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.

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.

Generation and sequencing of pulmonary carcinoid tumor cell lines.

INTRODUCTION: Pulmonary carcinoid tumors account for approximately 5% of all lung malignancies in adults, and comprise 30% of all carcinoid tumors. There are limited reagents available to study these rare tumors, and consequently no major advances have been made for patient treatment. We report the generation and characterization of human pulmonary carcinoid tumor cell lines to study underlying biology, and to provide models for testing novel chemotherapeutic agents. METHODS: Tissue was harvested from three patients with primary pulmonary typical carcinoid tumors undergoing surgical resection. The tumor was dissociated and plated onto dishes in culture media. The established cell lines were characterized by immunohistochemistry, Western blotting, and cell proliferation assays. Tumorigenicity was confirmed by soft agar growth and the ability to form tumors in a mouse xenograft model. Exome and RNA sequencing of patient tumor samples and cell lines was performed using standard protocols. RESULTS: Three typical carcinoid tumor lines grew as adherent monolayers in vitro, expressed neuroendocrine markers consistent with the primary tumor, and formed colonies in soft agar. A single cell line produced lung tumors in nude mice after intravenous injection. Exome and RNA sequencing of this cell line showed lineage relationship with the primary tumor, and demonstrated mutations in a number of genes related to neuronal differentiation. CONCLUSION: Three human pulmonary typical carcinoid tumor cell lines have been generated and characterized as a tool for studying the biology and novel treatment approaches for these rare tumors.

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.

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.