Multiple Signals Converge on a Differentiation MAPK Pathway

An important emerging question in the area of signal transduction is how information from different pathways becomes integrated into a highly coordinated response. In budding yeast, multiple pathways regulate filamentous growth, a complex differentiation response that occurs under specific environmental conditions. To identify new aspects of filamentous growth regulation, we used a novel screening approach (called secretion profiling) that measures release of the extracellular domain of Msb2p, the signaling mucin which functions at the head of the filamentous growth (FG) MAPK pathway. Secretion profiling of complementary genomic collections showed that many of the pathways that regulate filamentous growth (RAS, RIM101, OPI1, and RTG) were also required for FG pathway activation. This regulation sensitized the FG pathway to multiple stimuli and synchronized it to the global signaling network. Several of the regulators were required for MSB2 expression, which identifies the MSB2 promoter as a target “hub” where multiple signals converge. Accessibility to the MSB2 promoter was further regulated by the histone deacetylase (HDAC) Rpd3p(L), which positively regulated FG pathway activity and filamentous growth. Our findings provide the first glimpse of a global regulatory hierarchy among the pathways that control filamentous growth. Systems-level integration of signaling circuitry is likely to coordinate other regulatory networks that control complex behaviors

Inactivation of CDK/pRb Pathway Normalizes Survival Pattern of Lymphoblasts Expressing the FTLD-Progranulin Mutation c.709-1G>A

8 figuras, 2 tablasBackground Mutations in the progranulin (PGRN) gene, leading to haploinsufficiency, cause familial frontotemporal lobar degeneration (FTLD-TDP), although the pathogenic mechanism of PGRN deficit is largely unknown. Allelic loss of PGRN was previously shown to increase the activity of cyclin-dependent kinase (CDK) CDK6/pRb pathway in lymphoblasts expressing the c.709-1G>A PGRN mutation. Since members of the CDK family appear to play a role in neurodegenerative disorders and in apoptotic death of neurons subjected to various insults, we investigated the role of CDK6/pRb in cell survival/death mechanisms following serum deprivation. Methodology/Principal Findings We performed a comparative study of cell viability after serum withdrawal of established lymphoblastoid cell lines from control and carriers of c.709-1G>A PGRN mutation, asymptomatic and FTLD-TDP diagnosed individuals. Our results suggest that the CDK6/pRb pathway is enhanced in the c.709-1G>A bearing lymphoblasts. Apparently, this feature allows PGRN-deficient cells to escape from serum withdrawal-induced apoptosis by decreasing the activity of executive caspases and lowering the dissipation of mitochondrial membrane potential and the release of cytochrome c from the mitochondria. Inhibitors of CDK6 expression levels like sodium butyrate or the CDK6 activity such as PD332991 were able to restore the vulnerability of lymphoblasts from FTLD-TDP patients to trophic factor withdrawal. Conclusion/Significance The use of PGRN-deficient lymphoblasts from FTLD-TDP patients may be a useful model to investigate cell biochemical aspects of this disease. It is suggested that CDK6 could be potentially a therapeutic target for the treatment of the FTLD-TDPThis work has been supported by grants from Ministry of Education and Science (SAF2007-61701, SAF2010-15700, SAF2011-28603), Fundación Eugenio Rodríguez Pascual, and Basque Government (Saiotek program 2008–2009). NE holds a fellowship of the JAE predoctoral program of the CSICPeer reviewe

Anatomical Analysis of Saccharomyces cerevisiae Stalk-Like Structures Reveals Spatial Organization and Cell Specialization

Recently we reported an unusual multicellular organization in yeast that we termed stalk-like structures. These structures are tall (0.5 to 3 cm long) and narrow (1 to 3 mm in diameter). They are formed in response to UV radiation of cultures spread on high agar concentrations. Here we present an anatomical analysis of the stalks. Microscopic inspection of cross sections taken from stalks revealed that stalks are composed of an inner core in which cells are dense and vital and a layer of cells (four to six rows) that surrounds the core. This outer layer is physically separated from the core and contains many dead cells. The outer layer may form a protective shell for the core cells. Through electron microscopy analysis we observed three types of cells within the stalk population: (i) cells containing many unusual vesicles, which might be undergoing some kind of cell death; (ii) cells containing spores (usually one or two spores only); and (iii) familiar rounded cells. We suggest that stalk cells are not only spatially organized but may undergo processes that induce a certain degree of cell specialization. We also show that high agar concentration alone, although not sufficient to induce stalk formation, induces dramatic changes in a colony's morphology. Most striking among the agar effects is the induction of growth into the agar, forming peg-like structures. Colonies grown on 4% agar or higher are reminiscent of stalks in some aspects. The agar concentration effects are mediated in part by the Ras pathway and are related to the invasive-growth phenomenon

Structural basis for promiscuity and dpecificity during Candida Glabrata Invasion of Host Epithelia

The human pathogenic yeast Candida glabrata harbors more than 20 surface-exposed, epithelial adhesins (Epas) for host cell adhesion. The Epa family recognizes host glycans and discriminates between target tissues by their adhesin (A) domains, but a detailed structural basis for ligand-binding specificity of Epa proteins has been lacking so far. In this study, we provide high-resolution crystal structures of the Epa1A domain in complex with different carbohydrate ligands that reveal how host cell mucin-type O-glycans are recognized and allow a structure-guided classification of the Epa family into specific subtypes. Further detailed structural and functional characterization of subtype-switched Epa1 variants shows that specificity is governed by two inner loops, CBL1 and CBL2, involved in calcium binding as well as by three outer loops, L1, L2, and L3. In summary, our study provides the structural basis for promiscuity and specificity of Epa adhesins, which might further contribute to developing anti-adhesive antimycotics and combating Candida colonization