ERK-Mediated Loss of miR-199a-3p and Induction of EGR1 Act as a "Toggle Switch" of GBM Cell Dedifferentiation into NANOG- and OCT4-Positive Cells.

There is great interest in understanding how the cancer stem cell population may be maintained in solid tumors. Here, we show that tumor cells exhibiting stem-like properties and expression of pluripotency markers NANOG and OCT4 can arise from original differentiated tumor cells freshly isolated from human glioblastomas (GBM) and that have never known any serum culture conditions. Induction of EGR1 by EGFR/ERK signaling promoted cell conversion from a less aggressive, more differentiated cellular state to a self-renewing and strongly tumorigenic state, expressing NANOG and OCT4. Expression of these pluripotency markers occurred before the cells re-entered the cell cycle, demonstrating their capacity to change and dedifferentiate without any cell divisions. In differentiated GBM cells, ERK-mediated repression of miR-199a-3p induced EGR1 protein expression and triggered dedifferentiation. Overall, this signaling pathway constitutes an ERK-mediated "toggle switch" that promotes pluripotency marker expression and stem-like features in GBM cells. SIGNIFICANCE: This study defines an ERK-mediated molecular mechanism of dedifferentiation of GBM cells into a stem-like state, expressing markers of pluripotency.See related commentary by Koncar and Agnihotri, p. 3195.

Neurog3 misexpression unravels mouse pancreatic ductal cell plasticity.

In the context of type 1 diabetes research and the development of insulin-producing ß-cell replacement strategies, whether pancreatic ductal cells retain their developmental capability to adopt an endocrine cell identity remains debated, most likely due to the diversity of models employed to induce pancreatic regeneration. In this work, rather than injuring the pancreas, we developed a mouse model allowing the inducible misexpression of the proendocrine gene Neurog3 in ductal cells in vivo. These animals developed a progressive islet hypertrophy attributed to a proportional increase in all endocrine cell populations. Lineage tracing experiments indicated a continuous neo-generation of endocrine cells exhibiting a ductal ontogeny. Interestingly, the resulting supplementary ß-like cells were found to be functional. Based on these findings, we suggest that ductal cells could represent a renewable source of new ß-like cells and that strategies aiming at controlling the expression of Neurog3, or of its molecular targets/co-factors, may pave new avenues for the improved treatments of diabetes.

GABA signaling stimulates α-cell-mediated ß-like cell neogenesis.

Diabetes is a chronic and progressing disease, the number of patients increasing exponentially, especially in industrialized countries. Regenerating lost insulin-producing cells would represent a promising therapeutic alternative for most diabetic patients. To this end, using the mouse as a model, we reported that GABA, a food supplement, could induce insulin-producing beta-like cell neogenesis offering an attractive and innovative approach for diabetes therapeutics.

Long-Term GABA Administration Induces Alpha Cell-Mediated Beta-like Cell Neogenesis.

The recent discovery that genetically modified α cells can regenerate and convert into ß-like cells in vivo holds great promise for diabetes research. However, to eventually translate these findings to human, it is crucial to discover compounds with similar activities. Herein, we report the identification of GABA as an inducer of α-to-ß-like cell conversion in vivo. This conversion induces α cell replacement mechanisms through the mobilization of duct-lining precursor cells that adopt an α cell identity prior to being converted into ß-like cells, solely upon sustained GABA exposure. Importantly, these neo-generated ß-like cells are functional and can repeatedly reverse chemically induced diabetes in vivo. Similarly, the treatment of transplanted human islets with GABA results in a loss of α cells and a concomitant increase in ß-like cell counts, suggestive of α-to-ß-like cell conversion processes also in humans. This newly discovered GABA-induced α cell-mediated ß-like cell neogenesis could therefore represent an unprecedented hope toward improved therapies for diabetes.

Global gene expression analysis reveals a link between NDRG1 and vesicle transport.

N-myc downstream-regulated gene 1 (NDRG1) is induced by cellular stress such as hypoxia and DNA damage, and in humans, germ line mutations cause Charcot-Marie-Tooth disease. However, the cellular roles of NDRG1 are not fully understood. Previously, NDRG1 was shown to mediate doxorubicin resistance under hypoxia, suggesting a role for NDRG1 in cell survival under these conditions. We found decreased apoptosis in doxorubicin-treated cells expressing NDRG1 shRNAs under normoxia, demonstrating a requirement for NDRG1 in apoptosis in breast epithelial cells under normal oxygen pressure. Also, different cellular stress regimens, such as hypoxia and doxorubicin treatment, induced NDRG1 through different stress signalling pathways. We further compared expression profiles in human breast epithelial cells ectopically over-expressing NDRG1 with cells expressing NDRG1 shRNAs in order to identify biological pathways where NDRG1 is involved. The results suggest that NDRG1 may have roles connected to vesicle transport.

From pancreas morphogenesis to ß-cell regeneration.

Type 1 diabetes is a metabolic disease resulting in the selective loss of pancreatic insulin-producing ß-cells and affecting millions of people worldwide. The side effects of diabetes are varied and include cardiovascular, neuropathologic, and kidney diseases. Despite the most recent advances in diabetes care, patients suffering from type 1 diabetes still display a shortened life expectancy compared to their healthy counterparts. In an effort to improve ß-cell-replacement therapies, numerous approaches are currently being pursued, most of these aiming at finding ways to differentiate stem/progenitor cells into ß-like cells by mimicking embryonic development. Unfortunately, these efforts have hitherto not allowed the generation of fully functional ß-cells. This chapter summarizes recent findings, allowing a better insight into the molecular mechanisms underlying the genesis of ß-cells during the course of pancreatic morphogenesis. Furthermore, a focus is made on new research avenues concerning the conversion of pre-existing pancreatic cells into ß-like cells, such approaches holding great promise for the development of type 1 diabetes therapies.

The inactivation of Arx in pancreatic α-cells triggers their neogenesis and conversion into functional ß-like cells.

Recently, it was demonstrated that pancreatic new-born glucagon-producing cells can regenerate and convert into insulin-producing ß-like cells through the ectopic expression of a single gene, Pax4. Here, combining conditional loss-of-function and lineage tracing approaches, we show that the selective inhibition of the Arx gene in α-cells is sufficient to promote the conversion of adult α-cells into ß-like cells at any age. Interestingly, this conversion induces the continuous mobilization of duct-lining precursor cells to adopt an endocrine cell fate, the glucagon(+) cells thereby generated being subsequently converted into ß-like cells upon Arx inhibition. Of interest, through the generation and analysis of Arx and Pax4 conditional double-mutants, we provide evidence that Pax4 is dispensable for these regeneration processes, indicating that Arx represents the main trigger of α-cell-mediated ß-like cell neogenesis. Importantly, the loss of Arx in α-cells is sufficient to regenerate a functional ß-cell mass and thereby reverse diabetes following toxin-induced ß-cell depletion. Our data therefore suggest that strategies aiming at inhibiting the expression of Arx, or its molecular targets/co-factors, may pave new avenues for the treatment of diabetes.

[Reprogramming pancreatic cells to ß cells]. / Reprogrammation des cellules pancréatiques en cellules ß

Type 1 diabetes (T1DM) is a common metabolic disorder affecting an ever-increasing number of patients worldwide. T1DM is caused by the selective destruction of pancreatic insulin-producing ß-cells by the immune system. Such loss results in chronic hyperglycemia and could induce a number of cardio-vascular complications. Despite the classical insulin-based therapy, compared to healthy people, patients with T1DM display a shortened life expectancy due to the treatment's inability to strictly regulate glycemic levels. An alternative therapy involves pancreatic islet transplantation but the shortage of donors and the required immuno-suppressive treatments limit the widespread use of this approach. Therefore, the search of new approaches to generate functional ß-cells is of growing interest. In this review, we describe several novel strategies aiming at the conversion of diverse pancreatic cells into ß-cells, such as acinar, ductal, and endocrine cells. Clearly, such promising results could open new research avenues in the context of type 1 diabetes research.

Adult duct-lining cells can reprogram into ß-like cells able to counter repeated cycles of toxin-induced diabetes.

It was recently demonstrated that embryonic glucagon-producing cells in the pancreas can regenerate and convert into insulin-producing ß-like cells through the constitutive/ectopic expression of the Pax4 gene. However, whether α cells in adult mice display the same plasticity is unknown. Similarly, the mechanisms underlying such reprogramming remain unclear. We now demonstrate that the misexpression of Pax4 in glucagon(+) cells age-independently induces their conversion into ß-like cells and their glucagon shortage-mediated replacement, resulting in islet hypertrophy and in an unexpected islet neogenesis. Combining several lineage-tracing approaches, we show that, upon Pax4-mediated α-to-ß-like cell conversion, pancreatic duct-lining precursor cells are continuously mobilized, re-express the developmental gene Ngn3, and successively adopt a glucagon(+) and a ß-like cell identity through a mechanism involving the reawakening of the epithelial-to-mesenchymal transition. Importantly, these processes can repeatedly regenerate the whole ß cell mass and thereby reverse several rounds of toxin-induced diabetes, providing perspectives to design therapeutic regenerative strategies.

From pancreatic islet formation to beta-cell regeneration.

Diabetes mellitus represents a major healthcare burden and, due to the increasing prevalence of type I diabetes and the complications arising from current treatments, other alternative therapies must be found. Type I diabetes arises as a result of a cell-mediated autoimmune destruction of insulin producing pancreatic ß-cells. Thus, a cell replacement therapy would be appropriate, using either in vitro or in vivo cell differentiation/reprogramming from different cell sources. Increasing our understanding of the molecular mechanisms controlling endocrine cell specification during pancreas morphogenesis and gaining further insight into the complex transcriptional network and signaling pathways governing ß-cell development should facilitate efforts to achieve this ultimate goal, that is to regenerate insulin-producing ß-cells. This review will therefore describe briefly the genetic program underlying mouse pancreas development and present new insights regarding ß-cell regeneration.

The homeodomain-containing transcription factors Arx and Pax4 control enteroendocrine subtype specification in mice.

Intestinal hormones are key regulators of digestion and energy homeostasis secreted by rare enteroendocrine cells. These cells produce over ten different hormones including GLP-1 and GIP peptides known to promote insulin secretion. To date, the molecular mechanisms controlling the specification of the various enteroendocrine subtypes from multipotent Neurog3(+) endocrine progenitor cells, as well as their number, remain largely unknown. In contrast, in the embryonic pancreas, the opposite activities of Arx and Pax4 homeodomain transcription factors promote islet progenitor cells towards the different endocrine cell fates. In this study, we thus investigated the role of Arx and Pax4 in enteroendocrine subtype specification. The small intestine and colon of Arx- and Pax4-deficient mice were analyzed using histological, molecular, and lineage tracing approaches. We show that Arx is expressed in endocrine progenitors (Neurog3(+)) and in early differentiating (ChromograninA(-)) GLP-1-, GIP-, CCK-, Sct- Gastrin- and Ghrelin-producing cells. We noted a dramatic reduction or a complete loss of all these enteroendocrine cell types in Arx mutants. Serotonin- and Somatostatin-secreting cells do not express Arx and, accordingly, the differentiation of Serotonin cells was not affected in Arx mutants. However, the number of Somatostatin-expressing D-cells is increased as Arx-deficient progenitor cells are redirected to the D-cell lineage. In Pax4-deficient mice, the differentiation of Serotonin and Somatostatin cells is impaired, as well as of GIP and Gastrin cells. In contrast, the number of GLP-1 producing L-cells is increased concomitantly with an upregulation of Arx. Thus, while Arx and Pax4 are necessary for the development of L- and D-cells respectively, they conversely restrict D- and L-cells fates suggesting antagonistic functions in D/L cell allocation. In conclusion, these finding demonstrate that, downstream of Neurog3, the specification of a subset of enteroendocrine subtypes relies on both Arx and Pax4, while others depend only on Arx or Pax4.

Let-7 microRNA and HMGA2 levels of expression are not inversely linked in adipocytic tumors: analysis of 56 lipomas and liposarcomas with molecular cytogenetic data.

The aim of our study was first to assess the role of HMGA2 expression in the pathogenesis of adipocytic tumors (AT) and, second, to seek a potential correlation between overexpression of HMGA2 and let-7 expression inhibition by analyzing a series of 56 benign and malignant AT with molecular cytogenetic data. We measured the levels of expression of HMGA2 mRNA and of eight members of the let-7 microRNA family using quantitative RT-PCR and expression of HMGA2 protein using immunohistochemistry. HMGA2 was highly overexpressed in 100% of well-differentiated/dedifferentiated liposarcomas (WDLPS/DDLPS), all with HMGA2 amplification, and 100% of lipomas with HMGA2 rearrangement. Overexpression of HMGA2 mRNA was detected in 76% of lipomas without HMGA2 rearrangement. HMGA2 protein expression was detected in 100% of lipomas with HMGA2 rearrangement and 48% of lipomas without HMGA2 rearrangement. We detected decreased expression levels of some let-7 members in a significant proportion of AT. Notably, let-7b and let-7g were inhibited in 61% of WDLPS/DDLPS. In lipomas, each type of let-7 was inhibited in approximately one-third of the cases. Although overexpression of both HMGA2 mRNA and protein in a majority of ordinary lipomas without HMGA2 structural rearrangement may have suggested a potential role for let-7 microRNAs, we did not observe a significant link with let-7 inhibition in such cases. Our results indicate that inhibition of let-7 microRNA expression may participate in the deregulation of HMGA2 in AT but that this inhibition is neither a prominent stimulator for HMGA2 overexpression nor a surrogate to genomic HMGA2 rearrangements.

Regulated expression of a transgene introduced on an oriP/EBNA-1 PAC shuttle vector into human cells.

BACKGROUND: Sequencing of the human genome has led to most genes being available in BAC or PAC vectors. However, limited functional information has been assigned to most of these genes. Techniques for the manipulation and transfer of complete functional units on large DNA fragments into human cells are crucial for the analysis of complete genes in their natural genomic context. One limitation of the functional studies using these vectors is the low transfection frequency. RESULTS: We have constructed a shuttle vector, pPAC7, which contains both the EBNA-1 gene and oriP from the Epstein-Barr virus allowing stable maintenance of PAC clones in the nucleus of human cells. The pPAC7 vector also contains the EGFP reporter gene, which allows direct monitoring of the presence of PAC constructs in transfected cells, and the Bsr-cassette that allows highly efficient and rapid selection in mammalian cells by use of blasticidin. Positive selection for recombinant PAC clones is obtained in pPAC7 because the cloning sites are located within the SacBII gene. We show regulated expression of the CDH3 gene carried as a 132 kb genomic insert cloned into pPAC7, demonstrating that the pPAC7 vector can be used for functional studies of genes in their natural genomic context. Furthermore, the results from the transfection of a range of pPAC7 based constructs into two human cell lines suggest that the transfection efficiencies are not only dependent on construct size. CONCLUSION: The shuttle vector pPAC7 can be used to transfer large genomic constructs into human cells. The genes transferred could potentially contain all long-range regulatory elements, including their endogenous regulatory promoters. Introduction of complete genes in PACs into human cells would potentially allow complementation assays to identify or verify the function of genes affecting cellular phenotypes.

Clinical and biological significance of CDK4 amplification in well-differentiated and dedifferentiated liposarcomas.

PURPOSE: The MDM2 and HMGA2 genes are consistently amplified in well-differentiated/dedifferentiated liposarcomas (WDLPS/DDLPS) whereas CDK4 is frequently but not always amplified in these tumors. Our goal was to determine whether the absence of CDK4 amplification was (a) correlated to a specific clinico-histopathologic profile; and (b) compensated by another genomic anomaly involving the CCND1/CDK4/P16INK4a/RB1/E2F pathway. EXPERIMENTAL DESIGN: We compared the clinical characteristics of a series of 143 WDLPS/DDLPS with amplification of both MDM2 and CDK4 (MDM2+/CDK4+) to a series of 45 WDLPS/DDLPS with MDM2 amplification and no CDK4 amplification (MDM2+/CDK4-). We used fluorescence in situ hybridization, real time quantitative reverse transcription PCR, and immunohistochemistry to explore the status of CCND1, P16INK4a, P14ARF, and RB1. RESULTS: We found that MDM2+/CDK4- WDLPS/DDLPS represent a distinct clinical subgroup with favorable prognostic features, including low-grade lipoma-like histology, peripheral location, and lower rate of recurrence. By using fluorescence in situ hybridization, we found that genomic aberrations expected to be alternative mechanisms for compensating the lack of CDK4 amplification, such as RB1 and CDKN2A deletions or CCND1 amplification, were very uncommon. In contrast, by using real time quantitative reverse transcription PCR and immunohistochemistry, we observed that overexpression of P16INK4a (and P14ARF) and CCND1 and reduced expression of RB1 were very frequent, independently of the CDK4 status. CONCLUSIONS: Our results underscore the complex coordinated regulation of the RB and p53 growth-control pathways in WDLPS/DDLPS. Because the absence of CDK4 amplification is not specifically counterbalanced by a genomic alteration of the CCND1/CDK4/P16INK4a/RB1/E2F pathway, CDK4 amplification may only represent a "MDM2-HMGA2-helper" in WDLPS/DDLPS tumorigenesis.

A retroviral vector for siRNA expression in mammalian cells.

Utilization of RNA interference (RNAi) for knockdown of gene expression has become a standard tool for the study of gene function. Short hairpin RNAs (shRNAs) expressed from RNA polymerase III promoters are widely used to achieve stable knockdown of gene expression by RNAi. We have constructed a retroviralbased shRNA expression vector, pSiRPG, as a tool for shRNA-based functional genomic studies. This vector is based on a widely used shRNA expression system and was modified to harbor an enhanced green fluorescent protein (EGFP) and a puromycin selection marker. The functionality of the elements in the pSiRPG vector was validated. The H1(TetO2) promoter in the vector facilitates doxycycline-inducible shRNA expression, which was demonstrated in cells expressing the Tet repressor (TetR). However, we also demonstrated limited efficiency of the inhibition of shRNA expression in an uninduced TetR-expressing cell line. This observation strongly indicates that the H1(TetO2) promoter, which is used in a wide range of vectors, is not optimal for tightly regulated shRNA expression. Stable repression of the NDRG1 protein level was observed when introducing pSiRPG constructs expressing shRNAs targeting NDRG1 into two mammary epithelial cell lines by retroviral delivery. This vector should therefore facilitate functional studies in breast cell lines that are hard to transfect with conventional plasmid-based methods.

Prevalence and characterization of integrons in blood culture Enterobacteriaceae and gastrointestinal Escherichia coli in Norway and reporting of a novel class 1 integron-located lincosamide resistance gene.

BACKGROUND: Class 1 integrons contain genetic elements for site-specific recombination, capture and mobilization of resistance genes. Studies investigating the prevalence, distribution and types of integron located resistance genes are important for surveillance of antimicrobial resistance and to understand resistance development at the molecular level. METHODS: We determined the prevalence and genetic content of class 1 integrons in Enterobacteriaceae (strain collection 1, n = 192) and E. coli (strain collection 2, n = 53) from bloodstream infections in patients from six Norwegian hospitals by molecular techniques. Class 1 integrons were also characterized in 54 randomly selected multiresistant E. coli isolates from gastrointestinal human infections (strain collection 3). RESULTS: Class 1 integrons were present in 10.9% of the Enterobacteriaceae blood culture isolates of collection 1, all but one (S. Typhi) being E. coli. Data indicated variations in class 1 integron prevalence between hospitals. Class 1 integrons were present in 37% and 34% of the resistant blood culture isolates (collection 1 and 2, respectively) and in 42% of the resistant gastrointestinal E. coli. We detected a total of 10 distinct integron cassette PCR amplicons that varied in size between 0.15 kb and 2.2 kb and contained between zero and three resistance genes. Cassettes encoding resistance to trimethoprim and aminoglycosides were most common. We identified and characterized a novel plasmid-located integron with a cassette-bound novel gene (linF) located downstream of an aadA2 gene cassette. The linF gene encoded a putative 273 aa lincosamide nucleotidyltransferase resistance protein and conferred resistance to lincomycin and clindamycin. The deduced LinF amino acid sequence displayed approximately 35% identity to the Enterococcus faecium and Enterococcus faecalis nucleotidyl transferases encoded by linB and linB' CONCLUSIONS: The present study demonstrated an overall low and stable prevalence of class 1 integron gene cassettes in clinical Enterobacteriaceae and E. coli isolates in Norway. Characterization of the novel lincosamide resistance gene extends the growing list of class 1 integron gene cassettes that confer resistance to an increasing number of antibiotics.

DNA fingerprinting of Shiga-toxin producing Escherichia coli O157 based on Multiple-Locus Variable-Number Tandem-Repeats Analysis (MLVA).

BACKGROUND: The ability to react early to possible outbreaks of Escherichia coli O157:H7 and to trace possible sources relies on the availability of highly discriminatory and reliable techniques. The development of methods that are fast and has the potential for complete automation is needed for this important pathogen. METHODS: In all 73 isolates of shiga-toxin producing E. coli O157 (STEC) were used in this study. The two available fully sequenced STEC genomes were scanned for tandem repeated stretches of DNA, which were evaluated as polymorphic markers for isolate identification. RESULTS: The 73 E. coli isolates displayed 47 distinct patterns and the MLVA assay was capable of high discrimination between the E. coli O157 strains. The assay was fast and all the steps can be automated. CONCLUSION: The findings demonstrate a novel high discriminatory molecular typing method for the important pathogen E. coli O157 that is fast, robust and offers many advantages compared to current methods.

DNA fingerprinting of Salmonella enterica subsp. enterica serovar typhimurium with emphasis on phage type DT104 based on variable number of tandem repeat loci.

Seventy-eight human and environmental strains of Salmonella enterica subsp. enterica serovar Typhimurium, as well as 18 isolates of other Salmonella serovars and 6 isolates of Escherichia coli, were subjected to a novel variable number of tandem repeats (VNTR)-based fingerprinting method that showed high discrimination and reproducibility for typing serovar Typhimurium isolates. The method is based on capillary separation of PCR products from fluorescence-labeled VNTR in the serovar Typhimurium genome. The serovar Typhimurium isolates displayed 54 VNTR patterns, and the VNTR assay correctly identified strains from a well-characterized outbreak. Among 37 serovar Typhimurium phage type DT104 isolates, 28 distinct VNTR patterns were found. This VNTR-based method is fast and suitable for complete automation. Our VNTR-based method was capable of high discrimination within the homogeneous serovar Typhimurium DT104 phage type and can be used to trace outbreaks and to monitor DT104 as well as other phage types. The VNTR assay was compared to XbaI pulsed-field gel electrophoresis, amplified fragment length polymorphism analysis, integron-cassette profiles and gene PCR of intI1, qacEDelta1, sulI1, and floR. The VNTR assay showed greatly improved resolution compared to all other tested methods in this study.