Leishmania donovani cyclin 1 (LdCyc1) forms a complex with cell cycle kinase subunit CRK3 (LdCRK3) and is possibly involved in S-phase-related activities

Expression of Leishmania donovani cyclin 1 (LdCyc1) mRNA during the cell cycle of promastigotes is S-phase specific. Here, we show that the LdCyc1 protein is periodically expressed and the activity of its associated kinase varies during the cell cycle in line with its expression pattern. In addition, we have shown that LdCRK3, homologous to CRK3 from L. mexicana, is the cognate Cdk partner of LdCyc1 and that the activity of the complex is inhibited specifically by heat stable factor(s) from the parasite.

Proteolysis of the barley receptor-like protein kinase RPG1 by a proteasome pathway is correlated with Rpg1-mediated stem rust resistance

In plants, disease resistance mediated by the gene-for-gene mechanism involves the recognition of specific effector molecules produced by the pathogen either directly or indirectly by the resistance-gene products. This recognition triggers a series of signals, thereby serving as a molecular switch in regulating defense mechanisms by the plants. To understand the mechanism of action of the barley stem rust resistance gene Rpg1, we investigated the fate of the RPG1 protein in response to infection with the stem rust fungus, Puccinia graminis f. sp. tritici. The investigations revealed that RPG1 disappears to undetectable limits only in the infected tissues in response to avirulent, but not virulent pathotypes. The RPG1 protein disappearance is rapid and appears to be due to specific protein degradation via the proteasome-mediated pathway as indicated by inhibition with the proteasomal inhibitor MG132, but not by other protease inhibitors.

A link between virulence and homeostatic responses to hypoxia during infection by the human fungal pathogen Cryptococcus neoformans

Fungal pathogens of humans require molecular oxygen for several essential biochemical reactions, yet virtually nothing is known about how they adapt to the relatively hypoxic environment of infected tissues. We isolated mutants defective in growth under hypoxic conditions, but normal for growth in normoxic conditions, in Cryptococcus neoformans, the most common cause of fungal meningitis. Two regulatory pathways were identified: one homologous to the mammalian sterol-response element binding protein (SREBP) cholesterol biosynthesis regulatory pathway, and the other a two-component-like pathway involving a fungal-specific hybrid histidine kinase family member, Tco1. We show that cleavage of the SREBP precursor homolog Sre1—which is predicted to release its DNA-binding domain from the membrane—occurs in response to hypoxia, and that Sre1 is required for hypoxic induction of genes encoding for oxygen-dependent enzymes involved in ergosterol synthesis. Importantly, mutants in either the SREBP pathway or the Tco1 pathway display defects in their ability to proliferate in host tissues and to cause disease in infected mice, linking for the first time to our knowledge hypoxic adaptation and pathogenesis by a eukaryotic aerobe. SREBP pathway mutants were found to be a hundred times more sensitive than wild-type to fluconazole, a widely used antifungal agent that inhibits ergosterol synthesis, suggesting that inhibitors of SREBP processing could substantially enhance the potency of current therapies.

Opportunistic environmental pathogens adapt to hostile conditions within the host to cause disease. We describe two pathways in the pathogenic fungus Cryptococcus neoformans that are both necessary for adaptation to hypoxia and required for its virulence. One pathway uses a pathway homologous to the mammalian sterol-response element binding protein (SREBP) pathway to activate genes involved in sterol biosynthesis in response to low oxygen levels, while the other pathway involves the two-component hybrid histidine kinase protein Tco1. Mutant strains containing deletions of genes encoding components in either of these pathways were found to be less virulent in experimental mouse models. This study suggests that this pathogenic fungus experiences low levels of oxygen in the mammalian host, and that adaptation to these conditions is important for infection. Targeting components of the hypoxia response could yield more effective treatments for C. neoformans infections, which cause a large fraction of HIV/AIDS-related deaths worldwide. Notably, we find that mutants in the SREBP-like pathway are a hundred times more sensitive than wild-type cells to the widely used antifungal drug fluconazole.

Correction of prototypic ATM splicing mutations and aberrant ATM function with antisense morpholino oligonucleotides

We used antisense morpholino oligonucleotides (AMOs) to redirect and restore normal splicing of three prototypic splicing mutations in the ataxia-telangiectasia mutated (ATM) gene. Two of the mutations activated cryptic 5' or 3' splice sites within exonic regions; the third mutation activated a downstream 5' splice site leading to pseudoexon inclusion of a portion of intron 28. AMOs were targeted to aberrant splice sites created by the mutations; this effectively restored normal ATM splicing at the mRNA level and led to the translation of full-length, functional ATM protein for at least 84 h in the three cell lines examined, as demonstrated by immunoblotting, ionizing irradiation-induced autophosphorylation of ATM, and transactivation of ATM substrates. Ionizing irradiation-induced cytotoxicity was markedly abrogated after AMO exposure. The ex vivo data strongly suggest that the disease-causing molecular pathogenesis of such prototypic mutations is not the amino acid change of the protein but the mutated DNA code itself, which alters splicing. Such prototypic splicing mutations may be correctable in vivo by systemic administration of AMOs and may provide an approach to customized, mutation-based treatment for ataxia-telangiectasia and other genetic disorders.

Proteomics Analysis of Protein Kinases by Target Class-selective Prefractionation and Tandem Mass Spectrometry

Protein kinases constitute a large superfamily of enzymes with key regulatory functions in nearly all signal transmission processes of eukaryotic cells. However, due to their relatively low abundance compared with the vast majority of cellular proteins, currently available proteomics techniques do not permit the comprehensive biochemical characterization of protein kinases. To address these limitations, we have developed a prefractionation strategy that uses a combination of immobilized low molecular weight inhibitors for the selective affinity capture of protein kinases. This approach resulted in the direct purification of cell type-specific sets of expressed protein kinases, and more than 140 different members of this enzyme family could be detected by LC-MS/MS. Furthermore the enrichment technique combined with phosphopeptide fractionation led to the identification of more than 200 different phosphorylation sites on protein kinases, which often remain occluded in global phosphoproteome analysis. As the phosphorylation states of protein kinases can provide a readout for the signaling activities within a cellular system, kinase-selective phosphoproteomics based on the procedures described here has the potential to become an important tool in signal transduction analysis.

Real-time protein kinase assay

We report a novel, real-time fluorogenic kinase assay. The peptide substrates are synthesized with a fluorescent dye and a hydrocarbon tail. The substrate self-assembles into micelles, increasing the local concentration of the dye and quenching its fluorescence. Upon phosphorylation, the fluorescence intensity increases 4-6-fold due to micelle reorganization. Both dynamic light scattering data and cryoelectron microscope images show that the size and the shape of the phosphopeptide micelles are significantly different from micelles of substrate peptide. The system provides a robust fluorescence increase in a real-time protein kinase assay. Unlike other fluorogenic systems, the fluorophore may be distant from the serine, threonine, or tyrosine that is phosphorylated. Assays for several kinases, including PKA, PKC, p38, MAPKAP K2, akt, Erk1, and src-family kinases, have been developed. IC(50) values of inhibitors for PKC betaII determined with this technology are consistent with published values. The utility of this assay to high-throughput screening was demonstrated with Sigma's LOPAC library, a collection of 640 compounds with known biological activities, and satisfactory results were obtained.

A simple strategy for mitigating the effect of data variability on the identification of active chemotypes from high-throughput screening data

Among the several goals of a high-throughput screening campaign is the identification of as many active chemotypes as possible for further evaluation. Often, however, the number of concentration response curves (e.g., IC(50)s or K(i)s) that can be collected following a primary screen is limited by practical constraints such as protein supply, screening workload, and so forth. One possible approach to this dilemma is to cluster the hits from the primary screen and sample only a few compounds from each cluster. This introduces the question as to how many compounds must be selected from a cluster to ensure that an active compound is identified, if it exists at all. This article seeks to address this question using a Monte Carlo simulation in which the dependence of the success of sampling is directly linked to screening data variability. Furthermore, the authors demonstrate that the use of replicated compounds in the screening collection can easily assess this variability and provide a priori guidance to the screener and chemist as to the extent of sampling required to maximize chemotype identification during the triage process. The individual steps of the Monte Carlo simulation provide insight into the correspondence between the percentage inhibition and eventual IC(50) curves.

Analyzing protein kinase dynamics in living cells with FRET reporters

Genetically encoded reporters based on fluorescence resonance energy transfer (FRET) are being developed for analyzing spatiotemporal dynamics of kinase activities in living cells, as the activities of this class of enzymes are often dynamically regulated and spatially compartmentalized within specific signaling context. Here we describe a general modular design and engineering strategies for the development of activity reporters for kinases of interest, using A-kinase activity reporter (AKAR) as an illustrative example. Discussed here are basic structure of such reporters, design considerations, reporter gene construction, cellular and in vitro characterization. Strategies for improving specificity, dynamic range or sensitivity, reversibility and integrity of the reporter as well as basic methods for live-cell time-lapse imaging using these reporters are summarized. Discussion of using this approach in the study of MAPK cascades is also provided. These FRET-based kinase activity reporters, along with analogous probes based on alternative designs, provide real-time tracking of kinase dynamics with subcellular resolution, which should complement other methods and offer great opportunities to delineate the molecular mechanisms underlying the complex regulation of kinases.

Mass-tag technology responding to intracellular signals as a novel assay system for the diagnosis of tumor

A novel mass spectrometry-based assay system for determining protein kinase activity employing mass-tagged substrate peptide probes was used for the diagnosis of tumors. Two peptide probes (H-type and D-type) were synthesized containing the same substrate peptide sequence for protein kinase C (PKC). The molecular weights of the two probes differ because of the incorporation of deuterium into the acetyl groups of the D-type probe. The lysates of the normal and tumor tissue were prepared and reacted with the H- and D-type peptide probes, respectively. The PKC activities of the normal and tumor tissues can be compared simply and directly by calculating the phosphorylated ratio to each peptide probe, obtained from the peak intensity of the mass spectrum after mixing of the two reaction solutions. The phosphorylation ratio for the reaction of the H-type peptide probe with the tumor tissue lysate (B16 melanoma) was more than three times higher than that of the D type peptide probe with the normal skin tissue lysate. These results show that the novel assay system for detecting protein kinase activity using mass-tag technology can be a simple and useful means to profile protein kinase activity for cell or tissue lysate samples, and can be applied to the diagnosis of tumors.

Morphoproteomic confirmation of constitutively activated mTOR, ERK, and NF-kappaB pathways in high risk neuro-blastoma, with cell cycle and protein analyte correlates

Morphoproteomic analysis reveals the constitutive activation of the mTOR, ERK, and NF-kappaB pathways in high risk neuroblastoma (HRN) cases as evidenced by (a) collective commonalities of: phosphorylated (p)-mTOR, p70S6K, ERK 1/2, and NF-kappaBp65 protein analytes using phosphospecific probes directed against sites of activation; (b) nuclear translocation of p-p70S6K, p-ERK 1/2, and p-NF-kappaBp65; and (c) correlative expression of the S phase-associated kinase Skp-2 (at a relatively high percentage in tumoral nuclei) and of the anti-apoptotic protein bcl-2. Based on a review of the literature, these preliminary observations appear to be the first morphoproteomic study on primary neuroblastomas.

Activation of the mTOR Signaling Pathway in Renal Clear Cell Carcinoma

PURPOSE

We determined the frequency of mTOR/p70S6 kinase signaling pathway activation in clear cell renal cell carcinoma.

MATERIALS AND METHODS

Phospho-S6 (Ser235/236) and phospho-mTOR (Ser2448) staining was performed on renal tumor tissue microarrays containing 29 clear cell renal cell carcinomas. Mutational analysis of Rheb and RhebL1 was performed on DNA from phospho-mTOR/phospho-S6 positive clear cell renal cell carcinoma. The 3 clear cell renal cell carcinoma derived cell lines A498, 786-O and Caki1 were also assessed for mTOR activation and the effect of the mTOR inhibitor rapamycin (Biomol) on proliferation.

RESULTS

Moderate or strong phospho-S6 immunoreactivity was found in 17 of 29 clear cell carcinomas (59%), of which 14 were also moderately/strongly positive for phospho-mTOR (Ser2448). We hypothesized that this activation of the mTOR signaling pathway in clear cell renal cell carcinoma could reflect mutational activation of Rheb or RhebL1, which are Ras family members that directly activate mTOR. However, no mutations in exons 3 and 4 (homologous sites of Ras activating mutations) in Rheb or RhebL1 were identified. Two of 3 renal clear cell carcinoma derived cell lines also showed inappropriate S6 hyperphosphorylation. Treatment of all 3 cell lines with rapamycin significantly decreased S6 phosphorylation and proliferation.

CONCLUSIONS

The mTOR/p70S6 kinase signaling pathway is activated in most clear cell renal cell carcinomas. Moreover, the growth of renal clear cell carcinoma derived cell lines is inhibited by rapamycin. This is especially significant in light of new agents such as CCI-779, an ester of rapamycin and inhibitor of mTOR, which has shown promise in the treatment of renal carcinoma.

The SERK1 gene is expressed in procambium and immature vascular cells

The SOMATIC EMBRYOGENESIS RECEPTOR KINASE 1 (SERK1) gene is expressed in the procambium of the vascular bundles in roots, hypocotyls, and inflorescence stems. In younger parts of roots and hypocotyls, SERK1 expression was less restricted and was also observed in protoxylem cells, immature metaxylem cells and phloem companion cells. In roots, SERK1 expression was first detected in root vascular stem cells and was notably absent from the QC. In general, the SERK1 protein level as visualized by expression of a SERK1-YFP fusion protein closely followed the pattern of gene expression. In hypocotyls, prolonged application of 2,4-D resulted in extensive unorganized proliferation of SERK1 expressing cells originating from the procambium and pericycle. In roots, 2,4-D treatment results in an increase in SERK1 transcription that results in a moderate increase in the amount of SERK1-YFP fusion protein. The restricted vascular pattern of SERK1 expression in roots remains unaffected after 2,4-D treatment.

Angiotensin II-mediated protein kinase D activation stimulates aldosterone and cortisol secretion in H295R human adrenocortical cells

Protein kinases are important mediators in intracellular signaling. Angiotensin II is the most important modulator of adrenal zona glomerulosa cell physiology. Angiotensin II regulates steroidogenesis and proliferation among many other metabolic processes. H295R human adrenal cells are a widely used experimental model to study adrenal cell physiology and metabolism. We screened for protein kinase expression levels using the Kinetwork system in H295R cells after 3 h angiotensin II treatment. Protein kinase D (PKD) was the protein kinase that suffers the most dramatic changes. PKD is a member of a new class of serine/threonine protein kinases that is activated by phosphorylation. Our studies indicated that angiotensin II time- and dose-dependently increased PKD phosphorylation, which occurred within 2 min of angiotensin II treatment and at concentrations as low as 1 nm. PKD phosphorylation was also dose-dependently increased by the PKC activator phorbol 12-myristate 13-acetate. Angiotensin II-mediated PKD phosphorylation was blocked by several PKC inhibitors. Furthermore, PKCepsilon translocation inhibitor peptide decreased angiotensin II-mediated PKD phosphorylation, and PKCepsilon down-regulation by RNA interference also decreased PKD phosphorylation mediated by angiotensin II. Cotransfection of constitutively active PKD mutant constructs up-regulated aldosterone synthase and 11beta-hydroxylase expression in reporter assays. Constitutively active PKD mutants increased aldosterone and cortisol secretion under angiotensin II stimulatory conditions. This study reveals that PKD is an intracellular signaling mediator of angiotensin II regulation of steroidogenesis in human adrenal cells. These data provide new insights into the molecular mechanisms involved in angiotensin II-induced physiological and pathophysiological events in adrenal cells.

Expression and localization of calcium-dependent protein kinase isoforms in chickpea

Calcium-dependent protein kinases (CPKs) play important roles in multiple signal transduction pathways but the precise role of individual CPK is largely unknown. We isolated two cDNAs encoding two CPK isoforms (Cicer arietinum CPKs-CaCPK1 and CaCPK2) of chickpea. Their expression in various organs and in response to various phytohormones, and dehydration, high salt stress and fungal spore in excised leaves as well as localization in leaf and stem tissues were analyzed in this study. CaCPK1 protein and its activity were ubiquitous in all tissues examined. In contrast, CaCPK2 transcript, CaCPK2 protein and its activity were almost undetectable in flowers and fruits. Both CaCPK1 and CaCPK2 transcripts and proteins were abundant in roots but in minor quantities in leaves and stems. Of the three phytohormones tested, viz. indole-3-acetic acid (IAA), gibberellin (GA(3)) and benzyladenine (BA), only BA increased both CaCPK1 and CaCPK2 transcripts, proteins and their activities. GA(3) induced accumulation of CaCPK2 transcript and protein but CaCPK1 remained unaffected. The expression of CaCPK1 and CaCPK2 in leaves was enhanced in response to high salt stress. Treatments with Aspergillus sp. spores increased expression of CaCPK1 in chickpea leaf tissue but had no effect on CaCPK2. Excised leaves subjected to dehydration showed increase in CaCPK2 expression but not in CaCPK1. Both isoforms were located in the plasma membrane (PM) and chloroplast membrane of leaf mesophyll cells as well as in the PM of stem xylem parenchyma cells. These results suggest specific roles for CaCPK isoforms in phytohormone/defense/stress signaling pathways.

Biochemical activities of three pairs of Ehrlichia chaffeensis two-component regulatory system proteins involved in inhibition of lysosomal fusion

Ehrlichia chaffeensis, the etiologic agent of human monocytic ehrlichiosis, replicates in early endosomes by avoiding lysosomal fusion in monocytes and macrophages. In E. chaffeensis we predicted three pairs of putative two-component regulatory systems (TCSs) designated PleC-PleD, NtrY-NtrX, and CckA-CtrA based on amino acid sequence homology. In the present study to determine biochemical pairs and specificities of the TCSs, the recombinant proteins of the three putative histidine kinase (HK) kinase domains (rPleCHKD, rNtrYHKD, and MBP-rCckAHKD) and the full-length forms of three putative response regulators (RRs) (rPleD, rNtrX, and rCtrA) as well as the respective mutant recombinant proteins (rPleCHKDH244A, rNtrYHKDH498A, MBP-rCckAHKDH449A, rPleDD53A, rNtrXD59A, and rCtrAD53A) were expressed and purified as soluble proteins. The in vitro HK activity, the specific His residue-dependent autophosphorylation of the kinase domain, was demonstrated in the three HKs. The specific Asp residue-dependent in vitro phosphotransfer from the kinase domain to the putative cognate RR was demonstrated in each of the three RRs. Western blot analysis of E. chaffeensis membrane and soluble fractions using antibodies specific for each recombinant protein detected PleC and CckA in the membrane fraction, whereas it detected NtrY, NtrX, and PleD in the soluble fraction. CtrA was found in the two fractions at similar levels. E. chaffeensis was sensitive to closantel, an HK inhibitor. Closantel treatment induced lysosomal fusion of the E. chaffeensis inclusion in a human monocytic leukemia cell line, THP-1 cells, implying that functional TCSs are essential in preventing lysosomal fusion of the E. chaffeensis inclusion compartment.

Nebulin isoforms of extraocular muscle

The extraocular muscles (EOMs), which are responsible for reflexive and voluntary eye movements, have many unique biochemical, physiological, and ultrastructural features that set them apart from other skeletal muscles. For example, rodent EOMs lack M-lines and express EOM-specific myosin heavy chain (MYH13) and alpha-cardiac myosin heavy chain. Recent gene-expression profiling studies indicate the presence of other cardiac-specific proteins in adult EOMs. This interesting mixture of myofibrillar and cytoskeletal proteins poses the questions as to whether nebulette, as opposed to nebulin, might be expressed in EOM, and what isoforms of titin are expressed in the EOM. We have performed gel electrophoresis and immunological analyses to determine the titin and nebulin isoforms expressed in the EOM. We have found that the mass of the titin isoforms expressed in the EOM most closely resemble those found in the skeletal muscles tested, viz., the soleus and extensor digitorum longus (EDL). We also demonstrate that, although the EOM expresses cardiac isoforms of myosin, it does not express nebulette and contains a nebulin isoform with a mass consistent with that found in the prototypical fast hindlimb muscle EDL.

mTORC2 Caught in a SINful Akt

The target of rapamycin (TOR), a central controller of cell growth, is found in two distinct, highly conserved multiprotein complexes. Three recent papers in Cell (Jacinto et al., 2006), Developmental Cell (shiota et al., 2006; this issue), and Current Biology (Frias et al., 2006) shed light on mTOR complex 2 (mTORC2) composition and in vivo function. An important new finding is that mTORC2 determines Akt/PKB substrate specificity rather than absolute activity.

IN-1130, a novel transforming growth factor-β type I receptor kinase (ALK5) inhibitor, suppresses renal fibrosis in obstructive nephropathy

The transforming growth factor-beta (TGF-beta) plays a central role in the progression of renal fibrosis. TGF-beta transduces its signal through the activin receptor-like kinase (ALK)5. IN-1130, a novel small molecule ALK5 inhibitor, inhibited the purified kinase domain of ALK5-mediated Smad3 phosphorylation with an IC(50) value of 5.3 nM. IN-1130 proved to be highly selective in a panel of 27 serine/threonine and tyrosine kinases including p38alpha mitogen-activated protein kinase. We evaluated the efficacy of IN-1130 to block renal fibrogenesis induced by unilateral ureteral obstruction (UUO) in rats. Either vehicle (saline) or IN-1130 (10 and 20 mg/kg/day) was intraperitoneally administered to UUO rats for 7 and 14 days. Phosphorylated Smad2 (pSmad2) and markers of fibrosis were analyzed in kidney tissues. In UUO control kidneys, interstitial fibrosis including tubular atrophy, loss and dilation, inflammatory cell infiltration, and fibroblast cell proliferation was prominent. These morphological changes were notably reduced by IN-1130 treatment. IN-1130 decreased levels of TGF-beta1 messenger RNA (mRNA), type I collagen mRNA, and pSmad2, compared to UUO control rats. As determined by measuring the hydroxyproline content, total kidney collagen amount was increased in UUO control kidneys, but significantly reduced by IN-1130 treatment, which was comparable to results of histochemical staining for collagen. IN-1130 also suppressed the expression of alpha-smooth muscle actin (alpha-SMA) and fibronectin in UUO kidneys. Our results show that IN-1130 suppressed the fibrogenic process of UUO, further underscoring the potential clinical benefits of IN-1130 in the treatment of renal fibrosis.

IQGAP and mitotic exit network (MEN) proteins are required for cytokinesis and re-polarization of the actin cytoskeleton in the budding yeast, Saccharomyces cerevisiae

In budding yeast the final stages of the cell division cycle, cytokinesis and cell separation, are distinct events that require to be coupled, both together and with mitotic exit. Here we demonstrate that mutations in genes of the mitotic exit network (MEN) prevent cell separation and are synthetically lethal in combination with both cytokinesis and septation defective mutations. Analysis of the synthetic lethal phenotypes reveals that Iqg1p functions in combination with the MEN components, Tem1p, Cdc15p Dbf20p and Dbf2p to govern the re-polarization of the actin cytoskeleton to either side of the bud neck. In addition phosphorylation of the conserved PCH protein, Hof1p, is dependent upon these activities and requires actin ring assembly. Recruitment of Dbf2p to the bud neck is dependent upon actin ring assembly and correlates with Hof1p phosphorylation. Failure to phosphorylate Hof1p results in the increased stability of the protein and its persistence at the bud neck. These data establish a mechanistic dependency of cell separation upon an intermediate step requiring actomyosin ring assembly.

Open microscopy environment and findspots: integrating image informatics with quantitative multidimensional image analysis

Biomedical research and drug development increasingly involve the extraction of quantitative data from digital microscope images, such as those obtained using fluorescence microscopy. Here, we describe a novel approach for both managing and analyzing such images. The Open Microscopy Environment (OME) is a sophisticated open-source scientific image management database that coordinates the organization, storage, and analysis of the large volumes of image data typically generated by modern imaging methods. We describe FindSpots, a powerful image-analysis package integrated in OME that will be of use to those who wish to identify and measure objects within microscope images or time-lapse movies. The algorithm used in FindSpots is in fact only one of many possible segmentation (object detection) algorithms, and the underlying data model used by OME to capture and store its results can also be used to store results from other segmentation algorithms. In this report, we illustrate how image segmentation can be achieved in OME using one such implementation of a segmentation algorithm, and how this output subsequently can be displayed graphically or processed numerically using a spreadsheet.

Multiallelic disruption of the rictor gene in mice reveals that mTOR complex 2 is essential for fetal growth and viability

The rapamycin-insensitive mTOR complex 2 (mTORC2) has been suggested to play an important role in growth factor-dependent signaling. To explore this possibility further in a mammalian model system, we disrupted the expression of rictor, a specific component of mTORC2, in mice by using a multiallelic gene targeting strategy. Embryos that lack rictor develop normally until E9.5, and then exhibit growth arrest and die by E11.5. Although placental defects occur in null embryos, an epiblast-specific knockout of rictor only delayed lethality by a few days, thereby suggesting other important roles for this complex in the embryo proper. Analyses of rictor null embryos and fibroblasts indicate that mTORC2 is a primary kinase for Ser473 of Akt/PKB. Rictor null fibroblasts exhibit low proliferation rates, impaired Akt/PKB activity, and diminished metabolic activity. Taken together, these findings indicate that both rictor and mTORC2 are essential for the development of both embryonic and extraembryonic tissues.

Immunohistochemical studies of protein kinase D (PKD) 2 expression in malignant human lymphomas

AIM

To study the PKD2 expression, autophosphorylation and localization in reactive lymph nodes and tumors of lymphoid tissues.

MATERIALS AND METHODS

Specific antibodies, which recognize PKD1/2 or PKD2 and autophosphorylated PKD1/2, were used for immunohistochemical and biochemical studies of tonsils, reactive lymph nodes, tumor samples of non-Hodgkin's lymphoma (NHL) and Hodgkin's lymphoma (HL).

RESULTS

Immunohistochemical and biochemical analysis of PKD1 and PKD2 expression showed PKD2 expression in tonsils, reactive lymph nodes and tumor tissues from patients with NHL and HL. Furthermore, we were not able to reveal PKD1 expression in studied lymphoid tissues. In tonsils and reactive lymph nodes the PKD2 expression was detected in T and B cell zones with highest level in germinal centers of lymphoid follicles and the maximum level of autophosphorylation in the light zones of the germinal centers. We found that low level of PKD2 expression and autophosphorylation was characteristic feature for mantle cell lymphomas, Burkitt's lymphomas, and in 50% of CLL/small lymphocytic lymphomas. Lymphoma cells of germinal center origin and with activated B cell phenotype (diffuse large B cell lymphomas, HL) and anaplastic large cells lymphoma demonstrated the high level of PKD2 expression and autophosphorylation.

CONCLUSIONS

The level of PKD2 expression and autophosphorylation in neoplastic cells corresponds to the expression pattern of this kinase in their normal analogs, and to the level of cell differentiation and activation.

Time-resolved fluorescence resonance energy transfer kinase assays using physiological protein substrates: Applications of terbium–fluorescein and terbium–green fluorescent protein fluorescence resonance energy transfer pairs

Fluorescence-based kinase assays using peptide substrates are an established format for high-throughput screening and profiling of kinases. Among fluorescence-based formats, time-resolved fluorescence resonance energy transfer (TR-FRET) using a lanthanide donor species has advantages over other fluorescent formats in being resistant to many types of optical interference such as autofluorescent compounds, scattered light from precipitated compounds, or colored compounds that absorb excitation or emission radiation ("color quenchers"). By taking advantage of the fact that acceptors such as fluorescein or green fluorescent protein (GFP) can be paired with a terbium donor in a TR-FRET assay, we have developed TR-FRET kinase assays that use physiologically relevant native protein substrates, either labeled with fluorescein or expressed as GFP fusions. Phosphorylation of the labeled protein substrate results in an increase in TR-FRET when incubated with a terbium-labeled antibody that specifically recognizes the phosphorylated product. Thus, a strategy of using terbium-based TR-FRET can be applied to develop kinase assays, and the unique properties of terbium lead to a high degree of flexibility with regard to specific assay design.

Plasmodium berghei calcium-dependent protein kinase 3 is required for ookinete gliding motility and mosquito midgut invasion

Apicomplexan parasites critically depend on a unique form of gliding motility to colonize their hosts and to invade cells. Gliding requires different stage and species-specific transmembrane adhesins, which interact with an intracellular motor complex shared across parasite stages and species. How gliding is regulated by extracellular factors and intracellular signalling mechanisms is largely unknown, but current evidence suggests an important role for cytosolic calcium as a second messenger. Studying a Plasmodium berghei gene deletion mutant, we here provide evidence that a calcium-dependent protein kinase, CDPK3, has an important function in regulating motility of the ookinete in the mosquito midgut. We show that a cdpk3^– parasite clone produces morphologically normal ookinetes, which fail to engage the midgut epithelium, due to a marked reduction in their ability to glide productively, resulting in marked reduction in malaria transmission to the mosquito. The mutant was successfully complemented with an episomally maintained cdpk3 gene, restoring mosquito transmission to wild-type level. cdpk3^– ookinetes maintain their full genetic differentiation potential when microinjected into the mosquito haemocoel and cdpk3^– sporozoites produced in this way are motile and infectious, suggesting an ookinete-limited essential function for CDPK3.

AI-1 Influences the Kinase Activity but Not the Phosphatase Activity of LuxN of Vibrio harveyi

The Gram-negative bacterium Vibrio harveyi produces and responds to three autoinducers, AI-1, AI-2, and CAI-1 to regulate cell density dependent gene expression by a process referred to as quorum sensing. The concentration of the autoinducers is sensed by three cognate hybrid sensor kinases, and information is channeled via the HPt protein LuxU to the response regulator LuxO. Here, a detailed biochemical study on the enzymatic activities of the membrane-integrated hybrid sensor kinase LuxN, the sensor for N-(d-3-hydroxybutanoyl)homoserine lactone (AI-1), is provided. LuxN was heterologously overproduced as the full-length protein in Escherichia coli. LuxN activities were characterized in vitro and are an autophosphorylation activity with an unusually high ATP turnover rate, stable LuxU phosphorylation, and a slow phosphatase activity with LuxU approximately P as substrate. The presence of AI-1 affected the kinase but not the phosphatase activity of LuxN. The influence of AI-1 on the LuxN--> LuxU signaling step was monitored, and in the presence of AI-1, the kinase activity of LuxN, and hence the amount of LuxU approximately P produced, were significantly reduced. Half-maximal inhibition of kinase activity by AI-1 occurred at 20 mum. Together, these results indicate that AI-1 directly interacts with LuxN to down-regulate its autokinase activity and suggest that the key regulatory step of the AI-1 quorum sensing system of Vibrio harveyi is AI-1-mediated repression of the LuxN kinase activity.

Expression of mTOR signaling pathway markers in prostate cancer progression

BACKGROUND

The PI3K/AKT/mTOR pathway is central to prostate cancer progression. A preliminary investigation of immuno-histochemical expression of mammalian target of rapamycin (mTOR) pathway markers was undertaken to identify patterns of expression in prostate tissue.

METHODS

Immunohistochemistry was performed on a custom-made prostate tissue array. Mean long scores and variability of long scores for each marker were recorded for normal lumenal cells, prostate intraepithelial neoplasia (PIN), and cancer.

RESULTS

Expression of PTEN decreased and mTOR signaling pathway markers increased in PIN and in cancer as compared to normal cells in the majority of samples. Overexpression of 4E-BP1 and p-4E-BP1 was observed in PIN and cancer. However, in cancer, the overexpression of 4E-BP1 was significantly higher than with any other marker.

DISCUSSION

Results suggest that 4E-BP1 overexpression is strongly associated with prostate cancer, especially when combined with PTEN and mTOR expression data. Hierarchical clustering analysis utilizing PTEN, mTOR, and 4E-BP1 separated normal from cancer cell populations in most cases.

Assay of the pyruvate dehydrogenase complex by coupling with recombinant chicken liver arylamine N-acetyltransferase

The activity of the pyruvate dehydrogenase complex has long been determined in some laboratories by coupling the production of acetyl-coenzyme A (acetyl-CoA) to the acetylation of 4-aminoazobenzene-4'-sulfonic acid by arylamine N-acetyltransferase. The assay has some advantages, but its use has been limited by the need for large amounts of arylamine N-acetyltransferase. Here we report production of recombinant chicken liver arylamine N-acetyltransferase and optimization of its use in miniaturized assays for the pyruvate dehydrogenase complex and its kinase.

New targets for pharmacological intervention in the glutamatergic synapse

Excitotoxicity is thought to be a major mechanism in many human disease states such as ischemia, trauma, epilepsy and chronic neurodegenerative disorders. Briefly, synaptic overactivity leads to the excessive release of glutamate that activates postsynaptic cell membrane receptors, which upon activation open their associated ion channel pore to produce ion influx. To date, although molecular basis of glutamate toxicity remain uncertain, there is general agreement that N-methyl-d-aspartate (NMDA) subtype of ionotropic glutamate receptors plays a key role in mediating at least some aspects of glutamate neurotoxicity. On this view, research has focused in the discovery of new compounds able to either reduce glutamate release or activation of postsynaptic NMDA receptors. Although NMDA receptor antagonists prevent excitotoxicity in cellular and animal models, these drugs have limited usefulness clinically. Side effects such as psychosis, nausea, vomiting, memory impairment, and neuronal cell death accompany complete NMDA receptor blockade, dramatizing the crucial role of the NMDA receptor in normal neuronal processes. Recently, however, well-tolerated compounds such as memantine has been shown to be able to block excitotoxic cell death in a clinically tolerated manner. Understanding the biochemical properties of the multitude of NMDA receptor subtypes offers the possibility of developing more effective and clinically useful drugs. The increasing knowledge of the structure and function of this postsynaptic NMDA complex may improve the identification of specific molecular targets whose pharmacological or genetic manipulation might lead to innovative therapies for brain disorders.

Readout Technologies for Highly Miniaturized Kinase Assays Applicable to High-Throughput Screening in a 1536-Well Format

This article discusses the development of homogeneous, miniaturized assays for the identification of novel kinase inhibitors from very large compound collections. In particular, the suitability of time-resolved fluorescence resonance energy transfer (TR-RET) based on phospho-specific antibodies, an antibody-independent fluorescence polarization (FP) approach using metal-coated beads (IMAP™ technology), and the determination of adenosine triphosphate consumption through chemiluminescence is evaluated. These readouts are compared with regard to assay sensitivity, compound interference, reagent consumption, and performance in a 1536-well format, and practical considerations for their application in primary screening or in the identification of kinase substrates are discussed. All of the tested technologies were found to be suitable for miniaturized high-throughput screening (HTS) in principle, but each of them has distinct limitations and advantages. Therefore, the target-specific selection of the most appropriate readout technology is recommended to ensure maximal relevance of HTS campaigns.

Drosophila Anterior-Posterior Polarity Requires Actin-Dependent PAR-1 Recruitment to the Oocyte Posterior

The Drosophila anterior-posterior axis is established at stage 7 of oogenesis when the posterior follicle cells signal to polarize the oocyte microtubule cytoskeleton. This requires the conserved PAR-1 kinase, which can be detected at the posterior of the oocyte in immunostainings from stage 9. However, this localization depends on Oskar localization, which requires the earlier PAR-1-dependent microtubule reorganization, indicating that Oskar-associated PAR-1 cannot establish oocyte polarity. Here we analyze the function of the different PAR-1 isoforms and find that only PAR-1 N1 isoforms can completely rescue the oocyte polarity phenotype. Furthermore, PAR-1 N1 is recruited to the posterior cortex of the oocyte at stage 7 in response to the polarizing follicle cell signal, and this requires actin, but not microtubules. This suggests that posterior PAR-1 N1 polarizes the microtubule cytoskeleton. PAR-1 N1 localization is mediated by a cortical targeting domain and a conserved anterior-lateral exclusion signal in its C-terminal linker domain. PAR-1 is also required for the polarization of the C. elegans zygote and is recruited to the posterior cortex in an actin-dependent manner. Our results therefore identify a molecular parallel between axis formation in Drosophila and C. elegans and make Drosophila PAR-1 N1 the earliest known marker for the polarization of the oocyte.

Coordinated requirements of human topo II and cohesin for metaphase centromere alignment under Mad2-dependent spindle checkpoint surveillance

Cohesin maintains sister chromatid cohesion until its Rad21/Scc1/Mcd1 is cleaved by separase during anaphase. DNA topoisomerase II (topo II) maintains the proper topology of chromatid DNAs and is essential for chromosome segregation. Here we report direct observations of mitotic progression in individual HeLa cells after functional disruptions of hRad21, NIPBL, a loading factor for hRad21, and topo II alpha,beta by RNAi and a topo II inhibitor, ICRF-193. Mitosis is delayed in a Mad2-dependent manner after disruption of either or both cohesin and topo II. In hRad21 depletion, interphase pericentric architecture becomes aberrant, and anaphase is virtually permanently delayed as preseparated chromosomes are misaligned on the metaphase spindle. Topo II disruption perturbs centromere organization leading to intense Bub1, but no Mad2, on kinetochores and sustains a Mad2-dependent delay in anaphase onset with persisting securin. Thus topo II impinges upon centromere/kinetochore function. Disruption of topo II by RNAi or ICRF-193 overrides the mitotic delay induced by cohesin depletion: sister centromeres are aligned and anaphase spindle movements occur. The ensuing accumulation of catenations in preseparated sister chromatids may overcome the reduced tension arising from cohesin depletion, causing the override. Cohesin and topo II have distinct, yet coordinated functions in metaphase alignment.

A generic, homogenous method for measuring kinase and inhibitor activity via adenosine 5'-diphosphate accumulation

The authors describe an assay to measure the generation of adenosine 5'-diphosphate (ADP) resulting from phosphorylation of a substrate by a kinase. ADP accumulation is detected by conversion to a fluorescent signal via a coupled enzyme system. The technology has potential applications for the assessment of inhibitor potency and mode of action as well as kinetic analysis of enzyme activity. The assay has a wide dynamic range (0.25-75 microM) and has been validated with several kinases including the highly active cyclic adenosine monophosphate-dependent protein kinase (PKAalpha), casein kinase 1 (CK1), and the weakly active kinase Jun N-terminal kinase 2 (Jnk2alpha2). Kinase activity can be measured either in an end point or continuous mode. Assay performance in end point mode was compared with an adenosine 5'-triphosphate (ATP) depletion assay and in continuous mode with a pyruvate kinase/lactate dehydrogenase coupled assay. The ability to characterize kinase kinetics was demonstrated by deriving ATP/substrate affinity (Michaelis-Menten constant; K(m)) values for PKAalpha, CK1, and Jnk2alpha2. The assay readily measured activity with kinase reactions using protein substrates, indicating the suitability for use with large macromolecules. A wide range of inhibitor activities could be determined even in the presence of high ATP concentrations, making the assay highly suitable to characterize the mode of action of the inhibitor in question. Collectively, this assay provides a homogenous, generic method for a number of applications in kinase drug discovery.

Nucleocytoplasmic shuttling of Pak5 regulates its antiapoptotic properties

p21-activated kinase 5 (Pak5) is an effector for the small GTPase Cdc42, known to activate cell survival signaling pathways. Previously, we have shown that Pak5 localizes primarily to mitochondria. To study the relationship between Pak5 localization and its effects on apoptosis, we identified three N-terminal regions that regulate the localization of this kinase: a mitochondrial targeting sequence, a nuclear export sequence, and a nuclear localization sequence. When the first two sequences are deleted, Pak5 is retained in the nucleus and no longer protects cells from apoptosis. Moreover, blockade of nuclear export with leptomycin B causes endogenous Pak5 to accumulate in the nucleus. Additionally, the removal of the N-terminal nuclear localization sequence abolishes Pak5 translocation to the nucleus. Finally, we show that reduction of endogenous Pak5 expression in neuroblastoma and neural stem cells increases their sensitivity to apoptosis and that this effect is reversed upon reexpression of wild-type Pak5 but not of a mutant form of Pak5 that cannot localize to mitochondria. These results show that Pak5 shuttles from mitochondria to the nucleus and that the mitochondrial localization of Pak5 is vital to its effects on cell survival.

Correlation of human Bub1 expression with tumor-proliferating activity in salivary gland tumors

Human Bub1 plays an important role at the spindle assembly check-point to prevent cell cycle progression following spindle damage. We examined the expression of Bub1 mRNA and protein in 21 human salivary gland tumors (7 pleomorphic adenomas, 2 warthin tumors, 5 mucoepidermoid carcinomas, 3 adenoid cystic carcinomas and 4 acinic cell carcinomas) and 3 normal submandibular glands using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) or western blotting. The mean expression levels of Bub1 mRNA and protein were higher in malignant tumors (0.12+/-0.028/1.75+/-0.53) than normal submandibular glands (0.042+/-0.014/0.19+/-0.044) and benign tumors (0.058+/-0.01/0.97+/-0.44). We found a significant association between the level of Bub1 mRNA/protein expression and clinical stage in malignant tumors (Mann-Whitney U test, p=0.019/p=0.016). We analyzed its relation with the proliferative activity monitored by the Ki-67 labeling index by immunohistochemistry as well as the expression of proliferating cell nuclear antigen (PCNA) by Western blotting. A significant correlation was found between Bub1 mRNA/protein expression and the Ki-67 labeling index in salivary gland tumors (Spearman's correlation coefficient by rank test, p=0.026/p=0.002). These results indicate that increased expression of the human Bub1 gene is closely linked to abnormal cell proliferation in malignant conditions.

Protein microarrays as a discovery tool for studying protein-protein interactions

Exploring the function of the genome and the encoded proteins has emerged as a new and exciting challenge in the postgenomic era. Novel technologies come into view that promise to be valuable for the investigation not only of single proteins, but of entire protein networks. Protein microarrays are the innovative assay platform for highly parallel in vitro studies of protein-protein interactions. Due to their flexibility and multiplexing capacity, protein microarrays benefit basic research, diagnosis and biomedicine. This review provides an overview on the basic principles of protein microarrays and their potential to multiplex protein-protein interaction studies.

A Small Ras-like protein Ray/Rab1c modulates the p53-regulating activity of PRPK

PRPK phosphorylates serine-15 residue of p53 and enhances transcriptional activity. PRPK possesses a bipartite nuclear localization signal and localizes in nucleus when over-expressed in cells. However, intrinsic PRPK localizes mainly in the cytosol in situ. While studying the mechanisms in the distribution of intrinsic PRPK, we identified a PRPK binding protein, an ubiquitously expressed Small Ras-like GTPase, Rab1c, also named Ray or Rab35. The over-expressed Ray was distributed in the nucleus, cytosol, and cell membrane. Both Ray wild type and GTP-restrictively binding mutant Ray-Q67L, but not guanine nucleotide unstable binding mutant Ray-N120I, partially distributed the over-expressed PRPK to the cytosol and also suppressed the PRPK-induced p53-transcriptional activity profoundly. A Small Ras-like GTPase protein Ray was thus indicated to modulate p53 transcriptional activity of PRPK.

The Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 protein complex includes BRASSINOSTEROID-INSENSITIVE1

Arabidopsis thaliana SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 (SERK1) is a leucine-rich repeat receptor-like kinase (LRR-RLK) involved in the acquisition of embryogenic competence and in male sporogenesis. To determine the composition of the SERK1 signaling complex in vivo, we generated plants expressing the SERK1 protein fused to cyan fluorescent protein under SERK1 promoter control. The membrane receptor complex was immunoprecipitated from seedlings, and the coimmunoprecipitating proteins were identified using liquid chromatography/matrix-assisted laser desorption ionization-time of flight/mass spectrometry of the trypsin-released peptides. This approach identified two other LRR-RLKs, the BRASSINOSTEROID-INSENSITIVE1 (BRI1) receptor and its coreceptor, the SERK3 or BRI1-ASSOCIATED KINASE1 protein. In addition, KINASE-ASSOCIATED PROTEIN PHOSPHATASE, CDC48A, and 14-3-3nu were found. Finally, the MADS box transcription factor AGAMOUS-LIKE15 and an uncharacterized zinc finger protein, a member of the CONSTANS family, were identified as part of the SERK1 complex. Using blue native gel electrophoresis, we show that SERK1 and SERK3 are part of BRI1-containing multiple protein complexes with relative masses between 300 and 500 kD. The SERK1 mutant allele serk1-1 enhances the phenotype of the weak BRI1 allele bri1-119. Collectively, these results suggest that apart from SERK3, SERK1 is also involved in the brassinolide signaling pathway.

Abscisic acid stimulates a calcium-dependent protein kinase in grape berry

It has been demonstrated that calcium plays a central role in mediating abscisic acid (ABA) signaling, but many of the Ca2+-binding sensory proteins as the components of the ABA-signaling pathway remain to be elucidated. Here we identified, characterized, and purified a 58-kD ABA-stimulated calcium-dependent protein kinase from the mesocarp of grape berries (Vitis vinifera x Vitis labrusca), designated ACPK1 (for ABA-stimulated calcium-dependent protein kinase1). ABA stimulates ACPK1 in a dose-dependent manner, and the ACPK1 expression and enzyme activities alter accordantly with the endogenous ABA concentrations during fruit development. The ABA-induced ACPK1 stimulation appears to be transient with a rapid effect in 15 min but also with a slow and steady state of induction after 60 min. ABA acts on ACPK1 indirectly and dependently on in vivo state of the tissues. Two inactive ABA isomers, (-)-2-cis, 4-trans-ABA and 2-trans, 4-trans-(+/-)-ABA, are ineffective for inducing ACPK1 stimulation, revealing that the ABA-induced effect is stereo specific to physiological active (+)-2-cis, 4-trans-ABA. The other phytohormones such as auxin indoleacetic acid, gibberellic acid, synthetic cytokinin N-benzyl-6-aminopurine, and brassinolide are also ineffective in this ACPK1 stimulation. Based on sequencing of the two-dimensional electrophoresis-purified ACPK1, we cloned the ACPK1 gene. The ACPK1 is expressed specifically in grape berry covering a fleshy portion and seeds, and in a developmental stage-dependent manner. We further showed that ACPK1 is localized in both plasma membranes and chloroplasts/plastids and positively regulates plasma membrane H+-ATPase in vitro, suggesting that ACPK1 may be involved in the ABA-signaling pathway.

The Akt pathway in human breast cancer: a tissue-array-based analysis

The Akt pathway, an important regulator of cell proliferation and survival, is deregulated in many cancers. The pathway has achieved considerable importance due to the development of kinase inhibitors that are able to successfully reduce tumor growth. This study was conducted to determine the status of the Akt pathway in human breast cancers and to study the relationship between the different component proteins. Expression levels of PTEN, phosphorylated forms of the constituent proteins (Akt, FKHR, mTOR, and S6) and cyclin D1 were evaluated by immunohistochemistry, on consecutive sections from a tissue microarray containing 145 invasive breast cancers and 140 pure ductal carcinomas in-situ. Aberrant expression was correlated statistically with tumor characteristics and disease outcome. The Akt pathway was found to be activated early in breast cancer, in the in-situ stage. In all, 33, 15, 32, and 60% of ductal carcinoma in-situ showed overexpression of Akt, FKHR, mTOR, and cyclin D1. PTEN loss did not correlate statistically with expression of AKT or any of the other proteins with the exception of S6, indicating that Akt activation was not a result of PTEN loss. Expression levels of PTEN and S6 were significantly different in in-situ and invasive cancers, indicating association with disease progression. Loss of PTEN was noted in 11% of in-situ as compared to 26% of invasive cancers, while S6 overexpression was seen in 47% in-situ and in 72% invasive cancers. High-grade carcinomas were associated with PTEN loss, while low-grade carcinomas with good prognostic features showed cyclin D1 overexpression and were associated with longer disease free survival. Additionally, cancers with mTOR overexpression showed a three times greater risk for disease recurrence. Overall, a large proportion of in-situ and invasive breast cancers overexpressed cyclinD1 and S6. Our results may have significant implications in the development and application of targeted therapy.

The Arabidopsis receptor kinase FLS2 binds flg22 and determines the specificity of flagellin perception

Flagellin, the main building block of the bacterial flagellum, acts as a pathogen-associated molecular pattern triggering the innate immune response in animals and plants. In Arabidopsis thaliana, the Leu-rich repeat transmembrane receptor kinase FLAGELLIN SENSITIVE2 (FLS2) is essential for flagellin perception. Here, we demonstrate the specific interaction of the elicitor-active epitope flg22 with the FLS2 protein by chemical cross-linking and immunoprecipitation. The functionality of this receptor was further tested by heterologous expression of the Arabidopsis FLS2 gene in tomato (Lycopersicon esculentum) cells. The perception of flg22 in tomato differs characteristically from that in Arabidopsis. Expression of Arabidopsis FLS2 conferred an additional flg22-perception system on the cells of tomato, which showed all of the properties characteristic of the perception of this elicitor in Arabidopsis. In summary, these results show that FLS2 constitutes the pattern-recognition receptor that determines the specificity of flagellin perception.

Cellular localization and phosphorylation of Hrb1p is independent of Sky1p

Protein phosphorylation plays a major role in regulating cellular functions. We have previously demonstrated that Sky1p, the SR protein kinase of the budding yeast Saccharomyces cerevisiae, is a regulator of polyamine transport and ion homeostasis. Since its kinase activity was demonstrated essential for fulfilling these roles, we assumed that Sky1p function via substrates phosphorylation. Using an in vitro phosphorylation assay, we have identified Hrb1p as a putative Sky1p substrate. However, phosphorylation analysis in WT and sky1Delta cells and localization studies disproved Hrb1p as a true Sky1p substrate, although a segment of the RS domain is required for determining its subcellular localization. Furthermore, we demonstrate that Hrb1p and additional putative Sky1p substrates, identified by computational approach, are not involved in mediating the spermine tolerant phenotype of sky1Delta cells.

Carbohydrate metabolism during prolonged exercise and recovery: interactions between pyruvate dehydrogenase, fatty acids, and amino acids

During prolonged exercise, carbohydrate oxidation may result from decreased pyruvate production and increased fatty acid supply and ultimately lead to reduced pyruvate dehydrogenase (PDH) activity. Pyruvate also interacts with the amino acids alanine, glutamine, and glutamate, whereby the decline in pyruvate production could affect tricarboxycylic acid cycle flux as well as gluconeogenesis. To enhance our understanding of these interactions, we studied the time course of changes in substrate utilization in six men who cycled at 44+/-1% peak oxygen consumption (mean+/-SE) until exhaustion (exhaustion at 3 h 23 min+/-11 min). Femoral arterial and venous blood, blood flow measurements, and muscle samples were obtained hourly during exercise and recovery (3 h). Carbohydrate oxidation peaked at 30 min of exercise and subsequently decreased for the remainder of the exercise bout (P<0.05). PDH activity peaked at 2 h of exercise, whereas pyruvate production peaked at 1 h of exercise and was reduced (approximately 30%) thereafter, suggesting that pyruvate availability primarily accounted for reduced carbohydrate oxidation. Increased free fatty acid uptake (P<0.05) was also associated with decreasing PDH activity (P<0.05) and increased PDH kinase 4 mRNA (P<0.05) during exercise and recovery. At 1 h of exercise, pyruvate production was greatest and was closely linked to glutamate, which was the predominant amino acid taken up during exercise and recovery. Alanine and glutamine were also associated with pyruvate metabolism, and they comprised approximately 68% of total amino-acid release during exercise and recovery. Thus reduced pyruvate production was primarily associated with reduced carbohydrate oxidation, whereas the greatest production of pyruvate was related to glutamate, glutamine, and alanine metabolism in early exercise.

Immunolocalization of FsPK1 correlates this abscisic acid-induced protein kinase with germination arrest in Fagus sylvatica L. seeds

An enzymatically active recombinant protein kinase, previously isolated and characterized in Fagus sylvatica L. dormant seeds (FsPK1), was used to obtain a specific polyclonal antibody against this protein. Immunoblotting and immunohistochemical analysis of FsPK1 protein in beech seeds showed a strong immunostaining in the nucleus of the cells located in the vascular tissue of the embryonic axis corresponding to the future apical meristem of the root. This protein kinase was found to accumulate in the seeds only when embryo growth was arrested by application of ABA, while the protein amount decreased during stratification, previously proved to alleviate dormancy, and no protein was detected at all when seed germination was induced by addition of GA(3). These results indicate that FsPK1 may be involved in the control of the embryo growth mediated by ABA and GAs during the transition from dormancy to germination in Fagus sylvatica seeds.

[An involvement of polokinases in control of progress of the cell-cycle--the mechanism of transient translocation and formation of an activated protein-protein complexes during mitosis]

Polokinases are a subfamily of the mitotic serine/threonine kinases involved in coordination of a run of mitosis of eukaryotic cells. The main polo-like-kinase 1p (PLK1) is a passenger protein transiently localized to centrosomes, kinetochores and central spindle during mitosis and is required for bi-orientation of the normal metaphase spindle. Its activity is regulated at the level of protein stability and by action of upstream kinases, so that it peaks in metaphase and drops as cells exit mitosis. Regulation of location and activity of Plk1p is bi-phasic: the COOH terminal polo box domain binds to an array of mitotic phosphoproteins and followed by an allosteric conformation is activated to phosphorylate many its substrates. These mode of action involves polokinases into critical transitions of the cell cycle phases, and in control at some checkpoints of this cycle.

Extracellular signal-regulated kinase regulates clathrin-independent endosomal trafficking

Extracellular signal-regulated kinase (Erk) is widely recognized for its central role in cell proliferation and motility. Although previous work has shown that Erk is localized at endosomal compartments, no role for Erk in regulating endosomal trafficking has been demonstrated. Here, we report that Erk signaling regulates trafficking through the clathrin-independent, ADP-ribosylation factor 6 (Arf6) GTPase-regulated endosomal pathway. Inactivation of Erk induced by a variety of methods leads to a dramatic expansion of the Arf6 endosomal recycling compartment, and intracellular accumulation of cargo, such as class I major histocompatibility complex, within the expanded endosome. Treatment of cells with the mitogen-activated protein kinase kinase (MEK) inhibitor U0126 reduces surface expression of MHCI without affecting its rate of endocytosis, suggesting that inactivation of Erk perturbs recycling. Furthermore, under conditions where Erk activity is inhibited, a large cohort of Erk, MEK, and the Erk scaffold kinase suppressor of Ras 1 accumulates at the Arf6 recycling compartment. The requirement for Erk was highly specific for this endocytic pathway, because its inhibition had no effect on trafficking of cargo of the classical clathrin-dependent pathway. These studies reveal a previously unappreciated link of Erk signaling to organelle dynamics and endosomal trafficking.

Role of molecular markers in the diagnosis and therapy of renal cell carcinoma

Recent advances in the understanding of the pathogenesis, behavior, and molecular biology of renal cell carcinoma (RCC) have paved the way for developments that may enhance early diagnosis, better predict prognosis, and improve survival. Reliable predictive factors are essential for the stratification of patients into clinically meaningful categories that can be used to provide patients with counseling regarding prognosis, select treatment modalities, and determine eligibility for clinical trials. The TNM (tumor, nodes, metastasis) staging system is currently the most extensively used staging system for RCC, but it has undergone systematic revisions as a result of emerging data. Comprehensive integrated staging systems that combine important clinical and pathological variables have been created in an attempt to improve prognostication. Although staging has improved with the development of integrated systems, the incorporation of molecular tumor markers are expected to revolutionize the staging of RCC. This article reviews the important molecular markers in RCC to date and discusses their role in the diagnosis, prognostication, and therapy of patients with RCC.