BACKGROUND: Use of a calcineurin inhibitor (CNI) immunosuppressant following kidney transplantation is associated with development of vasomotor nephrotoxicity. This study was undertaken to evaluate and compare the influences of CNI-based and CNI-free immunosuppressant regimens on two intrarenal vascular resistance parameters, the resistive index (RI) and the pulsatility index (PI), in renal transplant recipients. METHODS: Forty-nine renal transplant patients who received ultrasonography examination between January 2007 and December 2007 were enrolled in this case-control study. Thirty-one subjects received a CNI-based regimen, and 18 received a CNI-free (sirolimus-based) regimen. RI and PI were determined by duplex Doppler ultrasonography. RESULTS: Patients receiving a CNI displayed lower cholesterol and triglyceride values and higher RI (mean: 0.7 vs. 0.6, P = 0.002) and PI values (mean: 1.3 vs. 1.1, P = 0.034). Multivariate analyses revealed that advanced age and use of alpha-blockers or diuretics were modestly associated with higher RI and PI values. By multivariate analysis, use of sirolimus was associated with a lower RI by -0.05 [95% confidence interval (CI): -0.085, -0.019; P = 0.003] but not with a lower PI (95% CI: -0.245, 0.001; P = 0.053). CONCLUSIONS: Use of sirolimus is only modestly correlated with a reduced RI and is not associated with a reduced PI. These observations question the superiority of CNI-free over CNI-based regimens with regard to reduction of intrarenal vascular resistance post-transplantation. These findings combined with those regarding recipient factors also cast doubt on the specificity of intrarenal resistance indices for predicting allograft function and/or survival. less...

Mycolactone is a diffusible lipid toxin produced by Mycobacterium ulcerans, the causative agent of a necrotizing skin disease referred to as Buruli ulcer. Intriguingly, patients with progressive lesions display a systemic suppression of Th1 responses that resolves on surgical excision of infected tissues. In this study, we examined the effects of mycolactone on the functional biology of T cells and identified two mechanisms by which mycolactone suppresses cell responsiveness to antigenic stimulation. At noncytotoxic concentrations, mycolactone blocked the activation-induced production of cytokines by a posttranscriptional, mammalian target of rapamycin, and cellular stress-independent mechanism In addition, mycolactone triggered the lipid-raft association and activation of the Src-family kinase, Lck. Mycolactone-mediated hyperactivation of Lck resulted in the depletion of intracellular calcium stores and downregulation of the TCR, leading to impaired T cell responsiveness to stimulation. These biochemical alterations were not observed when T cells were exposed to other bacterial lipids, or to structurally related immunosuppressors. Mycolactone thus constitutes a novel type of T cell immunosuppressive agent, the potent activity of which may explain the defective cellular responses in Buruli ulcer patients. less...

The target of rapamycin (TOR) is a conserved eukaryotic ser/thr kinase that regulates cellular growth in response to the nutrient and energy state. TOR signaling plays an important role for the development of diseases such as cancer, obesity, and diabetes and for different redox-sensitive processes (hypoxia, apoptosis, ageing). Because TOR has been detected at different cellular membranes and in the nucleus, its localization may influence the specific signaling readout. In order to better understand how TOR can associate with different membranes, the lipid-binding properties of the redox-sensitive yeast TOR1 FATC domain (y1fatc) have been characterized by solution NMR spectroscopy. Binding studies with different lipids indicate that y1fatc interacts specifically with a membrane-mimetic environment but appears not to recognize a specific lipid headgroup. In both, the structures of oxidized and reduced micelle-bound y1fatc, residues I2456 to W2470 of the lipid-binding motif form a hydrophobic bulb that has a rim of charged residues. The diffusion constants for both micelle-bound states are consistent with the rotational correlation times from the analysis of the 15N-relaxation data. Based on the Kd-values, the oxidized form (Kd ~ 0.31 mM) binds DPC micelles slightly tighter than the reduced form (Kd ~ 1.86 mM). Binding studies with y1fatc in which one or both tryptophans (W2466, W2470) were replaced by alanine suggest that these residues are important for the exact positioning in the membrane and that the other aromatic (H2462, Y2463, F2469) and aliphatic residues (I2456, L2459, I2464, P2468) in the lipid-binding motif contribute significantly to the affinity. less...

Inflammatory bowel disease (IBD) is a high-risk condition for human colorectal cancer. However, our mechanistic understanding of the link between inflammation and tumorigenesis in the colon is limited. Here we established a novel mouse model of colitis-associated cancer by genetically inactivating signal transducer and activator of transcription 3 (Stat3) in macrophages, with partial deletion in other myeloid and lymphoid cells. Inflammation developed in the colon of mutant mice spontaneously, and tumor lesions, including invasive carcinoma, arose in the inflamed region of the intestine with a frequency similar to that observed in human IBD patients. The development of both inflammation and tumors in the mutant mice required the presence of microflora. Indeed, inflammation was associated with disruption of colonic homeostasis, fulminant epithelial/tumor cell proliferation, and activation of the mammalian target of rapamycin (mTOR)-Stat3 pathway in epithelial and tumor cells. The activation of this pathway was essential for both the excess proliferation of epithelial/tumor cells and the disruption of colonic homeostasis in the mutant mice. Notably, a similar abnormal up-regulation of mTOR-Stat3 signaling was consistently observed in the colonic epithelial cells of human IBD patients with active disease. These studies demonstrate a novel mouse model of IBD-colorectal cancer progression in which disrupted immune regulation, mTOR-Stat3 signaling, and epithelial hyperproliferation are integrated and simultaneously linked to the development of malignancy. less...

AIMS AND BACKGROUND: Most gastrointestinal stromal tumor (GIST) patients respond to KIT inhibition therapy of imatinib, but eventually become resistant with a median time to progression of 2 years. The mechanism of acquired resistance to imatinib and oncogenic KIT signal transduction in GISTs has not been well defined. We sought to investigate the spectrum of molecular and genomic changes in imatinib-resistant GIST patients. METHODS: KIT and PDGFRA mutations were evaluated in 48 samples obtained from 32 GIST patients who underwent surgery after imatinib treatment. KIT downstream signaling profiles were also investigated in eight specimens of five patients who were clinically responsive or resistant to imatinib therapy. Biochemical inhibition of KIT, mitogen-activated protein kinase (MAPK), mammalian target of rapamycin (MTOR), AKT, proliferating cell nuclear antigen (PCNA) and BCL-2 were determined by western blotting for protein activation. RESULTS: In all 32 GIST patients, activating mutations in the KIT gene were seen in 26 (81.3%) patients, PDGFRA gene mutations were seen in 2 (6.2%) patients and no primary mutations were found in 4 (12.5%) patients. Secondary KIT mutations were identified in 11/14 (78.6%) imatinib-acquired-resistance patients, with nine patients in KIT gene exon17, and the other two in exon 13. The expressions of p-KIT, p-AKT, PCNA and BCL-2 were higher in the samples of imatinib-resistant GISTs than those of imatinib-responsive ones. P-KIT, p-AKT expressions were higher in imatinib acquired-resistance GISTs with secondary KIT mutations than imatinib-responsive ones with primary mutation. Total KIT, MAPK, p-MAPK, p-MTOR expressions were comparable in all varied GISTs. CONCLUSIONS: Novel additional mutations of KIT gene exon 13 or exon 17 indicate the likely mechanism of secondary resistance to imatinib. The PI3-K/AKT pathway might be more relevant than MEK/MAPK for therapeutic targeting in imatinib-resistant GIST patients with secondary mutation. less...

The vacuole of Saccharomyces cerevisiae has been a seminal model for studies of lysosomal trafficking, biogenesis, and function. Several yeast mutants defective in such vacuolar events have been unable to grow at low levels of hygromycin B, an aminoglycoside antibiotic. We hypothesized that such severe hypersensitivity to hygromycin B (hhy) is linked to vacuolar defects and performed a genomic screen for the phenotype using a haploid deletion strain library of non-essential genes Fourteen HHY genes were initially identified and were subjected to bioinformatics analyses. The uncovered hhy mutants were experimentally characterized with respect to vesicular trafficking, vacuole morphology, and growth under various stress and drug conditions. The combination of bioinformatics analyses and phenotypic characterizations implicate defects in vesicular trafficking, vacuole fusion/fission, or vacuole function in all hhy mutants. The collection was enriched for sensitivity to monensin, indicative of vacuolar trafficking defects. Additionally, all hhy mutants showed severe sensitivities to rapamycin and caffeine, suggestive of TOR kinase pathway defects. Our experimental results also establish a new role in vacuolar and vesicular functions for two genes: PAF1, encoding a RNAP II-associated protein required for expression of cell cycle-regulated genes, and TPD3, encoding the regulatory subunit of protein phosphatase 2A. Thus, our results support linkage between severe hypersensitivity to hygromycin B and vacuolar defects less...

Neurofibromatosis Type 1 (NF1) is a common autosomal dominant disease characterized by complex and multicellular neurofibroma tumors, and less frequently by malignant peripheral nerve sheath tumors (MPNSTs) and optic nerve gliomas. Significant advances have been made in elucidating the cellular, genetic, and molecular biology involved in tumor formation in NF1. Neurofibromatosis Type 1 is caused by germline mutations of the NF1 tumor suppressor gene, which generally result in decreased intracellular neurofibromin protein levels, leading to increased cascade Ras signaling to its downstream effectors. Multiple key pathways are involved with the development of tumors in NF1, including Ras/mitogen-activated protein kinase (MAPK) and Akt/mammalian target of rapamycin (mTOR). Interestingly, recent studies demonstrate that multiple other developmental syndromes (in addition to NF1) share phenotypic features resulting from germline mutations in genes responsible for components of the Ras/MAPK pathway. In general, a somatic loss of the second NF1 allele, also referred to as loss of heterozygosity, in the progenitor cell, either the Schwann cell or its precursor, combined with haploinsufficiency in multiple supporting cells is required for tumor formation. Importantly, a complex series of interactions with these other cell types in neurofibroma tumorigenesis is mediated by abnormal expression of growth factors and their receptors and modification of gene expression, a key example of which is the process of recruitment and involvement of the NF1(+/-) heterozygous mast cell. In general, for malignant transformation to occur, there must be accumulation of additional mutations of multiple genes including INK4A/ARF and P53, with resulting abnormalities of their respective signal cascades. Further, abnormalities of the NF1 gene and molecular cascade described above have been implicated in the tumorigenesis of NF1 and some sporadically occurring gliomas, and thus, these treatment options may have wider applicability. Finally, increased knowledge of molecular and cellular mechanisms involved with NF1 tumorigenesis has led to multiple preclinical and clinical studies of targeted therapy, including the mTOR inhibitor rapamycin, which is demonstrating promising preclinical results for treatment of MPNSTs and gliomas. less...

Glioblastoma is the most frequent and devastating primary malignant brain tumor in adults. Surgery followed by standard radiotherapy with concomitant and adjuvant chemotherapy with temozolomide is the standard of care in patients with glioblastoma, however the prognosis remains poor with a median survival in the range of 12-15 months. Common genetic abnormalities in glioblastoma are associated with aberrant activation or suppression of cellular signal transduction pathways and resistance to radiation and chemotherapy. Special attention has been focused on targets such as epidermal growth factor receptor, vascular endothelial growth factor receptor, platelet-derived growth factor receptor, and on pathways such as the phosphatidylinositol-3kinase/Akt/mammalian target of rapamycin and Ras/Raf/mitogen-activated protein-kinase pathways. Several signal transduction inhibitors have been examined in preclinical and clinical malignant glioma trials, including antiangiogenic agents (bevacizumab, enzastaurin), and inhibitors of epidermal growth factor receptor tyrosine kinase (gefitinib and erlotinib), mammalian target of rapamycin (temsirolimus, everolimus) and integrin (cilengitide). Although preliminary clinical results of the use of targeted agents have not translated into significantly better survival, more recent phase II trials are exploring the combination of multitargeted drugs with cytotoxic chemotherapy and radiotherapy in order to overcome the resistance of tumors to single-agent targeted therapies. This review summarizes the current results with cytotoxic and targeted molecular agents in glioblastoma and the development of new chemoradiation strategies under evaluation to increase their effectiveness. less...

Objective To investigate cholecystokinin (CCK),carbachol, and vasoactive intestinal peptide(VIP)stimulating peptide chain elongation in mouse pancreatic acini in vitro and its molecular mechanism. Methods (3)H-lecucine incorporation assay was used to measure the basal and secretagogues-stimulated pancreatic acini elongation rates. Western blot was applied to analyse the effect of phosphorylation of the elongation factor 2 (eEF2) and the eEF2 kinase. MEK inhibitor (PD98059), SAPK/p38 inhibitor (SB202190), and mTOR inhibitor (rapamycin) were used to respectively block MEK, SAPK/p38, and mTOR intracellular pathways or the phosphatase inhibitor (calyculin A) pretreatment before CCK treatment. Results All secretagogues except VIP increased the peptide chain elongation in mouse pancreatic acini in vitro. All secretagogues except VIP inhibited the phosphorylation level of eEF2 on Thr-56 and increased the phosphorylation level of eEF2K on Ser-366, which might correlate with their activation status. MEK inhibitor PD98059 partially reversed the dephosphorylation of eEF2 induced by CCK, as did treatment p38 MAPK inhibitor SB202190, mTOR inhibitor rapamycin, and the phosphatase inhibitor calyculin A.Conclusion CCK increases peptide chain elongation via inducement of dephosphorylation of eEF2 and eEF2 kinase phosphorylation in pancreatic acini in vitro. CCK-induced dephosphorylation of eEF2 in pancreatic acinar cells involves MEK, SAPK/p38, and mTOR, the three intracellular pathways. less...

TOR (target of rapamycin) is a serine-threonine protein kinase that is conserved across a diverse range of species from fungi to mammals. The signaling pathway that is anchored by TOR is also conserved across species. In mammals, mTOR integrates growth factor, amino acid, nutrient and energy sensing signals, and thus plays a major role in cell growth and proliferation, protein synthesis and autophagy. As a result of the pivotal role of mTOR in signaling, the aberrant regulation of mTOR has been implicated in several disease processes, including cancer, diabetes, ocular diseases and neurodegenerative disorders, as well as in lifespan extension. More recently, rapamycin (sirolimus) analogs that antagonize the mTOR signaling pathway have been approved for the treatment of several cancers. This review describes some recent advances in the understanding of mTOR signaling, with an emphasis on the functional consequences of mTOR inhibition and therapeutic intervention strategies. less...