The Experts below are selected from a list of 333 Experts worldwide ranked by ideXlab platform

Paul Ahlquist - One of the best experts on this subject based on the ideXlab platform.

  • An Amphipathic a-Helix Controls Multiple Roles of Brome Mosaic Virus Protein 1a in RNA Replication Complex Assembly and Function
    2016
    Co-Authors: Ling Liu, Arturo Diaz, Johan Den A Boon, Xiaofeng Wang, William M Westler, Adam H Steinberg, Paul Ahlquist
    Abstract:

    Brome mosaic virus (BMV) protein 1a has multiple key roles in viral RNA replication. 1a localizes to perinuclear endoplasmic reticulum (ER) Membranes as a peripheral Membrane protein, induces ER Membrane Invaginations in which RNA replication complexes form, and recruits and stabilizes BMV 2a polymerase (2aPol) and RNA replication templates at these sites to establish active replication complexes. During replication, 1a provides RNA capping, NTPase and possibly RNA helicase functions. Here we identify in BMV 1a an amphipathic a-helix, helix A, and use NMR analysis to define its structure and propensity to insert in hydrophobic Membrane-mimicking micelles. We show that helix A is essential for efficient 1a–ER Membrane association and normal perinuclear ER localization, and that deletion or mutation of helix A abolishes RNA replication. Strikingly, mutations in helix A give rise to two dramatically opposite 1a function phenotypes, implying that helix A acts as a molecular switch regulating the intricate balance between separable 1a functions. One class of helix A deletions and amino acid substitutions markedly inhibits 1a–Membrane association and abolishes ER Membrane Invagination, viral RNA template recruitment, and replication, but doubles the 1a-mediated increase in 2aPol accumulation. The second class of helix A mutations not only maintains efficient 1a–Membrane association but also amplifies the number of 1a-induced Membrane Invaginations 5- to 8-fold and enhances viral RNA template recruitment, while failing to stimulate 2aPol accumulation. The results provide new insights into the pathways of RNA replication complex assembly and show tha

  • intersection of the multivesicular body pathway and lipid homeostasis in rna replication by a positive strand rna virus
    Journal of Virology, 2011
    Co-Authors: Arturo Diaz, Brandi Gancarz, Johan Den A Boon, Paul Ahlquist, Xiaofeng Wang
    Abstract:

    Like many positive-strand RNA viruses, brome mosaic virus (BMV) RNA replication occurs in Membrane-invaginated vesicular compartments. BMV RNA replication compartments show parallels with Membrane-enveloped, budding retrovirus virions, whose release depends on the cellular multivesicular body (MVB) sorting pathway. BMV RNA replication compartments are not released from their parent Membranes, but might depend on MVB functions for Membrane Invagination. Prior results show that BMV RNA replication is severely inhibited by deletion of the crucial MVB gene DOA4 or BRO1. We report here that involvement of DOA4 and BRO1 in BMV RNA replication is not dependent on the MVB pathway's Membrane-shaping functions but rather is due to their roles in recycling ubiquitin from MVB cargos. We show that deleting DOA4 or BRO1 inhibits the ubiquitination- and proteasome-dependent activation of homologous transcription factors Mga2p and Spt23p, which regulate many lipid metabolism genes, including the fatty acid desaturase gene OLE1, which is essential for BMV RNA replication. However, Mga2p processing and BMV RNA replication are restored by supplementing free ubiquitin, which is depleted in doa4Δ and bro1Δ cells. The results identify Mga2p and Spt23p processing and lipid regulation as sensitive targets of ubiquitin depletion and correctly predict multiple effects of modulating additional host genes RFU1, UBP6, and UFD3. Our results also show that BMV RNA replication depends on additional Mga2p-regulated genes likely involved in lipid metabolism beyond OLE1. Among other points, these findings show the potential for blocking viral RNA replication by modulating lipid synthesis at multiple levels.

  • an amphipathic α helix controls multiple roles of brome mosaic virus protein 1a in rna replication complex assembly and function
    PLOS Pathogens, 2009
    Co-Authors: Ling Liu, Arturo Diaz, Johan Den A Boon, Paul Ahlquist, Xiaofeng Wang, William M Westler, Adam H Steinberg
    Abstract:

    Brome mosaic virus (BMV) protein 1a has multiple key roles in viral RNA replication. 1a localizes to perinuclear endoplasmic reticulum (ER) Membranes as a peripheral Membrane protein, induces ER Membrane Invaginations in which RNA replication complexes form, and recruits and stabilizes BMV 2a polymerase (2aPol) and RNA replication templates at these sites to establish active replication complexes. During replication, 1a provides RNA capping, NTPase and possibly RNA helicase functions. Here we identify in BMV 1a an amphipathic α-helix, helix A, and use NMR analysis to define its structure and propensity to insert in hydrophobic Membrane-mimicking micelles. We show that helix A is essential for efficient 1a–ER Membrane association and normal perinuclear ER localization, and that deletion or mutation of helix A abolishes RNA replication. Strikingly, mutations in helix A give rise to two dramatically opposite 1a function phenotypes, implying that helix A acts as a molecular switch regulating the intricate balance between separable 1a functions. One class of helix A deletions and amino acid substitutions markedly inhibits 1a–Membrane association and abolishes ER Membrane Invagination, viral RNA template recruitment, and replication, but doubles the 1a-mediated increase in 2aPol accumulation. The second class of helix A mutations not only maintains efficient 1a–Membrane association but also amplifies the number of 1a-induced Membrane Invaginations 5- to 8-fold and enhances viral RNA template recruitment, while failing to stimulate 2aPol accumulation. The results provide new insights into the pathways of RNA replication complex assembly and show that helix A is critical for assembly and function of the viral RNA replication complex, including its central role in targeting replication components and controlling modes of 1a action.

Hugo Jozef Bellen - One of the best experts on this subject based on the ideXlab platform.

  • hrs regulates endosome Membrane Invagination and tyrosine kinase receptor signaling in drosophila
    Cell, 2002
    Co-Authors: Thomas E Lloyd, Richard Atkinson, Mark N Wu, Giuseppa Pennetta, Yi Zhou, Hugo Jozef Bellen
    Abstract:

    Signaling through tyrosine kinase receptors (TKRs) is thought to be modulated by receptor-mediated endocytosis and degradation of the receptor in the lysosome. However, factors that regulate endosomal sorting of TKRs are largely unknown. Here, we demonstrate that Hrs (Hepatocyte growth factor-regulated tyrosine kinase substrate) is one such factor. Electron microscopy studies of hrs mutant larvae reveal an impairment in endosome Membrane Invagination and formation of multivesicular bodies (MVBs). hrs mutant animals fail to degrade active epidermal growth factor (EGF) and Torso TKRs, leading to enhanced signaling and altered embryonic patterning. These data suggest that Hrs and MVB formation function to downregulate TKR signaling.

  • hrs regulates endosome Membrane Invagination and tyrosine kinase receptor signaling in drosophila
    Cell, 2002
    Co-Authors: Thomas E Lloyd, Richard Atkinson, Mark N Wu, Giuseppa Pennetta, Yi Zhou, Hugo Jozef Bellen
    Abstract:

    Signaling through tyrosine kinase receptors (TKRs) is thought to be modulated by receptor-mediated endocytosis and degradation of the receptor in the lysosome. However, factors that regulate endosomal sorting of TKRs are largely unknown. Here, we demonstrate that Hrs (Hepatocyte growth factor-regulated tyrosine kinase substrate) is one such factor. Electron microscopy studies of hrs mutant larvae reveal an impairment in endosome Membrane Invagination and formation of multivesicular bodies (MVBs). hrs mutant animals fail to degrade active epidermal growth factor (EGF) and Torso TKRs, leading to enhanced signaling and altered embryonic patterning. These data suggest that Hrs and MVB formation function to downregulate TKR signaling.

Xiaofeng Wang - One of the best experts on this subject based on the ideXlab platform.

  • An Amphipathic a-Helix Controls Multiple Roles of Brome Mosaic Virus Protein 1a in RNA Replication Complex Assembly and Function
    2016
    Co-Authors: Ling Liu, Arturo Diaz, Johan Den A Boon, Xiaofeng Wang, William M Westler, Adam H Steinberg, Paul Ahlquist
    Abstract:

    Brome mosaic virus (BMV) protein 1a has multiple key roles in viral RNA replication. 1a localizes to perinuclear endoplasmic reticulum (ER) Membranes as a peripheral Membrane protein, induces ER Membrane Invaginations in which RNA replication complexes form, and recruits and stabilizes BMV 2a polymerase (2aPol) and RNA replication templates at these sites to establish active replication complexes. During replication, 1a provides RNA capping, NTPase and possibly RNA helicase functions. Here we identify in BMV 1a an amphipathic a-helix, helix A, and use NMR analysis to define its structure and propensity to insert in hydrophobic Membrane-mimicking micelles. We show that helix A is essential for efficient 1a–ER Membrane association and normal perinuclear ER localization, and that deletion or mutation of helix A abolishes RNA replication. Strikingly, mutations in helix A give rise to two dramatically opposite 1a function phenotypes, implying that helix A acts as a molecular switch regulating the intricate balance between separable 1a functions. One class of helix A deletions and amino acid substitutions markedly inhibits 1a–Membrane association and abolishes ER Membrane Invagination, viral RNA template recruitment, and replication, but doubles the 1a-mediated increase in 2aPol accumulation. The second class of helix A mutations not only maintains efficient 1a–Membrane association but also amplifies the number of 1a-induced Membrane Invaginations 5- to 8-fold and enhances viral RNA template recruitment, while failing to stimulate 2aPol accumulation. The results provide new insights into the pathways of RNA replication complex assembly and show tha

  • intersection of the multivesicular body pathway and lipid homeostasis in rna replication by a positive strand rna virus
    Journal of Virology, 2011
    Co-Authors: Arturo Diaz, Brandi Gancarz, Johan Den A Boon, Paul Ahlquist, Xiaofeng Wang
    Abstract:

    Like many positive-strand RNA viruses, brome mosaic virus (BMV) RNA replication occurs in Membrane-invaginated vesicular compartments. BMV RNA replication compartments show parallels with Membrane-enveloped, budding retrovirus virions, whose release depends on the cellular multivesicular body (MVB) sorting pathway. BMV RNA replication compartments are not released from their parent Membranes, but might depend on MVB functions for Membrane Invagination. Prior results show that BMV RNA replication is severely inhibited by deletion of the crucial MVB gene DOA4 or BRO1. We report here that involvement of DOA4 and BRO1 in BMV RNA replication is not dependent on the MVB pathway's Membrane-shaping functions but rather is due to their roles in recycling ubiquitin from MVB cargos. We show that deleting DOA4 or BRO1 inhibits the ubiquitination- and proteasome-dependent activation of homologous transcription factors Mga2p and Spt23p, which regulate many lipid metabolism genes, including the fatty acid desaturase gene OLE1, which is essential for BMV RNA replication. However, Mga2p processing and BMV RNA replication are restored by supplementing free ubiquitin, which is depleted in doa4Δ and bro1Δ cells. The results identify Mga2p and Spt23p processing and lipid regulation as sensitive targets of ubiquitin depletion and correctly predict multiple effects of modulating additional host genes RFU1, UBP6, and UFD3. Our results also show that BMV RNA replication depends on additional Mga2p-regulated genes likely involved in lipid metabolism beyond OLE1. Among other points, these findings show the potential for blocking viral RNA replication by modulating lipid synthesis at multiple levels.

  • an amphipathic α helix controls multiple roles of brome mosaic virus protein 1a in rna replication complex assembly and function
    PLOS Pathogens, 2009
    Co-Authors: Ling Liu, Arturo Diaz, Johan Den A Boon, Paul Ahlquist, Xiaofeng Wang, William M Westler, Adam H Steinberg
    Abstract:

    Brome mosaic virus (BMV) protein 1a has multiple key roles in viral RNA replication. 1a localizes to perinuclear endoplasmic reticulum (ER) Membranes as a peripheral Membrane protein, induces ER Membrane Invaginations in which RNA replication complexes form, and recruits and stabilizes BMV 2a polymerase (2aPol) and RNA replication templates at these sites to establish active replication complexes. During replication, 1a provides RNA capping, NTPase and possibly RNA helicase functions. Here we identify in BMV 1a an amphipathic α-helix, helix A, and use NMR analysis to define its structure and propensity to insert in hydrophobic Membrane-mimicking micelles. We show that helix A is essential for efficient 1a–ER Membrane association and normal perinuclear ER localization, and that deletion or mutation of helix A abolishes RNA replication. Strikingly, mutations in helix A give rise to two dramatically opposite 1a function phenotypes, implying that helix A acts as a molecular switch regulating the intricate balance between separable 1a functions. One class of helix A deletions and amino acid substitutions markedly inhibits 1a–Membrane association and abolishes ER Membrane Invagination, viral RNA template recruitment, and replication, but doubles the 1a-mediated increase in 2aPol accumulation. The second class of helix A mutations not only maintains efficient 1a–Membrane association but also amplifies the number of 1a-induced Membrane Invaginations 5- to 8-fold and enhances viral RNA template recruitment, while failing to stimulate 2aPol accumulation. The results provide new insights into the pathways of RNA replication complex assembly and show that helix A is critical for assembly and function of the viral RNA replication complex, including its central role in targeting replication components and controlling modes of 1a action.

Thomas E Lloyd - One of the best experts on this subject based on the ideXlab platform.

  • hrs regulates endosome Membrane Invagination and tyrosine kinase receptor signaling in drosophila
    Cell, 2002
    Co-Authors: Thomas E Lloyd, Richard Atkinson, Mark N Wu, Giuseppa Pennetta, Yi Zhou, Hugo Jozef Bellen
    Abstract:

    Signaling through tyrosine kinase receptors (TKRs) is thought to be modulated by receptor-mediated endocytosis and degradation of the receptor in the lysosome. However, factors that regulate endosomal sorting of TKRs are largely unknown. Here, we demonstrate that Hrs (Hepatocyte growth factor-regulated tyrosine kinase substrate) is one such factor. Electron microscopy studies of hrs mutant larvae reveal an impairment in endosome Membrane Invagination and formation of multivesicular bodies (MVBs). hrs mutant animals fail to degrade active epidermal growth factor (EGF) and Torso TKRs, leading to enhanced signaling and altered embryonic patterning. These data suggest that Hrs and MVB formation function to downregulate TKR signaling.

  • hrs regulates endosome Membrane Invagination and tyrosine kinase receptor signaling in drosophila
    Cell, 2002
    Co-Authors: Thomas E Lloyd, Richard Atkinson, Mark N Wu, Giuseppa Pennetta, Yi Zhou, Hugo Jozef Bellen
    Abstract:

    Signaling through tyrosine kinase receptors (TKRs) is thought to be modulated by receptor-mediated endocytosis and degradation of the receptor in the lysosome. However, factors that regulate endosomal sorting of TKRs are largely unknown. Here, we demonstrate that Hrs (Hepatocyte growth factor-regulated tyrosine kinase substrate) is one such factor. Electron microscopy studies of hrs mutant larvae reveal an impairment in endosome Membrane Invagination and formation of multivesicular bodies (MVBs). hrs mutant animals fail to degrade active epidermal growth factor (EGF) and Torso TKRs, leading to enhanced signaling and altered embryonic patterning. These data suggest that Hrs and MVB formation function to downregulate TKR signaling.

Soriano Castell David - One of the best experts on this subject based on the ideXlab platform.

  • Rac1 y Calmodulina regulan la dinámica de membrana durante la endocitosis independiente de Clatrina
    'Edicions de la Universitat de Barcelona', 2017
    Co-Authors: Soriano Castell David
    Abstract:

    [spa] El fosfolípido PI(4,5)P2 ha sido descrito ampliamente como un factor clave en la endocitosis. De hecho, numerosas proteínas endocíticas contienen dominios de unión específicos para PI(4,5)P2. La dinámica de su metabolismo está finamente regulada por diversos enzimas que pueden fosforilarlo, defosforilarlo, hidrolizarlo o sintetizarlo a partir de precursores, cambiando su concentración en dominios específicos de la membrana. En los primeros pasos de la endocitosis, la concentración de PI(4,5)P2 aumenta y recluta clatrina u otros tipos de proteínas de cubierta o asociadas a procesos de remodelación de membrana, dando lugar a una invaginación. Más tarde, los niveles de PI(4,5)P2 deben reducirse para completar el proceso de formación de vesículas. En los últimos años, nuestro grupo ha descrito como la calmodulina (CaM) está regulando la interacción entre Rac1 y PIP5K, el principal enzima productor de PI(4,5)P2. La inhibición de la CaM, que es el sensor de calcio (Ca2+) más importante en células no musculares, induce la formación de invaginaciones tubulares ricas en PI(4,5)P2 provenientes de la membrana plasmática, que parecen formar parte de un proceso endocítico independiente de clatrina. Sin embargo, también se observó que la sobreexpresión del Rac1 constitutivamente activo (Rac1G12V) inhibe las tubulaciones inducidas por la inhibición de CaM, lo que podría deberse a la acción de efectores de Rac1 relacionados con el metabolismo de PI(4,5)P2, como la fosfolipasa C (PLC), o relacionados con la dinámica del citoesqueleto. Durante esta tesis, hemos demostrado el requerimiento de PI(4,5)P2 en la formación de los túbulos endocíticos, y hemos descrito como la CaM puede estar regulando sus niveles a través de la regulación de Rac1 y posiblemente de PKC, específicamente en las balsas lipídicas, donde se producen la mayoría de procesos endocíticos independientes de clatrina. La dinámica de las adhesiones focales, que vinculan el citoesqueleto con la matriz extracelular a través de la integrina, está también regulada por la endocitosis durante la migración celular. Existe además una estrecha regulación recíproca entre las RhoGTPasas y el tráfico de integrinas, que se extiende a lo largo del eje anteroposterior de la célula en migración, en el que generalmente Rac1 está activado en la parte anterior, y RhoA en la parte posterior. Los análisis de internalización realizados nos han permitido descubrir que las tubulaciones inducidas por PI(4,5)P2 son una vía de entrada de beta1-integrina, que aceleran su internalización y la excluyen de los compartimentos endosomales tempranos, impidiendo posiblemente un reciclaje rápido hacia la membrana plasmática. La activación constitutiva de Rac1 impide esta entrada rápida a través de los túbulos. Los sitios de endocitosis están estrechamente ligados al citoesqueleto de actina, ya que éste puede contribuir a la deformación, invaginación o rotura de la membrana. La cortactina modula la dinámica del citoesqueleto de actina durante la CDE y la CIE, en asociación con diversas proteínas como WASP, dinamina o Arp2/3. Se sabe que la cortactina requiere de Rac1 para ser translocada a la membrana plasmática pero no se conoce bien el mecanismo. Asimismo, la tensión de la membrana plasmática es también un elemento clave en la regulación de la internalización, estimulándose la endocitosis en regiones con una baja tensión de membrana. La miosina, en especial la miosina II de células no musculares, es, junto con la actina, uno de los principales reguladores de la tensión de membrana, especialmente durante la migración celular. El estudio de la función de cortactina y miosina permitió demostrar que la actividad de Rac1 regula negativamente la formación de las invaginaciones tubulares inducidas por PI(4,5)P2. Hemos demostrado que la acción de POR1, un efector conocido de Rac1, media la translocación de cortactina a la membrana plasmática. Además, se ha descrito por vez primera una activación directa de ROCK1 por parte de Rac1, que pemite la activación de la miosina y su asociación con el citoesqueleto de actina, lo cual es necesario para la inhibición de las tubulaciones por Rac1 activo.[eng] It has been described that specific calmodulin inhibition, W13-treatment, increased the percentage of cells with tubular plasma Membrane structures, which corresponds to the Arf6-dependent and clathrin-independent endocytosis pathway. The present thesis shows that these tubular transport Membranes by which β1-integrin is endocytosed, depends on the increased PI(4,5)P2 levels in lipid rafts, dynamin and dynein motor proteins. As for W13, exogenous PI(4,5)P2 or PIP5K expression generated-tubules are inhibited by expression of the active Rac1 mutant (Rac1-G12V). Therefore, the molecular mechanisms downstream of Rac1 that controls such tubules formation have been analyzed biochemically and by the expression of different Rac1 mutants. The results indicate that PLC and ROCK1, possibly in combination with POR1, are the main Rac1 effectors to impede plasma Membrane Invagination, by decreasing the PI(4,5)P2 levels and promoting cortical actomyosin, respectively. Importantly, among the interplay of proteins that participates in Membrane remodeling, this study reveals for the first time that the well-known downstream RhoA effector ROCK1 acts as an important effector of Rac1 to regulate actin-myosin at the cell cortex. This study provides new insights in the mode of Rac1 action on plasma Membrane dynamics regulation

  • Rac1 y Calmodulina regulan la dinámica de membrana durante la endocitosis independiente de Clatrina
    'Edicions de la Universitat de Barcelona', 2016
    Co-Authors: Soriano Castell David
    Abstract:

    El fosfolípido PI(4,5)P2 ha sido descrito ampliamente como un factor clave en la endocitosis. De hecho, numerosas proteínas endocíticas contienen dominios de unión específicos para PI(4,5)P2. La dinámica de su metabolismo está finamente regulada por diversos enzimas que pueden fosforilarlo, defosforilarlo, hidrolizarlo o sintetizarlo a partir de precursores, cambiando su concentración en dominios específicos de la membrana. En los primeros pasos de la endocitosis, la concentración de PI(4,5)P2 aumenta y recluta clatrina u otros tipos de proteínas de cubierta o asociadas a procesos de remodelación de membrana, dando lugar a una invaginación. Más tarde, los niveles de PI(4,5)P2 deben reducirse para completar el proceso de formación de vesículas. En los últimos años, nuestro grupo ha descrito como la calmodulina (CaM) está regulando la interacción entre Rac1 y PIP5K, el principal enzima productor de PI(4,5)P2. La inhibición de la CaM, que es el sensor de calcio (Ca2+) más importante en células no musculares, induce la formación de invaginaciones tubulares ricas en PI(4,5)P2 provenientes de la membrana plasmática, que parecen formar parte de un proceso endocítico independiente de clatrina. Sin embargo, también se observó que la sobreexpresión del Rac1 constitutivamente activo (Rac1G12V) inhibe las tubulaciones inducidas por la inhibición de CaM, lo que podría deberse a la acción de efectores de Rac1 relacionados con el metabolismo de PI(4,5)P2, como la fosfolipasa C (PLC), o relacionados con la dinámica del citoesqueleto. Durante esta tesis, hemos demostrado el requerimiento de PI(4,5)P2 en la formación de los túbulos endocíticos, y hemos descrito como la CaM puede estar regulando sus niveles a través de la regulación de Rac1 y posiblemente de PKC, específicamente en las balsas lipídicas, donde se producen la mayoría de procesos endocíticos independientes de clatrina. La dinámica de las adhesiones focales, que vinculan el citoesqueleto con la matriz extracelular a través de la integrina, está también regulada por la endocitosis durante la migración celular. Existe además una estrecha regulación recíproca entre las RhoGTPasas y el tráfico de integrinas, que se extiende a lo largo del eje anteroposterior de la célula en migración, en el que generalmente Rac1 está activado en la parte anterior, y RhoA en la parte posterior. Los análisis de internalización realizados nos han permitido descubrir que las tubulaciones inducidas por PI(4,5)P2 son una vía de entrada de beta1-integrina, que aceleran su internalización y la excluyen de los compartimentos endosomales tempranos, impidiendo posiblemente un reciclaje rápido hacia la membrana plasmática. La activación constitutiva de Rac1 impide esta entrada rápida a través de los túbulos. Los sitios de endocitosis están estrechamente ligados al citoesqueleto de actina, ya que éste puede contribuir a la deformación, invaginación o rotura de la membrana. La cortactina modula la dinámica del citoesqueleto de actina durante la CDE y la CIE, en asociación con diversas proteínas como WASP, dinamina o Arp2/3. Se sabe que la cortactina requiere de Rac1 para ser translocada a la membrana plasmática pero no se conoce bien el mecanismo. Asimismo, la tensión de la membrana plasmática es también un elemento clave en la regulación de la internalización, estimulándose la endocitosis en regiones con una baja tensión de membrana. La miosina, en especial la miosina II de células no musculares, es, junto con la actina, uno de los principales reguladores de la tensión de membrana, especialmente durante la migración celular. El estudio de la función de cortactina y miosina permitió demostrar que la actividad de Rac1 regula negativamente la formación de las invaginaciones tubulares inducidas por PI(4,5)P2. Hemos demostrado que la acción de POR1, un efector conocido de Rac1, media la translocación de cortactina a la membrana plasmática. Además, se ha descrito por vez primera una activación directa de ROCK1 por parte de Rac1, que pemite la activación de la miosina y su asociación con el citoesqueleto de actina, lo cual es necesario para la inhibición de las tubulaciones por Rac1 activo.It has been described that specific calmodulin inhibition, W13-treatment, increased the percentage of cells with tubular plasma Membrane structures, which corresponds to the Arf6-dependent and clathrin-independent endocytosis pathway. The present thesis shows that these tubular transport Membranes by which β1-integrin is endocytosed, depends on the increased PI(4,5)P2 levels in lipid rafts, dynamin and dynein motor proteins. As for W13, exogenous PI(4,5)P2 or PIP5K expression generated-tubules are inhibited by expression of the active Rac1 mutant (Rac1-G12V). Therefore, the molecular mechanisms downstream of Rac1 that controls such tubules formation have been analyzed biochemically and by the expression of different Rac1 mutants. The results indicate that PLC and ROCK1, possibly in combination with POR1, are the main Rac1 effectors to impede plasma Membrane Invagination, by decreasing the PI(4,5)P2 levels and promoting cortical actomyosin, respectively. Importantly, among the interplay of proteins that participates in Membrane remodeling, this study reveals for the first time that the well-known downstream RhoA effector ROCK1 acts as an important effector of Rac1 to regulate actin-myosin at the cell cortex. This study provides new insights in the mode of Rac1 action on plasma Membrane dynamics regulation