Browsing by Subject "Cell signalling"

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    Activation of the cell integrity pathway is channelled through diverse signalling elements in fission yeast
    (ELSEVIER, 2008-01-04) Barba, Gregorio; Soto, Teresa; Madrid, Marisa; Núñez, Andrés; Vicente, Jero; Gacto, Mariano; Cansado Vizoso, José; Genética y Microbiología
    MAPK Pmk1p is the central element of a cascade involved in the maintenance of cell integrity and other functions in Schizosaccharomyces pombe. Pmk1p becomes activated by multiple stressing situations and also during cell separation. GTPase Rho2p acts upstream of the protein kinase C homolog Pck2p to activate the Pmk1 signalling pathway through direct interaction with MAPKKK Mkh1p. In this work we analyzed the functional significance of both Rho2p and Pck2p in the transduction of various stress signals by the cell integrity pathway. The results indicate that basal Pmk1p activity can be positively regulated by alternative mechanisms which are independent on the control by Rho2p and/or Pck2p. Unexpectedly, Pck1p, another protein kinase C homolog, negatively modulates Pmk1p basal activity by an unknown mechanism. Moreover, different elements appear to regulate the stress-induced activation of Pmk1p depending on the nature of the triggering stimuli. Whereas Pmk1p activation induced by hyper- or hypotonic stresses is channeled through Rho2p–Pck2p, other stressors, like glucose deprivation or cell wall disturbance, are transduced via other pathways in addition to that of Rho2p–Pck2p. On the contrary, Pmk1p activation observed during cell separation or after treatment with hydrogen peroxide does not involve Rho2p–Pck2p. Finally, Pck2p function is critical to maintain a Pmk1p basal activity that allows Pmk1p activation induced by heat stress. These data demonstrate the existence of a complex signalling network modulating Pmk1p activation in response to a variety of stresses in fission yeast.
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    Direct Cryo-ET observation of platelet deformation induced by SARS-CoV-2 spike protein
    (Nature Research, 2023-02-04) Cyrus Kuhn, Christopher; Basnet, Nirakar; Bodakuntla, Satish; Alvarez-Brecht, Pelayo; Nichols, Scott; Martínez-Sánchez, Antonio; Agostini, Lorenzo; Soh, Young-Min; Takagi, Junichi; Biertümpfel, Christian; Mizuno, Naoko; Ingeniería de la Información y las Comunicaciones
    SARS-CoV-2 is a novel coronavirus responsible for the COVID-19 pandemic. Its high pathogenicity is due to SARS-CoV-2 spike protein (S protein) contacting host-cell receptors. A critical hallmark of COVID-19 is the occurrence of coagulopathies. Here, we report the direct observation of the interactions between S protein and platelets. Live imaging shows that the S protein triggers platelets to deform dynamically, in some cases, leading to their irreversible activation. Cellular cryo-electron tomography reveals dense decorations of S protein on the platelet surface, inducing filopodia formation. Hypothesizing that S protein binds to filopodia-inducing integrin receptors, we tested the binding to RGD motif-recognizing platelet integrins and find that S protein recognizes integrin αvβ3. Our results infer that the stochastic activation of platelets is due to weak interactions of S protein with integrin, which can attribute to the pathogenesis of COVID-19 and the occurrence of rare but severe coagulopathies.
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    Stress-activated protein kinase-mediated down-regulation of the cell integrity pathway mitogen-activated protein kinase Pmk1p by protein phosphatases
    (American Society for Cell Biology, 2007-08-29) Madrid, Marisa; Núñez, Andrés; Soto, Teresa; Vicente, Jero; Gacto, Mariano; Cansado Vizoso, José; Genética y Microbiología
    Fission yeast mitogen-activated protein kinase (MAPK) Pmk1p is involved in morphogenesis, cytokinesis, and ion homeostasis as part of the cell integrity pathway, and it becomes activated under multiple stresses, including hyper- or hypotonic conditions, glucose deprivation, cell wall-damaging compounds, and oxidative stress. The only protein phosphatase known to dephosphorylate and inactivate Pmk1p is Pmp1p. We show here that the stress-activated protein kinase (SAPK) pathway and its main effector, Sty1p MAPK, are essential for proper deactivation of Pmk1p under hypertonic stress in a process regulated by Atf1p transcription factor. We demonstrate that tyrosine phosphatases Pyp1p and Pyp2p, and serine/threonine phosphatase Ptc1p, that negatively regulate Sty1p activity and whose expression is dependent on Sty1p-Atf1p function, are involved in Pmk1p dephosphorylation under osmostress. Pyp1p and Ptc1p, in addition to Pmp1p, also control the basal level of MAPK Pmk1p activity in growing cells and associate with, and dephosphorylate Pmk1p both in vitro and in vivo. Our results with Ptc1p provide the first biochemical evidence for a PP2C-type phosphatase acting on more than one MAPK in yeast cells. Importantly, the SAPK-dependent down-regulation of Pmk1p through Pyp1p, Pyp2p, and Ptc1p was not complete, and Pyp1p and Ptc1p phosphatases are able to negatively regulate MAPK Pmk1p activity by an alternative regulatory mechanism. Our data also indicate that Pmk1p phosphorylation oscillates as a function of the cell cycle, peaking at cell separation during cytokinesis, and that Pmp1p phosphatase plays a main role in regulating this process.
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    Transduction of centrifugation-induced gravity forces through mitogen-activated protein kinase pathways in the fission yeast Schizosaccharomyces pombe
    (Microbiology Society, 2007-05-01) Soto, Teresa; Núñez, Andrés; Madrid, Marisa; Vicente, Jero; Gacto, Mariano; Cansado Vizoso, José; Genética y Microbiología
    Centrifugation of cells of Schizosaccharomyces pombe in liquid medium prompted a marked activation of Sty1 and Pmk1, which are the effector mitogen-activated protein kinases (MAPKs) of the stress-activated protein kinase pathway and the cell-integrity pathway, respectively. Transduction of the centrifugation signals showed a sensitivity threshold above which the response was dependent on time and temperature. Centrifugation-induced phosphorylation of Sty1 and Pmk1 required the presence of the main functional components of the respective signalling cascades, i.e. Wak1 or Win1 plus Wis1, and Mkh1 plus Pek1. The transcription factor Atf1 also became phosphorylated in a Sty1-dependent way upon centrifugation. Hypergravity was an important factor in the activation of Sty1 induced by centrifugation, whilst activation of Pmk1 was mostly due to gravity-associated shear forces. Centrifugation did not increase cell survival against other stresses. Rather, the increased gravitational forces produced a delay in the cell cycle, probably related to alterations in the actin-polarization pattern. Phosphorylation of the MAPK Sty1 was needed for the depolarization of actin patches induced by the centrifugation stress.