mss4

Macroautophagy (hereafter autophagy) is a degradative cellular pathway that protects eukaryotic cells from stress, starvation, and microbial infection. This process must be tightly controlled because too little or too much autophagy can be deleterious to cellular physiology. The phosphatidylinositol (PtdIns) 3-kinase Vps34 is a lipid kinase that regulates autophagy, but the role of other PtdIns kinases has not been examined. Here we demonstrate a role for PtdIns 4-kinases and PtdIns4P 5-kinases in selective and nonselective types of autophagy in yeast...

Membrane lipids have been implicated in many critical cellular processes, yet little is known about the role of asymmetric lipid distribution in cell morphogenesis. The phosphoinositide bis-phosphate PI(4,5)P(2) is essential for polarized growth in a range of organisms. Although an asymmetric distribution of this phospholipid has been observed in some cells, long-range gradients of PI(4,5)P(2) have not been observed. Here, we show that in the human pathogenic fungus Candida albicans a steep, long-range gradient of PI(4,5)P(2) occurs concomitant with emergence of the hyphal filament...

Phosphatidylinositol-4,5-bisphosphate, PtdIns(4,5)P(2), is an essential signalling lipid that regulates key processes such as endocytosis, exocytosis, actin cytoskeletal organization and calcium signalling. Maintaining proper levels of PtdIns(4,5)P(2) at the plasma membrane (PM) is crucial for cell survival and growth. We show that the conserved PtdIns(4)P 5-kinase, Mss4, forms dynamic, oligomeric structures at the PM that we term PIK patches. The dynamic assembly and disassembly of Mss4 PIK patches may provide a mechanism to precisely modulate Mss4 kinase activity, as needed, for localized regulation of PtdIns(4,5)P(2) synthesis...

Mss4 (mammalian suppressor of Sec4) is an evolutionarily highly conserved protein and shows high sequence and structural similarity to nucleotide exchange factors. Although Mss4 tightly binds a series of exocytic Rab GTPases, it exercises only a low catalytic activity. Therefore Mss4 was proposed to work rather as a chaperone, protecting nucleotide free Rabs from degradation than as a nucleotide exchange factor. Here we provide further evidence for chaperone-like properties of Mss4. We show that expression levels of cellular Mss4 mRNA and protein are rapidly changed in response to a broad range of extracellular stress stimuli...

Foxg1 (previously named BF1) is a winged-helix transcription factor with restricted expression pattern in the telencephalic neuroepithelium of the neural tube and in the anterior half of the developing optic vesicle. Previous studies have shown that the targeted disruption of the Foxg1 gene leads to hypoplasia of the cerebral hemispheres with severe defect in the structures of the ventral telencephalon. To further investigate the molecular mechanisms by which Foxg1 plays essential roles during brain development, we have adopted a strategy to isolate genes whose expression changes immediately after introduction of Foxg1 in cultured neural precursor cell line, HiB5...

Eisosomes are large immobile assemblies at the cortex of a cell under the membrane compartment of Can1 (MCC) in yeast. Slm1 has recently been identified as an MCC component that acts downstream of Mss4 in a pathway that regulates actin cytoskeleton organization in response to stress. In this study, we showed that inactivation of Slm proteins disrupts proper localization of the primary eisosome marker Pil1, providing evidence that Slm proteins play a role in eisosome organization. Furthermore, we found that slm ts mutant cells exhibit actin defects in both the ability to polarize cortical F-actin and the formation of cytoplasmic actin cables even at the permissive temperature (30 degrees C)...

SPI1 is a gene whose expression responds to many environmental stimuli, including entry into stationary phase. We have performed a screening to identify genes that activate SPI1 promoter when overexpressed. The phosphatidylinositol-4-phosphate 5-kinase gene MSS4 was identified as a positive activator of SPI1. Another SPI1 transcriptional regulator isolated was the flavodoxin-like gene YCP4. YCP4 and its homolog RFS1 regulate the expression of many genes during the late stages of growth. The double deletion mutant in YCP4 and its homolog RFS1 has an impact on gene expression related to metabolism by increasing the expression of genes involved in hexose transport and glycolysis, and decreasing expression of genes of amino acid metabolism pathways...

We previously mapped several gene loci influencing cancer risk of inbred BDIV and BDIX rats, resistant and susceptible, respectively, to N-ethyl-N-nitrosourea (ENU)-induced malignant peripheral nerve sheath tumors (MPNSTs). On the basis of a genomewide association analysis using a (BDIV × BDIX) F(2) generation the Mss4 locus on rat chromosome 6 was predicted to mediate resistance to MPNST development in the trigeminal nerves, preferentially in females. F(2) females homozygous for D6Mit1 proved almost exclusively resistant to peripheral neurooncogenesis, with no effect detectable in males...

The Mss4 (mammalian suppressor of yeast Sec4) is an evolutionarily highly conserved protein and is expressed in all mammalian tissues. Although its precise biological function is still elusive, it has been shown to associate with a subset of secretory Rab proteins (Rab1b, Rab3a, Rab8a, Rab10) and to possess a rather low guanine nucleotide exchange factor (GEF) activity towards them in vitro (Rab1, Rab3a and Rab8a). By screening a human placenta cDNA library with Mss4 as bait, we identified several Rab GTPases (Rab12, Rab13 and Rab18) as novel Mss4-binding Rab proteins...

On 15 Mar. 1984, during the initial orbital corrections of Landsat 5, data were acquired virtually simultaneously by multispectral scanners (MSSs) and thematic mappers (TMs) on Landsats 4 and 5. A formulation is developed for comparing the calibration of matched instruments (MSS4, MSS5 and TM4, TM5), and spectral interpolation is used to compare the calibration of the nearly equivalent shortwave channels of all four instruments. The MSS instruments are more closely matched in gain with a difference of 6-10% vs -2-14% for the TMs, while radiance comparisons show that the MSSs and TM4 agree reasonably well for a dark surface (water), while TM5 indicates generally lower radiance values in the shortwave channels...

During response of budding yeast to peptide mating pheromone, the cell becomes markedly polarized and MAPK scaffold protein Ste5 localizes to the resulting projection (shmoo tip). We demonstrated before that this recruitment is essential for sustained MAPK signaling and requires interaction of a pleckstrin homology (PH) domain in Ste5 with phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] in the plasma membrane. Using fluorescently tagged high-affinity probes specific for PtdIns(4,5)P(2), we have now found that this phosphoinositide is highly concentrated at the shmoo tip in cells responding to pheromone...

The identification of cancer susceptibility- and resistance-mediating genes is an essential prerequisite for prevention and early diagnosis of malignant tumors. Model organisms are helpful to identify variant alleles involved in pathways affecting individual cancer risk. BDIX and BDIV rats of both sexes are highly susceptible and resistant, respectively, to the development of N-ethyl-N-nitrosourea (ENU)-induced malignant peripheral nerve sheath tumors (MPNST), predominantly in the trigeminal nerves. Nevertheless, female (BDIV x BDIX) F(2) intercross rats have a lower MPNST incidence and a longer latency time than males...

A novel halophilic bacterium, designated strain MSS4(T), was isolated from the solar salterns of Mesolongi, Greece. The micro-organism, a motile, Gram-stain-positive, aerobic rod, proliferated at salinities of 1.0-4.0 M NaCl, with optimal growth at 2.5 M NaCl. Endospores were not observed. Strain MSS4(T) showed optimal growth at 37 degrees C and pH 8.0. The G+C content of its DNA was 47.2 mol%. The polar lipid pattern of strain MSS4(T) consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidic acid and phosphatidylethanolamine...

The soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) family of proteins is required for eukaryotic intracellular membrane fusions. Vesicle fusion for formation of the prospore membrane (PSM), a membrane compartment that forms de novo during yeast sporulation, requires SNARE function, phosphatidylinositol-4,5-bisphosphate [PI(4,5)P(2)], and the activity of the phospholipase D (PLD) Spo14p, which generates phosphatidic acid (PA). The SNARE syntaxin Sso1p is essential for PSM production while the functionally redundant homolog in vegetative growth, Sso2p, is not...

The actin cytoskeleton rapidly depolarizes in yeast secretory (sec) mutants at restrictive temperatures. Thus, an unknown signal conferred upon secretion is necessary for actin polarity and exocytosis. Here, we show that a phosphatidylinositol (PI) transfer protein, Sfh5, and a phosphatidylinositol-4-phosphate 5-kinase, Mss4, facilitate Cdc42 activation to concomitantly regulate both actin and protein trafficking. Defects in Mss4 function led to actin depolarization, an inhibition of secretion, reduced levels of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)] in membranes, mislocalization of a pleckstrin homology domain fused to green fluorescent protein, and the mislocalization of Cdc42...

The Rab family of small GTPases functions in regulating vesicular transport in all eukaryotes. In the past few years, several important reports have linked some members of the Rab family to intriguing mechanistic aspects of cancer cell migration and invasiveness. Rab5 and Rab21 associate with alpha-integrin subunits and modulate their endosomal traffic and subcellular localization. Expression of the latter enhances adhesion and migration of certain cancer cell types. Rab25 has been functionally linked to tumor progression and the invasiveness of some epithelial cancers...

The guanine nucleotide binding protein Rab8A controls the final steps of exocytosis in mammalian cells. It has been implicated in the regulation of apical protein localization in intestinal epithelial cells and ciliary biogenesis. The in vitro structural and biochemical characterization of Rab8A and its interaction with regulator and effector molecules has been hampered by its insolubility in Escherichia coli expression systems. The conventional refolding procedure is laborious and yields only minute amounts of C-terminally truncated Rab8A (Rab8A(1-183): amino acids 1-183), not the full-length protein...

In four independent yeast two-hybrid screens with the integrin alpha-subunits alpha3A, alpha6A, alpha7A, and alpha7B, we identified the Mss4 protein, a nucleotide exchange factor for exocytic Rab GTPases, as a novel integrin interacting protein. We have previously shown that it binds to the conserved KXGFFKR region of integrin alpha-subunits located directly beneath the cell membrane. Here we show that the binding site for integrins on Mss4 is overlapping with those for Rab GTPases. Functional analysis of the Mss4/integrin interaction revealed its importance for activation of matrix metalloproteinases (MMPs) and remodeling of secreted extracellular matrix (ECM) proteins...

Sec2 is a reversibly membrane associated multi-domain protein with guanine nucleotide exchange activity towards the yeast Rab-protein Sec4. Both proteins are localized to secretory vesicles destined for exocytosis. We have used transient kinetic methods to show that Sec2 is a highly active exchange factor, in contrast to other proteins previously characterized as Rab exchange factors. With a K(d) value for the Sec2:Sec4.GDP interaction of ca 70 microM and a maximal rate of GDP displacement of ca 15 s(-1), it is 100-1000-fold more effective than other proteins showing exchange activity towards Rabs (MSS4, DSS4, Vps9) and ca tenfold faster than Cdc25 as a Ras specific exchanger, although still 100-fold slower than the fastest systems studied so far, EF-Tu/Ef-Ts and Ran/RCC1...

Regulation of PIPK (phosphatidylinositol phosphate kinase) and PtdIns(4,5)P2 signalling by small G-proteins and their effectors is key to many biological functions. Through selective recruitment and activation of different PIPK isoforms, small G-proteins such as Rho, Rac and Cdc42 modulate actin dynamics and cytoskeleton-dependent cellular events in response to extracellular signalling. These activities affect a number of processes, including endocytosis, bacterial penetration into host cells and cytolytic granule-mediated targeted cell killing...