The Regulatory Proteins Rtg1/3 Govern Sphingolipid Homeostasis in the Human-Associated Yeast Candida albicans

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Chronic rapamycin treatment or lack of S6K1 does not reduce ribosome activity in vivo

Reducing activity of the mTORC1/S6K1 pathway has been shown to extend lifespan in both vertebrate and invertebrate models. For instance, both pharmacological inhibition of mTORC1 with the drug rapamycin or S6K1 knockout extends lifespan in mice. Since studies with invertebrate models suggest that reducing translational activity can increase lifespan, we reasoned that the benefits of decreased mTORC1 or S6K1 activity might be due, at least in part, to a reduction of general translational activity. Here, we report that mice given a single dose of rapamycin have reduced translational activity, while mice receiving multiple injections of rapamycin over 4 weeks show no difference in translational activity compared with vehicle-injected controls. Furthermore, mice lacking S6K1 have no difference in global translational activity compared with wild-type littermates as measured by the percentage of ribosomes that are active in multiple tissues. Translational activity is reduced in S6K1-knockout mice following single injection of rapamycin, demonstrating that rapamycin’s effects on translation can occur independently of S6K1. Taken together, these data suggest that benefits of chronic rapamycin treatment or lack of S6K1 are dissociable from potential benefits of reduced translational activity, instead pointing to a model whereby changes in translation of specific subsets of mRNAs and/or translation-independent effects of reduced mTOR signaling underlie the longevity benefits.     

酿酒酵母促分裂原蛋白激酶Hog1p 介导的渗透胁迫反应调控机制

 高渗透性甘油促分裂原激酶信号转导途径（high osmolarity glycerol mitogen activated protein kinase signaling transduction pathway,HOG-MAPK）是调控酿酒酵母对外界高渗透压胁迫环境应答的主要途径,促分裂原蛋白激酶Hog1p（MAPK Hog1p）是其中的关键性作用因子.在高渗透压刺激时,MAPK Hog1p接受信号被特异性激活并进入核内,调控相关胁迫应答基因的表达,并介导该时期细胞周期的阻滞,从而增强细胞对外界不利环境的适应能力.对胁迫条件下酿酒酵母中MAPK Hog1p作用机制的进一步研究,有利于更深入地了解哺乳动物体内逆境激发促分裂原蛋白激酶途径的功能和调控机制.     

Role of 14-3-3 proteins in the regulation of neutral trehalase in the yeast Saccharomyces cerevisiae

In higher eukaryotes, 14-3-3 proteins participate in numerous cellular processes, and carry out their function through a variety of different molecular mechanisms, including regulation of protein localization and enzyme activation. Here, it is shown that the two yeast 14-3-3 homologues, Bmh1p and Bmh2p, form a complex with neutral trehalase (Nth1p), an enzyme that is responsible for trehalose degradation and is required in a variety of stress conditions. In a purified in vitro system, either one of the two 14-3-3 yeast isoforms are necessary for complete activation of neutral trehalase (Nth1p) after phosphorylation by PKA. It is further demonstrated that Bmh1p and Bmh2p bind to the amino-terminal region of phosphorylated trehalase, thereby modulating its enzymatic activity. This work represents the first demonstration of enzyme activation mediated by 14-3-3 binding in yeast.     

Identification and characterization of a functional Candida albicans homolog of the Saccharomyces cerevisiae TCO89 gene

As one of the components of target of rapamycin complex 1 (TORC1), ScTco89p is involved in rapamycin sensitivity and cellular integrity in Saccharomyces cerevisiae. Here we provide evidence showing that deletion of ScTCO89 causes yeast cells to be hypersensitive to salt stress in a high osmolarity glycerol pathway-independent fashion. In addition, we have identified and characterized a functional Candida albicans homolog (CaTCO89) of ScTCO89, which encodes a protein of 708 amino acids that shows overall 15% identity with ScTco89p at the amino acid level. However, CaTCO89 could complement the functions of ScTCO89 in rapamycin sensitivity, salt tolerance, and cellular integrity. Candida albicans cells disrupted for CaTCO89 are also sensitive to rapamycin and lithium salt, but not susceptible to challenges to cellular integrity.     

Stm1p, a ribosome-associated protein, is important for protein synthesis in Saccharomyces cerevisiae under nutritional stress conditions

Stm1p is a Saccharomyces cerevisiae protein that has been implicated in several biological processes, ranging from apoptosis to telomere biosynthesis. Likewise, Stm1p has been identified as a protein associated with supramolecular structures, including ribosomes and nuclear telomere cap complexes. Using a variety of biochemical methods, we found that the vast majority of cellular Stm1p is associated with free cytosolic 80S ribosomes and polysomes. In its association with ribosomes, Stm1p interacts in an equimolar complex with both ribosomal subunits and is not associated with mRNA. Functionally, targeted disruption of the STM1 gene results in rapamycin hypersensitivity and a defect in recovery following nitrogen starvation and replenishment. These effects coincide with severe polysome depletion and reduced total protein synthesis. Taken together, our data indicate that Stm1p plays a critical role in facilitating translation under nutrient stress conditions and suggest that Stm1p acts in concert with the target of rapamycin (TOR) signaling pathway.     

过量表达蛋白激酶YPK1使酵母细胞对高盐胁迫的高度敏感依赖于雷帕霉素靶蛋白

摘要：YPK1是酵母中和哺乳动物蛋白激酶SGK同源的一种丝氨酸∕苏氨酸蛋白激酶,在酿酒酵母（Saccharomyces cerevisiae）生理调节中有重要的作用,和酵母细胞壁的完整性、细胞骨架中肌动蛋白极性、细胞内吞作用、细胞在氮源缺乏和营养条件调节下细胞内部的翻译情况密切相关。【目的】为了深入研究YPK1蛋白激酶的细胞功能以及在细胞信号传导中的作用,【方法】我们构建了过量表达YPK1的高拷贝质粒,研究了过量表达YPK1的酵母细胞在盐胁迫条件下的生长情况,【结果】发现过量表达YPK1会导致酵母细胞对盐胁迫高度敏感,并且这种敏感性依赖于TOR1的存在。【结论】我们的研究结果首次初步揭示YPK1与细胞盐胁迫应答的关系,并初步证明YPK1的功能充分发挥需要TOR1的参与。     

MAPKs regulate mitophagy in Saccharomyces cerevisiae

The autophagy-dependent selective degradation of mitochondria (mitophagy) plays an important role in removing excessive, damaged and dysfunctional mitochondria to maintain a proper cellular homeostasis. Relative to its significance in cell physiology, very little is known about the molecular machinery and regulatory mechanism of mitophagy in mammalian cells or yeast. We found that two mitogen-activated protein kinases (MAPKs), Slt2 and Hog1, are required for mitophagy in Saccharomyces cerevisiae. Slt2 is involved in both mitophagy and pexophagy (the selective degradation of peroxisomes through autophagy), whereas Hog1 functions specifically in mitophagy.     

酿酒酵母菌葡萄糖信号传导途径研究进展

简要概述了酿酒酵母细胞的葡萄糖信号传导途径的研究进展,总结了葡萄糖的抑制途径和诱导途径.     

缺氧诱导因子1与PI3K/Akt/mTOR信号转导通路

缺氧诱导因子1（HIF-1）是参与缺氧调节的核心因子,可调控一系列缺氧诱导基因的表达,与机体许多生理和病理过程也密切相关。尽管一些研究显示缺氧和非缺氧性刺激可通过PI3K/Akt/mTOR信号途径诱导HIF-1的表达和活性,PI3K信号途径是否参与对HIF-1的调节仍然是个有争议的研究热点。明确HIF-1和PI3K的相互作用关系,能进一步为肿瘤等相关疾病的防治提供新的思路和方法。本文主要就HIF-1和PI3K/Akt/mTOR关系作一简要综述。     

Saccharomyces cerevisiae GTPase complex: Gtr1p-Gtr2p regulates cell-proliferation through Saccharomyces cerevisiae Ran-binding protein, Yrb2p

A Gtr1p GTPase, the GDP mutant of which suppresses both temperature-sensitive mutants of Saccharomyces cerevisiae RanGEF/Prp20p and RanGAP/Rna1p, was presently found to interact with Yrb2p, the S. cerevisiae homologue of mammalian Ran-binding protein 3. Gtr1p bound the Ran-binding domain of Yrb2p. In contrast, Gtr2p, a partner of Gtr1p, did not bind Yrb2p, although it bound Gtr1p. A triple mutant: yrb2delta gtr1delta gtr2delta was lethal, while a double mutant: gtr1delta gtr2delta survived well, indicating that Yrb2p protected cells from the killing effect of gtr1delta gtr2delta. Recombinant Gtr1p and Gtr2p were purified as a complex from Escherichia coli. The resulting Gtr1p-Gtr2p complex was comprised of an equal amount of Gtr1p and Gtr2p, which inhibited the Rna1p/Yrb2 dependent RanGAP activity. Thus, the Gtr1p-Gtr2p cycle was suggested to regulate the Ran cycle through Yrb2p.     

Molecular insights on DNA delivery into Saccharomyces cerevisiae

Understanding of the molecular system for DNA delivery into eucaryotic cells, a key to human DNA therapy, remains obscure. To understand this system, we undertook a study using the Saccharomyces cerevisiae model into which DNA delivery is easily assessed through competence (transformability) and for which all nonessential gene mutants (about 5000 strains) are available. We analyzed the competence of each of these mutants and identified three low-competence mutants, i.e., sin3Delta, she4Delta, and arc18Delta, and three high-competence mutants, i.e., pde2Delta, spf1Delta, and pmr1Delta. Through further studies using the six mutants, we concluded that the Arp2/3 activation machinery involving the Myo3/5p, Vrp1p, Las17p, Pan1p, and Arp2/3 complex is crucial to delivery (competence), and that high cAMP enhances competence via protein kinase A installing Tpk3p. We also propose that DNA is taken up via an endocytosis-like event, being at least partially different from well-known endocytosis.