Search

Regulator of G protein signaling 14 (RGS14) is a multifunctional scaffolding protein that integrates G protein and mitogen-activated protein kinase (MAPK) signaling pathways. In the adult mouse brain, RGS14 mRNA and protein are found almost exclusively in hippocampal CA2 neurons. We have shown that RGS14 is a natural suppressor of CA2 synaptic plasticity and hippocampal-dependent learning and memory. However, the protein distribution and spatiotemporal expression patterns of RGS14 in mouse brain during postnatal development are unknown. Here, using a newly characterized monoclonal anti-RGS14 antibody, we demonstrate that RGS14 protein immunoreactivity is undetectable at birth (P0), with very low mRNA expression in the brain. However, RGS14 protein and mRNA are upregulated during early postnatal development, with protein first detected at P7, and both increasing over time until reaching highest sustained levels throughout adulthood. Our immunoperoxidase data demonstrate that RGS14 protein is expressed in regions outside of hippocampal CA2 during development including the primary olfactory areas, the anterior olfactory nucleus and piriform cortex, and the olfactory associated orbital and entorhinal cortices. RGS14 is also transiently expressed in neocortical layers II/III and V during postnatal development. Finally, we show that RGS14 protein is first detected in the hippocampus at P7, with strongest immunoreactivity in CA2 and fasciola cinerea and sporadic immunoreactivity in CA1; labeling intensity in hippocampus increases until adulthood. These results show that RGS14 mRNA and protein are upregulated throughout postnatal mouse development, and RGS14 protein exhibits a dynamic localization pattern that is enriched in hippocampus and primary olfactory cortex in the adult mouse brain.

The protein kinase superfamily is one of the most important families of enzymes in molecular biology. Protein kinases typically catalyze the transfer of the -phosphate from ATP to a protein substrate (a highly ubiquitous cellular reaction), thereby controlling key areas of cell regulation. Deregulation of protein kinases is known to contribute to many human diseases, and selective inhibitors of protein kinases are a major area of interest in medicinal chemistry. However, a detailed understanding of many kinase pathways is currently lacking. Before we can effectively design medicinally relevant selective kinase inhibitors, it is necessary to understand the role played by a given kinase in specific signal-transduction cascades and to decipher its protein targets. Here, we describe recent advances towards dissecting protein kinase function through the use of chemical genetics. © 2009 Future Science Ltd.

Heterologous expression of alpha(1D)-adrenergic receptors (alpha(1D)-ARs) in most cell types results in intracellular retention and little or no functionality. We showed previously that heterodimerization with alpha(1B)-ARs promotes surface localization of alpha(1D)-ARs. Here, we report that the alpha(1B)-/alpha(1D)-AR interaction has significant effects on the pharmacology and signaling of the receptors, in addition to the effects on trafficking described previously. Upon coexpression of alpha(1B)-ARs and epitope-tagged alpha(1D)-ARs in both human embryonic kidney 293 and DDT(1)MF-2 cells, alpha(1D)-AR binding sites were not detectable with the alpha(1D)-AR selective antagonist 8-[2-(4-(2-methoxyphenyl)piperazin-1-yl)ethyl]-8-azaspiro[4,5]decane-7,9-dione (BMY 7378), despite the ability to detect alpha(1D)-AR protein using confocal microscopy, immunoprecipitation, and a luminometer cell-surface assay. However, the alpha(1B)-AR-selective mutant F18A conotoxin showed a striking biphasic inhibition in alpha(1B)/alpha(1D)-AR-expressing cells, revealing that alpha(1D)-ARs were expressed but did not bind BMY 7378 with high affinity. Studies of norepinephrine-stimulated inositol phosphate formation showed that maximal responses were greatest in alpha(1B)/alpha(1D)-AR-coexpressing cells. Stable coexpression of an uncoupled mutant alpha(1B)-AR (Delta12) with alpha(1D)-ARs resulted in increased responses to norepinephrine. However, Schild plots for inhibition of norepinephrine-stimulated inositol phosphate formation showed a single low-affinity site for BMY 7378. Thus, our findings suggest that alpha(1B)/alpha(1D)-AR heterodimers form a single functional entity with enhanced functional activity relative to either subtype alone and a novel pharmacological profile. These data may help to explain why alpha(1D)-ARs are often pharmacologically undetectable in native tissues when they are coexpressed with alpha(1B)-ARs.

The Dbf2 protein kinase functions as part of the mitotic-exit network (MEN), which controls the inactivation of the Cdc28-Clb2 kinase in late mitosis [1]. The MEN includes the Tem1 GTP binding protein; the kinases Cdc15 and Cdc5; Mob1, a protein of unknown function; and the phosphatase Cdc14 [2]. Here we have used Dbf2 kinase activity to investigate the regulation and order of function of the MEN. We find that Tem1 acts at the top of the pathway, upstream of Cdc15, which in turn functions upstream of Mob1 and Dbf2. The Cdc5 Polo-like kinase impinges at least twice on the MEN since it negatively regulates the network, probably upstream of Tem1, and is also required again for Dbf2 kinase activation. Furthermore, we find that regulation of Dbf2 kinase activity and actin ring formation at the bud neck are causally linked. In metaphase-arrested cells, the MEN inhibitor Bub2 restrains both Dbf2 kinase activity [3] and actin ring formation [4]. We find that the MEN proteins that are required for Dbf2 kinase activity are also required for actin ring formation. Thus, the MEN is crucial for the regulation of cytokinesis, as well as mitotic exit.

The elucidation of signalling pathways relies heavily upon the identification of protein kinase substrates. Recent investigations have demonstrated the efficacy of chemical genetics using ATP analogues and modified protein kinases for specific substrate labelling. Here we combine N(6) -(cyclohexyl)ATPγS with an analogue-sensitive cdk2 variant to thiophosphorylate its substrates and demonstrate a pH-dependent, chemoselective, one-step alkylation to facilitate the detection or isolation of thiophosphorylated peptides.

Chemical genetic studies with enlarged ATP binding sites and unnatural ATP analogues have been applied to protein kinases for characterisation and substrate identification. Although this system is becoming widely used, there are limited data available about the kinetic profile of the modified system. Here we describe a detailed comparison of the wild-type cdk2 and the mutant gatekeeper kinase to assess the relative efficiencies of these kinases with ATP and unnatural ATP analogues. Our data demonstrate that mutation of the kinase alters neither the substrate specificity nor the phosphorylation site specificity. We find comparable KM/Vmax values for mutant cdk2 and wild-type kinase. Furthermore, F80G cdk2 is efficiently able to compensate for a defective cdk in a biological setting. © 2009 Wiley-VCH Verlag GmbH and Co. KGaA.

Flexible sequence-random polymers containing cationic and lipophilic subunits that act as functional mimics of host-defense peptides have recently been reported. We used bacteria and lipid vesicles to study one such polymer, having an average length of 21 residues, that is active against both Gram-positive and Gram-negative bacteria. At low concentrations, this polymer is able to permeabilize model anionic membranes that mimic the lipid composition of Escherichia coli, Staphylococcus aureus, or Bacillus subtilis but is ineffective against model zwitterionic membranes, which explains its low hemolytic activity. The polymer is capable of binding to negatively charged vesicles, inducing segregation of anionic lipids. The appearance of anionic lipid-rich domains results in formation of phase-boundary defects through which leakage can occur. We had earlier proposed such a mechanism of membrane disruption for another antimicrobial agent. Experiments with the mutant E. coli ML-35p indicate that permeabilization is biphasic: at low concentrations, the polymer permeabilizes the outer and inner membranes; at higher polymer concentrations, permeabilization of the outer membrane is progressively diminished, while the inner membrane remains unaffected. Experiments with wild-type E. coli K12 show that the polymer blocks passage of solutes into the intermembrane space at high concentrations. Cell membrane integrity in E. coli K12 and S. aureus exhibits biphasic dependence on polymer concentration. Isothermal titration calorimetry indicates that the polymer associates with the negatively charged lipopolysaccharide of Gram-negative bacteria and with the lipoteichoic acid of Gram-positive bacteria. We propose that this polymer has two mechanisms of antibacterial action, one predominating at low concentrations of polymer and the other predominating at high concentrations.

Efforts to generate antibacterial agents via mimicry of host-defense peptides have focused on discrete oligomers that can adopt a regular globally amphiphilic conformation in the presence of bacterial cell membranes and ultimately disrupt those membranes. Although considerable success has been achieved with this approach, application of the resulting molecules is hampered by the high cost associated with stepwise oligomer synthesis. We show that random poly-β-peptide copolymers, prepared by ring-opening polymerization of β-lactams, can be tuned to display good activity against a panel of four bacteria along with low lytic activity toward human red blood cells. These findings support a nonclassical design hypothesis for antibacterial agents.

In eukaryotes an abnormal spindle activates a conserved checkpoint consisting of the MAD and BUB genes that results in mitotic arrest at metaphase. Recently, we and others identified a novel Bub2-dependent branch to this checkpoint that blocks mitotic exit. This cell-cycle arrest depends upon inhibition of the G-protein Tem1 that appears to be regulated by Bfa1/Bub2, a two-component GTPase-activating protein, and the exchange factor Lte1. Here, we find that Bub2 and Bfa1 physically associate across the entire cell cycle and bind to Tem1 during mitosis and early G1. Bfa1 is multiply phosphorylated in a cell-cycle-dependent manner with the major phosphorylation occurring in mitosis. This Bfa1 phosphorylation is Bub2-dependent. Cdc5, but not Cdc15 or Dbf2, partly controls the phosphorylation of Bfa1 and also Lte1. Following spindle checkpoint activation, the cell cycle phosphorylation of Bfa1 and Lte1 is protracted and some species are accentuated. Thus, the Bub2-dependent pathway is active every cell cycle and the effect of spindle damage is simply to protract its normal function. Indeed, function of the Bub2 pathway is also prolonged during metaphase arrests imposed by means other than checkpoint activation. In metaphase cells Bub2 is crucial to restrain downstream events such as actin ring formation, emphasising the importance of the Bub2 pathway in the regulation of cytokinesis. Our data is consistent with Bub2/Bfa1 being a rate-limiting negative regulator of downstream events during metaphase.

The incorporation of potentially catalytic groups into DNA is of interest for the in vitro selection of novel deoxyribozymes. We have devised synthetic routes to a series of three C7 modified 7-deaza-dATP derivatives with pendant aminopropyl, Z-aminopropenyl and aminopropynyl side chains. These modified triphosphates have been tested as substrates for Taq polymerase during PCR. All the modifications are tolerated by this enzyme, with the aminopropynyl side chain giving the best result. Most protein enzymes have more than one type of catalytic group located in their active site. By using C5-imidazolyl-modified dUTPs together with 3-(aminopropynyl)-7-deaza-dATP in place of the natural nucleotides dTTP and dATP, we have demonstrated the simultaneous incorporation of both amino and imidazolyl moieties into a DNA molecule during PCR. The PCR product containing the four natural bases was fully digested by XbaI, while PCR products containing the modified 7-deaza-dATP analogues were not cleaved. Direct evidence for the simultaneous incorporation during PCR of an imidazole-modified dUTP and an amino-modified 7-deaza-dATP has been obtained using mass spectrometry.

The incorporation of potentially catalytic groups in DNA is of interest for the in vitro selection of novel deoxyribozymes. A series of 10 C5-modified analogues of 2′-deoxyuridine triphosphate have been synthesised that possess side chains of differing flexibility and bearing a primary amino or imidazole functionality. For each series of nucleotide analogues differing degrees of flexibility of the C5 side chain was achieved through the use of alkynyl, alkenyl and alkyl moieties. The imidazole function was conjugated to these C5-amino-modified nucleotides using either imidazole 4-acetic acid or imidazole 4-acrylic acid (urocanic acid). The substrate properties of the nucleotides (fully replacing dTTP) with Taq polymerase during PCR have been investigated in order to evaluate their potential applications for in vitro selection experiments. 5-(3-Aminopropynyl)dUTP and 5-(E-3-aminopropenyl)dUTP and their imidazole 4-acetic acid- and urocanic acid-modified conjugates were found to be substrates. In contrast, C5-amino-modified dUTPs with alkane or Z-alkene linkers and their corresponding conjugates were not substrates. The incorporation of these analogues during PCR has been confirmed by inhibition of restriction enzyme digestion using XbaI and by mass spectrometry of the PCR products.

Dbf2 is a multifunctional protein kinase in Saccharomyces cerevisiae that functions in transcription, the stress response and as part of a network of genes in exit from mitosis. By analogy with fission yeast it seemed likely that these mitotic exit genes would be involved in cytokinesis. As a preliminary investigation of this we have used Dbf2 tagged with GFP to examine intracellular localisation of the protein in living cells. Dbf2 is found on the centrosomes/spindle pole bodies (SPBs) and also at the bud neck where it forms a double ring. The localisation of Dbf2 is cell cycle regulated. It is on the SPBs for much of the cell cycle and migrates from there to the bud neck in late mitosis, consistent with a role in cytokinesis. Dbf2 partly co-localises with septins at the bud neck. A temperature-sensitive mutant of dbf2 also blocks progression of cytokinesis at 37 degrees C. Following cytokinesis some Dbf2 moves into the nascent bud. Localisation to the bud neck depends upon the septins and also the mitotic exit network proteins Mob1, Cdc5, Cdc14 and Cdc15. The above data are consistent with Dbf2 acting downstream in a pathway controlling cytokinesis.

DNA sequence information underpins genetic research, enabling discoveries of important biological or medical benefit. Sequencing projects have traditionally used long (400-800 base pair) reads, but the existence of reference sequences for the human and many other genomes makes it possible to develop new, fast approaches to re-sequencing, whereby shorter reads are compared to a reference to identify intraspecies genetic variation. Here we report an approach that generates several billion bases of accurate nucleotide sequence per experiment at low cost. Single molecules of DNA are attached to a flat surface, amplified in situ and used as templates for synthetic sequencing with fluorescent reversible terminator deoxyribonucleotides. Images of the surface are analysed to generate high-quality sequence. We demonstrate application of this approach to human genome sequencing on flow-sorted X chromosomes and then scale the approach to determine the genome sequence of a male Yoruba from Ibadan, Nigeria. We build an accurate consensus sequence from >30x average depth of paired 35-base reads. We characterize four million single-nucleotide polymorphisms and four hundred thousand structural variants, many of which were previously unknown. Our approach is effective for accurate, rapid and economical whole-genome re-sequencing and many other biomedical applications.