TRPC3 regulates release of brain-derived neurotrophic factor from human airway smooth muscle.

Exogenous brain-derived neurotrophic factor (BDNF) enhances Ca(2+) signaling and cell proliferation in human airway smooth muscle (ASM), especially with inflammation. Human ASM also expresses BDNF, raising the potential for autocrine/paracrine effects. The mechanisms by which ASM BDNF secretion occurs are not known. Transient receptor potential channels (TRPCs) regulate a variety of intracellular processes including store-operated Ca(2+) entry (SOCE; including in ASM) and secretion of factors such as cytokines. In human ASM, we tested the hypothesis that TRPC3 regulates BDNF secretion. At baseline, intracellular BDNF was present, and BDNF secretion was detectable by enzyme linked immunosorbent assay (ELISA) of cell supernatants or by real-time fluorescence imaging of cells transfected with GFP-BDNF vector. Exposure to the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFα) (20ng/ml, 48h) or a mixture of allergens (ovalbumin, house dust mite, Alternaria, and Aspergillus extracts) significantly enhanced BDNF secretion and increased TRPC3 expression. TRPC3 knockdown (siRNA or inhibitor Pyr3; 10µM) blunted BDNF secretion, and prevented inflammation effects. Chelation of extracellular Ca(2+) (EGTA; 1mM) or intracellular Ca(2+) (BAPTA; 5µM) significantly reduced secreted BDNF, as did the knockdown of SOCE proteins STIM1 and Orai1 or plasma membrane caveolin-1. Functionally, secreted BDNF had autocrine effects suggested by phosphorylation of high-affinity tropomyosin-related kinase TrkB receptor, prevented by chelating extracellular BDNF with chimeric TrkB-Fc. These data emphasize the role of TRPC3 and Ca(2+) influx in the regulation of BDNF secretion by human ASM and the enhancing effects of inflammation. Given the BDNF effects on Ca(2+) and cell proliferation, BDNF secretion may contribute to altered airway structure and function in diseases such as asthma.

NHERF-2 maintains endothelial homeostasis.

The Na(+)/H(+) exchanger regulatory factor-2 (NHERF-2) is an integral component of almost all endothelial cells (ECs), yet its endothelial function is not known. Here, we found that NHERF-2, is a key regulator of endothelial homeostasis because NHERF-2-silenced ECs proliferate at a much higher rate even in the absence of mitogens such as VEGF compared with control ECs. We further show that the hyperproliferation phenotype of NHERF-2-silenced EC is because of an accelerated cell cycle that is probably caused by a combination of the following factors: increased cytoplasmic calcium, increased expression of c-Myc, increased expression of cyclin D1, and reduced expression of p27. Using an experimental mouse model of human hemangioma, we found that the endothelial neoplasms derived from NHERF-2-silenced cells were much larger in volume than those derived from control cells. Thus, NHERF-2 is a negative regulator of endothelial proliferation and may have important roles in endothelial homeostasis and vascular modeling.

Dopamine inhibits pulmonary edema through the VEGF-VEGFR2 axis in a murine model of acute lung injury.

The neurotransmitter dopamine and its dopamine receptor D2 (D2DR) agonists are known to inhibit vascular permeability factor/vascular endothelial growth factor (VEGF)-mediated angiogenesis and vascular permeability. Lung injury is a clinical syndrome associated with increased microvascular permeability. However, the effects of dopamine on pulmonary edema, a phenomenon critical to the pathophysiology of both acute and chronic lung injuries, have yet to be established. Therefore, we sought to determine the potential therapeutic effects of dopamine in a murine model of lipopolysaccharide (LPS)-induced acute lung injury (ALI). Compared with sham-treated controls, pretreatment with dopamine (50 mg/kg body wt) ameliorated LPS-mediated edema formation and lowered myeloperoxidase activity, a measure of neutrophil infiltration. Moreover, dopamine significantly increased survival rates of LPS-treated mice, from 0-75%. Mechanistically, we found that dopamine acts through the VEGF-VEGFR2 axis to reduce pulmonary edema, as dopamine pretreatment in LPS-treated mice resulted in decreased serum VEGF, VEGFR2 phosphorylation, and endothelial nitric oxide synthase phosphorylation. We used D2DR knockout mice to confirm that dopamine acts through D2DR to block vascular permeability in our lung injury model. As expected, a D2DR agonist failed to reduce pulmonary edema in D2DR(-/-) mice. Taken together, our results suggest that dopamine acts through D2DR to inhibit pulmonary edema-associated vascular permeability, which is mediated through VEGF-VEGFR2 signaling and conveys protective effects in an ALI model.

Expression of profibrotic genes in a murine remnant kidney model.

PURPOSE: To test the hypothesis that there is increased expression of several profibrotic genes, including matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitors of metalloproteinase (TIMP-1 and TIMP-2), a disintegrin and metalloproteinase with thrombospondin motif-1 (ADAMTS-1), and fibroblast specific protein-1 (FSP-1) in a murine remnant kidney model. MATERIALS AND METHODS: Chronic kidney disease (CKD) was created in 10 C57BL/6 male mice (20-25 g) by performing a right nephrectomy and ligation of the upper pole of the left kidney (remnant kidney). Animals were sacrificed 42 days and 56 days later. Reverse transcriptase polymerase chain reaction (RT-PCR) for MMP-2, MMP-9, TIMP-1, TIMP-2, ADAMTS-1, and FSP-1 was performed in the remnant kidney. Histologic evaluation of the remnant kidney was performed using Ki-67, α-smooth muscle cell actin (α-SMA), hematoxylin and eosin, and Masson' trichrome staining. Kidney function was assessed using serum blood urea nitrogen (BUN) and creatinine. RESULTS: The mean serum BUN and creatinine levels at day 42 and day 56 were significantly higher than baseline (P < .05). By day 42, the mean expression of MMP-2, MMP-9, TIMP-1, ADAMTS-1, and FSP-1 was significantly higher in the remnant kidney compared with the normal kidney (P < .05); by day 56, only FSP-1 expression was significantly higher (P < .05). There was increased fibrosis by Masson' trichrome, increased Ki-67, and increased α-SMA staining in the remnant kidney compared with the normal kidney. CONCLUSIONS: In the remnant kidney, there was increased fibrosis with increased α-SMA and Ki-67 staining and significantly increased expression of MMP-2, MMP-9, TIMP-1, ADAMTS-1, and FSP-1.

Targeting GIPC/synectin in pancreatic cancer inhibits tumor growth.

PURPOSE: Various studies have shown the importance of the GAIP interacting protein, COOH-terminus (GIPC, also known as Synectin) as a central adaptor molecule in different signaling pathways and as an important mediator of receptor stability. GIPC/Synectin is associated with different growth-promoting receptors such as insulin-like growth factor receptor I (IGF-IR) and integrins. These interactions were mediated through its PDZ domain. GIPC/Synectin has been shown to be overexpressed in pancreatic and breast cancer. The goal of this study was to show the importance of GIPC/Synectin in pancreatic cancer growth and to evaluate a possible therapeutic strategy by using a GIPC-PDZ domain inhibitor. Furthermore, the effect of targeting GIPC on the IGF-I receptor as one of its associated receptors was tested. EXPERIMENTAL DESIGN: The in vivo effects of GIPC/Synectin knockdown were studied after lentiviral transduction of luciferase-expressing pancreatic cancer cells with short hairpin RNA against GIPC/Synectin. Additionally, a GIPC-PDZ--targeting peptide was designed. This peptide was tested for its influence on pancreatic cancer growth in vitro and in vivo. RESULTS: Knockdown of GIPC/Synectin led to a significant inhibition of pancreatic adenocarcinoma growth in an orthotopic mouse model. Additionally, a cell-permeable GIPC-PDZ inhibitor was able to block tumor growth significantly without showing toxicity in a mouse model. Targeting GIPC was accompanied by a significant reduction in IGF-IR expression in pancreatic cancer cells. CONCLUSIONS: Our findings show that targeting GIPC/Synectin and its PDZ domain inhibits pancreatic carcinoma growth and is a potential strategy for therapeutic intervention of pancreatic cancer.

Analysis of ErbB receptors in pulmonary carcinoid tumors.

PURPOSE: This study aimed to investigate the expression of the ErbB family of receptor tyrosine kinases in pulmonary typical carcinoid and atypical carcinoid tumors and to understand the role of epidermal growth factor receptor (EGFR) signaling in pulmonary carcinoid tumor proliferation. EXPERIMENTAL DESIGN: Surgically resected typical carcinoid (n = 24) and atypical carcinoid (n = 7) tumor tissues were analyzed by immunohistochemical staining for EGFR, ErbB2, ErbB3, and ErbB4. Sequencing of tumor DNA of exons 18 to 21 of the EGFR gene and the KRAS gene was carried out. Biochemical analysis of lung carcinoid cell lines was used to investigate EGFR signal transduction and response to erlotinib inhibition. RESULTS: The analysis showed that 45.8% of typical carcinoid and 28.6% of atypical carcinoid tumors express EGFR, 100% of the tumors lack expression of ErbB2, and 100% have moderate to intense staining for ErbB3 and ErbB4. Sequencing of tumor DNA of exons 18 to 21 of the EGFR gene revealed the absence of tyrosine kinase domain mutations in these tumors. Instead, 80.6% tumors harbored a synonymous single nucleotide polymorphism in exon 20. Because EGFR and KRAS mutations tend not to be present at the same time, we sequenced the KRAS gene from pulmonary carcinoid tumor DNA and found that 100% were wild-type. Using a lung carcinoid cell line that expresses EGFR, we found that erlotinib reduced proliferation by inhibiting EGFR signal transduction. CONCLUSIONS: Our findings suggest clinical potential for the use of EGFR inhibitors in the treatment of patients with pulmonary carcinoid tumors, particularly for patients with EGFR-positive pulmonary carcinoid tumors not amenable to surgical resection.

Cloning and characterization of CYP51 from Mycobacterium avium.

Mycobacterium avium complex (MAC) causes chronic lung disease in immunocompetent people and disseminated infection in patients with AIDS. MAC is intrinsically resistant to many conventional antimycobacterial agents, it develops drug resistance rapidly to macrolide antibiotics, and patients with MAC infection experience frequent relapses or the inability to completely eradicate the infection with current treatment. Treatment regimens are prolonged and complicated by drug toxicity or intolerances. We sought to identify biochemical pathways in MAC that can serve as targets for novel antimycobacterial treatment. The cytochrome P450 enzyme, CYP51, catalyzes an essential early step in sterol metabolism, removing a methyl group from lanosterol in animals and fungi, or from obtusifoliol in plants. Azoles inhibit CYP51 function, leading to an accumulation of methylated sterol precursors. This perturbation of normal sterol metabolism compromises cell membrane integrity, resulting in growth inhibition or cell death. We have cloned and characterized a CYP51 from MAC that functions as a lanosterol 14alpha-demethylase. We show the direct interactions of azoles with purified MAC-CYP51 by absorbance and electron paramagnetic resonance spectroscopy, and determine the minimum inhibitory concentrations (MICs) of econazole, ketoconazole, itraconazole, fluconazole, and voriconazole against MAC. Furthermore, we demonstrate that econazole has a MIC of 4 mug/ml and a minimum bacteriocidal concentration of 4 mug/ml, whereas ketoconazole has a MIC of 8 mug/ml and a minimum bacteriocidal concentration of 16 mug/ml. Itraconazole, voriconazole, and fluconazole did not inhibit MAC growth to any significant extent.

Biochemical requirements for PCBCK1 kinase activity, the Pneumocystis carinii MEKK involved in cell wall integrity.

Fungal cell wall assembly is a complicated process involving multiple enzymes and coordinated signaling pathways. The cell wall integrity MAPK pathway acts to stabilize the fungal cell wall during conditions of elevated temperature by regulation of glucan synthesis. The upstream kinase, BCK1, is a critical component of this pathway. Pneumonia is a significant cause of death from the fungal opportunistic pathogen Pneumocystis in immunocompromised states, especially with HIV infection. We have previously shown that PCBCK1 functions in the cell wall integrity pathway in yeast as a functional protein kinase. Kinases have specific requirements for enzymatic function which have not been investigated in fungi. Here we examine the biochemical requirements for PCBCK1 kinase activity expressed in Saccharomyces cerevisiae bck1Delta yeast. PCBCK1 requires 10 mM MgCl(2), pH 6, temperature 30 degrees C, and 10 microM ATP for kinase activity. Interference of the Pneumocystis cell wall integrity pathway is an attractive target for drug development since glucan synthesis machinery is not present in humans.

Expression analysis of PCSTE3, a putative pheromone receptor from the lung pathogenic fungus Pneumocystis carinii.

The fungal pathogen Pneumocystis carinii remains the most prevalent opportunistic infection in patients infected with HIV. Fungal pheromone receptors are seven transmembrane domain G-protein-coupled receptors which are expressed on specific mating types, and have ligand-binding extracellular domains for specific pheromones from cells of the opposite mating type. We have cloned and characterized PCSTE3 from P. carinii, which encodes a seven transmembrane domain protein orthologous to the Saccharomyces cerevisiae pheromone receptor Ste3. We detect PCSTE3 by indirect immunofluorescence using antibodies designed to extracellular domains of the receptor in yeast expressing the protein. Using a downstream Fus1-lacZ reporter gene, we determined that PCSTE3 does not recognize a- or alpha-factor pheromones as ligands for the receptor. We isolated P. carinii life cycle stages and examined PCSTE3 expression by immunofluorescence microscopy and flow cytometry, and found PCSTE3 expression exclusively on a population of trophic forms. PCSTE3 receptor expression was not found on cysts.

Complementation and characterization of the Pneumocystis carinii MAPK, PCM.

Mitogen-activated protein kinase (MAPK) pathways transfer environmental signals into intracellular events such as proliferation and differentiation. Fungi utilize a specific pheromone-induced MAPK pathway to regulate conjugation, formation of an ascus, and entry into meiosis. We have previously identified a MAPK, PCM, from the fungal opportunist Pneumocystis, responsible for causing severe pneumonia in patients with AIDS. In order to gain insight into the function of PCM, we expressed it in Saccharomyces cerevisiae deficient in pheromone signaling and tested activation and inhibition of this MAPK pathway. PCM restored pheromone signaling in S. cerevisiae fus3Delta kss1Delta mutants with alpha-factor pheromone (six-fold increase) and was not activated by osmotic stress. Signaling through this pathway decreased 2.5-fold with 10 microM U0126, and was unaffected with SB203580. We evaluated the conditions for native PCM kinase activity isolated from Pneumocystis carinii organisms and found that 0.1 mM MgCl2, pH 6.5, temperature 30-35 degrees C, and 10 microM ATP were optimal. The activity of PCM is significantly elevated in P. carinii trophic forms compared to cysts, implicating a role for PCM in the life cycle transition of P. carinii from trophic forms to cysts.

Pneumocystis carinii STE11, an HMG-box protein, is phosphorylated by the mitogen activated protein kinase PCM.

A pheromone-induced mitogen activated protein kinase (MAPK) pathway controls mating in fungi by regulating gene transcription. In the opportunistic fungus Pneumocystis carinii, we have identified a protein containing a high-mobility group (HMG) motif which is homologous to the transcriptional activators STE11 of Schizosaccharomyces pombe and STE12 of Saccharomyces cerevisiae. In fungi, this transcriptional activator functions in sexual development, filamentous growth, and pathogenicity. The fungal pheromone-activated MAPK phosphorylates the transcriptional activator to allow binding to pheromone-response elements in the promoter regions of certain genes. We have previously identified a P. carinii MAPK, PCM, which has significant homology to fungal MAPKs involved in mating. As an initial step in understanding the downstream molecules which interact with the PCM kinase, we have cloned a STE11 homologue in P. carinii. PCSTE11 has an open-reading frame of 1.5 kb which encodes a protein of 501 amino acids with a molecular weight of 56 kDa. Greatest homology was to S. pombe STE11 (52%). We have expressed a His-tag fusion of PCSTE11 and purified the protein with nickel affinity resin. PCM phosphorylates the purified protein indicating that PCSTE11 is associated with the MAPK cascade in P. carinii.

Pneumocystis carinii BCK1 functions in a mitogen-activated protein kinase cascade regulating fungal cell-wall assembly.

Pneumocystis pneumonia remains the most common AIDS-defining opportunistic infection in people with HIV. The process by which Pneumocystis carinii constructs its cell wall is not well known, although recent studies reveal that molecules such as beta-1-3-glucan synthetase (GSC1) and environmental pH-responsive genes such as PHR1 are important for cell-wall integrity. In closely related fungi, a specific mitogen-activated protein kinase (MAPK) cascade regulates cell-wall assembly in response to elevated temperature. The upstream mitogen-activated protein kinase kinase kinase (MAPKKK, or MEKK), BCK1, is an essential component in this pathway for maintaining cell-wall integrity and preventing fungal cell lysis. We have identified a P. carinii MEKK gene and have expressed it in Saccharomyces cerevisiae to gain insights into its function. The P. carinii MEKK, PCBCK1, corrects the temperature-sensitive cell lysis defect of bck1Delta yeast. Further, at elevated temperature PCBCK1 restored the signaling defect in bck1Delta yeast to maintain expression of the temperature-inducible beta-1-3-glucan synthetase gene, FKS2. PCBCK1, as a functional kinase, is capable of autophosphorylation and substrate phosphorylation. Since glucan machinery is not present in mammals, a better understanding of this pathway in P. carinii might aid in the development of novel medications which interfere with the integrity of the Pneumocystis cell wall.

Characterization of a lanosterol 14 alpha-demethylase from Pneumocystis carinii.

Pneumocystis carinii (PC) causes severe pneumonia in immunocompromised patients. PC is intrinsically resistant to treatment with azole antifungal medications. The enzyme lanosterol 14 alpha-demethylase (Erg11) is the target for azole antifungals. We cloned PCERG11 and compared its sequence to Erg11 proteins present in azole-resistant organisms, and performed chromosomal and Northern blot analysis for PCERG11. Of 13 potential sites which could confer resistance to azoles, two were identical to azole-resistant Candida. By site-directed mutagenesis we changed these two sites in PCERG11 to those present in azole-sensitive Candida to generate PCERG11-SDM (E113D, T125K). We tested the susceptibility of ERG11 deletion strains of Saccharomyces cerevisiae (SC) expressing PCERG11, PCERG11-SDM, and wild-type SCERG11 to three azole antifungals: fluconazole, itraconazole, and voriconazole. PCERG11 required a 2.2-fold higher dose of voriconazole and 3.5-fold higher dose of fluconazole than SCERG11 for a 50% reduction in growth. No difference was observed in the sensitivity to itraconazole. PCERG11-SDM has increased sensitivity to fluconazole and voriconazole, but not itraconazole. We believe that the molecular structure of the lanosterol 14 alpha-demethylase encoded by PCERG11 confers inherent resistance to azole antifungals and plays an integral part in the overall resistance of this PC to azole therapy.