure, together with biochemical experiments, revealed the existence of a novel binding region in addition to the canonical phosphotyrosine 314-binding site of Cbp. Mutational analysis of this second region in cells showed that both canonical and novel binding sites are required for tumor suppression through the Cbp-Csk interaction. Furthermore, the data indicate an allosteric connection between Cbp binding and Csk activation that arises from residues in the βB/βC loop of the SH2 domain.

Calcium-dependent phospholipid scramblase activity of TMEM16 protein family members

BACKGROUND

TMEM16A and 16B work as Cl(-) channel, whereas 16F works as phospholipid scramblase. The function of other TMEM16 members is unknown.

RESULTS

Using TMEM16F(-/-) cells, TMEM16C, 16D, 16F, 16G, and 16J were shown to be lipid scramblases.

CONCLUSION

Some TMEM16 members are divided into two Cl(-) channels and five lipid scramblases.

SIGNIFICANCE

Learning the biochemical function ofTMEM16family members is essential to understand their physiological role. Asymmetrical distribution of phospholipids between the inner and outer plasma membrane leaflets is disrupted in various biological processes. We recently identified TMEM16F, an eight-transmembrane protein, as a Ca(2+)-dependent phospholipid scramblase that exposes phosphatidylserine (PS) to the cell surface. In this study, we established a mouse lymphocyte cell line with a floxed allele in the TMEM16F gene. When TMEM16F was deleted, these cells failed to expose PS in response to Ca(2+) ionophore, but PS exposure was elicited by Fas ligand treatment. We expressed other TMEM16 proteins in the TMEM16F(-/-) cells and found that not only TMEM16F, but also 16C, 16D, 16G, and 16J work as lipid scramblases with different preference to lipid substrates. On the other hand, a patch clamp analysis in 293T cells indicated that TMEM16A and 16B, but not other family members, acted as Ca(2+)-dependent Cl(-) channels. These results indicated that among 10 TMEM16 family members, 7 members could be divided into two subfamilies, Ca(2+)-dependent Cl(-) channels (16A and 16B) and Ca(2+)-dependent lipid scramblases (16C, 16D, 16F, 16G, and 16J).

Extended lifespan of normal human B lymphocytes experimentally infected by SV40 or transfected by SV40 large T antigen expression vector

SV40 footprints were detected in different lymphoproliferative disorders and in blood specimens of healthy donors. However, little is known on the ability of SV40 to infect/transform normal human B-lymphocytes. In this in vitro study, experimental SV40 infection and SV40 Tag transfection of normal human B-lymphocytes from healthy blood donors were carried out. In SV40 infected/transfected purified B-cells, during the time course analyses, viral DNA sequences were detected by PCR, while Tag mRNA and protein were revealed by RT-PCR and immunocytochemistry, respectively. Trypan blue and Alamar blue assays showed an increase in number of cells and cell viability of infected/transfected B-cells up to day 50, then a drastic and constant cell number reduction was observed in cultures. Approximately 50% of both infected and transfected B-cells appeared morphologically transformed. SV40 viral progeny and its titer from infected B-cells was determined by plaque assay in permissive CV-1 cells. Our data indicate that human B-cells can be efficiently infected by SV40, release a viral progeny, while at the same time are transformed. SV40 infected/Tag transfected B-cells may represent an experimental model of study for investigating new biomarkers and targets for innovative therapeutic approaches in human B-cell malignancies.

The transcription factors Tbx18 and Wt1 control the epicardial epithelial-mesenchymal transition through bi-directional regulation of Slug in murine primary epicardial cells

During cardiac development, a subpopulation of epicardial cells migrates into the heart as part of the epicardial epithelial-mesenchymal transition (EMT) and differentiates into smooth muscle cells and fibroblasts. However, the roles of transcription factors in the epicardial EMT are poorly understood. Here, we show that two transcription factors expressed in the developing epicardium, T-box18 (Tbx18) and Wilms’ tumor 1 homolog (Wt1), bi-directionally control the epicardial EMT through their effects on Slug expression in murine primary epicardial cells. Knockdown of Wt1 induced the epicardial EMT, which was accompanied by an increase in the migration and expression of N-cadherin and a decrease in the expression of ZO-1 as an epithelial marker. By contrast, knockdown of Tbx18 inhibited the mesenchymal transition induced by TGFβ1 treatment and Wt1 knockdown. The expression of Slug but not Snail decreased as a result of Tbx18 knockdown, but Slug expression increased following knockdown of Wt1. Knockdown of Slug also attenuated the epicardial EMT induced by TGFβ1 treatment and Wt1 knockdown. Furthermore, in normal murine mammary gland-C7 (NMuMG-C7) cells, Tbx18 acted to increase Slug expression, while Wt1 acted to decrease Slug expression. Chromatin immunoprecipitation and promoter assay revealed that Tbx18 and Wt1 directly bound to the Slug promoter region and regulated Slug expression. These results provide new insights into the regulatory mechanisms that control the epicardial EMT.

Inositol pyrophosphate synthesis by inositol hexakisphosphate kinase 1 is required for homologous recombination repair

Inositol pyrophosphates, such as diphosphoinositol pentakisphosphate (IP(7)), are water-soluble inositol phosphates that contain high energy diphosphate moieties on the inositol ring. Inositol hexakisphosphate kinase 1 (IP6K1) participates in inositol pyrophosphate synthesis, converting inositol hexakisphosphate (IP(6)) to IP(7). In the present study, we show that mouse embryonic fibroblasts (MEFs) lacking IP6K1 exhibit impaired DNA damage repair via homologous recombination (HR). IP6K1 knock-out MEFs show decreased viability and reduced recovery after induction of DNA damage by the replication stress inducer, hydroxyurea, or the radiomimetic antibiotic, neocarzinostatin. Cells lacking IP6K1 arrest after genotoxic stress, and markers associated with DNA repair are recruited to DNA damage sites, indicating that HR repair is initiated in these cells. However, repair does not proceed to completion because these markers persist as nuclear foci long after drug removal. A fraction of IP6K1-deficient MEFs continues to proliferate despite the persistence of DNA damage, rendering the cells more susceptible to chromosomal aberrations. Expression of catalytically active but not inactive IP6K1 can restore the repair process in knock-out MEFs, implying that inositol pyrophosphates are required for HR-mediated repair. Our study therefore highlights inositol pyrophosphates as novel small molecule regulators of HR signaling in mammals.

Potential for Respiratory Epithelium Regeneration from Induced Pluripotent Stem Cells

Objectives:

In cases of laryngeal inflammatory lesions and tracheal invasion of a malignant tumor, autologous tissue implantation techniques using skin or cartilage are often applied. However, these techniques are both invasive and unstable. The purpose of this study was to evaluate the potential use of induced pluripotent stem (iPS) cells in the regeneration of respiratory epithelium.

Methods:

We seeded iPS cells on low-attachment plates in serum-free media to generate embryoid bodies (EBs). After a 3-day culture, the EBs were transferred to a gelatin-coated dish supplemented with activin A alone or with basic fibroblast growth factor (induction groups). As a control, EBs were cultured without these growth factors (control group). Cultured tissues from all groups were histologically examined for 2 weeks.

Results:

In the induction groups, the presence of respiratory epithelium-like tissue was observed with hematoxylin and eosin staining after 14 days of culture.

Conclusions:

This study demonstrated the potential use of iPS cells in regeneration of the respiratory epithelium.

Inhibition of GSH synthesis potentiates temozolomide-induced bystander effect in glioblastoma

Glioblastoma multiforme (GBM) is one of the most aggressive human tumors with poor prognosis. Current standard treatment includes chemotherapy using DNA alkylating agent temozolomide (TMZ) concomitant with surgical resection and/or irradiation. However, GBM patients exhibit various levels of the elevated expression of DNA repair enzyme, due to MGMT causing resistance to TMZ. Determination of the MGMT-positive population of primary tumor is important to evaluate the therapeutic efficacy of TMZ. Here we generated TMZ-resistant GBM cells by introducing MGMT into TMZ-sensitive GBM cell line KMG4, and established a model to assess the TMZ-induced bystander effect on TMZ-resistant cells. By mixing TMZ-resistant and -sensitive cells, GBM tumors with MGMT positivity as 50%, 10%, and 1% were generated in vivo. We could not observe any bystander effect of TMZ-induced cell death in tumor with 50% MGMT positivity. Although the bystander effect was observed within 20 days in the case of tumor with 1% MGMT positivity, final tumor size at day 28 was the same as control without sensitive cells. This bystander effect was observed in vitro using conditioned medium of TMZ-damaged GBM cells, and PCR array analysis indicated that the conditioned medium stimulated stress and toxicity pathway and upregulated anti-oxidants genes expression such as catalase and SOD2 in TMZ-resistant cells. In addition, the reduction of the activity of anti-stress mechanism by using inhibitor of GSH synthesis potentiated TMZ-induced bystander effect. These results suggest that GSH inhibitor might be one of the candidates for combination therapy with TMZ for TMZ-resistant GBM patients.

Dissecting the nanoscale distributions and functions of microtubule-end-binding proteins EB1 and ch-TOG in interphase HeLa cells

Recently, the EB1 and XMAP215/TOG families of microtubule binding proteins have been demonstrated to bind autonomously to the growing plus ends of microtubules and regulate their behaviour in in vitro systems. However, their functional redundancy or difference in cells remains obscure. Here, we compared the nanoscale distributions of EB1 and ch-TOG along microtubules using high-resolution microscopy techniques, and also their roles in microtubule organisation in interphase HeLa cells. The ch-TOG accumulation sites protruded ∼100 nm from the EB1 comets. Overexpression experiments showed that ch-TOG and EB1 did not interfere with each other’s localisation, confirming that they recognise distinct regions at the ends of microtubules. While both EB1 and ch-TOG showed similar effects on microtubule plus end dynamics and additively increased microtubule dynamicity, only EB1 exhibited microtubule-cell cortex attachment activity. These observations indicate that EB1 and ch-TOG regulate microtubule organisation differently via distinct regions in the plus ends of microtubules.

N-terminal truncation of Lats1 causes abnormal cell growth control and chromosomal instability

The tumor suppressors Lats1 and Lats2 are mediators of the Hippo pathway that regulates tissue growth and proliferation. Their N-terminal non-kinase regions are distinct except for Lats conserved domains 1 and 2 (LCD1 and LCD2), which may be important for Lats1/2-specific functions. Lats1 knockout mice were generated by disrupting the N-terminal region containing LCD1 (Lats1(ΔN/ΔN)). Some Lats1(ΔN/ΔN) mice were born safely and grew normally. However, mouse embryonic fibroblasts (MEFs) from Lats1(ΔN/ΔN) mice displayed mitotic defects, centrosomal overduplication, chromosomal misalignment, multipolar spindle formation, chromosomal bridging and cytokinesis failure. They also showed anchorage-independent growth and continued cell cycles and cell growth, bypassing cell-cell contact inhibition similar to tumor cells. Lats1(ΔN/ΔN) MEFs produced tumors in nude mice after subcutaneous injection, although the tumor growth rate was much slower than that of ordinary cancer cells. Yap, a key transcriptional coactivator of the Hippo pathway, was overexpressed and stably retained in Lats1(ΔN/ΔN) MEFs in a cell density independent manner, and Lats2 mRNA expression was downregulated. In conclusion, N-terminally truncated Lats1 induced Lats2 downregulation and Yap protein accumulation, leading to chromosomal instability and tumorigenesis.

Apaf-1- and Caspase-8-independent apoptosis

Two major apoptosis pathways, the mitochondrial and death receptor pathways, are well recognized. Here we established cell lines from the fetal thymus of Apaf-1-, Caspase-9-, or Bax/Bak-deficient mice. These cell lines were resistant to apoptosis induced by DNA-damaging agents, RNA or protein synthesis inhibitors, or stress in the endoplasmic reticulum. However, they underwent efficient apoptosis when treated with kinase inhibitors such as staurosporine and H-89, indicating that these inhibitors induce a caspase-dependent apoptosis that is different from the mitochondrial pathway. CrmA, a Caspase-8 inhibitor, did not prevent staurosporine-induced apoptosis of fetal thymic cell lines, suggesting that the death receptor pathway was also not involved in this process. The staurosporine-induced cell death was inhibited by okadaic acid, a serine/threonine phosphatase inhibitor, suggesting that dephosphorylation of a proapoptotic molecule triggered the death process, or that phosphorylation of an antiapoptotic molecule could block the process. Cells of various types (fetal thymocytes, bone marrows, thymocytes, and splenocytes), but not embryonic fibroblasts, were sensitive to the noncanonical staurosporine-induced apoptosis, suggesting that the noncanonical apoptosis pathway is tissue specific.

Tetraspanin is required for generation of reactive oxygen species by the dual oxidase system in Caenorhabditis elegans

Reactive oxygen species (ROS) are toxic but essential molecules responsible for host defense and cellular signaling. Conserved NADPH oxidase (NOX) family enzymes direct the regulated production of ROS. Hydrogen peroxide (H₂O₂) generated by dual oxidases (DUOXs), a member of the NOX family, is crucial for innate mucosal immunity. In addition, H₂O₂ is required for cellular signaling mediated by protein modifications, such as the thyroid hormone biosynthetic pathway in mammals. In contrast to other NOX isozymes, the regulatory mechanisms of DUOX activity are less understood. Using Caenorhabditis elegans as a model, we demonstrate that the tetraspanin protein is required for induction of the DUOX signaling pathway in conjunction with the dual oxidase maturation factor (DUOXA). In the current study, we show that genetic mutation of DUOX (bli-3), DUOXA (doxa-1), and peroxidase (mlt-7) in C. elegans causes the same defects as a tetraspanin tsp-15 mutant, represented by exoskeletal deficiencies due to the failure of tyrosine cross-linking of collagen. The deficiency in the tsp-15 mutant was restored by co-expression of bli-3 and doxa-1, indicating the involvement of tsp-15 in the generation of ROS. H₂O₂ generation by BLI-3 was completely dependent on TSP-15 when reconstituted in mammalian cells. We also demonstrated that TSP-15, BLI-3, and DOXA-1 form complexes in vitro and in vivo. Cell-fusion-based analysis suggested that association with TSP-15 at the cell surface is crucial for BLI-3 activation to release H₂O₂. This study provides the first evidence for an essential role of tetraspanin in ROS generation.

ROS are highly reactive molecules, which can be inappropriately produced during aerobic metabolism or by exogenous stresses such as exposure to UV light and radiation. ROS interact with cellular components including nucleic acids, lipids, and proteins and irreversibly inhibit their functions. However, ROS are essential for innate host defense and multiple physiological processes and are generated by conserved NADPH oxidase (NOX) family enzymes. The release of ROS by ROS generator enzymes must be properly controlled, as chronic oxidative stress can cause an imbalance of the redox state and is often associated with disease and aging. Using C. elegans as a model, we identified a tetraspanin (TSP-15) protein as a new key component of the ROS generation system controlled by dual oxidase (BLI-3), a unique NOX isozyme in C. elegans. Mutants of both bli-3 and tsp-15 developed the same defects in extracellular matrix cross-linking. Using a combination of genetics and reconstitution experiments in mammalian cells, we have demonstrated a novel requirement of tetraspanin for dual oxidase-dependent ROS generation via complex formation at the cell surface.

Evaluation of the use of induced pluripotent stem cells (iPSCs) for the regeneration of tracheal cartilage

The treatment of laryngotracheal stenosis remains a challenge as treatment often requires multistaged procedures, and successful decannulation sometimes fails after a series of operations. Induced pluripotent stem cells (iPSCs) were generated in 2006. These cells are capable of unlimited symmetrical self-renewal, thus providing an unlimited cell source for tissue-engineering applications. We have previously reported tracheal wall regeneration using a three-dimensional (3D) scaffold containing iPSCs. However, the efficiency of differentiation into cartilage was low. In addition, it could not be proven that the cartilage tissues were in fact derived from the implanted iPSCs. The purpose of this study was to evaluate and improve the use of iPSCs for the regeneration of tracheal cartilage. iPSCs were cultured in vitro in a 3D scaffold in chondrocyte differentiation medium. After cultivation, differentiation into chondrocytes was examined. The ratio of undifferentiated cells was analyzed by flow cytometry. The 3D scaffolds were implanted into tracheal defects, as an injury site, in 24 nude rats. Differentiation into chondrocytes in vitro was confirmed histologically, phenotypically, and genetically. Flow cytometric analysis demonstrated that the population of undifferentiated cells was decreased. Cartilage tissue was observed in the regenerated tracheal wall in 6 of 11 rats implanted with induced iPSCs, but in none of 13 rats implanted with the control and noninduced iPSCs. The expression of cartilage-specific protein was also demonstrated in vivo in 3D scaffolds containing iPSCs. The presence of the GFP gene derived from iPSCs was confirmed in samples of cartilage tissue by the combination of laser microdissection (LMD) and polymerase chain reaction (PCR) techniques. Our study demonstrated that iPSCs have the potential to differentiate into chondrogenic cells in vitro. Cartilage tissue was regenerated in vivo. Our results suggest that iPSCs could be a new cell source for the regeneration of tracheal cartilage.

Essential role for miR-196a in brown adipogenesis of white fat progenitor cells

Brown adipocytes can differentiate from white fat progenitor cells in mice exposed to cold or β3-adrenergic stimulation, and this process is regulated by a microRNA that regulates the expression of Hoxc8, a master regulator of brown adipogenesis.

The recent discovery of functional brown adipocytes in adult humans illuminates the potential of these cells in the treatment of obesity and its associated diseases. In rodents, brown adipocyte-like cells are known to be recruited in white adipose tissue (WAT) by cold exposure or β-adrenergic stimulation, but the molecular machinery underlying this phenomenon is not fully understood. Here, we show that inducible brown adipogenesis is mediated by the microRNA miR-196a. We found that miR-196a suppresses the expression of the white-fat gene Hoxc8 post-transcriptionally during the brown adipogenesis of white fat progenitor cells. In mice, miR-196a is induced in the WAT-progenitor cells after cold exposure or β-adrenergic stimulation. The fat-specific forced expression of miR-196a in mice induces the recruitment of brown adipocyte-like cells in WAT. The miR-196a transgenic mice exhibit enhanced energy expenditure and resistance to obesity, indicating the induced brown adipocyte-like cells are metabolically functional. Mechanistically, Hoxc8 targets and represses C/EBPβ, a master switch of brown-fat gene program, in cooperation with histone deacetylase 3 (HDAC3) through the C/EBPβ 3′ regulatory sequence. Thus, miR-196a induces functional brown adipocytes in WAT through the suppression of Hoxc8, which functions as a gatekeeper of the inducible brown adipogenesis. The miR-196a-Hoxc8-C/EBPβ signaling pathway may be a therapeutic target for inducing brown adipogenesis to combat obesity and type 2 diabetes.

Obesity is caused by the accumulation of surplus energy in a fatty tissue called white adipose tissue (WAT) and can lead to important health problems such as diabetes. Mammals additionally possess brown adipose tissue (BAT), which serves to generate body heat to stabilize body temperature under exposure to cold, and is abundant in hibernating animals and human neonates. In performing its function BAT consumes energy, thereby reducing WAT fat accumulation. Recent studies have shown that exposure to a cold environment stimulates the partial conversion of WAT to BAT in mice, and given that human adults have a limited amount of BAT, such a conversion has the potential to afford a novel method of obesity control. Here, we analyze the molecular mechanism of this conversion using genetically manipulated mice and cells isolated from human adipose tissue. We find that the expression levels of a microRNA, miR-196a, positively correlate with the conversion of WAT to BAT under cold exposure conditions. We show that forced expression of miR-196a in mouse adipose tissue increases BAT content and energy expenditure, thereby rendering the animals resistant to obesity and diabetes. Mechanistically, we observe that miR-196a acts by inhibiting the expression of the homeotic gene Hoxc8, a repressor of brown adipogenesis. These findings introduce the therapeutic possibility of using microRNAs to control obesity and its associated diseases in humans.

p27kip1 protein levels reflect a nexus of oncogenic signaling during cell transformation

SV40 small t-antigen (ST) collaborates with SV40 large T-antigen (LT) and activated rasv12 to promote transformation in a variety of immortalized human cells. A number of oncogenes or the disruption of the general serine-threonine phosphatase protein phosphatase 2A (PP2A) can replace ST in this paradigm. However, the relationship between these oncogenes and PP2A activity is not clear. To address this, we queried the connectivity of these molecules in silico. We found that p27 was connected to each of those oncogenes that could substitute for ST. We further determined that p27 loss can substitute for the expression of ST during transformation of both rodent and human cells. Conversely, knock-in cells expressing the degradation-resistant S10A and T187A mutants of p27 were resistant to the transforming activities of ST. This suggests that p27 is an important target of the tumor-suppressive effects of PP2A and likely an important target of the multitude of cellular oncoproteins that emulate the transforming function of ST.

Siglec-15 protein regulates formation of functional osteoclasts in concert with DNAX-activating protein of 12 kDa (DAP12)

Osteoclasts are multinucleated giant cells that reside in osseous tissues and resorb bone. Signaling mediated by receptor activator of nuclear factor (NF)-κB (RANK) and its ligand leads to the nuclear factor of activated T cells 2/c1 (NFAT2 or NFATc1) expression, a critical step in the formation of functional osteoclasts. In addition, adaptor proteins harboring immunoreceptor tyrosine-based activation motifs, such as DNAX-activating protein of 12 kDa (DAP12), play essential roles. In this study, we identified the gene encoding the lectin Siglec-15 as NFAT2-inducible, and we found that the protein product links RANK ligand-RANK-NFAT2 and DAP12 signaling in mouse osteoclasts. Both the recognition of sialylated glycans by the Siglec-15 V-set domain and the association with DAP12 through its Lys-272 are essential for its function. When Siglec-15 expression was knocked down, fewer multinucleated cells developed, and those that did were morphologically contracted with disordered actin-ring structures. These changes were accompanied by significantly reduced bone resorption. Siglec-15 formed complexes with Syk through DAP12 in response to vitronectin. Furthermore, chimeric molecules consisting of the extracellular and transmembrane regions of Siglec-15 with a K272A mutation and the cytoplasmic region of DAP12 significantly restored bone resorption in cells with knocked down Siglec-15 expression. Together, these results suggested that the Siglec-15-DAP12-Syk-signaling cascade plays a critical role in functional osteoclast formation.

Probing sporadic and familial Alzheimer's disease using induced pluripotent stem cells

Our understanding of Alzheimer’s disease pathogenesis is currently limited by difficulties in obtaining live neurons from patients and the inability to model the sporadic form of the disease. It may be possible to overcome these challenges by reprogramming primary cells from patients into induced pluripotent stem cells (iPSCs). Here we reprogrammed primary fibroblasts from two patients with familial Alzheimer’s disease, both caused by a duplication of the amyloid-β precursor protein gene¹ (APP; termed APP^Dp), two with sporadic Alzheimer’s disease (termed sAD1, sAD2) and two non-demented control individuals into iPSC lines. Neurons from differentiated cultures were purified with fluorescence-activated cell sorting and characterized. Purified cultures contained more than 90% neurons, clustered with fetal brain messenger RNA samples by microarray criteria, and could form functional synaptic contacts. Virtually all cells exhibited normal electrophysiological activity. Relative to controls, iPSC-derived, purified neurons from the two APP^Dp patients and patient sAD2 exhibited significantly higher levels of the pathological markers amyloid-β(1–40), phospho-tau(Thr 231) and active glycogen synthase kinase-3β (aGSK-3β). Neurons from APP^Dp and sAD2 patients also accumulated large RAB5-positive early endosomes compared to controls. Treatment of purified neurons with β-secretase inhibitors, but not γ-secretase inhibitors, caused significant reductions in phospho-Tau(Thr 231) and aGSK-3β levels. These results suggest a direct relationship between APP proteolytic processing, but not amyloid-β, in GSK-3β activation and tau phosphorylation in human neurons. Additionally, we observed that neurons with the genome of one sAD patient exhibited the phenotypes seen in familial Alzheimer’s disease samples. More generally, we demonstrate that iPSC technology can be used to observe phenotypes relevant to Alzheimer’s disease, even though it can take decades for overt disease to manifest in patients.

RelA Ser276 phosphorylation-coupled Lys310 acetylation controls transcriptional elongation of inflammatory cytokines in respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a negative-sense single-stranded RNA virus responsible for lower respiratory tract infections (LRTIs) in humans. In experimental models of RSV LRTI, the actions of the nuclear factor κB (NF-κB) transcription factor mediate inflammation and pathology. We have shown that RSV replication induces a mitogen-and-stress-related kinase 1 (MSK-1) pathway that activates NF-κB RelA transcriptional activity by a process involving serine phosphorylation at serine (Ser) residue 276. In this study, we examined the mechanism by which phospho-Ser276 RelA mediates expression of the NF-κB-dependent gene network. RelA-deficient mouse embryonic fibroblasts (MEFs) complemented with the RelA Ser276Ala mutant are deficient in CXCL2/Groβ, KC, and interleukin-6 (IL-6) expression, but NFKBIA/IκBα is preserved. We show that RSV-induced RelA Ser276 phosphorylation is required for acetylation at Lys310, an event required for transcriptional activity and stable association of RelA with the activated positive transcriptional elongation factor (PTEF-b) complex proteins, bromodomain 4 (Brd4), and cyclin-dependent kinase 9 (CDK9). In contrast to gene loading pattern of PTEF-b proteins produced by tumor necrosis factor (TNF) stimulation, RSV induces their initial clearance followed by partial reaccumulation coincident with RelA recruitment. The RSV-induced binding patterns of the CDK9 substrate, phospho-Ser2 RNA polymerase (Pol) II, follows a similar pattern of clearance and downstream gene reaccumulation. The functional role of CDK9 was examined using CDK9 small interfering RNA (siRNA) and CDK inhibitors, where RSV-induced NF-κB-dependent gene expression was significantly inhibited. Finally, although RSV induces a transition from short transcripts to fully spliced mRNA in wild-type RelA (RelA WT)-expressing cells, this transition is not seen in cells expressing RelA Ser276Ala. We conclude that RelA Ser276 phosphorylation mediates RelA acetylation, Brd4/CDK9 association, and activation of downstream inflammatory genes by transcriptional elongation in RSV infection.

Hypoxia induces tumor aggressiveness and the expansion of CD133-positive cells in a hypoxia-inducible factor-1α-dependent manner in pancreatic cancer cells

BACKGROUND

Intratumoral hypoxia is known to lead to increased aggressiveness and distant metastasis. However, the interplay underlying these actions is still unknown.

OBJECTIVE

We explored whether cancer cells might acquire a stem-like phenotype under hypoxia, consequently leading to an aggressive phenotype, including invasiveness and metastasis.

METHODS

Under normoxia (20% O(2)) or hypoxia (1% O(2)), the expression of CD133 (cancer stem cell marker), CXC chemokine receptor 4 (CXCR4) and hypoxia-inducible factor-1α (HIF-1α) was examined by RT-PCR and immunostaining using human pancreatic cancer cell lines. We also examined if hypoxia facilitates the invasiveness of CD133+ cancer cells. Furthermore, we transfected dominant active HIF-1α (HIF-1αΔODD) by the retroviral gene transfer and examined the effects both in vitro and in vivo.

RESULTS

Compared with normoxia, hypoxia elevated the expression of CD133, CXCR4 and HIF-1α. Moreover, hypoxia facilitated the invasiveness of CD133+ pancreatic cancer cells. The behavior of HIF-1αΔODD-transfected cells under normoxia was compatible with that of the parent cells under hypoxia. Furthermore, a xenograft model of HIF-1αΔODD cells showed aggressiveness, including metastasis and highly tumorigenic ability.

CONCLUSION

Hypoxia induces tumor aggressiveness associated with the expansion of CD133+ pancreatic cancer cells in a predominantly HIF-1α-dependent manner.

Immortalized cells as experimental models to study cancer

The development of cancer is a multi-step process in which normal cells sustain a series of genetic alterations that together program the malignant phenotype. Much of our knowledge of cancer biology results from the detailed study of specimens and cell lines derived from patient tumors. While these approaches continue to yield critical information regarding the identity, number, and types of alterations found in human tumors, further progress in understanding the molecular basis of malignant transformation depends upon the generation and use of increasingly sophisticated experimental models of cancer. Over the past several years, the recognition that telomeres and telomerase play essential roles in regulating cell lifespan now permits the development of new models of human cancer. Here we review recent progress in the use of immortalized human cells as a foundation for understanding the molecular basis of cancer.

A population of BJ fibroblasts escaped from Ras-induced senescence susceptible to transformation

Oncogenic stimuli such as H-Ras induce oncogene-induced senescence (OIS) in fibroblasts to protect against transformation. Here we found that a population of the human diploid fibroblasts can escape from OIS induced by H-RasV12. We designated these OIS-escaped cells as OISEC (OIS-escaped cells). OISEC lost the expression of p16 which plays an important role for cell cycle arrest for induction of senescence, but OISEC preserved the p16 expression machinery and exhibited senescence by the treatment with hydrogen peroxide (H(2)O(2)) as stress-induced premature senescence (SIPS). OISEC did not possess anchorage-independent growth potential, and functional disruption of p53 and Rb by SV40 early region encoding large T and small t antigens, induced the aneuploidy phenotype and colony-forming potential of OISEC together with the exhibition of in vivo tumor formation. Finally, we also found that the distinctive feature of OISEC is expression of transcription factors, Oct3/4, SOX2, and Nanog which is closely related to stem-like cell features. This study highlights the presence of a cell population which escaped from OIS, and this OISEC may transform into malignant cancer cells by the additional hits of several genes in vivo.

Quantification of activated NF-kappaB/RelA complexes using ssDNA aptamer affinity-stable isotope dilution-selected reaction monitoring-mass spectrometry

Nuclear Factor-κB (NF-κB) is a family of inducible transcription factors regulated by stimulus-induced protein interactions. In the cytoplasm, the NF-κB member RelA transactivator is inactivated by binding inhibitory IκBs, whereas in its activated state, the serine-phosphorylated protein binds the p300 histone acetyltransferase. Here we describe the isolation of a ssDNA aptamer (termed P028F4) that binds to the activated (IκBα-dissociated) form of RelA with a K(D) of 6.4 × 10(-10), and its application in an enrichment-mass spectrometric quantification assay. ssDNA P028F4 competes with cognate duplex high affinity NF-κB binding sites for RelA binding in vitro, binds activated RelA in eukaryotic nuclei and reduces TNFα-stimulated endogenous NF-κB dependent gene expression. Incorporation of P028F4 as an affinity isolation step enriches for serine 536 phosphorylated and p300 coactivator complexed RelA, simultaneously depleting IκBα·RelA complexes. A stable isotope dilution (SID)-selected reaction monitoring (SRM)- mass spectrometry (MS) assay for RelA was developed that produced a linear response over 1,000 fold dilution range of input protein and had a 200 amol lower limit of quantification. This multiplex SID-SRM-MS RelA assay was used to quantify activated endogenous RelA in cytokine-stimulated eukaryotic cells isolated by single-step P028F4 enrichment. The aptamer-SID-SRM-MS assay quantified the fraction of activated RelA in subcellular extracts, detecting the presence of a cytoplasmic RelA reservoir unresponsive to TNFα stimulation. We conclude that aptamer-SID-SRM-MS is a versatile tool for quantification of activated NF-κB/RelA and its associated complexes in response to pathway activation.

The guanine nucleotide exchange factor Arhgef5 plays crucial roles in Src-induced podosome formation

Podosomes and invadopodia are actin-rich membrane protrusions that play a crucial role in cell adhesion and migration, and extracellular matrix remodeling in normal and cancer cells. The formation of podosomes and invadopodia is promoted by upregulation of some oncogenic molecules and is closely related to the invasive potential of cancer cells. However, the molecular mechanisms underlying the podosome and invadopodium formation still remain unclear. Here, we show that a guanine nucleotide exchange factor (GEF) for Rho family GTPases (Arhgef5) is crucial for Src-induced podosome formation. Using an inducible system for Src activation, we found that Src-induced podosome formation depends upon the Src SH3 domain, and identified Arhgef5 as a Src SH3-binding protein. RNA interference (RNAi)-mediated depletion of Arhgef5 caused robust inhibition of Src-dependent podosome formation. Overexpression of Arhgef5 promoted actin stress fiber remodeling through activating RhoA, and the activation of RhoA or Cdc42 was required for Src-induced podosome formation. Arhgef5 was tyrosine-phosphorylated by Src and bound to Src to positively regulate its activity. Furthermore, the pleckstrin homology (PH) domain of Arhgef5 was required for podosome formation, and Arhgef5 formed a ternary complex with Src and phosphoinositide 3-kinase when Src and/or Arhgef5 were upregulated. These findings provide novel insights into the molecular mechanisms of podosome and invadopodium formation induced by Src upregulation.

Oncogene-mediated human lung epithelial cell transformation produces adenocarcinoma phenotypes in vivo

It has been challenging to engineer lung adenocarcinoma models via oncogene-mediated transformation of primary cultured normal human cells. Although viral oncoprotein-mediated malignant transformation has been reported, xenografts derived from such transformed cells generally represent poorly differentiated cancers. Here, we demonstrate that the combined expression of multiple cellular factors induces malignant transformation in normal human lung epithelial cells. Although a combination of four genetic alterations, including hTERT overexpression, inactivation of the pRB and p53 pathways, and KRAS activation, is insufficient for normal human small airway epithelial cells to be fully transformed, expression of one additional oncogene induces malignant transformation. Notably, we have succeeded in reproducing human lung adenocarcinoma phenotypes in the flanks of nude mice by introducing an active form of PIK3CA, CYCLIN-D1, or a dominant-negative form of LKB1 in combination with the four genetic alterations above. Besides differentiated lung cancer, poorly differentiated cancer models can also be engineered by employing c-MYC as one of the genetic elements, indicating that histologic features and degree of differentiation of xenografts are controllable to some extent by changing the combination of genetic elements introduced. This is the first study reporting malignant transformation of normal lung epithelial cells in the absence of viral oncoproteins. We propose that our model system would be useful to identify the minimal and most crucial set of changes required for lung tumorigenesis, and that it would provide a broadly applicable approach for discovering attractive therapeutic targets.

Down-regulation of the tumor suppressor C-terminal Src kinase (Csk)-binding protein (Cbp)/PAG1 is mediated by epigenetic histone modifications via the mitogen-activated protein kinase (MAPK)/phosphatidylinositol 3-kinase (PI3K) pathway

The transmembrane adaptor protein Cbp (or PAG1) functions as a suppressor of Src-mediated tumor progression by promoting the inactivation of Src. The expression of Cbp is down-regulated in Src-transformed cells and in various human cancer cells, suggesting a potential role for Cbp as a tumor suppressor. However, the mechanisms underlying the down-regulation of Cbp remain unknown. The present study shows that Cbp expression is down-regulated by epigenetic histone modifications via the MAPK/PI3K pathway. In mouse embryonic fibroblasts, transformation by oncogenic Src and Ras induced a marked down-regulation of Cbp expression. The levels of Cbp expression were inversely correlated with the activity of MEK and Akt, and Cbp down-regulation was suppressed by inhibiting MEK and PI3K. Src transformation did not affect the stability of Cbp mRNA, the transcriptional activity of the cbp promoter, or the DNA methylation status of the cbp promoter CpG islands. However, Cbp expression was restored by treatment with histone deacetylase (HDAC) inhibitors and by siRNA-mediated knockdown of HDAC1/2. Src transformation significantly decreased the acetylation levels of histone H4 and increased the trimethylation levels of histone H3 lysine 27 in the cbp promoter. EGF-induced Cbp down-regulation was also suppressed by inhibiting MEK and HDAC. Furthermore, the inhibition of MEK or HDAC restored Cbp expression in human cancer cells harboring Cbp down-regulation through promoter hypomethylation. These findings suggest that Cbp down-regulation is primarily mediated by epigenetic histone modifications via oncogenic MAPK/PI3K pathways in a subset of cancer cells.

Somatic coding mutations in human induced pluripotent stem cells

Defined transcription factors can induce epigenetic reprogramming of adult mammalian cells into induced pluripotent stem cells. Although DNA factors are integrated during some reprogramming methods, it is unknown whether the genome remains unchanged at the single nucleotide level. Here we show that 22 human induced pluripotent stem (hiPS) cell lines reprogrammed using five different methods each contained an average of five protein-coding point mutations in the regions sampled (an estimated six protein-coding point mutations per exome). The majority of these mutations were non-synonymous, nonsense or splice variants, and were enriched in genes mutated or having causative effects in cancers. At least half of these reprogramming-associated mutations pre-existed in fibroblast progenitors at low frequencies, whereas the rest occurred during or after reprogramming. Thus, hiPS cells acquire genetic modifications in addition to epigenetic modifications. Extensive genetic screening should become a standard procedure to ensure hiPS cell safety before clinical use.

Antiviral activities of ISG20 in positive-strand RNA virus infections

ISG20 is an interferon-inducible 3'-5' exonuclease that inhibits replication of several human and animal RNA viruses. However, the specificities of ISG20's antiviral action remain poorly defined. Here we determine the impact of ectopic expression of ISG20 on replication of several positive-strand RNA viruses from distinct viral families. ISG20 inhibited infections by cell culture-derived hepatitis C virus (HCV) and a pestivirus, bovine viral diarrhea virus and a picornavirus, hepatitis A virus. Moreover, ISG20 demonstrated cell-type specific antiviral activity against yellow fever virus, a classical flavivirus. Overexpression of ISG20, however, did not inhibit propagation of severe acute respiratory syndrome coronavirus, a highly-pathogenic human coronavirus in Huh7.5 cells. The antiviral effects of ISG20 were all dependent on its exonuclease activity. The closely related cellular exonucleases, ISG20L1 and ISG20L2, did not inhibit HCV replication. Together, these data may help better understand the antiviral specificity and action of ISG20.

Exendin-4 suppresses SRC activation and reactive oxygen species production in diabetic Goto-Kakizaki rat islets in an Epac-dependent manner

OBJECTIVE

Reactive oxygen species (ROS) is one of most important factors in impaired metabolism secretion coupling in pancreatic β-cells. We recently reported that elevated ROS production and impaired ATP production at high glucose in diabetic Goto-Kakizaki (GK) rat islets are effectively ameliorated by Src inhibition, suggesting that Src activity is upregulated. In the present study, we investigated whether the glucagon-like peptide-1 signal regulates Src activity and ameliorates endogenous ROS production and ATP production in GK islets using exendin-4.

RESEARCH DESIGN AND METHODS

Isolated islets from GK and control Wistar rats were used for immunoblotting analyses and measurements of ROS production and ATP content. Src activity was examined by immunoprecipitation of islet lysates followed by immunoblotting. ROS production was measured with a fluorescent probe using dispersed islet cells.

RESULTS

Exendin-4 significantly decreased phosphorylation of Src Tyr416, which indicates Src activation, in GK islets under 16.7 mmol/l glucose exposure. Glucose-induced ROS production (16.7 mmol/l) in GK islet cells was significantly decreased by coexposure of exendin-4 as well as PP2, a Src inhibitor. The Src kinase-negative mutant expression in GK islets significantly decreased ROS production induced by high glucose. Exendin-4, as well as PP2, significantly increased impaired ATP elevation by high glucose in GK islets. The decrease in ROS production by exendin-4 was not affected by H-89, a PKA inhibitor, and an Epac-specific cAMP analog (8CPT-2Me-cAMP) significantly decreased Src Tyr416 phosphorylation and ROS production.

CONCLUSIONS

Exendin-4 decreases endogenous ROS production and increases ATP production in diabetic GK rat islets through suppression of Src activation, dependently on Epac.

The transmembrane adaptor Cbp/PAG1 controls the malignant potential of human non-small cell lung cancers that have c-src upregulation

The tyrosine kinase c-Src is upregulated in various human cancers, although the precise regulatory mechanism underlying this upregulation is unclear. We previously reported that a transmembrane adaptor Csk-binding protein (Cbp; PAG1) plays an important role in controlling the cell transformation that is induced by the activation of c-Src. To elucidate the in vivo role of Cbp, we examined the function of Cbp in lung cancer cell lines and tissues. In this study, we found that Cbp was markedly downregulated in human non-small cell lung cancer (NSCLC) cells. The ectopic expression of Cbp suppressed the anchorage-independent growth of the NSCLC cell lines (A549 and Lu99) that had upregulated c-Src, whereas the Cbp expression had little effect on other NSCLC cell lines (PC9 and Lu65) that express normal levels of c-Src. The expression of Cbp suppressed the kinase activity of c-Src in A549 cells by recruiting c-Src and its negative regulator, C-terminal Src kinase (Csk), to lipid rafts. The treatment with Src inhibitors, such as PP2, dasatinib, and saracatinib, also suppressed the growth of A549 cells. Furthermore, Cbp expression attenuated the ability of A549 cells to form tumors in nude mice, invade in vitro, and metastasize in vivo. In addition, we found a significant inverse correlation between the level of Cbp expression and the extent of lymph node metastasis in human lung cancers. These results indicate that Cbp is required for the Csk-mediated inactivation of c-Src and may control the promotion of malignancy in NSCLC tumors that are characterized by c-Src upregulation.

Development of defective and persistent Sendai virus vector: a unique gene delivery/expression system ideal for cell reprogramming

The ectopic expression of transcription factors can reprogram differentiated tissue cells into induced pluripotent stem cells. However, this is a slow and inefficient process, depending on the simultaneous delivery of multiple genes encoding essential reprogramming factors and on their sustained expression in target cells. Moreover, once cell reprogramming is accomplished, these exogenous reprogramming factors should be replaced with their endogenous counterparts for establishing autoregulated pluripotency. Complete and designed removal of the exogenous genes from the reprogrammed cells would be an ideal option for satisfying this latter requisite as well as for minimizing the risk of malignant cell transformation. However, no single gene delivery/expression system has ever been equipped with these contradictory characteristics. Here we report the development of a novel replication-defective and persistent Sendai virus (SeVdp) vector based on a noncytopathic variant virus, which fulfills all of these requirements for cell reprogramming. The SeVdp vector could accommodate up to four exogenous genes, deliver them efficiently into various mammalian cells (including primary tissue cells and human hematopoietic stem cells) and express them stably in the cytoplasm at a prefixed balance. Furthermore, interfering with viral transcription/replication using siRNA could erase the genomic RNA of SeVdp vector from the target cells quickly and thoroughly. A SeVdp vector installed with Oct4/Sox2/Klf4/c-Myc could reprogram mouse primary fibroblasts quite efficiently; ∼1% of the cells were reprogrammed to Nanog-positive induced pluripotent stem cells without chromosomal gene integration. Thus, this SeVdp vector has potential as a tool for advanced cell reprogramming and for stem cell research.