Establishment of a Chemical Synthetic Lethality Screen in Cultured Human Cells

The synthetic lethality screen is a powerful genetic method for unraveling functional interactions between proteins in yeast. Here we demonstrate the feasibility of a chemical synthetic lethality screen in cultured human cells, based in part on the concept of the yeast method. The technology employs both an immortalized human cell line, deficient in a gene of interest, which is complemented by an episomal survival plasmid expressing the gene of interest, and the use of a novel double-label fluorescence system. Selective pressure imposed by any one of several synthetic lethal metabolic inhibitors prevented the spontaneous loss of the episomal survival plasmid. Retention or loss over time of this plasmid could be sensitively detected in a blind test, while cells were grown in microtiter plates. Application of this method should thus permit high throughput screening of drugs, which are synthetically lethal with any mutant human gene of interest, whose normal counterpart can be expressed. This usage is particularly attractive for the search of drugs, which kill malignant cells in a gene-specific manner, based on their predetermined cellular genotype. Moreover, by replacing the chemicals used in this example with a library of either DNA oligonucleotides or expressible dominant negative genetic elements, one should be able to identify synthetic lethal human genes

β3-Adrenergic relaxation of bovine iris sphincter

AbstractBovine iris sphincter in vitro responded to β-adrenergic stimulation with pronounced relaxation (EC50 of isoproterenol=0.3 nM), which was potentiated by the cAMP phosphodiesterase inhibitor, isobutylmethylxanthine, and mimicked by the adenylyl cyclase activator, forskolin. The β1/β2 antagonist, propranolol, exhibited low potency with calculated Ki of 200 nM. The β3-selective antagonist, bupranolol, exhibited a biphasic inhibition profile, with calculated Kis of approximately 20–50 and 200–300 nM. The β3-selective agonist, BRL 37344, elicited 70% of maximal relaxation (EC50=30 nM). When relaxation was induced by BRL 37344, bupranolol exhibited much higher potency (calculated Ki=1 nM). Our data suggest that the β-adrenergic relaxation response in bovine iris sphincter is mediated by a mixed population of β-adrenergic receptors, with a predominant contribution of atypical, most likely β3 subtype, receptors

Kaposi's Sarcoma-Associated Herpesvirus-G Protein-Coupled Receptor-Expressing Endothelial Cells Exhibit Reduced Migration and Stimulated Chemotaxis by Chemokine Inverse Agonists

A constitutively active G protein-coupled receptor (GPCR) encoded by Kaposi's sarcoma-associated herpesvirus (human herpesvirus-8) (KSHV) is expressed in endothelial (spindle) cells of Kaposi's sarcoma lesions. In this study, we report novel effects of basal signaling by this receptor and of inverse agonist chemokines on migration of KSHV-GPCR-expressing mouse lung endothelial cells. We show that basal signaling by KSHV-GPCR inhibits migration of endothelial cells in two systems, movement through porous filters and in vitro wound closure. Naturally occurring chemokines, interferon γ-inducible protein-10 and stromal-derived factor-1, which act as inverse agonists at KSHV-GPCR, abrogate the inhibition of migration and stimulate directed migration (or chemotaxis) of these cells. Thus, the expression of KSHV-GPCR may allow infected endothelial cells in situ to remain in a localized environment or to directionally migrate along a gradient of specific chemokines that are inverse agonists at KSHV-GPCR

A novel HMM-based method for detecting enriched transcription factor binding sites reveals RUNX3 as a potential target in pancreatic cancer biology.

BACKGROUND: Pancreatic adenocarcinoma (PAC) is one of the most intractable malignancies. In order to search for potential new therapeutic targets, we relied on computational methods aimed at identifying transcription factor binding sites (TFBSs) over-represented in the promoter regions of genes differentially expressed in PAC. Though many computational methods have been implemented to accomplish this, none has gained overall acceptance or produced proven novel targets in PAC. To this end we have developed DEMON, a novel method for motif detection. METHODOLOGY: DEMON relies on a hidden Markov model to score the appearance of sequence motifs, taking into account all potential sites in a promoter of potentially varying binding affinities. We demonstrate DEMON's accuracy on simulated and real data sets. Applying DEMON to PAC-related data sets identifies the RUNX family as highly enriched in PAC-related genes. Using a novel experimental paradigm to distinguish between normal and PAC cells, we find that RUNX3 mRNA (but not RUNX1 or RUNX2 mRNAs) exhibits time-dependent increases in normal but not in PAC cells. These increases are accompanied by changes in mRNA levels of putative RUNX gene targets. CONCLUSIONS: The integrated application of DEMON and a novel differentiation system led to the identification of a single family member, RUNX3, which together with four of its putative targets showed a robust response to a differentiation stimulus in healthy cells, whereas this regulatory mechanism was absent in PAC cells, emphasizing RUNX3 as a promising target for further studies