On the mechanism of the inhibition of transducin function by farnesylcysteine analogs

The gamma subunits of heterotrimeric G proteins are isoprenylated/methylated on their carboxy termini. The photoreceptor G protein, transducin, is farnesylated/methylated at this position. Since the isoprenyl group is required for G protein function, it is of great interest to determine the mechanism by which the farnesyl group of T gamma interacts with the other transducin subunits and/or the activated photoreceptor, rhodopsin. Farnesylcysteine derivatives (N-acetyl-S-farnesyl-L-cysteine and farnesylated peptides) have been previously shown to have effects on transducin activity at high concentrations. Here, an extensive survey is done of farnesylcysteine analogs and other lipid molecules, which are tested for their ability to inhibit GTP/GDP exchange in transducin catalyzed by photolyzed rhodopsin. These studies are carried out to determine the nature of the inhibition process. While it does not appear that these molecules exhibit the specificity which would characterize a ligand-receptor type mechanism, the results suggest that these compounds are not acting in a nonspecific detergent-like manner either. The most likely mode of action of farnesylcysteine analogs is that they interfere with the lipid-lipid based association of T alpha and T beta gamma through the lipid modifications present on each subunit.

Molecular Dynamics of HIV1-Integrase in Complex with 93del - A Structural Perspective on the Mechanism of Inhibition

HIV1 integrase is an important target for the antiviral therapy. Guanine-rich quadruplex, such as 93del, have been shown to be potent inhibitors of this enzyme and thus representing a new class of antiviral agents. Although X-ray and NMR structures of HIV1 integrase and 93del have been reported, there is no structural information of the complex and the mechanism of inhibition still remains unexplored. A number of computational methods including automated protein-DNA docking and molecular dynamics simulation in explicit solvent were used to model the binding of 93del to HIV1 integrase. Analysis of the dynamic behaviour of the complex using principal components analysis and elastic network modelling techniques allow us to understand how the binding of 93del aptamer and its interactions with key residues affect the intrinsic motions of the catalytic loops by stabilising them in catalytically inactive conformations. Such insights into the structural mechanism of inhibition can aid in improving the design of anti-HIV aptamers.

Evolutionary dynamics of the spatial Prisoner's Dilemma with self-inhibition

In this paper we study the influence of interventions on self-interactions in a spatial Prisoner's Dilemma on a two-dimensional grid with periodic boundary conditions and synchronous updating of the dynamics. We investigate two different types of self-interaction modifications. The first type (FSIP) is deterministic, effecting each self-interaction of a player by a constant factor, whereas the second type (PSIP) performs a probabilistic interventions. Both types of interventions lead to a reduction of the payoff of the players and, hence, represent inhibiting effects. We find that a constant but moderate reduction of self-interactions has a very beneficial effect on the evolution of cooperators in the population, whereas probabilistic interventions on self-interactions are in general counter productive for the coexistence of the two different strategies. (C) 2011 Elsevier Inc. All rights reserved.

Heat shock protein 90 inhibition is cytotoxic to primary AML cells expressing mutant FLT3 and results in altered downstream signalling

Activating mutations of the FMS-like tyrosine kinase 3 gene (FLT3) occur in approximately one-third of patients with acute myeloid leukaemia (AML) and predict for a poor outcome. Heat shock protein 90 (Hsp90) is a molecular chaperone that is frequently used by cancer cells to stabilise mutant oncoproteins. Mutant FLT3 is chaperoned by Hsp90 in primary AML blasts whereas unmutated FLT3 is not, making Hsp90 inhibitors potentially useful therapeutically. The present study showed that inhibition of Hsp90 by 17-allylamino-17-demethoxygeldanamycin (17-AAG) was cytotoxic to primary AML cells expressing mutant FLT3. Inhibition of Hsp90 results in altered downstream signalling effects in primary AML cells with disruption of Janus kinase-signal transducer and activator of transcription (JAK-STAT), mitogen-activated protein kinase and phosphatidylinositol 3/AKT signalling pathways. Co-treatment of blasts with 17-AAG and cytarabine resulted in a synergistic or additive effect in approximately 50% of AML cases tested. Our results confirm that Hsp90 is a valid molecular target in the therapy of AML. Inhibition of Hsp90 in parallel with conventional AML therapies may have particular benefit in those patients with the poor prognostic FLT3 mutant disease.

PTPase inhibition restores ERK1/2 phosphorylation and protects mammary epithelial cells from apoptosis

Specific survival signals derived from extracellular matrix (ECM) and growth factors are required for mammary epithelial cell survival. We have previously demonstrated that inhibition of ECM-induced ERK1/2 MAPK pathway with PD98059 leads to apoptosis in primary mouse mammary epithelial cells. In this study, we have further investigated MAPK signal transduction in cell survival of these cells cultured on a laminin rich reconstituted basement membrane. ERK1/2 phosphorylation is activated in the absence of insulin by cell-cell substratum interactions that cause ligand-independent EGFR transactivation. Intact EGFR signal transduction is required for ECM determined cell survival as the EGFR pathway inhibitor, AG1478, induces apoptosis of these cultures. Rescue of AG1478 or PD98059 treated cultures by PTPase inhibition with vanadate restores cellular phospho-ERK1/2 levels and prevents apoptosis. These results emphasize that ERK1/2 phosphorylation and inhibition of PTPase activity are necessary for PMMEC cell survival.