LAMMER kinase homolog, Lkh1, is involved in oxidative-stress response of fission yeast

The dual-specificity kinase MoLKH1-mediated cell cycle, autophagy, and suppression of plant immunity is critical for development and pathogenicity of Magnaporthe oryzae

Cell cycle progression, autophagic cell death during appressorium development, and ROS degradation at the infection site are important for the development of rice blast disease. However, the association of cell cycle, autophagy and ROS detoxification remains largely unknown in M. oryzae. Here, we identify the dual-specificity kinase MoLKH1, which serves as an important cell cycle regulator required for appressorium formation by regulating cytokinesis and cytoskeleton in M. oryzae. MoLKH1 is transcriptionally activated by H2O2 and required for H2O2-induced autophagic cell death and suppression of ROS-activated plant defense during plant invasion of M. oryzae. In addition, the Molkh1 mutant also showed several phenotypic defects, including delayed growth, abnormal conidiation, damaged cell wall integrity, impaired glycogen and lipid transport, reduced secretion of extracellular enzymes and effectors, and attenuated virulence of M. oryzae. Nuclear localization of MoLKH1 requires the nuclear localization sequence, Lammer motif, as well as the kinase active site and ATP-binding site in this protein. Site-directed mutagenesis showed that each of them plays crucial roles in fungal growth and pathogenicity of M. oryzae. In conclusion, our results demonstrate that MoLKH1-mediated cell cycle, autophagy, and suppression of plant immunity play crucial roles in development and pathogenicity of M. oryzae.

Pleiotropic roles of LAMMER kinase, Lkh1 in stress responses and virulence of Cryptococcus neoformans

Dual-specificity LAMMER kinases are highly evolutionarily conserved in eukaryotes and play pivotal roles in diverse physiological processes, such as growth, differentiation, and stress responses. Although the functions of LAMMER kinase in fungal pathogens in pathogenicity and stress responses have been characterized, its role in Cryptococcus neoformans, a human fungal pathogen and a model yeast of basidiomycetes, remains elusive. In this study, we identified a LKH1 homologous gene and constructed a strain with a deleted LKH1 and a complemented strain. Similar to other fungi, the lkh1Δ mutant showed intrinsic growth defects. We observed that C. neoformans Lkh1 was involved in diverse stress responses, including oxidative stress and cell wall stress. Particularly, Lkh1 regulates DNA damage responses in Rad53-dependent and -independent manners. Furthermore, the absence of LKH1 reduced basidiospore formation. Our observations indicate that Lkh1 becomes hyperphosphorylated upon treatment with rapamycin, a TOR protein inhibitor. Notably, LKH1 deletion led to defects in melanin synthesis and capsule formation. Furthermore, we found that the deletion of LKH1 led to the avirulence of C. neoformans in a systemic cryptococcosis murine model. Taken together, Lkh1 is required for the stress response, sexual differentiation, and virulence of C. neoformans.

The LAMMER Kinase MoKns1 Regulates Growth, Conidiation and Pathogenicity in Magnaporthe oryzae

Magnaporthe oryzae is an important pathogen that causes a devastating disease in rice. It has been reported that the dual-specificity LAMMER kinase is conserved from yeast to animal species and has a variety of functions. However, the functions of the LAMMER kinase have not been reported in M. oryzae. In this study, we identified the unique LAMMER kinase MoKns1 and analyzed its function in M. oryzae. We found that in a MoKNS1 deletion mutant, growth and conidiation were primarily decreased, and pathogenicity was almost completely lost. Furthermore, our results found that MoKns1 is involved in autophagy. The ΔMokns1 mutant was sensitive to rapamycin, and MoKns1 interacted with the autophagy-related protein MoAtg18. Compared with the wild-type strain 70−15, autophagy was significantly enhanced in the ΔMokns1 mutant. In addition, we also found that MoKns1 regulated DNA damage stress pathways, and the ΔMokns1 mutant was more sensitive to hydroxyurea (HU) and methyl methanesulfonate (MMS) compared to the wild-type strain 70−15. The expression of genes related to DNA damage stress pathways in the ΔMokns1 mutant was significantly different from that in the wild-type strain. Our results demonstrate that MoKns1 is an important pathogenic factor in M. oryzae involved in regulating autophagy and DNA damage response pathways, thus affecting virulence. This research on M. oryzae pathogenesis lays a foundation for the prevention and control of M. oryzae.

The LAMMER kinase is involved in morphogenesis and response to cell wall- and DNA-damaging stresses in Candida albicans

Dual specificity LAMMER kinase has been reported to be conserved across species ranging from yeasts to animals and has multiple functions. Candida albicans undergoes dimorphic switching between yeast cells and hyphal growth forms as its key virulence factors. Deletion of KNS1, which encodes for LAMMER kinase in C. albicans, led to pseudohyphal growth on YPD media and defects in filamentous growth both on spider and YPD solid media containing 10% serum. These cells exhibited expanded central wrinkled regions and specifically reduced peripheral filaments. Among the several stresses tested, the kns1Δ strains showed sensitivity to cell-wall and DNA-replicative stress. Under fluorescent microscopy, an increase in chitin decomposition was observed near the bud necks and septa in kns1Δ cells. When the expression levels of genes for cell wall integrity (CWI) and the DNA repair mechanism were tested, the kns1 double-deletion cells showed abnormal patterns compared to wild-type cells; The transcript levels of genes for glycosylphosphatidylinositol (GPI)-anchored proteins were increased upon calcofluor white (CFW) treatment. Under DNA replicative stress, the expression of MluI-cell cycle box binding factor (MBF)-targeted genes, which are expressed during the G1/S transition in the cell cycle, was not increased in the kns1 double-deletion cells. This strain showed increased adhesion to the surface of an agar plate and zebrafish embryo. These results demonstrate that Kns1 is involved in dimorphic transition, cell wall integrity, response to DNA replicative stress, and adherence to the host cell surface in C. albicans.

The Dual-Specificity LAMMER Kinase Affects Stress-Response and Morphological Plasticity in Fungi

The morphological plasticity of fungal pathogens has long been implicated in their virulence and is often influenced by extracellular factors. Complex signal transduction cascades are critical for sensing stresses imposed by external cues such as antifungal drugs, and for mediating appropriate cellular responses. Many of these signal transduction cascades are well-conserved and involve in the distinct morphogenetic processes during the life cycle of the pathogenic fungi. The dual-specificity LAMMER kinases are evolutionarily conserved across species ranging from yeasts to mammals and have multiple functions in various physiological processes; however, their functions in fungi are relatively unknown. In this review, we first describe the involvement of LAMMER kinases in cell surface changes, which often accompany alterations in growth pattern and differentiation. Then, we focus on the LAMMER kinase-dependent molecular machinery responsible for the stress responses and cell cycle regulation. Last, we discuss the possible cross-talk between LAMMER kinases and other signaling cascades, which integrates exogenous and host signals together with genetic factors to affect the morphological plasticity and virulence in fungi.

Oxidative stress response pathways: Fission yeast as archetype

Schizosaccharomyces pombe is a popular model eukaryotic organism to study diverse aspects of mammalian biology, including responses to cellular stress triggered by redox imbalances within its compartments. The review considers the current knowledge on the signaling pathways that govern the transcriptional response of fission yeast cells to elevated levels of hydrogen peroxide. Particular attention is paid to the mechanisms that yeast cells employ to promote cell survival in conditions of intermediate and acute oxidative stress. The role of the Sty1/Spc1/Phh1 mitogen-activated protein kinase in regulating gene expression at multiple levels is discussed in detail.

High sucrose consumption promotes obesity whereas its low consumption induces oxidative stress in Drosophila melanogaster

The effects of sucrose in varied concentrations (0.25-20%) with constant amount of yeasts in larval diet on development and metabolic parameters of adult fruit fly Drosophila melanogaster were studied. Larvae consumed more food at low sucrose diet, overeating with yeast. On high sucrose diet, larvae ingested more carbohydrates, despite consuming less food and obtaining less protein derived from yeast. High sucrose diet slowed down pupation and increased pupa mortality, enhanced levels of lipids and glycogen, increased dry body mass, decreased water content, i.e. resulted in obese phenotype. Furthermore, it suppressed reactive oxygen species-induced oxidation of lipids and proteins as well as the activity of superoxide dismutase. The activity of catalase was gender-related. In males, at all sucrose concentrations used catalase activity was higher than at its concentration of 0.25%, whereas in females sucrose concentration virtually did not influence the activity. High sucrose diet increased content of protein thiols and the activity of glucose-6-phosphate dehydrogenase. The increase in sucrose concentration also enhanced uric acid level in females, but caused opposite effects in males. Development on high sucrose diets was accompanied by elevated steady-state insulin-like peptide 3 mRNA level. Finally, carbohydrate starvation at yeast overfeeding on low sucrose diets resulted in oxidative stress reflected by higher levels of oxidized lipids and proteins accompanied by increased superoxide dismutase activity. Potential mechanisms involved in regulation of redox processes by carbohydrates are discussed.

Fission yeast LAMMER kinase Lkh1 regulates the cell cycle by phosphorylating the CDK-inhibitor Rum1

In eukaryotes, LAMMER kinases are involved in various cellular events, including the cell cycle. However, no attempt has been made to investigate the mechanisms that underlie the involvement of LAMMER kinase. In this study, we performed a functional analysis of LAMMER kinase using the fission yeast, Schizosaccharomyces pombe. FACS analyses revealed that deletion of the gene that encodes the LAMMER kinase Lkh1 made mutant cells pass through the G1/S phase faster than their wild-type counterparts. Co-immunoprecipitation and an in vitro kinase assay also revealed that Lkh1 can interact with and phosphorylate Rum1 to activate this molecule as a cyclin-dependent kinase inhibitor, which blocks cell cycle progression from the G1 phase to the S phase. Peptide mass fingerprinting and kinase assay with Rum1(T110A) confirmed T110 as the Lkh1-dependent phosphorylation residue. In this report we present for the first time a positive acting mechanism that is responsible for the CKI activity of Rum1, in which the LAMMER kinase-mediated phosphorylation of Rum1 is involved.

LAMMER kinase Kic1 is involved in pre-mRNA processing

The LAMMER kinases are conserved through evolution. They play vital roles in cell growth/differentiation, development, and metabolism. One of the best known functions of the kinases in animal cells is the regulation of pre-mRNA splicing. Kic1 is the LAMMER kinase in fission yeast Schizosaccharomyces pombe. Despite the reported pleiotropic effects of kic1+ deletion/overexpression on various cellular processes the involvement of Kic1 in splicing remains elusive. In this study, we demonstrate for the first time that Kic1 not only is required for efficient splicing but also affects mRNA export, providing evidence for the conserved roles of LAMMER kinases in the unicellular context of fission yeast. Consistent with the hypothesis of its direct participation in multiple steps of pre-mRNA processing, Kic1 is predominantly present in the nucleus during interphase. In addition, the kinase activity of Kic1 plays a role in modulating its own cellular partitioning. Interestingly, Kic1 expression oscillates in a cell cycle-dependent manner and the peak level coincides with mitosis and cytokinesis, revealing a potential mechanism for controlling the kinase activity during the cell cycle. The novel information about the in vivo functions and regulation of Kic1 offers insights into the conserved biological roles fundamental to LAMMER kinases in eukaryotes.

Possible Roles of LAMMER Kinase Lkh1 in Fission Yeast by Comparative Proteome Analysis

To investigate the possible roles of LAMMER kinase homologue, Lkh1, in Schizosaccharomyces pombe, whole proteins were extracted from wild type and lkh1-deletion mutant cells and subjected to polyacrylamide gel electrophoresis. Differentially expressed proteins were identified by tandem mass spectrometry (MS/MS) and were compared with a protein database. In whole-cell extracts, 10 proteins were up-regulated and 9 proteins were down-regulated in the mutant. In extracellular preparations, 6 proteins were up-regulated in the lkh1 (+) null mutant and 4 proteins successfully identified: glycolipid anchored surface precursor, β-glucosidase (Psu1), cell surface protein, glucan 1,3-β-glucosidase (Bgl2), and exo-1,3 β-glucanase (Exg1). These results suggest that Lkh1 is involved in regulating cell wall assembly.

The LAMMER kinase homolog, Lkh1, regulates Tup transcriptional repressors through phosphorylation in Schizosaccharomyces pombe

Disruption of the fission yeast LAMMER kinase, Lkh1, gene resulted in diverse phenotypes, including adhesive filamentous growth and oxidative stress sensitivity, but an exact cellular function had not been assigned to Lkh1. Through an in vitro pull-down approach, a transcriptional repressor, Tup12, was identified as an Lkh1 binding partner. Interactions between Lkh1 and Tup11 or Tup12 were confirmed by in vitro and in vivo binding assays. Tup proteins were phosphorylated by Lkh1 in a LAMMER motif-dependent manner. The LAMMER motif was also necessary for substrate recognition in vitro and cellular function in vivo. Transcriptional activity assays using promoters negatively regulated by Tup11 and Tup12 showed 6 or 2 times higher activity in the Δlkh1 mutant than the wild type, respectively. Northern analysis revealed derepressed expression of the fbp1⁺ mRNA in Δlkh1 and in Δtup11Δtup12 mutant cells under repressed conditions. Δlkh1 and Δtup11Δtup12 mutant cells showed flocculation, which was reversed by co-expression of Tup11 and -12 with Ssn6. Here, we presented a new aspect of the LAMMER kinase by demonstrating that the activities of global transcriptional repressors, Tup11 and Tup12, were positively regulated by Lkh1-mediated phosphorylation.

Superoxide dismutase is regulated by LAMMER kinase in Drosophila and human cells

LAMMER kinases (also known as CDC-2-like or CLKs) are a family of dual specificity serine/threonine protein kinases that are found in all sequenced eukaryotic genomes. In the fission yeast, Schizosaccharomyces pombe, the LAMMER kinase gene, Lkh1, positively regulates the expression of the antioxidant defense genes, superoxide dismutase 1 (sod1+, CuZn-SOD) and catalase (ctt1+, CAT). We have shown that mutations in the Drosophila LAMMER kinase gene, Darkener of apricot (Doa), protect against the decrease in life span caused by the reactive oxygen species (ROS) generator paraquat, and at the same time show an increase in cytoplasmic (CuZn-Sod or SOD1) and mitochondrial superoxide dismutase (Mn-Sod or SOD2) protein levels and activity. The siRNA-mediated knock down of the human LAMMER kinase gene, CLK-1, in HeLa and MCF-7 human cell lines leads to an increase in both SOD1 activity and mRNA transcript levels. These data suggest that SOD1 is negatively regulated by LAMMER kinases in Drosophila and human cell lines and that this regulation may be conserved during evolution.

Dsk1p kinase phosphorylates SR proteins and regulates their cellular localization in fission yeast

Evolutionarily conserved SR proteins (serine/arginine-rich proteins) are important factors for alternative splicing and their activity is modulated by SRPKs (SR protein-specific kinases). We previously identified Dsk1p (dis1-suppressing protein kinase) as the orthologue of human SRPK1 in fission yeast. In addition to its similarity of gene structure to higher eukaryotes, fission yeast Schizosaccharomyces pombe is a unicellular eukaryotic organism in which alternative splicing takes place. In the present study, we have revealed for the first time that SR proteins, Srp1p and Srp2p, are the in vivo substrates of Dsk1p in S. pombe. Moreover, the cellular localization of the SR proteins and Prp2p splicing factor is dependent on dsk1(+): Dsk1p is required for the efficient nuclear localization of Srp2p and Prp2p, while it promotes the cytoplasmic distribution of Srp1p, thereby differentially influencing the destinations of these proteins in the cell. The present study offers the first biochemical and genetic evidence for the in vivo targets of the SRPK1 orthologue, Dsk1p, in S. pombe and the significant correlation between Dsk1p-mediated phosphorylation and the cellular localization of the SR proteins, providing information about the physiological functions of Dsk1p. Furthermore, the results demonstrate that the regulatory function of SRPKs in the nuclear targeting of SR proteins is conserved from fission yeast to human, indicating a general mechanism of reversible phosphorylation to control the activities of SR proteins in RNA metabolism through cellular partitioning.

RNA-binding protein Csx1 is phosphorylated by LAMMER kinase, Lkh1, in response to oxidative stress inSchizosaccharomyces pombe

Recent studies have shown that global gene expression during oxidative stress in Schizosaccharomyces pombe is regulated by stress-induced activation and binding of Csx1 to atf1(+) mRNA. However, the kinase responsible for the activation of Csx1 has not been identified. Here, we describe, for the first time, that Csx1 is phosphorylated by S. pombe LAMMER kinase, Lkh1, under oxidative conditions and that the stress-activated binding of the Csx1 to the atf1(+) mRNA was also affected by Lkh1 and Spc1. These data indicate that concerted actions of Spc1 and Lkh1 are required for the activation of Csx1 during oxidative condition in the fission yeast S. pombe.

Potential relationship between glutathione metabolism and flocculation in the yeast Kluyveromyces lactis

Reduced glutathione (GSH) is involved in biochemical and physiological processes in cells. Flocculation is an important mechanism in microorganisms. The present study concerned the potential relationship between GSH metabolism and flocculation. Two yeast strains, a flocculent (Kluyveromyces lactis 5c) and a nonflocculent (Kluyveromyces lactis 5a) strain, were used. The level of intracellular GSH measured during the growth period was significantly higher in the nonflocculent than in the flocculent strain; in contrast, the flocculent strain exhibited brighter staining of vacuoles than the nonflocculent strain when observed using epifluorescence microscopy. Compounds acting either on flocculation (EDTA, galactose) or on GSH metabolism (buthionine sulfoximine, and N-acetylcysteine) were tested on the flocculent strain during the growth period. Both EDTA and galactose fully inhibited flocculation and induced GSH overproduction of 58% and 153%, respectively. Buthionine sulfoximine decreased GSH level by 76% but had no effect on flocculation; N-acetylcysteine increased the GSH level and flocculation by 106% and 41%, respectively. Combination of EDTA and N-acetylcysteine produced similar effects than with each of them. Combination of galactose and N-acetylcysteine increased the GSH level but decreased flocculation. These results demonstrated that GSH homeostasis is linked to the flocculation mechanism. A hypothesis related to stress is given.