Protein tyrosine phosphatase-PEST regulates focal adhesion disassembly, migration, and cytokinesis in fibroblasts

In this article, we show that, in transfected COS-1 cells, protein tyrosine phosphatase (PTP)-PEST translocates to the membrane periphery following stimulation by the extracellular matrix protein fibronectin. When plated on fibronectin, PTP-PEST (-/-) fibroblasts display a strong defect in motility. 3 h after plating on fibronectin, the number and size of vinculin containing focal adhesions were greatly increased in the homozygous PTP-PEST mutant cells as compared with heterozygous cells. This phenomenon appears to be due in part to a constitutive increase in tyrosine phosphorylation of p130(CAS), a known PTP-PEST substrate, paxillin, which associates with PTP-PEST in vitro, and focal adhesion kinase (FAK). Another effect of this constitutive hyperphosphorylation, consistent with the focal adhesion regulation defect, is that (-/-) cells spread faster than the control cell line when plated on fibronectin. In the PTP-PEST (-/-) cells, an increase in affinity for the SH2 domains of Src and Crk towards p130(CAS) was also observed. In (-/-) cells, we found a significant increase in the level of tyrosine phosphorylation of PSTPIP, a cleavage furrow-associated protein that interacts physically with all PEST family members. An effect of PSTPIP hyperphosphorylation appears to be that some cells remain attached at the site of the cleavage furrow for an extended period of time. In conclusion, our data suggest PTP-PEST plays a dual role in cell cytoskeleton organization, by promoting the turnover of focal adhesions required for cell migration, and by directly or indirectly regulating the proline, serine, threonine phosphatase interacting protein (PSTPIP) tyrosine phosphorylation level which may be involved in regulating cleavage furrow formation or disassembly during normal cell division.

Association of the multisubstrate docking protein Gab1 with the hepatocyte growth factor receptor requires a functional Grb2 binding site involving tyrosine 1356

Hepatocyte growth factor/scatter factor is a multifunctional factor that induces mitogenesis, motility, invasion, and branching tubulogenesis of several epithelial and endothelial cell lines in culture. The receptor for hepatocyte growth factor has been identified as the Met-tyrosine kinase. Upon stimulation with hepatocyte growth factor, the Met beta subunit becomes highly phosphorylated on tyrosine residues, one of which, tyrosine 1356 within the carboxyl terminus, is crucial for dissociation, motility, and branching tubule formation in Madin-Darby canine kidney epithelial cells. Tyrosine 1356 forms a multisubstrate binding site for the Grb2 and Shc adaptor proteins, the p85 subunit of phosphatidylinositol 3'-kinase, phospholipase Cgamma, and a phosphatase, SHP2. To investigate additional signaling molecules that are activated by the Met receptor, we have identified hepatocyte growth factor-induced phosphoproteins in tubular epithelial cells. We have established that proteins of 100-130 kDa are highly phosphorylated following stimulation of epithelial cells and that one of these is the Grb2-associated binding protein Gab1, a possible insulin receptor substrate-1-like signal transducer. We show that Gab1 is the major substrate for the Met kinase in vitro and in vivo. Association of Gab1 with Met requires a functional Grb2 binding site involving tyrosine 1356 and to a lesser extent tyrosine 1349. Met receptor mutants that fail to induce branching tubulogenesis are impaired in their ability to interact with Gab1, suggesting that Gab1 may play a role in these processes.

Single-cell RNA sequencing reveals evolution of immune landscape during glioblastoma progression

Glioblastoma (GBM) is an incurable primary malignant brain cancer hallmarked with a substantial protumorigenic immune component. Knowledge of the GBM immune microenvironment during tumor evolution and standard of care treatments is limited. Using single-cell transcriptomics and flow cytometry, we unveiled large-scale comprehensive longitudinal changes in immune cell composition throughout tumor progression in an epidermal growth factor receptor-driven genetic mouse GBM model. We identified subsets of proinflammatory microglia in developing GBMs and anti-inflammatory macrophages and protumorigenic myeloid-derived suppressors cells in end-stage tumors, an evolution that parallels breakdown of the blood-brain barrier and extensive growth of epidermal growth factor receptor+ GBM cells. A similar relationship was found between microglia and macrophages in patient biopsies of low-grade glioma and GBM. Temozolomide decreased the accumulation of myeloid-derived suppressor cells, whereas concomitant temozolomide irradiation increased intratumoral GranzymeB+ CD8+T cells but also increased CD4+ regulatory T cells. These results provide a comprehensive and unbiased immune cellular landscape and its evolutionary changes during GBM progression.

ROS fusion tyrosine kinase activates a SH2 domain-containing phosphatase-2/phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling axis to form glioblastoma in mice

Glioblastoma multiforme is the most common and lethal form of primary brain cancer. Diagnosis of this advanced glioma has a poor prognosis due to the ineffectiveness of current therapies. Aberrant expression of receptor tyrosine kinases (RTK) in glioblastoma multiformes is suggestive of their role in initiation and maintenance of these tumors of the central nervous system. In fact, ectopic expression of the orphan RTK ROS is a frequent event in human brain cancers, yet the pathologic significance of this expression remains undetermined. Here, we show that a glioblastoma-associated, ligand-independent rearrangement product of ROS (FIG-ROS) cooperates with loss of the tumor suppressor gene locus Ink4a;Arf to produce glioblastomas in the mouse. We show that this FIG-ROS-mediated tumor formation in vivo parallels the activation of the tyrosine phosphatase SH2 domain-containing phosphatase-2 (SHP-2) and a phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling axis in tumors and tumor-derived cell lines. We have established a fully penetrant preclinical model for adult onset of glioblastoma multiforme in keeping with major genetic events observed in the human disease. These findings provide novel and important insights into the role of ROS and SHP-2 function in solid tumor biology and set the stage for preclinical testing of targeted therapeutic approaches.

The 5-HT1A receptor: signaling, desensitization, and gene transcription

The hypothesis that antianxiety or antidepressant agents (e.g., 5-HT1A agonists, 5-HT uptake blockers) exert their clinical actions via enhancement of serotonergic neurotransmission due to desensitization of 5-HT1A autoreceptors predicts that regulation of this receptor plays a crucial role in the therapeutic actions of these agents. A multidisciplinary strategy is described for the characterization of the 5-HT1A receptor at the level of cellular signaling mechanisms and genetic regulation, using heterologous expression of the cloned receptor in cell lines, site-directed mutagenesis, isolation of receptor-positive neuronal cell lines, and promoter analysis of the 5-HT1A receptor gene. These analyses will yield new insights into the possible mechanisms down-regulation of 5-HT1A receptor signaling, and may suggest novel sites of inherent defect involved in anxiety syndromes or major depression.

The multifaceted roles of the receptor tyrosine kinase ROS in development and cancer

The proto-oncogene receptor tyrosine kinase ROS was originally discovered through the identification of oncogenic variants isolated from tumors. These discoveries spearheaded a body of work aimed at elucidating the function of this evolutionarily conserved receptor in development and cancer. Through genetic and biochemical approaches, progress in the characterization of ROS points to distinctive roles in the program of epithelial cell differentiation during the development of a variety of organs. Although substantial, these advances remain hampered by the absence of an identified ligand, making ROS one of the last two remaining orphan receptor tyrosine kinases. Recent studies on the oncogenic activation of ROS as a result of different chromosomal rearrangements found in brain and lung cancers have shed light on the molecular mechanisms underlying ROS transforming activities. ROS and its oncogenic variants therefore constitute clinically relevant targets for cancer therapeutic intervention. This review highlights the various roles that this receptor plays in multiple system networks in normalcy and disease and points to future directions towards the elucidation of ROS function in the context of ligand identification, signaling pathways and clinical applications.

Association of a novel PDZ domain-containing peripheral Golgi protein with the Q-SNARE (Q-soluble N-ethylmaleimide-sensitive fusion protein (NSF) attachment protein receptor) protein syntaxin 6

PDZ domains are involved in the scaffolding and assembly of multi-protein complexes at various subcellular sites. We describe here the isolation and characterization of a novel PDZ domain-containing protein that localizes to the Golgi apparatus. Using an in silico cloning approach, we have identified and isolated a cDNA encoding a ubiquitously expressed 59-kDa protein that we call FIG. It is composed of two coiled coil regions, a leucine zipper, and a single PDZ domain. Cytological studies using indirect immunofluorescence microscopy revealed that FIG is a peripheral protein that uses one of its coiled coil domains to localize to the Golgi apparatus. To ascertain the modalities of this Golgi localization, the same coiled coil region was tested for its ability to interact with a panel of coiled coil domain-containing integral membrane Golgi proteins. Using a series of GST fusion protein binding assays, co-immunofluorescence and co-immunoprecipitation experiments, we show that FIG specifically binds to the coiled coil domain-containing Q-SNARE (Q-soluble NSF attachment protein receptor) protein syntaxin 6 both in vitro and in vivo. The structural features of FIG and its interaction with a SNARE protein suggest that FIG may play a role in membrane vesicle trafficking. This is the first example of a PDZ domain-containing peripheral protein that localizes to the Golgi through a coiled coil-mediated interaction with a resident membrane protein. Our results broaden the scope of PDZ domain-mediated functions.

Combination of gene targeting and substrate trapping to identify substrates of protein tyrosine phosphatases using PTP-PEST as a model

Identification of physiological substrates of protein tyrosine phosphatases is a key step in understanding the function of these enzymes. We have generated fibroblast cell lines having a gene-targeted PTP-PEST in order to identify potential substrates with the premise that specific substrates of this enzyme would exist in a hyperphosphorylated state. Analysis of the profile of the phosphotyrosine proteins in the PTP-PEST -/- cells revealed the presence of hyperphosphorylated proteins of 180, 130, and 97 kDa when compared to control cells. The p130 was identified as p130(Cas), and direct immunoprecipitates of p130(Cas) demonstrate that this protein is constitutively hyperphosphorylated in cells lacking PTP-PEST. In addition, p130(Cas) was also isolated by the substrate-trapping mutant of PTP-PEST in the PTP-PEST -/- cell lysates. Interestingly, we have demonstrated for the first time that PTP-PEST, through its first proline-rich sequence 332PPKPPR337, interacts with other members of the p130(Cas) family (Hef1 and Sin) via their SH3 domain in vitro. This result suggests that Hef1 and Sin could also be potential substrates of PTP-PEST. In conclusion, we have combined genetic and biochemical strategies to allow the identification of PTP-PEST substrates. This experimental approach could potentially be used to identify substrates of other PTPases. Furthermore, the Cas-like molecules Hef1 and Sin associate via their SH3 domains with a proline-rich motif found on PTP-PEST, suggesting the possibility that PTP-PEST could be a general modulator of the Cas family of proteins.

Extracellular Vesicles from High-Grade Glioma Exchange Diverse Pro-oncogenic Signals That Maintain Intratumoral Heterogeneity

A lack of experimental models of tumor heterogeneity limits our knowledge of the complex subpopulation dynamics within the tumor ecosystem. In high-grade gliomas (HGG), distinct hierarchical cell populations arise from different glioma stem-like cell (GSC) subpopulations. Extracellular vesicles (EV) shed by cells may serve as conduits of genetic and signaling communications; however, little is known about how HGG heterogeneity may impact EV content and activity. In this study, we performed a proteomic analysis of EVs isolated from patient-derived GSC of either proneural or mesenchymal subtypes. EV signatures were heterogeneous, but reflected the molecular make-up of the GSC and consistently clustered into the two subtypes. EV-borne protein cargos transferred between proneural and mesenchymal GSC increased protumorigenic behaviors in vitro and in vivo Clinically, analyses of HGG patient data from the The Cancer Genome Atlas database revealed that proneural tumors with mesenchymal EV signatures or mesenchymal tumors with proneural EV signatures were both associated with worse outcomes, suggesting influences by the proportion of tumor cells of varying subtypes in tumors. Collectively, our findings illuminate the heterogeneity among tumor EVs and the complexity of HGG heterogeneity, which these EVs help to maintain. Cancer Res; 76(10); 2876-81. ©2016 AACR.

Genetic modeling of gliomas in mice: new tools to tackle old problems

The recently published comprehensive profiles of genomic alterations in glioma have led to a refinement in our understanding of the molecular events that underlie this cancer. Using state-of-the-art genomic tools, several laboratories have created and characterized accurate genetically engineered mouse models of glioma based on specific genetic alterations observed in human tumors. These in vivo brain tumor models faithfully recapitulate the histopathology, etiology, and biology of gliomas and provide an exceptional experimental system to discover novel therapeutic targets and test therapeutic agents. This review focuses on mouse models of glioma with a special emphasis on genetically engineered models developed around key genetic glioma signature mutations in the PDGFR, EGFR, and NF1 genes and pathways. The resulting animal models have provided insight into many fundamental and mechanistic facets of tumor initiation, maintenance and resistance to therapeutic intervention and will continue to do so in the future.

Phosphotyrosine-independent binding of SHC to the NPLH sequence of murine protein-tyrosine phosphatase-PEST. Evidence for extended phosphotyrosine binding/phosphotyrosine interaction domain recognition specificity

The phosphotyrosine binding (PTB) or phosphotyrosine interaction (PI) domain of the proto-oncoprotein p52SHC binds to an NPXpY consensus sequence found in several growth factor receptors (Kavanaugh, W. M., Turck, C. W., and Williams, L. T. (1994) Science 268, 1177-1179). The amino-terminal region of p52SHC, which includes the PTB/PI domain, has been previously shown to associate with protein-tyrosine phosphatase-PEST (PTP-PEST) in vivo (Habib, T. , Herrera, R., and Decker, S. J. (1994) J. Biol. Chem. 269, 25243-25246). We report here the detailed mapping of this interaction in a murine context using glutathione S-transferase fusion protein binding studies and peptide competition assays. We show that the interaction between murine SHC and murine PTP-PEST is mediated through the PTB/PI domain of murine SHC and an NPLH sequence found in the carboxyl terminus of murine PTP-PEST. Since this interaction is not dependent on the presence of a tyrosine-phosphorylated residue in the target sequence, this reveals that the PTB/PI domain of SHC can recognize both tyrosine-phosphorylated sequences and non-tyrosine-based recognition motifs.

Distribution of SPARC during neovascularisation of degenerative aortic stenosis

OBJECTIVE

To examine the hypothesis that degenerative aortic stenosis (AS) is associated with the development of blood vessels and the expression of the secreted protein, acidic and rich in cysteine/osteonectin (SPARC), a matricellular protein that is involved in ossification, the modulation of angiogenesis and the production of metalloproteinases.

METHODS

30 surgically excised AS valves and 20 normal aortic valves were studied.

RESULTS

Blood vessels were detected in the aortic valves from patients with degenerative AS, whereas normal valves were avascular structures. Blood vessels in AS valves expressed endothelial nitric oxide synthase, CD34 and von Willebrand factor (vWF). Blood vessels were located in three distinct regions: near calcified nodules, under the leaflet border and in rich cellular areas forming cell islands. Blood vessels were predominantly present in early and intermediate grades of calcification. Cell islands were densely populated by CD45-positive cells where endothelial cells (CD34+, vWF+) forming cord-like structures were present. Immunoblotting detected SPARC only in AS valves and immunohistological analysis located SPARC in mature blood vessels. The proportion of blood vessels positive for SPARC was higher in valves with a lower grade of calcification. In cell islands, SPARC was distributed to mature blood vessels and to macrophages, where it co-located with matrix metalloproteinase-9, whereas no expression was detected in endothelial cells forming cord-like structures.

CONCLUSION

The localisation of SPARC to mature blood vessels and its predominant expression in AS valves with a lower calcification grade suggest that the spatial and temporal distribution of this matricellular protein is tightly controlled to participate in the neovascularisation of AS valves.

Murine protein tyrosine phosphatase-PEST, a stable cytosolic protein tyrosine phosphatase

We have isolated the murine cDNA homologue of the human protein tyrosine phosphatase PTP-PEST (MPTP-PEST) from an 18.5-day mouse embryonic kidney library. The cDNA isolated has a single open reading frame predicting a protein of 775 amino acids. When expressed in vitro as a glutathione S-transferase fusion protein, the catalytic domain (residues 1-453) shows intrinsic phosphatase activity. Reverse transcriptase PCR and Northern-blot analysis show that MPTP-PEST mRNA is expressed throughout murine development. Indirect immunofluorescence in COS-1 cells against a heterologous epitope tag attached to the N-terminus of MPTP-PEST, together with cellular fractionation and Western-blot experiments from different murine cell lines, indicate that MPTP-PEST is a free cytosolic protein of 112 kDa. Finally, sequence analysis indicates that the C-terminal portion of the protein contains four regions rich in proline, glutamate, serine and threonine, otherwise known as PEST sequences. These are characteristic of proteins that display very short intracellular half-lives. Despite the presence of these motifs, pulse-chase labelling experiments demonstrate that MPTP-PEST has a half-life of more than 4 h.

Surgery combined with controlled-release doxorubicin silk films as a treatment strategy in an orthotopic neuroblastoma mouse model

BACKGROUND

Neuroblastoma tumour resection goal is maximal tumour removal. We hypothesise that combining surgery with sustained, local doxorubicin application can control tumour growth.

METHODS

We injected human neuroblastoma cells into immunocompromised mouse adrenal gland. When KELLY cell-induced tumour volume was >300 mm(3), 80-90% of tumour was resected and treated as follows: instantaneous-release silk film with 100 μg doxorubicin (100IR), controlled-release film with 200 μg (200CR) over residual tumour bed; and 100 and 200 μg intravenous doxorubicin (100IV and 200IV). Tumour volume was measured and histology analysed.

RESULTS

Orthotopic tumours formed with KELLY, SK-N-AS, IMR-32, SH-SY5Y cells. Tumours reached 1800±180 mm(3) after 28 days, 2200±290 mm(3) after 35 days, 1280±260 mm(3) after 63 days, and 1700±360 mm(3) after 84 days, respectively. At 3 days post KELLY tumour resection, tumour volumes were similar across all groups (P=0.6210). Tumour growth rate was similar in untreated vs control film, 100IV vs 100IR, and 100IV vs 200IV. There was significant difference in 100IR vs 200CR (P=0.0004) and 200IV vs 200CR (P=0.0003). Tumour growth with all doxorubicin groups was slower than that of control (P: <0.0001-0.0069). At the interface of the 200CR film and tumour, there was cellular necrosis, surrounded by apoptotic cells before reaching viable tumour cells.

CONCLUSIONS

Combining surgical resection and sustained local doxorubicin treatment is effective in tumour control. Administering doxorubicin in a local, controlled manner is superior to giving an equivalent intravenous dose in tumour control.

SMAR1, a novel, alternatively spliced gene product, binds the Scaffold/Matrix-associated region at the T cell receptor beta locus

Rearrangement and expression of the T cell receptor beta gene are critical events for early T lymphocyte development. To characterize cis-regulatory elements and their associated trans-factors that mediate these events, we have previously identified a nuclear matrix/scaffold-associated region, referred to as MARbeta, 400 bp upstream of the Ebeta enhancer. Electrophoretic mobility shift assay showed that two known MAR-binding proteins, SATB1 and Cux, bind MARbeta. In this article, we report the identification of a novel MAR-binding protein, named SMAR1, that also binds MARbeta. SMAR1 shares homology with SATB1 and Cux in the MAR-binding domain/Cut repeat and also with the tetramerization domain of a B cell-specific MAR-binding protein, Bright. The binding of GST-SMAR1 fusion protein to MARbeta is inhibited by the presence of an excess amount of MAR-containing DNA from the immunoglobulin kappa locus. Smar1 transcripts are most abundant in the thymus and are alternatively spliced. The smar1 gene maps to the distal portion of mouse chromosome 8 at a distance of 111.8 cM.

Cloning and chromosomal mapping of an orphan chemokine receptor: mouse RDC1

Degenerate RT-PCR was used to identify a new seven-transmembrane-spanning receptor expressed in astrocytes. A receptor, termed RDC1, displaying the characteristic structural features of a chemokine receptor was cloned. The predicted 362-amino-acid sequence displayed 92% and 91% similarity to the human and dog orphan receptor RDC1, respectively. In addition, RDC1 shares 43% amino acid similarity to rabbit and mouse CXCR2. Transcripts of RDC1 were found in astrocytes, heart, kidney, the mesangial tumor line MES-13, spleen, and neutrophils by means of northern blot. Using linkage analysis of interspecies backcross mice, we localized to chromosome 1 the genes for mouse CXCR2, CXCR4, and RDC1. Mouse RDC1 is linked to and lies between the genes for the mouse CXC chemokine receptors CXCR2 and CXCR4. The combined data of chromosomal location and sequence similarity suggest that RDC1 is an orphan CXC chemokine receptor.

Inhibition of EGFR induces a c-MET-driven stem cell population in glioblastoma

Glioblastoma multiforme (GBM) is the most lethal form of primary brain tumors, characterized by highly invasive and aggressive tumors that are resistant to all current therapeutic options. GBMs are highly heterogeneous in nature and contain a small but highly tumorigenic and self-renewing population of stem or initiating cells (glioblastoma stem cells or GSCs). GSCs have been shown to contribute to tumor propagation and resistance to current therapeutic modalities. Recent studies of human GBMs have elucidated the genetic alterations common in these tumors, but much remains unknown about specific signaling pathways that regulate GSCs. Here we identify a distinct fraction of cells in a genetically engineered mouse model of EGFR-driven GBM that respond to anti-EGFR therapy by inducing high levels of c-MET expression. The MET-positive cells displayed clonogenic potential and long-term self-renewal ability in vitro and are capable of differentiating into multiple lineages. The MET-positive GBM cells are resistant to radiation and highly tumorigenic in vivo. Activation of MET signaling led to an increase in expression of the stemness transcriptional regulators Oct4, Nanog, and Klf4. Pharmacological inhibition of MET activity in GSCs prevented the activation of Oct4, Nanog, and Klf4 and potently abrogated stemness. Finally, the MET expressing cells were preferentially localized in perivascular regions of mouse tumors consistent with their function as GSCs. Together, our findings indicate that EGFR inhibition in GBM induces MET activation in GSCs, which is a functional requisite for GSCs activity and thus represents a promising therapeutic target.

Effect of the Mediterranean diet with and without weight loss on cardiovascular risk factors in men with the metabolic syndrome

BACKGROUND AND AIMS

No study has yet examined how weight loss modifies the impact of the Mediterranean diet (MedDiet) on cardiovascular risk factors in men with the metabolic syndrome (MetS). The objective of the study was to assess the efficacy of MedDiet, with and without weight loss, to modify the cardiometabolic risk profile of male patients with MetS.

METHODS AND RESULTS

Twenty-six men aged between 24 and 62 years with the MetS consumed a North American control diet for 5 weeks followed by a 5-week MedDiet, both under weight-maintaining conditions. Participants then underwent a 20-week weight loss period, after which they consumed the MedDiet for five weeks under weight stable conditions. Body weight was reduced by 10.2% ± 2.9% after the weight loss period (p < 0.001). All foods were provided to participants during the weight stable phases of the study. The MedDiet in the absence of weight loss decreased total plasma cholesterol (C) (-7.1%), LDL-C (-9.3%) and the total/HDL-C ratio (-6.5%) compared to the control diet (all p < 0.04). The MedDiet combined with weight loss led to reductions in systolic blood pressure (-4.7%), diastolic blood pressure (-7.7%), triglycerides (-18.2%), ApoB (-10.7%), fasting glucose (-4.2%) and insulin (-29.9%) compared to the control diet (all p < 0.001).

CONCLUSION

The MedDiet in the absence of weight loss leads to significant changes in plasma cholesterol concentrations but has little effects on other cardiometabolic risk factors associated with the MetS in men.

Coupling of the murine protein tyrosine phosphatase PEST to the epidermal growth factor (EGF) receptor through a Src homology 3 (SH3) domain-mediated association with Grb2

The involvement of murine protein tyrosine phosphatase-PEST (MPTP-PEST) in signal transduction pathways is suggested by its ability to dephosphorylate phosphotyrosine residues, its interaction with the adaptor protein SHC and by the presence of five proline-rich stretches in its non-catalytic carboxyl terminus. Proline-rich sequences have been identified as binding sites for Src homology 3 (SH3) domains found in proteins associated with signal transduction events. The ability of these sequences to act as SH3 domain recognition motifs was investigated using bacterially expressed SH3 domains derived from several different signalling proteins. In vitro binding assays indicate that four of these proline-rich sequences constitute specific binding sites for both SH3 domains of the adaptor molecule Grb2. Wild type Grb2, but not Grb2 proteins corresponding to loss-of-function mutants in the Caenorhabditis elegans sem-5 protein, associate with MPTP-PEST in vivo. Experiments in EGF receptor expressing cells show that the interaction between MPTP-PEST and Grb2 results in the binding of this complex to activated EGF receptors. In addition, identification of putative substrate(s) of MPTP-PEST have revealed a candidate protein of approximately 120 kDa which is tyrosine phosphorylated upon EGF stimulation. Together, these results describe a novel SH3 domain-dependent recruitment of a protein tyrosine phosphatase to an activated receptor tyrosine kinase and establish a potential role for MPTP-PEST in signalling pathways at the molecular level.

Physical and Molecular Landscapes of Mouse Glioma Extracellular Vesicles Define Heterogeneity

Cancer extracellular vesicles (EVs) are highly heterogeneous, which impedes our understanding of their function as intercellular communication agents and biomarkers. To deconstruct this heterogeneity, we analyzed extracellular RNAs (exRNAs) and extracellular proteins (exPTNs) from size fractionation of large, medium, and small EVs and ribonucleoprotein complexes (RNPs) from mouse glioblastoma cells by RNA sequencing and quantitative proteomics. mRNA from medium-sized EVs most closely reflects the cellular transcriptome, whereas small EV exRNA is enriched in small non-coding RNAs and RNPs contain precisely processed tRNA fragments. The exPTN composition of EVs and RNPs reveals that they are closely related by vesicle type, independent of their cellular origin, and single EV analysis reveals that small EVs are less heterogeneous in their protein content than larger ones. We provide a foundation for better understanding of segregation of macromolecules in glioma EVs through a catalog of diverse exRNAs and exPTNs.

Implantable diagnostic device for cancer monitoring

Biopsies provide required information to diagnose cancer but, because of their invasiveness, they are difficult to use for managing cancer therapy. The ability to repeatedly sample the local environment for tumor biomarker, chemotherapeutic agent, and tumor metabolite concentrations could improve early detection of metastasis and personalized therapy. Here we describe an implantable diagnostic device that senses the local in vivo environment. This device, which could be left behind during biopsy, uses a semi-permeable membrane to contain nanoparticle magnetic relaxation switches. A cell line secreting a model cancer biomarker produced ectopic tumors in mice. The transverse relaxation time (T(2)) of devices in tumor-bearing mice was 20+/-10% lower than devices in control mice after 1 day by magnetic resonance imaging (p<0.01). Short term applications for this device are numerous, including verification of successful tumor resection. This may represent the first continuous monitoring device for soluble cancer biomarkers in vivo.

TATA-driven transcriptional initiation and regulation of the rat serotonin 5-HT1A receptor gene

The transcriptional initiation and regulation of the rat serotonin 5-HT1A receptor gene were characterized. By three types of analyses, a single brain-specific site of transcriptional initiation was localized to -967 bp upstream of the translation initiation codon that is utilized both in hippocampus and in the rat raphe RN46A cell line. This major site of transcriptional initiation was located 58 bp downstream from a consensus TATA element, suggesting TATA-driven transcription of the rat 5-HT1A receptor. To identify the promoter activity of the receptor gene, progressive 5' deletions of the -2,719/-117-bp fragment of the 5-HT1A promoter linked to luciferase gene were transfected into 5-HT1A-negative (pituitary GH4C1, L6 myoblast, and C6 glioma) and 5-HT1A-positive (septal SN-48 and raphe RN46A) cell lines. Enhancer regions were identified within a fragment between nucleotides -426 and -117 that selectively enhanced transcription in 5-HT1A-positive cells. A nonselective enhancer/promoter that mediated expression in all cell lines was located upstream between -1,519 and -426 bp in a DNA segment containing consensus TATA, CCAAT, SP-1, and AP-1 elements as well as a poly-GT26 dinucleotide repeat. Strong repression of transcription in all cell lines was conferred by the region upstream of -1,519 bp that contains a 152-bp DNA segment with >80% identity to RANTES, tumor necrosis factor-beta, and other immune system genes. Our results indicate that TATA-driven expression of the 5-HT1A receptor is regulated by a novel proximal tissue-specific enhancer region, a nonselective promoter, and an upstream repressor region that is distinct from previously identified neuron-specific repressors.

The novel Hsp90 inhibitor NXD30001 induces tumor regression in a genetically engineered mouse model of glioblastoma multiforme

Glioblastoma multiforme (GBM) has an abysmal prognosis. We now know that the epidermal growth factor receptor (EGFR) signaling pathway and the loss of function of the tumor suppressor genes p16Ink4a/p19ARF and PTEN play a crucial role in GBM pathogenesis: initiating the early stages of tumor development, sustaining tumor growth, promoting infiltration, and mediating resistance to therapy. We have recently shown that this genetic combination is sufficient to promote the development of GBM in adult mice. Therapeutic agents raised against single targets of the EGFR signaling pathway have proven rather inefficient in GBM therapy, showing the need for combinatorial therapeutic approaches. An effective strategy for concurrent disruption of multiple signaling pathways is via the inhibition of the molecular chaperone heat shock protein 90 (Hsp90). Hsp90 inhibition leads to the degradation of so-called client proteins, many of which are key effectors of GBM pathogenesis. NXD30001 is a novel second generation Hsp90 inhibitor that shows improved pharmacokinetic parameters. Here we show that NXD30001 is a potent inhibitor of GBM cell growth in vitro consistent with its capacity to inhibit several key targets and regulators of GBM biology. We also show the efficacy of NXD30001 in vivo in an EGFR-driven genetically engineered mouse model of GBM. Our findings establish that the Hsp90 inhibitor NXD30001 is a therapeutically multivalent molecule, whose actions strike GBM at the core of its drivers of tumorigenesis and represent a compelling rationale for its use in GBM treatment.

A PDGFRα-driven mouse model of glioblastoma reveals a stathmin1-mediated mechanism of sensitivity to vinblastine

Glioblastoma multiforme (GBM) is an aggressive primary brain cancer that includes focal amplification of PDGFRα and for which there are no effective therapies. Herein, we report the development of a genetically engineered mouse model of GBM based on autocrine, chronic stimulation of overexpressed PDGFRα, and the analysis of GBM signaling pathways using proteomics. We discover the tubulin-binding protein Stathmin1 (STMN1) as a PDGFRα phospho-regulated target, and that this mis-regulation confers sensitivity to vinblastine (VB) cytotoxicity. Treatment of PDGFRα-positive mouse and a patient-derived xenograft (PDX) GBMs with VB in mice prolongs survival and is dependent on STMN1. Our work reveals a previously unconsidered link between PDGFRα activity and STMN1, and highlight an STMN1-dependent cytotoxic effect of VB in GBM.

Effect of sitagliptin therapy on triglyceride-rich lipoprotein kinetics in patients with type 2 diabetes

AIM

To investigate the effects of sitagliptin therapy on the kinetics of triglyceride-rich lipoprotein (TRL) apolipoprotein (apo)B-48, VLDL apoB-100, apoE and apoC-III in patients with type 2 diabetes.

METHODS

Twenty-two subjects with type 2 diabetes were recruited in this double-blind crossover study, during which the subjects received sitagliptin (100 mg/day) or placebo for a 6-week period each. At the end of each phase of treatment, the in vivo kinetics of the different apolipoproteins were assessed using a primed-constant infusion of l-[5,5,5-D3]leucine for 12 h, with the participants in a constantly fed state.

RESULTS

Sitagliptin therapy significantly reduced fasting plasma triglyceride (-15.4%, p = 0.03), apoB-48 (-16.3%, p = 0.03) and free fatty acid concentrations (-9.5%, p = 0.04), as well as plasma HbA1c (placebo: 7.0% ± 0.8 vs. sitagliptin: 6.6% ± 0.7, p < 0.0001) and plasma glucose levels (-13.5%, p = 0.001), without any significant effect on insulin levels. Kinetic results showed that treatment with sitagliptin significantly reduced the pool size of TRL apoB-48 by -20.8% (p = 0.03), paralleled by a reduction in the production rate of these particles (-16.0%, p = 0.03). The VLDL apoB-100 pool size was also significantly decreased by sitagliptin therapy (-9.3%, p = 0.03), mainly because of a reduction in the hepatic secretion of these lipoproteins, although this difference did not reach statistical significance (-9.2%, p = 0.06).

CONCLUSIONS

Treatment with sitagliptin for 6 weeks reduced triglyceride-rich apoB-containing lipoprotein levels by reducing the synthesis of these particles.