Characterization of PKC2, a gene encoding a second protein kinase C isotype of Saccharomyces cerevisiae

BACKGROUND: Protein kinase C (PKC) has attracted considerable attention over the past decade, primarily because of its presumed role in cellular growth control and tumourigenesis. Mammalian cells express at least 10 different isozymes of PKC; it is this complexity that has made elucidating the precise functions of PKC: so difficult. The identification of PKC homologues in organisms such as Drosophila, Xenopus, Dictyostelium, Aplysia and Caenorhabditis indicates that the enzyme is evolutionarily conserved, and this has stimulated our search for counterparts in the yeast Saccharomyces cerevisiae, in which powerful genetic analyses can be used. To date, only one PKC homologue, PKC1, has been identified in yeast and no biochemical activity has been definitively ascribed to the encoded protein. This, and the inability to identify other PKC homologues in yeast by DNA hybridization, has led to doubts about the existence of PKC isozymes in yeast. We have taken the approach of screening yeast expression libraries with anti-PKC antibodies in an attempt to identify further homologues. RESULTS: We have identified a novel PKC isozyme, Pkc2p, encoded by the gene PKC2. We report here the sequence of PKC2 and a comparison showing its similarity to other PKCs. Phylogenetic analysis suggests that all known PKC genes, including PKC2, originated from a common ancestor. Disruption of the PKC2 protein-coding region, deleting the entire catalytic domain of the encoded enzyme, is not lethal to yeast growing on rich media. However, the pkc2 mutant, unlike wild-type strains, fails to grow on minimal media containing limited concentrations of amino acids. This implicates Pkc2p in the response of yeast cells to amino-acid starvation. CONCLUSION: We have shown that yeast cells do express more than one PKC isozyme, by identifying and characterizing a novel PKC gene PKC2, the product of which may be involved in the cellular response to amino-acid starvation.     

Protein-protein interactions in the yeastPKC1 pathway: Pkc1p interacts with a component of the MAP kinase cascade

The two-hybrid system for the identification of protein-protein interactions was used to screen for proteins that interact in vivo with theSaccharomyces cerevisiae Pkc1 protein, a homolog of mammalian protein kinase C. Four positive clones were isolated that encoded portions of the protein kinase Mkk1, which acts downstream of Pkc1p in thePKC1-mediated signalling pathway. Subsequently, Pkc1p and the otherPKC1 pathway components encoding members of a MAP kinase cascade, Bck1p (a MEKK), Mkk1p, Mkk2p (two functionally homologous MEKs), and Mpk1p (a MAP kinase), were tested pairwise for interaction in the two-hybrid assay. Pkc1p interacted specifically with small N-terminal deletions of Mkk1p, and no interaction between Pkc1p and any of the other known pathway components could be detected. Interaction between Pkc1p and Mkk1p, however, was found to be independent of Mkk1p kinase activity. Bck1p was also found to interact with Mkk1p and Mkk2p, and the interaction required only the predicted C-terminal catalytic domain of Mkk1p. Furthermore, we detected protein-protein interactions between two Bck1p molecules via their N-terminal regions. Finally, Mkk2p and Mpk1p also interacted in the two-hybrid assay. These results suggest that the members of thePKC1-mediated MAP kinase cascade form a complex in vivo and that Pkc1p is capable of directly interacting with at least one component of this pathway.     

A pair of putative protein kinase genes (YPK1 and YPK2) is required for cell growth in Saccharomyces cerevisiae

Summary Probes derived from cDNAs encoding isozymes of rat protein kinase C (PKC) were used to screen the genome of the budding yeast Saccharomyces cerevisiae. We reported previously the isolation of the yeast PKC1 gene, a homolog of the , , and subspecies of mammalian PKC. Here we report the isolation and genetic characterization of a pair of previously described genes (YPK1 and YPK2) which are predicted to encode protein kinases that share 90% amino acid identity with each other and 44–46% identity with various isozymes of PKC throughout their putative catalytic domains. Deletion of YPK2 resulted in no apparent phenotypic defect, but loss of YPK1 resulted in slow growth. Cells deleted for both YPK1 and YPK2 were defective in vegetative growth, indicating that the protein kinases predicted to be encoded by these genes are functionally overlapping and play an essential role in the proliferation of yeast cells. The YPK1 gene was mapped to the left arm of chromosome XI and YPK2 was mapped to the right arm of chromosome XIII.     

The synthetic genetic network around PKC1 identifies novel modulators and components of protein kinase C signaling in Saccharomyces cerevisiae

Budding yeast Saccharomyces cerevisiae contains one protein kinase C (PKC) isozyme encoded by the essential gene PKC1. Pkc1 is activated by the small GTPase Rho1 and plays a central role in the cell wall integrity (CWI) signaling pathway. This pathway acts primarily to remodel the cell surface throughout the normal life cycle and upon various environmental stresses. The pathway is heavily branched, with multiple nonessential branches feeding into and out of the central essential Rho1-Pkc1 module. In an attempt to identify novel components and modifiers of CWI signaling, we determined the synthetic lethal genetic network around PKC1 by using dominant-negative synthetic genetic array analysis. The resulting mutants are hypersensitive to lowered Pkc1 activity. The corresponding 21 nonessential genes are closely related to CWI function: 14 behave in a chemical-genetic epistasis test as acting in the pathway, and 6 of these genes encode known components. Twelve of the 21 null mutants display elevated CWI reporter activity, consistent with the idea that the pathway is activated by and compensates for loss of the gene products. Four of the 21 mutants display low CWI reporter activity, consistent with the idea that the pathway is compromised in these mutants. One of the latter group of mutants lacks Ack1(Ydl203c), an uncharacterized SEL-1 domain-containing protein that we find modulates pathway activity. Epistasis analysis places Ack1 upstream of Pkc1 in the CWI pathway and dependent on the upstream Rho1 GTP exchange factors Rom2 and Tus1. Overall, the synthetic genetic network around PKC1 directly and efficiently identifies known and novel components of PKC signaling in yeast.     

A screen for upstream components of the yeast protein kinase C signal transduction pathway identifies the product of the SLG1 gene

We employed the constitutive BCK1-20 allele of the gene for the MAP kinase kinase kinase (MAPKKK) in the yeast Pkc signal transduction pathway to develop a genetic screen for mutants in genes encoding upstream components. Transposon mutagenesis yielded a mutant that was completely dependent on the active allele in the absence of osmotic stabilization. The transposon had integrated at the yeast SLG1 (HCS77) locus. This gene encodes a putative membrane protein. Haploid slg1 deletion strains are sensitive to caffeine, as expected for mutants in the Pkc pathway, as well as a variety of other drugs. The response to elevated temperatures and the dependence on osmotic stabilization depends on the genetic background. Thus, in the strain used for mutagenesis, disruption of SLG1 causes the cells to become non-viable in the absence of osmotic stabilization at both 30° C and 37° C. In a different genetic background this phenotype was not observed. Sensitivity of the haploid deletion mutants to caffeine can be partially suppressed by overexpression of genes for other components of the Pkc pathway, such as PKC1, SLT2, ROM2, and STE20. In addition, a SLG1-lacZ reporter construct shows higher expression in the presence of caffeine or magnesium chloride in a wild-type diploid background. Received: 2 December 1997 / Accepted: 15 December 1997     

Protein kinase C controls activation of the DNA integrity checkpoint

The protein kinase C (PKC) superfamily plays key regulatory roles in numerous cellular processes. Saccharomyces cerevisiae contains a single PKC, Pkc1, whose main function is cell wall integrity maintenance. In this work, we connect the Pkc1 protein to the maintenance of genome integrity in response to genotoxic stresses. Pkc1 and its kinase activity are necessary for the phosphorylation of checkpoint kinase Rad53, histone H2A and Xrs2 protein after deoxyribonucleic acid (DNA) damage, indicating that Pkc1 is required for activation of checkpoint kinases Mec1 and Tel1. Furthermore, Pkc1 electrophoretic mobility is delayed after inducing DNA damage, which reflects that Pkc1 is post-translationally modified. This modification is a phosphorylation event mediated by Tel1. The expression of different mammalian PKC isoforms at the endogenous level in yeast pkc1 mutant cells revealed that PKCδ is able to activate the DNA integrity checkpoint. Finally, downregulation of PKCδ activity in HeLa cells caused a defective activation of checkpoint kinase Chk2 when DNA damage was induced. Our results indicate that the control of the DNA integrity checkpoint by PKC is a mechanism conserved from yeast to humans.     

Molecular analysis reveals localization of Saccharomyces cerevisiae protein kinase C to sites of polarized growth and Pkc1p targeting to the nucleus and mitotic spindle

The catalytic activity and intracellular localization of protein kinase C (PKC) are both highly regulated in vivo. This family of kinases contains conserved regulatory motifs, i.e., the C1, C2, and HR1 domains, which target PKC isoforms to specific subcellular compartments and restrict their activity spatially. Saccharomyces cerevisiae contains a single PKC isozyme, Pkc1p, which contains all of the regulatory motifs found in mammalian PKCs. Pkc1p localizes to sites of polarized growth, consistent with its main function in maintaining cell integrity. We dissected the molecular basis of Pkc1p localization by expressing each of its domains individually and in combinations as green fluorescent protein fusions. We find that the Rho1p-binding domains, HR1 and C1, are responsible for targeting Pkc1p to the bud tip and cell periphery, respectively. We demonstrate that Pkc1p activity is required for its normal localization to the bud neck, which also depends on the integrity of the septin ring. In addition, we show for the first time that yeast protein kinase C can accumulate in the nucleus, and we identify a nuclear exit signal as well as nuclear localization signals within the Pkc1p sequence. Thus, we propose that Pkc1p shuttles in and out of the nucleus and consequently has access to nuclear substrates. Surprisingly, we find that deletion of the HR1 domain results in Pkc1p localization to the mitotic spindle and that the C2 domain is responsible for this targeting. This novel nuclear and spindle localization of Pkc1p may provide a molecular explanation for previous observations that suggest a role for Pkc1p in regulating microtubule function.     

Expression of a VEGF-like Protein from Parapoxvirus ovis in the Yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe

We report on the expression of a VEGF-like protein encoded by Parapoxvirus ovis in the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. We show that a lysine residue at amino acid position 2 (K2) is an important determinant for the stability of this protein in S. cerevisiae. Replacement of K2 by an arginine results in stabilization of the protein. This observation suggests that this lysine may be a target for ubiquitinylation, which is a prerequisite for proteasome-mediated protein degradation. Interestingly, in S. pombe the lysine (K2) has no influence on the stability of the protein. This result indicates that the two yeast species exhibit significant differences in their protein degradation pathways.     

Protein-protein interactions in the yeastPKC1 pathway: Pkc1p interacts with a component of the MAP kinase cascade

The two-hybrid system for the identification of protein-protein interactions was used to screen for proteins that interact in vivo with theSaccharomyces cerevisiae Pkc1 protein, a homolog of mammalian protein kinase C. Four positive clones were isolated that encoded portions of the protein kinase Mkk1, which acts downstream of Pkc1p in thePKC1-mediated signalling pathway. Subsequently, Pkc1p and the otherPKC1 pathway components encoding members of a MAP kinase cascade, Bck1p (a MEKK), Mkk1p, Mkk2p (two functionally homologous MEKs), and Mpk1p (a MAP kinase), were tested pairwise for interaction in the two-hybrid assay. Pkc1p interacted specifically with small N-terminal deletions of Mkk1p, and no interaction between Pkc1p and any of the other known pathway components could be detected. Interaction between Pkc1p and Mkk1p, however, was found to be independent of Mkk1p kinase activity. Bck1p was also found to interact with Mkk1p and Mkk2p, and the interaction required only the predicted C-terminal catalytic domain of Mkk1p. Furthermore, we detected protein-protein interactions between two Bck1p molecules via their N-terminal regions. Finally, Mkk2p and Mpk1p also interacted in the two-hybrid assay. These results suggest that the members of thePKC1-mediated MAP kinase cascade form a complex in vivo and that Pkc1p is capable of directly interacting with at least one component of this pathway.     

The yeast gene MSH3 defines a new class of eukaryotic MutS homologues

We have identified a gene in Saccharomyces cerevisiae, MSH3, whose predicted protein product shares extensive sequence similarity with bacterial proteins involved in DNA mismatch repair as well as with the predicted protein product of the Rep-3 gene of mouse. MSH3 was obtained by performing a polymerase chain reaction on yeast genomic DNA using degenerate oligonucleotide primers designed to anneal with the most conserved regions of a gene that would be homologous to Rep-3 and Salmonella typhimurium mutS. MSH3 seems to play some role in DNA mismatch repair, inasmuch as its inactivation results in an increase in reversion rates of two different mutations and also causes an increase in postmeiotic segregation. However, the effect of MSH3 disruption on reversion rates and postmeiotic segregation appears to be much less than that of previously characterized yeast DNA mismatch repair genes. Alignment of the MSH3 sequence with all of the known MutS homologues suggests that its primary function may be different from the role of MutS in repair of replication errors. MSH3 appears to be more closely related to the mouse Rep-3 gene and other similar eukaryotic mutS homologues than to the yeast gene MSH2 and other mutS homologues that are involved in replication repair. We suggest that the primary function of MSH3 may be more closely related to one of the other known functions of mutS, such as its role in preventing recombination between non-identical sequences.     

Asc1 Supports Cell-Wall Integrity Near Bud Sites by a Pkc1 Independent Mechanism

Background

The yeast ribosomal protein Asc1 is a WD-protein family member. Its mammalian ortholog, RACK1 was initially discovered as a receptor for activated protein C kinase (PKC) that functions to maintain the active conformation of PKC and to support its movement to target sites. In the budding yeast though, a connection between Asc1p and the PKC signaling pathway has never been reported.

Methodology/Principal Findings

In the present study we found that asc1-deletion mutant (asc1Δ) presents some of the hallmarks of PKC signaling mutants. These include an increased sensitivity to staurosporine, a specific Pkc1p inhibitor, and susceptibility to cell-wall perturbing treatments such as hypotonic- and heat shock conditions and zymolase treatment. Microscopic analysis of asc1Δ cells revealed cell-wall invaginations near bud sites after exposure to hypotonic conditions, and the dynamic of cells'' survival after this stress further supports the involvement of Asc1p in maintaining the cell-wall integrity during the mid-to late stages of bud formation. Genetic interactions between asc1 and pkc1 reveal synergistic sensitivities of a double-knock out mutant (asc1Δ/pkc1Δ) to cell-wall stress conditions, and high basal level of PKC signaling in asc1Δ. Furthermore, Asc1p has no effect on the cellular distribution or redistribution of Pkc1p at optimal or at cell-wall stress conditions.

Conclusions/Significance

Taken together, our data support the idea that unlike its mammalian orthologs, Asc1p acts remotely from Pkc1p, to regulate the integrity of the cell-wall. We speculate that its role is exerted through translation regulation of bud-site related mRNAs during cells'' growth.     

Regulation of protein kinase C and ornithine decarboxylase in the epidermis of juvenile white suckers (Catostomus commersoni) by 12-O-tetradecanoylphorbol-13-acetate, 17 α-ethinylestradiol and testosterone

This study was designed to investigate whether potent regulators of mammalian protein kinase C (PKC) and ornithine decarboxylase (ODC) activity also regulate epidermal PKC and ODC activity in fish. Juvenile white suckers (Catostomus commersoni) were given single or multiple subdermal injections of testosterone, 17α-ethinylestradiol or 12-O-tetradeconylphorbol-13-acetate (TPA) dissolved in sunflower oil. Sequential activation of epidermal PKC and ODC was observed in single injection protocols. Maximal PKC activity occurred at 12–48 hr post-injection, with a corresponding increase in ODC activity in the 12–48 hr immediately following this event. In the multiple injection protocols, PKC activity was almost completely depressed after 1 week of injections, during which ODC activity was stimulated 2- to 5-fold, indicating possible differential activation of these two enzymes. Multiple injections of testosterone, 17α-ethinylestradiol and TPA induced histologically distinct epidermal hyperplasia in suckers, although this did not occur in single injection treatments. The mammalian isozymes of PKC are known to be dependent on Ca²⁺ and phospholipid for optimum activity. This study demonstrated that the fish isozyme of PKC is also Ca²⁺ and phospholipid dependent. Our results indicate that PKC and ODC may be good biochemical markers for neoplasia and hyperplasia in fish.     

Translocation of protein kinase C isozymes in rat pituitary lactotroph-enriched cell cultures by substance P: effects of sex and age

Abstract

It is generally accepted that the phospholipid and calcium-dependent enzyme protein kinase C (PKC) plays a significant role in secretion of hormones from anterior piuitary cells. The present study was undertaken to study age and sex-related changes in 1. levels of immunoreactivity of PKC isozymes and 2. distribution of immunoreactivity of PKC isozymes after stimulation with substance P (SP) in rat lactotroph-enriched cell cultures. The α, β, δ and ζ isozymes were present in both sexes and at all ages. There was a sex-specific differential regulation of the different PKC isozymes as a function of sexual maturation. In male rats there was an up-regulation of the α isozyme throughout the sexual development, while the β subtype showed a small, but significant decrease in immunoreactivity with increasing age. In female rats, on the other hand, the β species was up-regulated with increasing age while the other subtypes remained constant. The concentration of the δ and ζ isozymes was unaffected of sex and age. Stimulation of lactotroph-enriched cell cultures with substance P (SP) resulted in translocation of the α and β isozymes from the soluble to the particulate fraction while the δ and ζ species were left unchanged independently of age and sex. However, a decrease in responsiveness was observed in adult male rats, although a significant degree of translocation of α and β species was still detected. On the basis of these results it is suggested that in lactotroph-enriched cell cultures basal levels of PKC subtype immunoreactivity and distribution of immunoreactivity of PKC isozymes after SP challenge might be regulated as a function of sex and age.     

Genetic interactions among genes involved in the STT4-PKC1 pathway of Saccharomyces cerevisiae

Loss of yeast protein kinase C function results in three distinct phenotypes: staurosporine sensitivity, cell lysis and blockage of cell cycle progression at the G2/M boundary. Genetic analysis of the PKC1/STT1 protein kinase C gene and its interactions with STT4, encoding an upstream phosphatidylinositol 4-kinase, and BCK1, encoding a downstream protein kinase, reveal that they form part of a single pathway. However, the BCK1-20 mutation (a gain-of-function mutation of BCK1) or overexpression of PKC1 cannot suppress all of the phenotypes caused by the loss of STT4 function, strongly suggesting the existence of a branch point between STT4 and PKC1. We also describe the MSS4 gene, a multicopy suppressor of the temperature-sensitive stt4-1 mutation. MSS4 is predicted to encode a hydrophilic protein of 779 amino acid residues and is essential for cell growth. Based on genetic and biochemical data, we suggest that MSS4 acts downstream of STT4, but in a pathway that does not involve PKC1. GenBank accession number: The accession number for the MSS4 sequence reported in this paper is D13716.     

A novel 2,4-diaminopyrimidine derivative as selective inhibitor of protein kinase C theta prevents allograft rejection in a rat heart transplant model

Protein kinase C theta (PKCθ) plays a critical role in T cell signaling and is an attractive target for the treatment of T cell-mediated diseases such as transplant rejection and autoimmune disease. To identify PKCθ inhibitors, we focused on the 2,6-diamino-3-carbamoyl-5-cyanopyrazine derivative 2, which exhibited moderate PKCθ inhibitory activity. Optimization of 2 identified the 2,4-diamino-5-cyanopyrimidine derivative 16c, which exhibited potent PKCθ inhibitory activity and showed good selectivity against other PKC isozymes. Compound 16c prolonged graft survival in an in vivo rat heterotopic cardiac transplant model.     

球孢白僵菌Hog1 MAPK同源基因BbHog1的克隆及特征分析

根据几种丝状真菌Hog1 MAPK的保守氨基酸序列设计简并引物,从昆虫病原真菌球孢白僵菌中扩增出MAPK同源基因的部分片段,然后利用YADE法延伸该片段的上、下游邻接序列,获得MAPK编码基因的全长序列,命名为BbHog1。序列分析表明,该基因编码358个氨基酸的多肽,推测分子量为40.99kDa,等电点为5.49。BbHog1含有MAPK保守的蛋白激酶激活域(TGY),序列与粗糙脉孢霉os-2(AF297032)、烟曲霉OSM1(XM_747571)、隐球酵母HOG1(AF243531)和酿酒酵母Hog1(Z73285)等Hog1 MAPK高度同源,相似性分别为94%、89%、83%和80%。系统聚类结果表明,BbHog1与酵母Hog1 MAPK同源。Southern杂交表明,BbHog1在球孢白僵菌基因组中以单拷贝形式存在。Northern分析表明,BbHog1在高渗、亚高温和营养胁迫等条件下的表达明显升高。由此推测,BbHog1基因可能与球孢白僵菌对逆境胁迫的适应性调节密切相关。     

Activation of PKC isoforms by ATP/UTP and PMA in murine astrocytes

Abnormal myelin formation appears to be one defect contributing to the neuropathology associated with the fetal alcohol syndrome, the major cause of noncongenital mental retardation. Using the CG-4 cell line we previously showed that 25–75 m m ethanol (EtOH) down-regulates myelin basic protein (MBP) expression in differentiating oligodendrocytes (OLGs) without affecting the 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) expression or morphological development (Bichenkov and Ellingson 2001). Here we observed that a relatively low concentration of 12-phorbol-13-myristate acetate (PMA) mimicked the EtOH-caused inhibition of MBP expression without affecting CNP expression or morphology. The inhibition of MBP expression by 100 m m EtOH or 1 n m PMA was completely counteracted by three inhibitors of protein kinase C (PKC); bisinodoylmaleimide I, chelerythrine chloride, and calphostin C, indicating that EtOH down-regulated MBP expression by activating PKC. We investigated whether the EtOH-caused activation resulted in part from up-regulation of the expression of PKC isozymes. Of 11 PKC isozymes examined, CG-4 OLGs expressed nine; PKC α, β1, β2, δ, ε, λ, μ, nu and zeta; while PKC isozymes γ and theta were not detected. Only five PKC isozymes, α, β1, β2, μ, and nu, displayed developmental changes in expression. However, EtOH did not up-regulate the early expression of any PKC isozyme during the first two days of differentiation, the developmental stage when it down-regulates the MBP expression in CG-4 cells. The results indicate that EtOH delays MBP expression by activating at least one phorbol ester-sensitive PKC isozyme in differentiating oligodendrocytes without up-regulating its expression.
Acknowledgements:   Support: NIAAA Grant AA072185.       

球孢白僵菌Hog1 MAPK同源基因BbHog1的克隆及特征分析

根据几种丝状真菌Hog1 MAPK的保守氨基酸序列设计简并引物,从昆虫病原真菌球孢白僵菌中扩增出MAPK同源基因的部分片段,然后利用YADE法延伸该片段的上、下游邻接序列,获得MAPK编码基因的全长序列,命名为BbHog1。序列分析表明,该基因编码358个氨基酸的多肽,推测分子量为40.99kDa,等电点为5.49。BbHog1含有MAPK保守的蛋白激酶激活域(TGY),序列与粗糙脉孢霉os-2(AF297032)、烟曲霉OSM1(XM_747571)、隐球酵母HOG1(AF243531)和酿酒酵母Hog1(Z73285)等Hog1 MAPK高度同源,相似性分别为94%、89%、83%和80%。系统聚类结果表明,BbHog1与酵母Hog1 MAPK同源。Southern杂交表明,BbHog1在球孢白僵菌基因组中以单拷贝形式存在。Northern分析表明,BbHog1在高渗、亚高温和营养胁迫等条件下的表达明显升高。由此推测,BbHog1基因可能与球孢白僵菌对逆境胁迫的适应性调节密切相关。