Two ST11 Klebsiella pneumoniae strains exacerbate colorectal tumorigenesis in a colitis-associated mouse model

Sequence type (ST) 11 is one of the major lineages of carbapenem-resistant Klebsiella pneumoniae (CRKP). Although the gastrointestinal (GI) carriage of CRKP predisposes individuals to subsequent infections, little is known for its impact on gut homeostasis. In this study, we investigated the association between ST11 CRKP colonization and colorectal cancer (CRC). Two ST11 CRKP, KPC160111 (KL47) and KPC160132 (KL64), were selected as the representative strains. We used azoxymethane (AOM) and dextran sodium sulfate (DSS) to initiate a colitis-associated CRC model. Both strains established prolonged colonization in the GI tract of the AOM-DSS-treated BALB/c mice and aggravated gut dysbiosis. Under this AOM-DSS-induced setting, ST11 K. pneumoniae colonization significantly promoted the growth and progression of colorectal adenomas to high-grade dysplasia. Numerous crypts were formed inside the enlarged adenomas, in which CD163⁺ tumor-associated macrophages accumulated. Similarly, ST11 K. pneumoniae also increased the population size of the CD163⁺ macrophages with the M2 phenotype in the peritoneal cavity of LPS-primed BALB/c mice. When applied to RAW264.7 cells, ST11 K. pneumoniae polarized the macrophages toward an M2 phenotype through the inhibition of IKK-NFκB and the activation of STAT6-KLF4-IL-10. Through the M2-skewing ability, ST11 K. pneumoniae promoted the accumulation of CD163⁺ macrophages in the adenomatous crypts to create an immunosuppressive niche, which not only accommodated the extended stay for its own sake but also deteriorated colorectal tumorigenesis.

Transmission and evolution of OXA-48-producing Klebsiella pneumoniae ST11 in a single hospital in Taiwan

OBJECTIVES

Epidemic spread of OXA-48-producing Klebsiella pneumoniae, mainly mediated by the transmission of a blaOXA-48-carrying plasmid, has threatened global health during the last decade. Since its introduction to Taiwan in 2013, OXA-48 has become the second most common carbapenemase. We described the transmission and evolution of an OXA-producing K. pneumoniae clone in a single hospital.

METHODS

Twenty-two OXA-48 K. pneumoniae were isolated between October 2013 and December 2015. Comparative genomic analysis was performed based on the WGS data generated with Illumina and MinION techniques.

RESULTS

Seventeen of the 22 OXA-48 K. pneumoniae that belonged to ST11, with the same capsular genotype, KL64, and differed from each other by seven or fewer SNPs, were considered outbreak strains. Eight of the 17 outbreak strains harboured a 65499 bp blaOXA-48-carrying IncL plasmid (called pOXA48). pOXA48 was absent from the remaining nine strains. Instead, a 24.9 kb blaOXA-48-carrying plasmid fragment was integrated into a prophage region of their chromosomes. Transmission routes of the ST11_KL64 K. pneumoniae sublineages, which carried either pOXA48 or chromosomally integrated blaOXA-48, were reconstructed.

CONCLUSIONS

Clonal expansion of ST11_KL64 sublineages contributed to the nosocomial outbreak of OXA-48 K. pneumoniae. The chromosome-borne blaOXA-48 lineage emerged during a 2 year period in a single hospital. Dissemination of OXA-48, which is vertically transmitted in K. pneumoniae even in the absence of selective pressure from antimicrobials, deserves public health attention.

Epigenetic Silencing of STAT3-Targeted miR-193a, by Constitutive Activation of JAK/STAT Signaling, Leads to Tumor Progression Through Overexpression of YWHAZ in Gastric Cancer

Purpose

The purpose of this study was to identify genes that were epigenetically silenced by STAT3 in gastric cancer.

Methods

MBDcap-Seq and expression microarray were performed to identify genes that were epigenetically silenced in AGS gastric cancer cell lines depleted of STAT3. Cell lines and animal experiments were performed to investigate proliferation and metastasis of miR-193a and YWHAZ in gastric cancer cell lines. Bisulfite pyrosequencing and tissue microarray were performed to investigate the promoter methylation of miR-193a and expression of STAT3, YWHAZ in patients with gastritis (n = 8) and gastric cancer (n = 71). Quantitative methylation-specific PCR was performed to examine miR-193a promoter methylation in cell-free DNA of serum samples in gastric cancer patients (n = 19).

Results

As compared with parental cells, depletion of STAT3 resulted in demethylation of a putative STAT3 target, miR-193a, in AGS gastric cancer cells. Although bisulfite pyrosequencing and epigenetic treatment confirmed that miR-193a was epigenetically silenced in gastric cancer cell lines, ChIP-PCR found that it may be indirectly affected by STAT3. Ectopic expression of miR-193a in AGS cells inhibited proliferation and migration of gastric cancer cells. Further expression microarray and bioinformatics analysis identified YWHAZ as one of the target of miR-193a in AGS gastric cancer cells, such that depletion of YWHAZ reduced migration in AGS cells, while its overexpression increased invasion in MKN45 cells in vitro and in vivo. Clinically, bisulfite pyrosequencing revealed that promoter methylation of miR-193a was significantly higher in human gastric cancer tissues (n = 11) as compared to gastritis (n = 8, p < 0.05). Patients infected with H. pylori showed a significantly higher miR-193a methylation than those without H. pylori infection (p < 0.05). Tissue microarray also showed a positive trend between STAT3 and YWHAZ expression in gastric cancer patients (n = 60). Patients with serum miR-193a methylation was associated with shorter overall survival than those without methylation (p < 0.05).

Conclusions

Constitutive activation of JAK/STAT signaling may confer epigenetic silencing of the STAT3 indirect target and tumor suppressor microRNA, miR-193a in gastric cancer. Transcriptional suppression of miR-193a may led to overexpression of YWHAZ resulting in tumor progression. Targeted inhibition of STAT3 may be a novel therapeutic strategy against gastric cancer.

2,4-Diamino-Quinazoline, a Wnt Signaling Inhibitor, Suppresses Gastric Cancer Progression and Metastasis

Gastric cancer (GC) is among the most treatment-refractory epithelial malignancies. Aberrant activation of Wnt/β-catenin-signaling has been implicated in a variety of human cancers, including gastric cancer. Here we report that the elevated expression of lymphoid enhancer binding factor 1 (Lef1) is associated with the TNM (tumor- node-metastasis) stage of gastric cancer. Subsequently, 2,4-diamino-quinazoline (2,4-DAQ), a selective inhibitor of Lef1, was identified to suppress the expression of Wnt/β-catenin target genes such as AXIN2, MYC and LGR5 and result in the suppression of gastric cancer cell growth through the apoptotic pathway. The 2,4-DAQ also exhibited an inhibitory effect on the migration/invasion of gastric cancer cells. Importantly, the treatment of human gastric tumor xenograft with 2,4-DAQ suppressed tumor growth in a nude mouse model. Furthermore, 2,4-DAQ appears effective on patient-derived organoids (PDOs). Transcriptome sequencing analysis also revealed that 2,4-DAQ are more effective on the gastric cancers that exhibit higher expression levels of Wnt-signaling pathway-related genes than their adjacent normal gastric tissues.

Abstract 5753: Inhibition of CCAR1, a coactivator of β-catenin, suppresses the proliferation and migration of gastric cancer cells

Given a current hypothesis that cancer arises from cancer stem cells (CSCs), targeting key signaling pathways that support CSC self-renewal appears to be a useful approach to cancer therapy. Derranged expression of Wnt signaling is among the major pathways implicated in regulating the stenmess properties of a variety of human cancers, including gastric cancer. Cell cycle and apoptosis regulator 1 (CCAR1) is a transcriptional coactivator which has been shown to be a component of Wnt/β-catenin signaling, and plays an important role in transcriptional regulation by β-catenin. However, the function and clinical significance of CCAR1 in gastric cancer have not been elucidated. Here we show the elevated CCAR1 nuclear expression correlates with the occurrence of gastric cancer. In addition, RNAi-mediated CCAR1 reduction not only suppressed the cell growth and increased apoptosis in gastric cell lines AGS and MKN28, but also reduced the migration and invasion ability of these cells. Furthermore, In vivo xenograft assay revealed that the expression level of CCAR1 was critical for tumorigenesis. Our data demonstrates that CCAR1 contributes to carcinogenesis in gastric cancer and is required for the survival of gastric cancer cells. Moreover, CCAR1 may serve as a diagnostic marker and a potential therapeutic target.

Citation Format: Te-Sheng Chang, Chung-Kuang Lu, Kuo-Liang Wei, Yi-Hsing Chen, Ying-Tung Cheng, Shui-Yi Tung, Cheng-Shyong Wu, Ming-Ko Chiang. Inhibition of CCAR1, a coactivator of β-catenin, suppresses the proliferation and migration of gastric cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5753. doi:10.1158/1538-7445.AM2017-5753

Colibactin Contributes to the Hypervirulence of pks+ K1 CC23 Klebsiella pneumoniae in Mouse Meningitis Infections

Klebsiella pneumoniae is the most common pathogen of community-acquired meningitis in Taiwan. However, the lack of a physiologically relevant meningitis model for K. pneumoniae has impeded research into its pathogenesis mechanism. Based on the core genome MLST analyses, the hypervirulent K1 K. pneumoniae strains, which are etiologically implicated in adult meningitis, mostly belong to a single clonal complex, CC23. Some K1 CC23 K. pneumoniae strains carry a gene cluster responsible for colibactin production. Colibactin is a small genotoxic molecule biosynthesized by an NRPS-PKS complex, which is encoded by genes located on the pks island. Compared to other hypervirulent K. pneumoniae which primarily infect the liver, the colibactin-producing (pks⁺) K1 CC23 strains had significant tropism toward the brain of BALB/c mice. We aimed in this study to develop a physiologically relevant meningitis model with the use of pks⁺ K1 CC23 K. pneumoniae. Acute meningitis was successfully induced in adult BALB/c male mice through orogastric, intranasal, and intravenous inoculation of pks⁺ K1 CC23 K. pneumoniae. Besides the typical symptoms of bacterial meningitis, severe DNA damages, and caspase 3-independent cell death were elicited by the colibactin-producing K1 CC23 K. pneumoniae strain. The deletion of clbA, which abolished the production of colibactin, substantially hindered K. pneumoniae hypervirulence in the key pathogenic steps toward the development of meningitis. Our findings collectively demonstrated that colibactin was necessary but not sufficient for the meningeal tropism of pks⁺ K1 CC23 K. pneumoniae, and the mouse model established in this study can be applied to identify other virulence factors participating in the development of this life-threatening disease.

Inhibition of CCAR1, a Coactivator of β-Catenin, Suppresses the Proliferation and Migration of Gastric Cancer Cells

The aberrant activation of Wnt signaling has been implicated in a variety of human cancers, including gastric cancer. Given the current hypothesis that cancer arises from cancer stem cells (CSCs), targeting the critical signaling pathways that support CSC self-renewal appears to be a useful approach for cancer therapy. Cell cycle and apoptosis regulator 1 (CCAR1) is a transcriptional coactivator which has been shown to be a component of Wnt/β-catenin signaling, and which plays an important role in transcriptional regulation by β-catenin. However, the function and clinical significance of CCAR1 in gastric cancer have not been elucidated. Here, we show that elevated CCAR1 nuclear expression correlates with the occurrence of gastric cancer. In addition, RNAi-mediated CCAR1 reduction not only suppressed the cell growth and increased apoptosis in AGS and MKN28 cells, but also reduced the migration and invasion ability of these cells. Furthermore, an in vivo xenograft assay revealed that the expression level of CCAR1 was critical for tumorigenesis. Our data demonstrates that CCAR1 contributes to carcinogenesis in gastric cancer and is required for the survival of gastric cancer cells. Moreover, CCAR1 may serve as a diagnostic marker and a potential therapeutic target.

Genotoxic Klebsiella pneumoniae in Taiwan

Background

Colibactin is a nonribosomal peptide-polyketide synthesized by multi-enzyme complexes encoded by the pks gene cluster. Colibactin-producing Escherichia coli have been demonstrated to induce host DNA damage and promote colorectal cancer (CRC) development. In Taiwan, the occurrence of pyogenic liver abscess (PLA) has been suggested to correlate with an increasing risk of CRC, and Klebsiella pneumoniae is the predominant PLA pathogen in Taiwan

Methodology/Principal Findings

At the asn tRNA loci of the newly sequenced K. pneumoniae 1084 genome, we identified a 208-kb genomic island, KPHPI208, of which a module identical to the E. coli pks colibactin gene cluster was recognized. KPHPI208 consists of eight modules, including the colibactin module and the modules predicted to be involved in integration, conjugation, yersiniabactin production, microcin production, and unknown functions. Transient infection of BALB/c normal liver cells with K. pneumoniae 1084 increased the phosphorylation of histone H2AX, indicating the induction of host DNA damage. Colibactin was required for the genotoxicity of K. pneumoniae 1084, as it was diminished by deletion of clbA gene and restored to the wild type level by trans-complementation with a clbA coding plasmid. Besides, BALB/c mice infected with K. pneumoniae 1084 exhibited enhanced DNA damage in the liver parenchymal cells when compared to the isogenic clbA deletion mutant. By PCR detection, the prevalence of pks-positive K. pneumoniae in Taiwan is 25.6%, which is higher than that reported in Europe (3.5%), and is significantly correlated with K1 type, which predominantly accounted for PLA in Taiwan.

Conclusions

Our knowledge regarding how bacteria contribute to carcinogenesis has just begun. The identification of genotoxic K. pneumoniae and its genetic components will facilitate future studies to elucidate the molecular basis underlying the link between K. pneumoniae, PLA, and CRC.

TCTP is essential for β-cell proliferation and mass expansion during development and β-cell adaptation in response to insulin resistance

The perinatal period is critical for β-cell mass establishment, which is characterized by a transient burst in proliferation to increase β-cell mass in response to the need for glucose homeostasis throughout life. In adulthood, the ability of β-cells to grow, proliferate, and expand their mass is also characteristic of pathological states of insulin resistance. Translationally controlled tumor-associated protein (TCTP), an evolutionarily highly conserved protein that is implicated in cell growth and proliferation, has been identified as a novel glucose-regulated survival-supporting protein in pancreatic β-cells. In this study, the enhanced β-cell proliferation detected both during the perinatal developmental period and in insulin-resistant states in high-fat diet-fed mice was found to parallel the expression of TCTP in pancreatic β-cells. Specific knockout of TCTP in β-cells led to increased expression of total and nuclear Forkhead box protein O1 and tumor suppressor protein 53, and decreased expression of p70S6 kinase phosphorylation and cyclin D2 and cyclin-dependent kinase 2. This resulted in decreased β-cell proliferation and growth, reduced β-cell mass, and insulin secretion. Together, these effects led to hyperglycemia. These observations suggest that TCTP is essential for β-cell mass expansion during development and β-cell adaptation in response to insulin resistance.

Activation of IFN-γ/STAT/IRF-1 in hepatic responses to Klebsiella pneumoniae infection

BACKGROUND

Klebsiella pneumoniae-caused liver abscess (KLA) has become a health problem in Taiwan and is continually reported in other countries. Diabetes mellitus, the most common metabolic disorder, underlies half of the KLA patients in Taiwan. The clinical impact of KLA has been well-documented. Nevertheless, the molecular basis regarding how K. pneumoniae causes liver infection, particularly in diabetic individuals, remains unclear.

METHODOLOGY/PRINCIPLE FINDINGS

Auto-bioluminescence-expressing K. pneumoniae was inoculated into diabetic mice and age-match naïve control. With the use of in vivo imaging system, translocation of the bioluminescence-expressing K. pneumoniae from intestine to extraintestinal organs, mainly the liver, was noted in 80% of the diabetic mice, whereas the same bacteria causes extraintestinal infections in only 31% of naïve mice. Besides increased morbidity, the severity of hepatic tissue injury was also enhanced in the K. pneumoniae-infected diabetic mice. Upon K. pneumoniae infection, IFN-γ production was significantly evoked in the liver. To mediate IFN-γ signal, STAT (signal transducers and activators of transcription) 1 and 3 were activated in hepatocytes, and so was the expression of IRF (interferon regulatory factor)-1. Moreover, accumulation of neutrophils which was triggered by prolonged production of IL-1β and MIP-2, and significant increases in the level of active caspase 3 and phospho-eIF2α, were exclusively revealed in the K. pneumoniae-infected diabetic mice.

CONCLUSION

The activation of IFN-γ/STAT/IRF-1 signaling demonstrated by this work emphasizes the role of IFN-γ for mediating the hepatic response to K. pneumoniae infection.

Arecoline downregulates levels of p21 and p27 through the reactive oxygen species/mTOR complex 1 pathway and may contribute to oral squamous cell carcinoma

Arecoline, the major alkaloid of areca nut, has been shown to cause strong genotoxicity and is considered a potential carcinogen. However, the detailed mechanism for arecoline-induced carcinogenesis remains obscure. In this study, we noticed that the levels of p21 and p27 increased in two oral squamous cell carcinoma cell lines with high confluence. Furthermore, when treated with arecoline, elevated levels of p21 and p27 could be downregulated through the reactive oxygen species/mTOR complex 1 (ROS/mTORC1) pathway. Although arecoline decreased the activity of mTORC1, the amounts of autophagosome-like vacuoles or type II LC3 remained unchanged, suggesting that the downregulation of p21 and p27 was independent of autophagy-mediated protein destruction. Arecoline also caused DNA damage through ROS, indicating that the reduced levels of p21 and p27 might facilitate G (1) /S transition of the cell cycle and subsequently lead to error-prone DNA replication. In conclusion, these data have provided a possible mechanism for arecoline-induced carcinogenesis in subcytolytic doses in vivo.

CCAR1 is required for Ngn3-mediated endocrine differentiation

Neurogenin3 (Ngn3) is a basic helix-loop-helix transcription factor that specifies pancreatic endocrine cell fates during pancreas development. It can also initiate a transdifferentiation program when expressed in pancreatic exocrine and ductal cells. However, how Ngn3 initiates a transcriptional cascade to achieve endocrine differentiation is still poorly understood. Here, we show that cell cycle and apoptosis regulator 1 (CCAR1), which is a transcriptional coactivator for nuclear receptors, also interacts with Ngn3. The association between Ngn3 and CCAR1 was verified by pull-down assays and co-immunoprecipitation analyses. Using gene reporter assays, we found that CCAR1 is essential for Ngn3 to activate the expression of the reporter genes containing the NeuroD promoter. Moreover, down-regulation of endogenous CCAR1 in the PANC-1 pancreatic ductal cell line inhibits the transdifferentiation program initiated by Ngn3. CCAR1 is, therefore, a novel partner of Ngn3 in mediating endocrine differentiation.

Impact of Hfq on global gene expression and virulence in Klebsiella pneumoniae

Klebsiella pneumoniae is responsible for a wide range of clinical symptoms. How this bacterium adapts itself to ever-changing host milieu is still a mystery. Recently, small non-coding RNAs (sRNAs) have received considerable attention for their functions in fine-tuning gene expression at a post-transcriptional level to promote bacterial adaptation. Here we demonstrate that Hfq, an RNA-binding protein, which facilitates interactions between sRNAs and their mRNA targets, is critical for K. pneumoniae virulence. A K. pneumoniae mutant lacking hfq (Δhfq) failed to disseminate into extra-intestinal organs and was attenuated on induction of a systemic infection in a mouse model. The absence of Hfq was associated with alteration in composition of envelope proteins, increased production of capsular polysaccharides, and decreased resistance to H₂O₂, heat shock, and UV irradiation. Microarray-based transcriptome analyses revealed that 897 genes involved in numerous cellular processes were deregulated in the Δhfq strain. Interestingly, Hfq appeared to govern expression of many genes indirectly by affecting sigma factor RpoS and RpoE, since 19.5% (175/897) and 17.3% (155/897) of Hfq-dependent genes belong to the RpoE- and RpoS-regulon, respectively. These results indicate that Hfq regulates global gene expression at multiple levels to modulate the physiological fitness and virulence potential of K. pneumoniae.

Assessment of hypermucoviscosity as a virulence factor for experimental Klebsiella pneumoniae infections: comparative virulence analysis with hypermucoviscosity-negative strain

Background

Klebsiella pneumoniae displaying the hypermucoviscosity (HV) phenotype are considered more virulent than HV-negative strains. Nevertheless, the emergence of tissue-abscesses-associated HV-negative isolates motivated us to re-evaluate the role of HV-phenotype.

Results

Instead of genetically manipulating the HV-phenotype of K. pneumoniae, we selected two clinically isolated K1 strains, 1112 (HV-positive) and 1084 (HV-negative), to avoid possible interference from defects in the capsule. These well-encapsulated strains with similar genetic backgrounds were used for comparative analysis of bacterial virulence in a pneumoniae or a liver abscess model generated in either naïve or diabetic mice. In the pneumonia model, the HV-positive strain 1112 proliferated to higher loads in the lungs and blood of naïve mice, but was less prone to disseminate into the blood of diabetic mice compared to the HV-negative strain 1084. In the liver abscess model, 1084 was as potent as 1112 in inducing liver abscesses in both the naïve and diabetic mice. The 1084-infected diabetic mice were more inclined to develop bacteremia and had a higher mortality rate than those infected by 1112. A mini-Tn5 mutant of 1112, isolated due to its loss of HV-phenotype, was avirulent to mice.

Conclusion

These results indicate that the HV-phenotype is required for the virulence of the clinically isolated HV-positive strain 1112. The superior ability of the HV-negative stain 1084 over 1112 to cause bacteremia in diabetic mice suggests that factors other than the HV phenotype were required for the systemic dissemination of K. pneumoniae in an immunocompromised setting.

Inactivation of tensin3 in mice results in growth retardation and postnatal lethality

Tensin family is a group of focal adhesion proteins that interact with integrins, actin, and phosphotyrosine-containing proteins. To explore the in vivo functions of a new member of the family, tensin3, we have generated mutant mice with a disrupted tensin3 gene. Inactivation of tensin3 resulted in growth retardation and postnatal lethality in one third of the homozygous mutants. Histological analysis of those mutants showed incomplete development of the small intestine, lung, and bone. Villus formation in the small intestine was affected and cells migrated slower in the runt mutants. Their lungs also displayed enlarged air space suggesting defects in alveogenesis. In addition, the resting zone was thicker and fewer proliferating cells were present in the growth plates of tensin3(-/-) tibiae. These observations indicate that tensin3 is essential for normal development and functions of the small intestine, lung, and bone. These phenotypes of the runt tensin3(-/-) mice are similar to some clinical features of Silver-Russell syndrome (SRS) which is a genetically inherited defect. About 10% of SRS cases have been linked to abnormality in chromosome 7p11.2-13, where human tensin3 gene is located, suggesting a potential link between tensin3 and SRS.

Single-cell transcript analysis of pancreas development

DNA microarray analysis was combined with a modified single-cell PCR procedure to study gene expression profiles of single cells at different stages of pancreatic development. This method identifies distinct cell types at embryonic day 10.5, a stage when the pancreatic epithelium is morphologically uniform. Some cells express unexpected combinations of genes, and these expression patterns provide new insights into pancreas development. Following on these findings, we use PCR products from different cell types to identify novel pancreatic genes, some of which mark subtypes of developing pancreatic cells. By integrating these data with previous genetic and biochemical studies, we propose a pathway for pancreatic cell development. This form of single-cell transcriptional analysis can be applied to any developmental process or tissue to characterize distinct cell types.

Ephrin-B3, a ligand for the receptor EphB3, expressed at the midline of the developing neural tube

The ephrins are a family of ligands that bind to Eph family receptor tyrosine kinases, and have been implicated in axon guidance and other patterning processes during vertebrate development. We describe here the identification and characterization of murine ephrin-B3. The cDNA encodes a 340 amino acid transmembrane molecule, most closely related to the two other known transmembrane ligands, ephrin-B1 and ephrin-B2. In addition to homology in their extracellular receptor binding domains, these transmembrane ligands share striking homology between their cytoplasmic domains, with 31 of the last 34 amino acids of ephrin-B3 being identical to ephrin-B2, suggesting functional interactions of the cytoplasmic tail. While most Eph family ligands are promiscuous in their interactions with Eph receptors, binding studies with the five receptors known to bind other transmembrane ligands only revealed a high affinity interaction of ephrin-B3 with EphB3, with a dissociation constant of approximately 1 nM. In situ hybridization of mouse embryos showed ephrin-B3 is expressed prominently at the dorsal and ventral midline of the neural tube, particularly in the floor plate, a structure with key functions in patterning the nervous system. The isolation of this ligand may help to elucidate the molecular basis of patterning activities at the neural tube midline.

PTP-NP, a new member of the receptor protein tyrosine phosphatase family, implicated in development of nervous system and pancreatic endocrine cells

The regulation of protein tyrosine phosphorylation is an important mechanism for developmental control. We describe here a new member of the protein tyrosine phosphatase (PTP) family, called PTP-NP (for neural and pancreatic). The cDNA sequence indicates a receptor-type transmembrane molecule. At early organogenesis, in situ hybridization with a probe for the PTP-NP extracellular region detects expression confined to the region of the developing pancreas, an organ of medical importance, but poorly understood with regard to molecular mechanisms of developmental control. This localized expression appears early, even before morphological differentiation of the pancreas, and is found in presumptive precursors of the endocrine cells by the earliest times that they can be distinguished. In neural development, an alternate RNA with a different or missing extracellular region is expressed transiently at early stages of neurogenesis and the full-length PTP-NP RNA appears later. To search for a ligand of PTP-NP, a fusion protein probe was made with the extracellular domain fused to an alkaline phosphatase tag. This probe bound strongly to pancreatic islets, providing evidence for a ligand-receptor interaction that could be involved in endocrine cell regulation. The results show PTP-NP is an especially early marker for pancreatic development and suggest it may be a receptor that could control the development of pancreatic endocrine cells.

Heterodimers of placenta growth factor/vascular endothelial growth factor. Endothelial activity, tumor cell expression, and high affinity binding to Flk-1/KDR

Here we show that the Escherichia coli expressed monomers of placenta growth factor (PLGF)129 and vascular endothelial growth factor (VEGF)165 can be re-folded in vitro to form PLGF/VEGF heterodimers. The purified recombinant PLGF/VEGF heterodimers and VEGF homodimers have potent mitogenic and chemotactic effects on endothelial cells. However, PLGF/VEGF heterodimers display 20-50-fold less mitogenic activity than VEGF165 homodimers. In contrast, PLGF129 homodimers have little or no effect in these in vitro assays. We also demonstrate the presence of natural PLGF/VEGF heterodimers in the conditioned media of various human tumor cell lines. While PLGF/VEGF heterodimers bind with high affinity to a soluble Flk-1/KDR receptor, PLGF129 homodimers fail to bind to this receptor. Cross-linking of 125I-ligands to human umbilical vein endothelial cells reveals that PLGF/VEGF heterodimers and VEGF165 homodimers, but not PLGF129 homodimers, form complexes with membrane receptors. VEGF165 homodimers and PLGF/VEGF heterodimers stimulate tyrosine phosphorylation of a 220-kDa protein, the expected size for the KDR receptor in human umbilical vein endothelial cells, whereas PLGF129 homodimers are unable to induce tyrosine phosphorylation of this protein. These data indicate that PLGF may modulate VEGF-induced angiogenesis by the formation of PLGF/VEGF heterodimers in cells producing both factors.

Interactions between the Flk-1 receptor, vascular endothelial growth factor, and cell surface proteoglycan identified with a soluble receptor reagent

Fetal liver kinase-1 (Flk-1) is a transmembrane tyrosine kinase that was identified in endothelial cells and populations of cells enriched in hematopoietic progenitors. To characterize the interaction of Flk-1 with potential ligands the receptor extracellular domain was genetically fused to an alkaline phosphatase (AP) tag. A soluble ligand for Flk-1 was identified in the supernatants of numerous mesenchymal cell lines by co-immunoprecipitation with the Flk1-AP fusion protein. This polypeptide was shown by N-terminal sequencing to be vascular endothelial growth factor (VEGF). Receptor-AP fusion proteins can thus be used to identify soluble ligands as well as transmembrane ligands, and this approach is therefore likely to be widely applicable to many types of orphan receptor. The Flk1-AP soluble receptor was also found to bind to cell surfaces, showing two apparent classes of binding site with different affinities. This interaction could be reconstructed by introducing a VEGF expression plasmid into cells. These results indicate that VEGF presented at the cell surface can bind to the Flk-1 receptor, and could mediate a direct cell-cell interaction. The Flk1-AP fusion protein was also found to bind heparin, implying that ligand binding by the Flk-1 receptor may involve a three way interaction between the Flk-1 receptor, VEGF, and heparin-like cell surface proteoglycans.

Murine c-mpl: a member of the hematopoietic growth factor receptor superfamily that transduces a proliferative signal

The murine myeloproliferative leukemia virus has previously been shown to contain a fragment of the coding region of the c-mpl gene, a member of the cytokine receptor superfamily. We have isolated cDNA and genomic clones encoding murine c-mpl and localized the c-mpl gene to mouse chromosome 4. Since some members of this superfamily function by transducing a proliferative signal and since the putative ligand of mpl is unknown, we have generated a chimeric receptor to test the functional potential of mpl. The chimera consists of the extracellular domain of the human interleukin-4 receptor and the cytoplasmic domain of mpl. A mouse hematopoietic cell line transfected with this construct proliferates in response to human interleukin-4, thereby demonstrating that the cytoplasmic domain of mpl contains all elements necessary to transmit a growth stimulatory signal. In addition, we show that 25-40% of mpl mRNA found in the spleen corresponds to a novel truncated and potentially soluble isoform of mpl and that both full-length and truncated forms of mpl protein can be immunoprecipitated from lysates of transfected COS cells. Interestingly, however, although the truncated form of the receptor possesses a functional signal sequence and lacks a transmembrane domain, it is not detected in the culture media of transfected cells.