Multiple Ca2+/calmodulin-dependent protein kinase genes in a unicellular eukaryote

Identification of the Beta Subunit Fas1p of Fatty Acid Synthetase as an Interacting Partner of Yeast Calcium/Calmodulin-Dependent Protein Kinase Cmk2p Through Mass Spectrometry Analysis

The calcium/calmodulin-dependent protein kinase II (CaMKII) is a mediator of calcium signals and regulates fatty acid metabolism in mammalian cells. Cmk2p is a yeast homolog of CaMKII and functions as a negative regulator of calcium signaling. However, its substrates remain to be identified. Combination of immunoprecipitation (IP) and mass spectrometry has been proven to be very useful for identification of interacting partner proteins and interactome. In this study, through these approaches, we have identified 65 and 110 potential Cmk2p-interacting proteins in yeast cells in the absence or presence of calcium stress, respectively. In yeast cells expressing both CMK2-HA and FAS1-GFP fusion proteins, in the absence or presence of calcium stress, less amounts of FAS1-GFP proteins are present in cell lysates after IP with anti-HA antibody than cell lysates before IP, while FAS1-GFP proteins are detected on both types of IP beads. However, as an internal control, similar amounts of Pgk1p proteins were detected in both after-IP and before-IP cell lysates but not on the IP beads. Therefore, our biochemical analysis demonstrates that the β subunit Fas1p of fatty acid synthetase interacts with Cmk2p in yeast cells independent of calcium stress. It is also interesting to note that, in addition to the expected 52-kDa CMK2-HA band, a faster-moving 48-kDa CMK2-HA band is present in the calcium-stressed cell lysate but not in the cell lysate without calcium stress. Our data would provide important clues for understanding the functions of CaMKII in the regulation of fatty acid metabolism as well as related diseases such as cancers, diabetes, and obesity.

Characterization and Functional Analysis of a New Calcium/Calmodulin-Dependent Protein Kinase (CaMK1) in the Citrus Pathogenic Fungus Penicillium italicum

Calcium (Ca2+)/calmodulin-dependent protein kinases (CaMKs) act as a class of crucial elements in Ca2+-signal transduction pathways that regulate fungal growth, sporulation, virulence, and environmental stress tolerance. However, little is known about the function of such protein kinase in phytopathogenic Penicillium species. In the present study, a new CaMK gene from the citrus pathogenic fungus P. italicum, designated PiCaMK1, was cloned and functionally characterized by gene knockout and transcriptome analysis. The open reading frame of PiCaMK1 is 1209 bp in full length, which encodes 402 amino acid residues (putative molecular weight ~45.2 KD) with the highest homologous (~96.3%) to the P. expansum CaMK. The knockout mutant ΔPiCaMK1 showed a significant reduction in vegetative growth, conidiation, and virulence (i.e., to induce blue mold decay on citrus fruit). ΔPiCaMK1 was less sensitive to NaCl- or KCl-induced salinity stress and less resistant to mannitol-induced osmotic stress, indicating the functional involvement of PiCaMK1 in such environmental stress tolerance. In contrast, the PiCaMK1-complemented strain ΔPiCaMK1COM can restore all the defective phenotypes. Transcriptome analysis revealed that knockout of PiCaMK1 down-regulated expression of the genes involved in DNA replication and repair, cell cycle, meiosis, pyrimidine and purine metabolisms, and MAPK signaling pathway. Our results suggested the critical role of PiCaMK1 in regulating multiple physical and cellular processes of citrus postharvest pathogen P. italicum, including growth, conidiation, virulence, and environmental stress tolerance.

Narcolepsy in Parkinson's disease with insulin resistance

Background: Parkinson’s disease (PD) is characterized by its progression of motor-related symptoms such as tremors, rigidity, slowness of movement, and difficulty with walking and balance. Comorbid conditions in PD individuals include insulin resistance (IR) and narcolepsy-like sleep patterns. The intersecting sleep symptoms of both conditions include excessive daytime sleepiness, hallucinations, insomnia, and falling into REM sleep more quickly than an average person. Understanding of the biological basis and relationship of these comorbid disorders with PD may help with early detection and intervention strategies to improve quality of life. Methods: In this study, an integrative genomics and systems biology approach was used to analyze gene expression patterns associated with PD, IR, and narcolepsy in order to identify genes and pathways that may shed light on how these disorders are interrelated. A correlation analysis with known genes associated with these disorders (LRRK2, HLA-DQB1, and HCRT) was used to query microarray data corresponding to brain regions known to be involved in PD and narcolepsy. This includes the hypothalamus, dorsal thalamus, pons, and subcoeruleus nucleus. Risk factor genes for PD, IR, and narcolepsy were also incorporated into the analysis. Results: The PD and narcolepsy signaling networks are connected through insulin and immune system pathways. Important genes and pathways that link PD, narcolepsy, and IR are CACNA1C, CAMK1D, BHLHE41, HMGB1, and AGE-RAGE. Conclusions: We have identified the genetic signatures that link PD with its comorbid disorders, narcolepsy and insulin resistance, from the convergence and intersection of dopaminergic, insulin, and immune system related signaling pathways. These findings may aid in the design of early intervention strategies and treatment regimes for non-motor symptoms in PD patients as well as individuals with diabetes and narcolepsy.

A kinase cascade on the yeast lysosomal vacuole regulates its membrane dynamics: conserved kinase Env7 is phosphorylated by casein kinase Yck3

Membrane fusion/fission is a highly dynamic and conserved process that responds to intra- and extracellular signals. Whereas the molecular machineries involved in membrane fusion/fission have been dissected, regulation of membrane dynamics remains poorly understood. The lysosomal vacuole of budding yeast (Saccharomyces cerevisiae) has served as a seminal model in studies of membrane dynamics. We have previously established that yeast ENV7 encodes an ortholog of STK16-related kinases that localizes to the vacuolar membrane and downregulates vacuolar membrane fusion. Additionally, we have previously reported that Env7 phosphorylation in vivo depends on YCK3, a gene that encodes a vacuolar membrane casein kinase I (CKI) homolog that nonredundantly functions in fusion regulation. Here, we report that Env7 physically interacts with and is directly phosphorylated by Yck3. We also establish that Env7 vacuole fusion/fission regulation and vacuolar localization are mediated through its Yck3-dependent phosphorylation. Through extensive site-directed mutagenesis, we map phosphorylation to the Env7 C terminus and confirm that Ser-331 is a primary and preferred phosphorylation site. Phospho-deficient Env7 mutants were defective in negative regulation of membrane fusion, increasing the number of prominent vacuoles, whereas a phosphomimetic substitution at Ser-331 increased the number of fragmented vacuoles. Bioinformatics approaches confirmed that Env7 Ser-331 is within a motif that is highly conserved in STK16-related kinases and that it also anchors an SXXS CKI phosphorylation motif (328SRFS331). This study represents the first report on the regulatory mechanism of an STK16-related kinase. It also points to regulation of vacuolar membrane dynamics via a novel Yck3-Env7 kinase cascade.

The protein kinase Cmk2 negatively regulates the calcium/calcineurin signalling pathway and expression of calcium pump genes PMR1 and PMC1 in budding yeast

Through a genome-wide screen we have identified calcium-tolerant deletion mutants for five genes in the budding yeast Saccharomyces cerevisiae. In addition to CNB1 and RCN1 that are known to play a role in the calcium signalling pathway, the protein kinase gene CMK2, the sphingolipid homeostasis-related gene ORM2 and the gene SIF2 encoding the WD40 repeat-containing subunit of Set3C histone deacetylase complex are involved in the calcium sensitivity of yeast cells to extracellular calcium. Cmk2 and the transcription factor Crz1 have opposite functions in the response of yeast cells to calcium stress. Deletion of CMK2 elevates the level of calcium/calcineurin signalling and increases the expression level of PMR1 and PMC1, which is dependent on Crz1. Effects of Cmk2 on calcium sensitivity and calcium/calcineurin signalling are dependent on its kinase activity. Therefore, Cmk2 is a negative feedback controller of the calcium/calcineurin signalling pathway. Furthermore, the cmk2 crz1 double deletion mutant is more resistant than the crz1 deletion mutant, suggesting that Cmk2 has an additional Crz1-independent role in promoting calcium tolerance.

Regulation of MAP kinase Hog1 by calmodulin during hyperosmotic stress

Mitogen-activated protein kinase (Hog1 in yeast and ortholog p38 in human cells) plays a critical role in the signal transduction pathway that is rapidly activated under multiple stress conditions. Environmental stress stimuli such as hyperosmotic stress cause changes in cellular ATP metabolism required for hyperosmotic stress tolerance. Furthermore, hyperosmotic stress induces rapid Ca²⁺ signals in eukaryotic cells. These Ca²⁺ signals can be decoded by Ca²⁺ sensor calmodulin (CaM). By using genetic and biochemical approaches, we demonstrate that Hog1 is a novel CaM-binding protein, and that CaM-binding to Hog1 is involved in the mediation of the hyperosmotic stress signaling pathway. In addition, we show that p38α, a human ortholog of Hog1, interacts with CaM, suggesting that the CaM-binding feature of Hog1/p38α is evolutionarily conserved in eukaryotic cells. Hog1 is likely involved in cellular ATP regulation through CaM signaling during hyperosmotic stress. Therefore, this work suggests that Hog1 plays an important role in connecting CaM signaling with the hyperosmotic stress pathway by directly interacting with CaM in Saccharomyces cerevisiae.

The diverse role of Pdr12 in resistance to weak organic acids

Resistance to weak organic acids is important relative to both weak organic acid preservatives and the development of inhibitor tolerant yeast as industrial production organisms. The ABC transporter Pdr12 is important for resistance to sorbic and propionic acid, but its role in tolerance to other weak organic acids with industrial relevance is not well established. In this study, yeast strains with altered expression of PDR12 and/or CMK1, a protein kinase associated with post-transcriptional negative regulation of Pdr12, were exposed to seven weak organic acids: acetic, formic, glycolic, lactic, propionic, sorbic and levulinic acid. These are widely used as preservatives, present in lignocellulosic hydrolysates or attractive as chemical precursors. Overexpression of PDR12 increased tolerance to acids with longer chain length, such as sorbic, propionic and levulinic acid, whereas deletion of PDR12 increased tolerance to the shorter acetic and formic acid. The viability of all strains decreased dramatically in acetic or propionic acid, but the Δpdr12 strains recovered more rapidly than other strains in acetic acid. Furthermore, our results indicated that Cmk1 plays a role in weak organic acid tolerance, beyond its role in regulation of Pdr12, since deletion of both Cmk1 and Pdr12 resulted in different responses to exposure to acids than were explained by deletion of Pdr12 alone.

Cellular localization of CoPK12, a Ca(2+)/calmodulin-dependent protein kinase in mushroom Coprinopsis cinerea, is regulated by N-myristoylation

Multifunctional Ca(2+)/calmodulin-dependent protein kinases (CaMKs) have been extensively studied in mammals, whereas fungus CaMKs still remain largely uncharacterized. We previously obtained CaMK homolog in Coprinopsis cinerea, designated CoPK12, and revealed its unique catalytic properties in comparison with the mammalian CaMKs. To further clarify the regulatory mechanisms of CoPK12, we investigated post-translational modification and subcellular localization of CoPK12 in this study. In C. cinerea, full-length CoPK12 (65 kDa) was fractionated in the membrane fraction, while the catalytically active fragment (46 kDa) of CoPK12 was solely detected in the soluble fraction by differential centrifugation. Expressed CoPK12-GFP was localized on the cytoplasmic and vacuolar membranes as visualized by green fluorescence in yeast cells. In vitro N-myristoylation assay revealed that CoPK12 is N-myristoylated at Gly-2 in the N-terminal position. Furthermore, calmodulin could bind not only to CaM-binding domain but also to the N-terminal myristoyl moiety of CoPK12. These results, taken together, suggest that the cellular localization and function of CoPK12 are regulated by protein N-myristoylation and limited proteolysis.

The type II Ca2+/calmodulin-dependent protein kinases are involved in the regulation of cell wall integrity and oxidative stress response in Candida albicans

The type II Ca(2+)/calmodulin-dependent protein kinases (CaMKs) are thought to play a vital role in cellular regulation in mammalian cells. Two genes CMK1 and CMK2 in the Candida albicans genome encode homologues of mammalian CaMKs. In this work, we constructed the cmk1Δ/Δ, the cmk2Δ/Δ and the cmk1Δ/Δcmk2Δ/Δ mutants and found that CaMKs function in cell wall integrity (CWI) and cellular redox regulation. Loss of either CMK1 or CMK2, or both resulted in increased expression of CWI-related genes under Calcofluor white (CFW) treatment. Besides, CaMKs are essential for the maintenance of cellular redox balance. Disruption of either CMK1 or CMK2, or both not only led to a significant increase of intracellular ROS levels, but also led to a decrease of the mitochondrial membrane potential (MMP), suggesting the important roles that CaMKs play in the maintenance of the mitochondrial function.

Calcium/calmodulin-dependent kinases are involved in growth, thermotolerance, oxidative stress survival, and fertility in Neurospora crassa

Calcium/calmodulin-dependent kinases (Ca(2+)/CaMKs) are Ser/Thr protein kinases that respond to change in cytosolic free Ca(2+) ([Ca(2+)]c) and play multiple cellular roles in organisms ranging from fungi to humans. In the filamentous fungus Neurospora crassa, four Ca(2+)/CaM-dependent kinases, Ca(2+)/CaMK-1 to 4, are encoded by the genes NCU09123, NCU02283, NCU06177, and NCU09212, respectively. We found that camk-1 and camk-2 are essential for full fertility in N. crassa. The survival of ∆camk-2 mutant was increased in induced thermotolerance and oxidative stress conditions. In addition, the ∆camk-1 ∆camk-2, ∆camk-4 ∆camk-2, and ∆camk-3 ∆camk-2 double mutants display slow growth phenotype, reduced aerial hyphae, decreased thermotolerance, and increased sensitivity to oxidative stress, revealing the genetic interactions among these kinases. Therefore, Ca(2+)/CaMKs are involved in growth, thermotolerance, oxidative stress tolerance, and fertility in N. crassa.

Functional wiring of the yeast kinome revealed by global analysis of genetic network motifs

A combinatorial genetic perturbation strategy was applied to interrogate the yeast kinome on a genome-wide scale. We assessed the global effects of gene overexpression or gene deletion to map an integrated genetic interaction network of synthetic dosage lethal (SDL) and loss-of-function genetic interactions (GIs) for 92 kinases, producing a meta-network of 8700 GIs enriched for pathways known to be regulated by cognate kinases. Kinases most sensitive to dosage perturbations had constitutive cell cycle or cell polarity functions under standard growth conditions. Condition-specific screens confirmed that the spectrum of kinase dosage interactions can be expanded substantially in activating conditions. An integrated network composed of systematic SDL, negative and positive loss-of-function GIs, and literature-curated kinase-substrate interactions revealed kinase-dependent regulatory motifs predictive of novel gene-specific phenotypes. Our study provides a valuable resource to unravel novel functional relationships and pathways regulated by kinases and outlines a general strategy for deciphering mutant phenotypes from large-scale GI networks.

Ste11p MEKK signals through HOG, mating, calcineurin and PKC pathways to regulate the FKS2 gene

Background

The S. cerevisiae MAPKKK Ste11p, a homologue of mammalian MEKK1, regulates three MAPK cascades for mating, invasive growth and osmotic stress and provides functions that are additive with the cell wall integrity pathway. Cell wall integrity requires the FKS2 gene that encodes a stress-induced alternative subunit of beta-1, 3 glucan synthase that is the target of echinocandin 1,3- beta glucan synthase inhibitors. The major signal transduction pathways that activate transcription of the FKS2 gene include the cell wall integrity and calcineurin pathways, and the Ste11p pathway.

Results

Here it is shown that catalytically active Ste11p regulates FKS2-lacZ reporter genes through Ste12, calcineurin/Crz1p- and PKC pathways and the high osmolarity pathway. Ste11p stimulated the cell wall integrity MAPK Mpk1p (Erk5 homologue) and FKS2 independently of the mating pathway. Ste11p regulated FKS2 through all known and putative substrates: Pbs2p MAPKK, Ste7 MAPKK, Cmk2p calmodulin dependent kinase and Ptk2p kinase. Ste11p increased the expression level of Cmk2p through transcription-dependent and -independent mechanisms.

Conclusions

The data suggest Ste11p regulates the FKS2 gene through all its known and putative downstream kinase substrates (Pbs2p, Ste7p, Cmk2p, and Ptk2p) and separately through Mpk1p MAPK. The patterns of control by Ste11p targets revealed novel functional linkages, cross-regulation, redundancy and compensation.

Calcium/calmodulin kinase1 and its relation to thermotolerance and HSP90 in Sporothrix schenckii: an RNAi and yeast two-hybrid study

Background

Sporothrix schenckii is a pathogenic dimorphic fungus of worldwide distribution. It grows in the saprophytic form with hyaline, regularly septated hyphae and pyriform conidia at 25°C and as the yeast or parasitic form at 35°C. Previously, we characterized a calcium/calmodulin kinase in this fungus. Inhibitors of this kinase were observed to inhibit the yeast cell cycle in S. schenckii.

Results

The presence of RNA interference (RNAi) mechanism in this fungus was confirmed by the identification of a Dicer-1 homologue in S. schenckii DNA. RNAi technology was used to corroborate the role of calcium/calmodulin kinase I in S. schenckii dimorphism. Yeast cells were transformed with the pSilent-Dual2G (pSD2G) plasmid w/wo inserts of the coding region of the calcium/calmodulin kinase I (sscmk1) gene. Transformants were selected at 35°C using resistance to geneticin. Following transfer to liquid medium at 35°C, RNAi transformants developed as abnormal mycelium clumps and not as yeast cells as would be expected. The level of sscmk1 gene expression in RNAi transformants at 35°C was less than that of cells transformed with the empty pSD2G at this same temperature. Yeast two-hybrid analysis of proteins that interact with SSCMK1 identified a homologue of heat shock protein 90 (HSP90) as interacting with this kinase. Growth of the fungus similar to that of the RNAi transformants was observed in medium with geldanamycin (GdA, 10 μM), an inhibitor of HSP90.

Conclusions

Using the RNAi technology we silenced the expression of sscmk1 gene in this fungus. RNAi transformants were unable to grow as yeast cells at 35°C showing decreased tolerance to this temperature. The interaction of SSCMK1 with HSP90, observed using the yeast two-hybrid assay suggests that this kinase is involved in thermotolerance through its interaction with HSP90. SSCMK1 interacted with the C terminal domain of HSP90 where effector proteins and co-chaperones interact. These results confirmed SSCMK1 as an important enzyme involved in the dimorphism of S. schenckii, necessary for the development of the yeast phase of this fungus. Also this study constitutes the first report of the transformation of S. schenckii and the use of RNAi to study gene function in this fungus.

Simultaneous genome-wide inference of physical, genetic, regulatory, and functional pathway components

Biomolecular pathways are built from diverse types of pairwise interactions, ranging from physical protein-protein interactions and modifications to indirect regulatory relationships. One goal of systems biology is to bridge three aspects of this complexity: the growing body of high-throughput data assaying these interactions; the specific interactions in which individual genes participate; and the genome-wide patterns of interactions in a system of interest. Here, we describe methodology for simultaneously predicting specific types of biomolecular interactions using high-throughput genomic data. This results in a comprehensive compendium of whole-genome networks for yeast, derived from ∼3,500 experimental conditions and describing 30 interaction types, which range from general (e.g. physical or regulatory) to specific (e.g. phosphorylation or transcriptional regulation). We used these networks to investigate molecular pathways in carbon metabolism and cellular transport, proposing a novel connection between glycogen breakdown and glucose utilization supported by recent publications. Additionally, 14 specific predicted interactions in DNA topological change and protein biosynthesis were experimentally validated. We analyzed the systems-level network features within all interactomes, verifying the presence of small-world properties and enrichment for recurring network motifs. This compendium of physical, synthetic, regulatory, and functional interaction networks has been made publicly available through an interactive web interface for investigators to utilize in future research at http://function.princeton.edu/bioweaver/.

To maintain the complexity of living biological systems, many proteins must interact in a coordinated manner to integrate their unique functions into a cooperative system. Pathways are typically constructed to capture modular subsets of this dynamic network, each made up of a collection of biomolecular interactions of diverse types that together carry out a specific cellular function. Deciphering these pathways at a global level is a crucial step for unraveling systems biology, aiding at every level from basic biological understanding to translational biomarker and drug target discovery. The combination of high-throughput genomic data with advanced computational methods has enabled us to infer the first genome-wide compendium of bimolecular pathway networks, comprising 30 distinct bimolecular interaction types. We demonstrate that this interaction network compendium, derived from ∼3,500 experimental conditions, can be used to direct a range of biomedical hypothesis generation and testing. We show that our results can be used to predict novel protein interactions and new pathway components, and also that they enable system-level analysis to investigate the network characteristics of cell-wide regulatory circuits. The resulting compendium of biological networks is made publicly available through an interactive web interface to enable future research in other biological systems of interest.

Cellular roles of neuronal calcium sensor-1 and calcium/calmodulin-dependent kinases in fungi

The neuronal calcium sensor-1 (NCS-1) possesses a consensus signal for N-terminal myristoylation and four EF-hand Ca(2+)-binding sites, and mediates the effects of cytosolic Ca(2+). Minute changes in free intracellular Ca(2+) are quickly transformed into changes in the activity of several kinases including calcium/calmodulin-dependent protein kinases (Ca(2+)/CaMKs) that are involved in regulating many eukaryotic cell functions. However, our current knowledge of NCS-1 and Ca(2+)/CaMKs comes mostly from studies of the mammalian enzymes. Thus far very few fungal homologues of NCS-1 and Ca(2+)/CaMKs have been characterized and little is known about their cellular roles. In this minireview, we describe the known sequences, interactions with target proteins and cellular roles of NCS-1 and Ca(2+)/CaMKs in fungi.

Identification of a cell death pathway in Candida albicans during the response to pheromone

Mating in hemiascomycete yeasts involves the secretion of pheromones that induce sexual differentiation in cells of the opposite mating type. Studies in Saccharomyces cerevisiae have revealed that a subpopulation of cells experiences cell death during exposure to pheromone. In this work, we tested whether the phenomenon of pheromone-induced death (PID) also occurs in the opportunistic pathogen Candida albicans. Mating in C. albicans is uniquely regulated by white-opaque phenotypic switching; both cell types respond to pheromone, but only opaque cells undergo the morphological transition and cell conjugation. We show that approximately 20% of opaque cells, but not white cells, of laboratory strain SC5314 experience pheromone-induced death. Furthermore, analysis of mutant strains revealed that PID was significantly reduced in strains lacking Fig1 or Fus1 transmembrane proteins that are induced during the mating process and, we now show, are necessary for efficient mating in C. albicans. The level of PID was also Ca(2+) dependent, as chelation of Ca(2+) ions increased cell death to almost 50% of the population. However, in contrast to S. cerevisiae PID, pheromone-induced killing of C. albicans cells was largely independent of signaling via the Ca(2+)-dependent protein phosphatase calcineurin, even when combined with the loss of Cmk1 and Cmk2 proteins. Finally, we demonstrate that levels of PID vary widely between clinical isolates of C. albicans, with some strains experiencing close to 70% cell death. We discuss these findings in light of the role of prodeath and prosurvival pathways operating in yeast cells undergoing the morphological response to pheromone.

Schizosaccharomyces pombe cell division cycle under limited glucose requires Ssp1 kinase, the putative CaMKK, and Sds23, a PP2A-related phosphatase inhibitor

Calcium/calmodulin-dependent protein kinase (CaMK) is required for diverse cellular functions, and similar kinases exist in fungi. Although mammalian CaMK kinase (CaMKK) activates CaMK and also evolutionarily-conserved AMP-activated protein kinase (AMPK), CaMKK is yet to be established in yeast. We here report that the fission yeast Schizosaccharomyces pombe Ssp1 kinase, which controls G2/M transition and response to stress, is the putative CaMKK. Ssp1 has a CaM binding domain (CBD) and associates with 14-3-3 proteins as mammalian CaMKK does. Temperature-sensitive ssp1 mutants isolated are defective in the tolerance to limited glucose, and this tolerance requires the conserved stretch present between the kinase domain and CBD. Sds23, multi-copy suppressor for mutants defective in type 1 phosphatase and APC/cyclosome, also suppresses the ssp1 phenotype, and is required for the tolerance to limited glucose. We demonstrate that Sds23 binds to type 2A protein phosphatases (PP2A) and PP2A-related phosphatase Ppe1, and that Sds23 inhibits Ppe1 phosphatase activity. Ssp1 and Ppe1 thus seem to antagonize in utilizing limited glucose. We also show that Ppk9 and Ssp2 are the catalytic subunits of AMPK and AMPK-related kinases, respectively, which bind to common beta-(Amk2) and gamma-(Cbs2) subunits.

Nonapoptotic death of Saccharomyces cerevisiae cells that is stimulated by Hsp90 and inhibited by calcineurin and Cmk2 in response to endoplasmic reticulum stresses

Endoplasmic reticulum (ER) stress can trigger apoptosis and necrosis in many types of mammalian cells. Previous studies in yeast found little or no cell death in response to the ER stressor tunicamycin, but a recent study suggested widespread apoptosis-like death. Here we show that wild-type laboratory Saccharomyces cerevisiae cells responding to tunicamycin die by nonapoptotic mechanisms in low-osmolyte culture media and survive for long periods of time in standard synthetic media. Survival requires calcineurin, a Ca(2+)/calmodulin-dependent protein phosphatase, but none of its known targets. The Ca(2+)/calmodulin-dependent protein kinase Cmk2 was identified as an indirect target of calcineurin that suppresses death of calcineurin-deficient cells. Death of Cmk2- and/or calcineurin-deficient S. cerevisiae cells was preceded by accumulation of reactive oxygen species but was not associated with hallmarks of apoptosis and was not dependent on Mca1, Aif1, Nuc1, or other factors implicated in apoptosis-like death. Cmk2 and calcineurin also independently suppressed the death of S. cerevisiae cells responding to dithiothreitol or miconazole, a common azole-class antifungal drug. Though inhibitors of Hsp90 have been shown to diminish calcineurin signaling in S. cerevisiae and to synergistically inhibit growth in combination with azoles, they did not stimulate death of S. cerevisiae cells in combination with miconazole or tunicamycin, and instead they prevented the death of calcineurin- and Cmk2-deficient cells. These findings reveal a novel prodeath role for Hsp90 and antideath roles for calcineurin and Cmk2 that extend the life span of S. cerevisiae cells responding to both natural and clinical antifungal compounds.

The MAP kinase-activated protein kinase Rck2p plays a role in rapamycin sensitivity in Saccharomyces cerevisiae and Candida albicans

Rck2p is a Hog1p-MAP kinase-activated protein kinase and regulates osmotic and oxidative stresses in budding yeast. In this study, we have demonstrated in both Saccharomyces cerevisiae and, the most medically important human fungal pathogen, Candida albicans that deletion of RCK2 renders cells sensitive to rapamycin, the inhibitor of target of rapamycin protein kinase controlling cell growth. The kinase activity of Rck2p does not seem to be required for this rapamycin sensitivity function in both eukaryotic microorganisms. Interestingly, the HOG pathway is not directly involved in cell sensitivity to rapamycin in S. cerevisiae, whereas disruption of CaHOG1 renders cells sensitive to rapamycin in C. albicans. In addition, we have shown that CaRck2p and its kinase activity are required for cell growth in C. albicans.

Functional, genetic and bioinformatic characterization of a calcium/calmodulin kinase gene in Sporothrix schenckii

Background

Sporothrix schenckii is a pathogenic, dimorphic fungus, the etiological agent of sporotrichosis, a subcutaneous lymphatic mycosis. Dimorphism in S. schenckii responds to second messengers such as cAMP and calcium, suggesting the possible involvement of a calcium/calmodulin kinase in its regulation. In this study we describe a novel calcium/calmodulin-dependent protein kinase gene in S. schenckii, sscmk1, and the effects of inhibitors of calmodulin and calcium/calmodulin kinases on the yeast to mycelium transition and the yeast cell cycle.

Results

Using the PCR homology approach a new member of the calcium/calmodulin kinase family, SSCMK1, was identified in this fungus. The cDNA sequence of sscmk1 revealed an open reading frame of 1,221 nucleotides encoding a 407 amino acid protein with a predicted molecular weight of 45.6 kDa. The genomic sequence of sscmk1 revealed the same ORF interrupted by five introns. Bioinformatic analyses of SSCMK1 showed that this protein had the distinctive features that characterize a calcium/calmodulin protein kinase: a serine/threonine protein kinase domain and a calmodulin-binding domain. When compared to homologues from seven species of filamentous fungi, SSCMK1 showed substantial similarities, except for a large and highly variable region that encompasses positions 330 – 380 of the multiple sequence alignment. Inhibition studies using calmodulin inhibitor W-7, and calcium/calmodulin kinase inhibitors, KN-62 and lavendustin C, were found to inhibit budding by cells induced to re-enter the yeast cell cycle and to favor the yeast to mycelium transition.

Conclusion

This study constitutes the first evidence of the presence of a calcium/calmodulin kinase-encoding gene in S. schenckii and its possible involvement as an effector of dimorphism in this fungus. These results suggest that a calcium/calmodulin dependent signaling pathway could be involved in the regulation of dimorphism in this fungus. The results suggest that the calcium/calmodulin kinases of yeasts are evolutionarily distinct from those in filamentous fungi.

Translation elongation factor 2 anticodon mimicry domain mutants affect fidelity and diphtheria toxin resistance

Eukaryotic elongation factor 2 (eEF2) mediates translocation in protein synthesis. The molecular mimicry model proposes that the tip of domain IV mimics the anticodon loop of tRNA. His-699 in this region is post-translationally modified to diphthamide, the target for Corynebacterium diphtheriae and Pseudomonas aeruginosa toxins. ADP-ribosylation by these toxins inhibits eEF2 function causing cell death. Mutagenesis of the tip of domain IV was used to assess both functions. A H694A mutant strain was non-functional, whereas D696A, I698A, and H699N strains conferred conditional growth defects, sensitivity to translation inhibitors, and decreased total translation in vivo. These mutant strains and those lacking diphthamide modification enzymes showed increased -1 frameshifting. The effects are not due to reduced protein levels, ribosome binding, or GTP hydrolysis. Functional eEF2 forms substituted in domain IV confer dominant diphtheria toxin resistance, which correlates with an in vivo effect on translation-linked phenotypes. These results provide a new mechanism in which the translational machinery maintains the accurate production of proteins, establishes a role for the diphthamide modification, and provides evidence of the ability to suppress the lethal effect of a toxin targeted to eEF2.

Toxicity of anionic detergents determined by Saccharomyces cerevisiae microarray analysis

Sodium n-dodecyl benzene sulfonate (LAS) and sodium dodecyl sulfate (SDS) are popular anionic detergents (surfactants) that are used worldwide and the toxicities of these chemicals have been characterized. We applied these chemicals in a DNA microarray bioassay and determined that the microarray data reflects previous findings and also provides some new information about anionic detergent toxicity. The mRNA expression profiles suggest that LAS and SDS cause damage to membranes and alterations in carbon metabolism, and induce the oxidative stress response. We also found that LAS and SDS induce the pleiotropic drug-resistance network, and that LAS and SDS may be pumped out of yeast cells by this network. Hierarchical clustering of the expression profiles showed that LAS and SDS cause similar features of toxicity and that the toxicity is similar to that of capsaicin but different from that of cadmium and mercury.

Binding of calmodulin to Nuf1p is required for karyogamy in Saccharomyces cerevisiae

The role of calmodulin (CaM) during mating in Saccharomyces cerevisiae was examined by using a set of Phe-to-Ala substitutions. We identified ten CaM mutants that exhibited significantly reduced mating efficiencies when crossed to a strain of the opposite mating type harboring the same CaM mutation. Most of the mating-defective CaM mutants were bilateral, i.e., they also exhibited mating defects, albeit minor ones, when crossed to the wild type. When strains carrying different bilateral CaM mutations were mated, the mating efficiencies recovered dramatically. We termed this phenomenon "intragenic mating complementation", and classified the mating-defective CaM mutations into two intragenic mating complementation groups. Two mutant alleles belonging to different groups showed minor defects in cell adhesion and cell fusion, but exhibited severe defects in karyogamy. CaM is known to bind to the essential spindle pole body component Nuf1p. This binding appears to be important for karyogamy because the nuf1(C911R) mutation, which impairs CaM-Nuf1p binding, resulted in a severe defect in karyogamy. Indeed, the two mating-defective CaM mutations were found to compromise formation of the CaM/Nuf1p complex, and the mating defects of these two CaM mutants were suppressible by a dominant, CaM-independent, mutation in NUF1. Taken together, these results suggest that loss of CaM binding to Nuf1p causes a defect in karyogamy, thereby inhibiting productive mating.

Genome-wide analysis of yeast transcription upon calcium shortage

Several regulatory circuits related to important functions, like membrane excitation, immunoresponse, replication, control of the cell cycle and differentiation, among others, cause an increase in intracellular calcium level that finally has a consequence upon transcription of specific genes. The sequencing of the whole genome of eukaryotic cells enables genome-wide analysis of gene expression under many conditions not yet assessed by conventional methods. Using the array technology, the effect of calcium shortage in yeast cells was studied. Correspondence analysis of data showed that there is a response in transcription that is correlated to calcium shortage. The distribution of up-regulated-genes in functional categories suggests a regulatory connection between the cell-cycle progression and the energetic metabolic requirements for growth and division. In silico analysis of promoters reveals the frequent appearance of the Mlu I cell cycle box (MCB) cis element that binds the transcriptional regulatory factor Mcm1.

p85 binds to G-actin in a Ca(2+)/calmodulin-dependent manner, thus regulating the initiation of cytokinesis in tetrahymena

Tetrahymena p85 is localized to the presumptive division plane before the formation of contractile ring microfilaments. p85 binds to calmodulin in a Ca(2+)-dependent manner and both proteins colocalize to the division furrow. Inhibition of the binding of p85 and Ca(2+)/calmodulin prevents both the localization of p85 and calmodulin to the division plane and the formation of the contractile ring, suggesting that the interaction of p85 and Ca(2+)/calmodulin is important in the formation of the contractile ring. We investigated the mechanisms of the formation of contractile ring, and the relationship among p85, CaM, and actin using co-sedimentation assay: p85 binds to G-actin in a Ca(2+)/calmodulin-dependent manner, but does not bind to F-actin. Therefore, we propose that a Ca(2+)/calmodulin signal and its target protein p85 are cooperatively involved in the recruitment of G-actin to the division plane and the formation of the contractile ring.

Genetic analysis of calmodulin and its targets in Saccharomyces cerevisiae

Calmodulin, a small, ubiquitous Ca2+-binding protein, regulates a wide variety of proteins and processes in all eukaryotes. CMD1, the single gene encoding calmodulin in S. cerevisiae, is essential, and this review discusses studies that identified many of calmodulin's physiological targets and their functions in yeast cells. Calmodulin performs essential roles in mitosis, through its regulation of Nuf1p/Spc110p, a component of the spindle pole body, and in bud growth, by binding Myo2p, an unconventional class V myosin required for polarized secretion. Surprisingly, mutant calmodulins that fail to bind Ca2+ can perform these essential functions. Calmodulin is also required for endocytosis in yeast and participates in Ca2+-dependent, stress-activated signaling pathways through its regulation of a protein phosphatase, calcineurin, and the protein kinases, Cmk1p and Cmk2p. Thus, calmodulin performs important physiological functions in yeast cells in both its Ca2+-bound and Ca2+-free form.

Determination of division plane and organization of contractile ring in Tetrahymena

In the molecular mechanism of division plane determination and contractile ring formation, Tetrahymena 85kDa protein (p85) is localized to the presumptive division plane before the formation of the contractile ring. p85 directly interacts with Tetrahymena calmodulin (CaM) in a Ca2+-dependent manner, and p85 and CaM colocalize in the division furrow. A Ca2+/CaM inhibitor N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide HCI (W7) inhibits the direct interaction between p85 and Ca2+/CaM. W7 also inhibits the localization of p85 and CaM to the division plane, and the formation of the contractile ring and division furrow. In addition, p85 binds to G-actin in a Ca2+/CaM dependent manner, but does not bind F-actin. Tetrahymena profilin is localized to division furrow and binds Tetrahymena elongation factor-1alpha (EF-1alpha). EF-1alpha, which induces bundling of Tetrahymena F-actin, is also localized to the division furrow during cytokinesis. The evidence also indicates that Ca2+/CaM inhibits the F-actin-bundling activity of EF-1alpha, and that EF-1alpha and CaM colocalize in the division furrow. In this review, we propose that the Ca2+/CaM signal and its target protein p85 cooperatively regulate the determination of the division plane and the initiation of the contractile ring formation, and that profilin and a Ca2+/CaM-sensitive actin-bundling protein, EF-1alpha, play pivotal roles in regulating the organization of the contractile ring microfilaments.

A homolog of voltage-gated Ca(2+) channels stimulated by depletion of secretory Ca(2+) in yeast

In animal cells, capacitative calcium entry (CCE) mechanisms become activated specifically in response to depletion of calcium ions (Ca(2+)) from secretory organelles. CCE serves to replenish those organelles and to enhance signaling pathways that respond to elevated free Ca(2+) concentrations in the cytoplasm. The mechanism of CCE regulation is not understood because few of its essential components have been identified. We show here for the first time that the budding yeast Saccharomyces cerevisiae employs a CCE-like mechanism to refill Ca(2+) stores within the secretory pathway. Mutants lacking Pmr1p, a conserved Ca(2+) pump in the secretory pathway, exhibit higher rates of Ca(2+) influx relative to wild-type cells due to the stimulation of a high-affinity Ca(2+) uptake system. Stimulation of this Ca(2+) uptake system was blocked in pmr1 mutants by expression of mammalian SERCA pumps. The high-affinity Ca(2+) uptake system was also stimulated in wild-type cells overexpressing vacuolar Ca(2+) transporters that competed with Pmr1p for substrate. A screen for yeast mutants specifically defective in the high-affinity Ca(2+) uptake system revealed two genes, CCH1 and MID1, previously implicated in Ca(2+) influx in response to mating pheromones. Cch1p and Mid1p were localized to the plasma membrane, coimmunoprecipitated from solubilized membranes, and shown to function together within a single pathway that ensures that adequate levels of Ca(2+) are supplied to Pmr1p to sustain secretion and growth. Expression of Cch1p and Mid1p was not affected in pmr1 mutants. The evidence supports the hypothesis that yeast maintains a homeostatic mechanism related to CCE in mammalian cells. The homology between Cch1p and the catalytic subunit of voltage-gated Ca(2+) channels raises the possibility that in some circumstances CCE in animal cells may involve homologs of Cch1p and a conserved regulatory mechanism.

Loss of Cmk1 Ca(2+)-calmodulin-dependent protein kinase in yeast results in constitutive weak organic acid resistance, associated with a post-transcriptional activation of the Pdr12 ATP-binding cassette transporter

Yeast cells display an adaptive stress response when exposed to weak organic acids at low pH. This adaptation is important in the spoilage of preserved foods, as it allows growth in the presence of weak acid food preservatives. In Saccharomyces cerevisiae, this stress response leads to strong induction of the Pdr12 ATP-binding cassette (ABC) transporter, which catalyses the active efflux of weak acid anions from the cytosol of adapted cells. S. cerevisiae cells lacking the Cmk1 isoform of Ca2+-calmodulin-dependent protein kinase are intrinsically resistant to weak acid stress, in that they do not need to spend a long adaptive period in lag phase before resuming growth after exposure to this stress. This resistance of the cmk1 mutant is Pdr12 dependent and, unlike with wild-type S. cerevisiae, cmk1 cells are capable of performing Pdr12-specific functions such as energy-dependent cellular extrusion of fluorescein and benzoate. However, they have neither higher PDR12 gene promoter activity nor higher Pdr12 protein levels. The increased Pdr12 activity in cmk1 cells is therefore caused by Cmk1 exerting a negative post-transcriptional influence over the activity of the Pdr12 ABC transporter, a transporter protein that is constitutively expressed in low-pH yeast cultures. This is the first preliminary evidence that shows a protein kinase, either directly or indirectly, regulating the activity of a yeast ABC transporter.

Cytokinesis in Tetrahymena: determination of division plane and organization of contractile ring

A protein, Tetrahymena p85, is localized to the presumptive division plane before the formation of the contractile ring. p85 directly interacts with Tetrahymena calmodulin (CaM) in a Ca(2+)-dependent manner, and p85 and CaM colocalize in the division furrow. A Ca(2+)/CaM inhibitor N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide HCl (W7) inhibits the direct interaction between p85 and Ca(2+)/CaM. W7 also inhibits the localization of p85 and CaM to the division plane, and the formation of the contractile ring and division furrow. Tetrahymena fimbrin and elongation factor-1a (EF-1alpha), which induce bundling of Tetrahymena F-actin, are also localized to the division furrow during cytokinesis. The Tetrahymena fimbrin has two actin-binding domains, but lacks the EF-hand Ca(2+)-binding motif, suggesting that Tetrahymena fimbrin probably cross-links actin filaments in a Ca(2+)- insensitive manner during cytokinesis. The evidence also indicates that Ca(2+)/CaM inhibits the F-actin-bundling activity of EF-1alpha; and EF-1alpha and CaM colocalize in the division furrow. In this review, we propose that the Ca(2+)/CaM signal and its target protein p85 cooperatively regulate the determination of the division plane, and that a Ca(2+)-insensitive actin-bundling protein, Tetrahymena fimbrin, and a Ca(2+)/CaM-sensitive actin-bundling protein, EF-1alpha, play pivotal roles in regulating the organization of the contractile ring microfilaments.

Ca(2+)/calmodulin and p85 cooperatively regulate an initiation of cytokinesis in Tetrahymena

Tetrahymena p85 differs in mobility in two-dimensional SDS-polyacrylamide gel electrophoresis between wild-type and temperature-sensitive cell-division-arrest mutant cdaA1 cell extracts, and is localized to the presumptive division plane before the formation of the division furrow. The p85 contained three identical sequences which show homology to the calmodulin binding site of Ca(2+)/calmodulin dependent protein kinase Type II in Saccharomyces cerevisiae. We found the p85 directly interacts with Tetrahymena calmodulin in a Ca(2+)-dependent manner, using a co-sedimentation assay. We next examined the localization of p85 and calmodulin during cytokinesis using indirect immunofluorescence. The results showed that both proteins colocalize in the division furrow. This is the first observation that calmodulin is localized in the division furrow. Moreover, the direct interaction between p85 and Ca(2+)/calmodulin was inhibited by Ca(2+)/calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide HCl. When the cells were treated with the drug just before the beginning of cytokinesis, the drug also inhibited the localization of p85 and calmodulin to the division plane, and the formation of the contractile ring and division furrow. Therefore, we propose that the Ca(2+)/calmodulin signal and its target protein p85 cooperatively regulate an initiation of cytokinesis and may be also concerned with the progression of cytokinesis in Tetrahymena.

Molecular cloning of the gene for p85 that regulates the initiation of cytokinesis in Tetrahymena

Tetrahymena p85 is localized to the presumptive division plane before division furrow formation; its molecular weight in SDS-polyacrylamide gel electrophoresis differs in wild-type and temperature-sensitive cell-division-arrest mutant cdaA1 cells. At the restrictive temperature, p85 localization and division furrow formation are not observed in cdaA1 cells. In this study, we purified p85 and cloned a wild-type p85 cDNA. The deduced amino acid sequence of p85 was composed mainly of two kinds of repeat sequences. One of these contained regions homologous to a calmodulin-binding site and a part of actin, and the other contained a region homologous to a part of a cdc2 kinase homologue. Moreover, we cloned a cDNA encoding the cdaA1 p85. There was no difference in the predicted amino acid sequences of wild-type and cdaA1 p85, suggesting that the difference in molecular weight between p85 in wild-type and mutant cells is caused by a disorder of posttranslational-modification mechanisms of p85 in the cdaA1 cell.

Downregulation of delta CaM kinase II in human tumor cells

Over two dozen alternative splice variants of CaMK-II, the type II Ca(2+)/CaM-dependent protein kinase, are encoded from four genes (alpha, beta, gamma and delta) in mammalian cells. Isozymes of alpha and beta CaMK-II are well characterized in brain; however, an understanding of the relative endogenous levels of CaMK-II isozymes in a wide variety of non-neuronal cells has not yet been described. In this study, we have demonstrated that CaMK-II consists primarily of the 54 kDa delta CaMK-II (delta(2) or delta(C)) isozyme in rodent fibroblasts. beta and gamma CaMK-II isozymes are minor and alpha CaMK-II was not expressed. The primary delta CaMK-II in human fibroblasts and the MCF10A mammary epithelial cell line was the 52 kDa delta(4) CaMK-II, an isozyme identical to delta(2) except for a missing 21-amino-acid C-terminal tail. delta CaMK-II levels were diminished in both human and rodent fibroblasts after SV40 transformation and in the mammary adenocarcinoma MCF7 cell line when compared to MCF10A cells. In fact, most tumor cells exhibited CaMK-II specific activities which were two- to tenfold lower than in untransformed fibroblasts. We conducted complementary CaMK-II studies on the NGF-induced differentiation of rat PC-12 cells. Although no new synthesis of CaMK-II occurs, neurite outgrowth in these cells is accompanied by a preferential activation of delta CaMK-II. Endogenous delta CaMK-II has a perinuclear distribution in fibroblasts and extends along neurites in PC-12 cells. These findings point to a role for delta CaMK-II isozymes in cellular differentiation.

Apocalmodulin

Intracellular Ca2+ is normally maintained at submicromolar levels but increases during many forms of cellular stimulation. This increased Ca2+ binds to receptor proteins such as calmodulin (CaM) and alters the cell's metabolism and physiology. Calcium-CaM binds to target proteins and alters their function in such a way as to transduce the Ca2+ signal. Calcium-free or apocalmodulin (ApoCaM) binds to other proteins and has other specific effects. Apocalmodulin has roles in the cell that apparently do not require the ability to bind Ca2+ at all, and these roles appear to be essential for life. Apocalmodulin differs from Ca2+-CaM in its tertiary structure. It binds target proteins differently, utilizing different binding motifs such as the IQ motif and noncontiguous binding sites. Other kinds of binding potentially await discovery. The ApoCaM-binding proteins are a diverse group of at least 15 proteins including enzymes, actin-binding proteins, as well as cytoskeletal and other membrane proteins, including receptors and ion channels. Much of the cellular CaM is bound in a Ca2+-independent manner to membrane structures within the cell, and the proportion bound changes with cell growth and density, suggesting it may be a storage form. Apocalmodulin remains tightly bound to other proteins as subunits and probably hastens the response of these proteins to Ca2+. The overall picture that emerges is that CaM cycles between its Ca2+-bound and Ca2+-free states and in each state binds to different proteins and performs essential functions. Although much of the research focus has been on the roles of Ca2+-CaM, the roles of ApoCaM are equally vital but less well understood.

Calcium/calmodulin-dependent phosphorylation and activation of human Cdc25-C at the G2/M phase transition in HeLa cells

The human tyrosine phosphatase (p54(cdc25-c)) is activated by phosphorylation at mitosis entry. The phosphorylated p54(cdc25-c) in turn activates the p34-cyclin B protein kinase and triggers mitosis. Although the active p34-cyclin B protein kinase can itself phosphorylate and activate p54(cdc25-c), we have investigated the possibility that other kinases may initially trigger the phosphorylation and activation of p54(cdc25-c). We have examined the effects of the calcium/calmodulin-dependent protein kinase (CaM kinase II) on p54(cdc25-c). Our in vitro experiments show that CaM kinase II can phosphorylate p54(cdc25-c) and increase its phosphatase activity by 2.5-3-fold. Treatment of a synchronous population of HeLa cells with KN-93 (a water-soluble inhibitor of CaM kinase II) or the microinjection of AC3-I (a specific peptide inhibitor of CaM kinase II) results in a cell cycle block in G2 phase. In the KN-93-arrested cells, p54(cdc25-c) is not phosphorylated, p34(cdc2) remains tyrosine phosphorylated, and there is no increase in histone H1 kinase activity. Our data suggest that a calcium-calmodulin-dependent step may be involved in the initial activation of p54(cdc25-c).

Importance of phenylalanine residues of yeast calmodulin for target binding and activation

Recent genetic studies of yeast calmodulin (yCaM) have shown that alterations of different sets of Phe residues result in distinct functional defects (Ohya, Y., and Botstein, D. (1994) Science 263, 963-966). To examine the importance of Phe residues for target binding and activation, we purified mutant yCaMs containing single or double Phe to Ala substitutions and determined their ability to bind and activate two target proteins, calcineurin and CaM-dependent protein kinase (CaMK). Binding assays using the gel overlay technique and quantitative analyses using surface plasmon resonance measurements indicated that the binding of yCaM to calcineurin is impaired by either double mutations of F16A/F19A or a single mutation of F140A, while binding to CaMK is impaired by F89A, F92A, or F140A. These same mutant yCaMs fail to activate calcineurin and CaMK, respectively, in vitro. In addition, F19A exhibited a severe defect in activation of both enzymes. F12A activated calcineurin to only 50% of the level achieved by wild-type calmodulin but fully activated CaMK. These results suggest that each target protein requires a specific and distinct subset of Phe residues in yCaM for target binding and activation.

Induction of Ca2+-calmodulin signaling by hard-surface contact primes Colletotrichum gloeosporioides conidia to germinate and form appressoria

Hard-surface contact primes the conidia of Colletotrichum gloeosporioides to respond to plant surface waxes and a fruit-ripening hormone, ethylene, to germinate and form the appressoria required for infection of the host. Our efforts to elucidate the molecular events in the early phase of the hard-surface contact found that EGTA (5 mM) and U73122 (16 nM), an inhibitor of phospholipase C, inhibited (50%) germination and appressorium formation. Measurements of calmodulin (CaM) transcripts with a CaM cDNA we cloned from C. gloeosporioides showed that CaM was induced by hard-surface contact maximally at 2 h and then declined; ethephon enhanced this induction. The CaM antagonist, compound 48/80, completely inhibited conidial germination and appressorium formation at a concentration of 3 microM, implying that CaM is involved in this process. A putative CaM kinase (CaMK) cDNA of C. gloeosporioides was cloned with transcripts from hard-surface-treated conidia. A selective inhibitor of CaMK, KN93 (20 microM), inhibited (50%) germination and appressorium formation, blocked melanization, and caused the formation of abnormal appressoria. Scytalone, an intermediate in melanin synthesis, reversed the inhibition of melanization but did not restore appressorium formation. The phosphorylation of 18- and 43-kDa proteins induced by hard-surface contact and ethephon was inhibited by the treatment with KN93. These results strongly suggest that hard-surface contact induces Ca2+-calmodulin signaling that primes the conidia to respond to host signals by germination and differentiation into appressoria.

Murine CASK is disrupted in a sex-linked cleft palate mouse mutant

A transgenic mouse insertional mutant displayed the phenotype of altered cranial morphology with sex-linked cleft palate. We have cloned the disrupted genomic X-linked locus and report the identification of the mCASK gene. The gene is transcribed to produce two messages of 4.5 and 9.5 kb expressed during development and in adult tissues, particularly the brain. We describe the isolation of two differentially spliced mouse cDNAs from the locus (mCASK-A and mCASK-B). The mCASK-B cDNA probably represents the full-length product of the 4.5-kb transcript. The identical N-termini of the predicted encoded proteins (mCASK-A and -B) are highly homologous to Ca2+/calmodulin-dependent protein kinase II, while the deduced C-terminus of mCASK-B is highly homologous to a family of multidomain proteins containing a guanylate kinase motif, the MAGUK proteins. mCASK-B is a new member of an emerging family of genes in which the encoded proteins combine these domains, termed here, the CAMGUKs, including rat CASK, Caenorhabditis elegans lin-2, and Drosophila caki/camguk. The CAMGUKs are likely to be effectors in signal transduction as regulatory partners of transmembrane molecules, modulated by calcium and nucleotides. The transgene in this mutant mouse line integrated into an intron that bisects the encoded calmodulin-binding domain, a potentially important regulatory domain of the predicted protein, generating hybrid transcripts.

CaMK-II inhibition reduces cyclin D1 levels and enhances the association of p27kip1 with Cdk2 to cause G1 arrest in NIH 3T3 cells

The calmodulin-dependent protein kinase-II (CaMK-II) inhibitor KN-93 has been shown to reversibly arrest mouse and human cells in the G1 phase of the cell cycle [Tombes, R. M., Westin, E., Grant. S., and Krystal, G. (1995) Cell Growth Differ. 6, 1073-1070; Rasmussen, G., and Rasmussen, C. (1995) Biochem. Cell Biol. 71, 201-207]. The stimulation of Ca(2+)-independent (autonomous) CaMK-II enzymatic activity, a barometer of in situ activated CaMK-II, was prevented by the same KN-93 concentrations that cause G1 phase arrest. KN-93 caused the retinoblastoma protein pRB to become dephosphorylated and the activity of both cdk2 and cdk4, two potential pRb kinases, to decrease. Neither the activity of p42MAP kinase, an early response G1 signaling molecule, nor the phosphorylation status or DNA-binding capability of the transcription factors serum response factor and cAMP responsive element-binding protein was altered during this G1 arrest. The protein levels of cyclin-dependent kinase 2 (cdk2) and cdk4 were unaffected during this G1 arrest and the total cellular levels of the cdk inhibitors p21cip1 and p27kip1 were not increased. Instead, the cdk4 activity decreases resulting from KN-93 were the result of a 75% decrease in cyclin D1 levels. In contrast, cyclin A and E levels were relatively constant. Cdk2 activity decreases were primarily the result of enhanced p27kip1 association with cdk2/cyclin E. All of these phenomena were unaffected by KN-93's inactive analog, KN-92, and were reversible upon KN-93 washout. The kinetics of recovery from cell cycle arrest were similar to those reported for other G1 phase blockers. These results suggest a mechanism by which G1 Ca2+ signals could be linked via calmodulin-dependent phosphorylations to the cell cycle-controlling machinery through cyclins and cdk inhibitors.

Role of Ca++/calmodulin binding proteins in Aspergillus nidulans cell cycle regulation

The goal of this review is to summarise the current knowledge concerning the targets of Ca++/calmodulin that are essential for cell cycle progression in lower eukaryotes. Emphasis is placed on Aspergillus nidulans since this is the only organism to date shown to posses essential Ca++ dependent calmodulin activated enzymes. Two such enzymes are the calmodulin activated protein phosphatase, calcineurin and the calmodulin dependent protein kinase. These proteins, each the product of a unique gene, are required for progression of quiescent spores into the proliferative cycle and also for execution of the nuclear division cycle in exponentially growing germlings.

Characterization of calcium/calmodulin-dependent protein kinase II activity in the nervous system of the lobster, Panulirus interruptus

Nervous system tissue from Panulirus interruptus has an enzyme activity that behaves like calcium/calmodulin-dependent protein kinase II (CaM KII) This activity phosphorylates known targets of CaM KII, such as synapsin I and autocamtide 3. It is inhibited by a CaM KII-specific autoinhibitory domain peptide. In addition, this lobster brain activity displays calcium-independent activity after autophosphorylation, another characteristic of CaM KII. A cDNA from the lobster nervous system was amplified using polymerase chain reaction. The fragment was cloned and found to be structurally similar to CaM KII. Serum from rabbits immunized with a fusion protein containing part of this sequence immunoprecipitated a CaM KII enzyme activity and a family of phosphoproteins of the appropriate size for CaM KII subunits. Lobster CaM KII activity is found in the brain and stomatogastric nervous system including the commissural ganglia, commissures, stomatogastric ganglion and stomatogastric nerve. Immunoblot analysis of these same regions also identifies bands at an apparent molecular weight characteristic of CaM KII.

Tcn1p/Crz1p, a calcineurin-dependent transcription factor that differentially regulates gene expression in Saccharomyces cerevisiae

Ca2+ signals regulate gene expression in animal and yeast cells through mechanisms involving calcineurin, a protein phosphatase activated by binding Ca2+ and calmodulin. Tcn1p, also named Crz1p, was identified as a transcription factor in yeast required for the calcineurin-dependent induction of PMC1, PMR1, PMR2A, and FKS2 which confer tolerance to high Ca2+, Mn2+, Na+, and cell wall damage, respectively. Tcn1p was not required for other calcineurin-dependent processes, such as inhibition of a vacuolar H+/Ca2+ exchanger and inhibition of a pheromone-stimulated Ca2+ uptake system, suggesting that Tcn1p functions downstream of calcineurin on a branch of the calcium signaling pathway leading to gene expression. Tcn1p contains three zinc finger motifs at its carboxyl terminus resembling the DNA-binding domains of Zif268, Swi5p, and other transcription factors. When fused to the transcription activation domain of Gal4p, the carboxy terminal domain of Tcn1p directed strong calcineurin-independent expression of PMC1-lacZ and other target genes. The amino-terminal domain of Tcn1p was found to function as a calcineurin-dependent transcription activation domain when fused to the DNA-binding domain of Gal4p. This amino-terminal domain also formed Ca2+-dependent and FK506-sensitive interactions with calcineurin in the yeast two-hybrid assay. These findings suggest that Tcn1p functions as a calcineurin-dependent transcription factor. Interestingly, induction of Tcn1p-dependent genes was found to be differentially controlled in response to physiological Ca2+ signals generated by treatment with mating pheromone and high salt. We propose that different promoters are sensitive to variations in the strength of Ca2+ signals generated by these stimuli and to effects of other signaling pathways.

Identification and characterization of the CLK1 gene product, a novel CaM kinase-like protein kinase from the yeast Saccharomyces cerevisiae

The CLK1 gene of Saccharomyces cerevisiae encodes a 610-residue protein kinase that resembles known type II Ca2+/calmodulin-dependent protein kinases (CaM kinases), including the CMK1 and CMK2 gene products from the same yeast. The Clk1 kinase domain is preceded by a 162-residue N-terminal extension, followed by a 132-residue C-terminal extension (which contains a basic segment resembling known calmodulin-binding sites) and is as similar to mammalian CaM kinase (38% identity to rat CaM kinase alpha) as it is to yeast CaM kinase (37% identity to Cmk2). However, Clk1 shares 52% identity with Rck1, another putative protein kinase encoded in the S. cerevisiae genome. Clk1 tagged with a c-myc epitope (expressed in yeast) and a GST-Clk1 fusion (expressed in bacteria) underwent autophosphorylation and phosphorylated an exogenous substrate (yeast protein synthesis elongation factor 2), primarily on Ser. Neither Clk1 activity was stimulated by purified yeast calmodulin (CMD1 gene product), with or without Ca2+; no association of Clk1 with Cmd1 was detectable by other methods. C-terminally truncated Clk1(Delta487-610) was growth-inhibitory when overexpressed, whereas catalytically inactive Clk1(K201R Delta487-610) was not, suggesting that the C terminus is a negative regulatory domain. Using immunofluorescence, Clk1 was localized to the cytosol and excluded from the nucleus. A clk1Delta mutant, a clk1Delta rck1Delta double mutant, a clk1Delta cmk1Delta cmk2Delta triple mutant, and a clk1Delta rck1Delta cmk1Delta cmk2Delta quadruple mutant were all viable and manifested no other overt growth phenotype.

A novel protein kinase gene family in Giardia duodenalis

Two protein kinase (PK) genes, gPK1 and gPK2, were cloned from the genome of the ancient protozoan parasite, Giardia duodenalis (Gd). Both gPK genes and their products are highly homologous (85% and 77% identical, respectively). gPK1 and gPK2 contain all the motifs characteristic of PK, but they are not highly homologous to other PK and therefore belong to a novel PK gene family. Northern blot analysis showed that the gPK genes are expressed in vivo. Southern blot analysis indicated that there are other homologous PK genes in the Gd genome. gPK1 and gPK2 are the first full-length PK genes cloned from this primitive eukaryote. The unique amino acid (aa) sequences of gPK1 and gPK2 suggest that they are involved in unique biological functions in Gd.

Regulation of Ca2+/calmodulin-dependent protein kinase from Trypanosoma cruzi

A multifunctional Ca2+/calmodulin-dependent protein kinase (TcCaM K) was purified and characterized from the cytosol of Trypanosoma cruzi epimastigote forms. Like mammalian CaM KII, TcCaM K has a broad substrate specificity and a similar subunit composition. Western blot analysis revealed that this TcCaM K possesses two subunits of 50 and 60 kDa, which exhibited autophosphorylating activity. A panel of monoclonal and polyclonal antibodies raised against rat brain CaM KII could also recognize TcCaM K. However, experimental evidence suggests a different conformational arrangement of the TcCaM K subunits. Like its mammalian counterpart, two highly active autonomous, Ca(2+)-independent, states of TcCaM K can be isolated. These states, caused by high phosphate incorporation, differ only in their extent of Ca2+/CaM-dependence. About 15-20% of the autophosphorylated TcCaM K can be reverted using protein phosphatase 2A, and, consequently, its Ca(2+)-dependent activity is also partially restored. The situation is somewhat different when the enzyme is linked to the cytoskeleton, as we have previously shown. The membrane-bound form is present only in the native form. Activation increases its protein kinase activity from 5- to 14-fold. In this study, we provide evidence of another form of TcCaM K present in soluble fractions of the parasite that can be isolated in autonomous states. Our results suggest that autophosphorylation of membrane-bound TcCaM K may be responsible for kinase release in a Ca2+/CaM-independent state. These properties of TcCaM K may play an important role in regulating Ca(2+)-dependent processes in the parasite.

Characterization of a calcium/calmodulin-dependent protein kinase homolog from maize roots showing light-regulated gravitropism

Roots of many species respond to gravity (gravitropism) and grow downward only if illuminated. This light-regulated root gravitropism is phytochrome-dependent, mediated by calcium, and inhibited by KN-93, a specific inhibitor of calcium/calmodulin-dependent protein kinase II (CaMK II). A cDNA encoding MCK1, a maize homolog of mammalian CaMK, has been isolated from roots of maize (Zea mays L.). The MCK1 gene is expressed in root tips, the site of perception for both light and gravity. Using the [35S]CaM gel-overlay assay we showed that calmodulin-binding activity of the MCK1 is abolished by 50 microM KN-93, but binding is not affected by 5 microM KN-93, paralleling physiological findings that light-regulated root gravitropism is inhibited by 50 microM KN-93, but not by 5 microM KN-93. KN-93 inhibits light-regulated gravitropism by interrupting transduction of the light signal, not light perception, suggesting that MCK1 may play a role in transducing light. This is the first report suggesting a physiological function for a CaMK homolog in light signal transduction.