Dry Stress-Induced Phosphorylation ofPhysarumActin

Furuhashi, Kiyoshi; Ishigami, Masa; Suzuki, Masami; Titani, Koiti

doi:10.1006/bbrc.1997.8044

Cited by 18 publications

(26 citation statements)

References 33 publications

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“…Previously, we showed that fragminP and fragminA both possess a unique quality by promoting phosphorylation of actin in vitro at Thr-203 by the actin-fragmin kinase (AFK), a protein kinase with a kelch domain and a catalytic domain that contains barely 5 conserved amino acids encountered in regular protein kinases (16,29,30). We demonstrate here that fragmin60 is involved in controlling actin phosphorylation in plasmodia and particularly in sclerotia, which contain exceptionally high levels of phospho-actin (31).…”

mentioning

confidence: 77%

“…Fragmin60 Is Associated with Phosphorylated Actin in Physarum Sclerotia and in Plasmodia-In sclerotia of Physarum, a dormant stage of the organism formed from plasmodia under dry stress, no less than 50% of all actin is phosphorylated (31). The majority of phosphorylated actin is present as a monomer.…”

Section: Actin In the Actin-fragmin60 Complex Is Phosphorylated In VImentioning

confidence: 99%

“…This may be expected when the physiological role of the actin-fragmin kinase and actin-binding proteins are correlated with respect to actin phosphorylation. Phospho-actin in sclerotia, however, occurs mostly in free monomeric form (31). Because neither G-nor F-actin is phosphorylated by AFK (16), actin in sclerotia has to associate temporarily with fragminP or fragmin60 in order to be phosphorylated.…”

Section: Frg60 Expression Is Developmentally Regulatedmentioning

confidence: 99%

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Fragmin60 Encodes an Actin-binding Protein with a C2 Domain and Controls Actin Thr-203 Phosphorylation in PhysarumPlasmodia and Sclerotia

Sklyarova

Corte

Meerschaert

et al. 2002

Journal of Biological Chemistry

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We report the isolation of a cDNA clone encoding a 60-kDa protein termed fragmin60 that cross-reacts with fragmin antibodies. Unlike other gelsolin-related proteins, fragmin60 contains a unique N-terminal domain that shows similarity with C2 domains of aczonin, protein kinase C, and synaptotagmins. The fragmin60 C2 domain binds three calcium ions, one with nanomolar affinity and two with micromolar affinity. Actin binding by fragmin60 requires higher calcium concentrations than does binding of actin by a fragmin60 mutant lacking the C2 domain, suggesting that the C2 domain secures the actin binding moiety in a conformation preventing actin binding at low calcium concentrations. The fragmin60 C2 domain does not bind phospholipids but interacts with the endogenous homologue of Saccharomyces cerevisiae S-phase kinase-associated protein (Skp1), as shown by pull-down assays and co-expression in mammalian cells. Recombinant fragmin60 promotes in vitro phosphorylation of actin Thr-203 by the actin-fragmin kinase. We further show that in vivo phosphorylation of actin in the fragmin60-actin complex occurs in sclerotia, a dormant stage of Physarum development, as well as in plasmodia. Our findings indicate that we have cloned a novel type of gelsolin-related actin-binding protein that is involved in controlling regulation of actin phosphorylation in vivo.

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mentioning

confidence: 77%

Section: Actin In the Actin-fragmin60 Complex Is Phosphorylated In VImentioning

confidence: 99%

Section: Frg60 Expression Is Developmentally Regulatedmentioning

confidence: 99%

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Fragmin60 Encodes an Actin-binding Protein with a C2 Domain and Controls Actin Thr-203 Phosphorylation in PhysarumPlasmodia and Sclerotia

Sklyarova

Corte

Meerschaert

et al. 2002

Journal of Biological Chemistry

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“…Previous studies have suggested that the phosphorylation of actin has a variable effect on cells depending on the cell type, the experimental conditions, and the site of phosphorylation. Phosphorylation can occur at the threonine [Furuhashi and Hatano, 1990;De Corte et al, 1996;Furuhashi et al, 1998], tyrosine [Schweiger et al, 1992;Howard et al, 1993;Delft et al 1997;Gauthier et al, 1997;Kishi et al, 1998;Kameyama et al, 2000], and serine residues [Carrascosa and Wieland, 1986;Delft et al, 1997] of actin. In the drought-dormant sclerotia of the slime mold Physarum polycephalum, threonine phosphorylation of actin has been found to inhibit actin polymerization [Furuhashi et al, 1998].…”

Section: Introductionmentioning

confidence: 99%

“…Phosphorylation can occur at the threonine [Furuhashi and Hatano, 1990;De Corte et al, 1996;Furuhashi et al, 1998], tyrosine [Schweiger et al, 1992;Howard et al, 1993;Delft et al 1997;Gauthier et al, 1997;Kishi et al, 1998;Kameyama et al, 2000], and serine residues [Carrascosa and Wieland, 1986;Delft et al, 1997] of actin. In the drought-dormant sclerotia of the slime mold Physarum polycephalum, threonine phosphorylation of actin has been found to inhibit actin polymerization [Furuhashi et al, 1998]. High levels of actin tyrosine phosphorylation in Dictyostelium discoideum, specific to the spore stage, may be required for maintaining dormancy to withstand starvation stress; however, phosphorylated actin still has the ability to polymerize [Kishi et al, 1998].…”

Section: Introductionmentioning

confidence: 99%

Regulation of levels of actin threonine phosphorylation during life cycle of Physarum polycephalum

Shirai

Sasaki

Kishi

et al. 2005

Cell Motil. Cytoskeleton

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Under various environmental stresses, the true slime mold Physarum polycephalum converts into dormant forms, such as microcysts, sclerotia, and spores, which can survive in adverse environments for a considerable period of time. In drought-induced sclerotia, actin is threonine phosphorylated, which blocks its ability to polymerize into filaments. It is known that fragmin and actin-fragmin kinase (AFK) mediate this phosphorylation event. In this work, we demonstrate that high levels of actin threonine phosphorylation are also found in other dormant cells, including microcysts and spores. As the threonine phosphorylation of actin in microcysts and sclerotia were induced by drought stress but not by other stresses, we suggest that drought stress is essential for actin phosphorylation in both cell types. Although characteristic filamentous actin structures (dot- or rod-like structures) were observed in microcysts, sclerotia, and spores, actin phosphorylation was not required for the formation of these structures. Prior to the formation of both microcysts and sclerotia, AFK mRNA expression was activated transiently, whereas fragmin mRNA levels decreased. Our results suggest that drought stress and AFK might be involved in the threonine phosphorylation of actin.

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Calyculin A–induced actin phosphorylation and depolymerization in renal epithelial cells

Gu¹,

Zhang²,

Chen³

et al. 2003

Cell Motil. Cytoskeleton

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This study reports actin phosphorylation and coincident actin cytoskeleton alterations in renal epithelial cell line, LLC-PK1. Serine phosphorylation of actin was first observed in vitro after the cell lysate was incubated with phosphatase inhibitors and ATP. Both the phosphorylated actin and actin kinase activities were found in the cytoskeletal fraction. Actin phosphorylation was later detected in living LLC-PK1 cells after incubation with the phosphatase inhibitor calyculin A. Calyculin A-induced actin phosphorylation was associated with reorganization of the actin cytoskeleton, including net actin depolymerization, loss of cell-cell junction and stress fiber F-actin filaments, and redistribution of F-actin filaments in the periphery of the rounded cells. Actin phosphorylation was abolished by 3-h ATP depletion but not by the non-specific kinase inhibitor staurosporine. These results demonstrate that renal epithelial cells contain kinase/phosphatase activities and actin can be phosphorylated in LLC-PK1 cells. Actin phosphorylation may play an important role in regulating the organization of the actin cytoskeleton in renal epithelium.

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Dry Stress-Induced Phosphorylation ofPhysarumActin

Cited by 18 publications

References 33 publications

Fragmin60 Encodes an Actin-binding Protein with a C2 Domain and Controls Actin Thr-203 Phosphorylation in PhysarumPlasmodia and Sclerotia

Fragmin60 Encodes an Actin-binding Protein with a C2 Domain and Controls Actin Thr-203 Phosphorylation in PhysarumPlasmodia and Sclerotia

Regulation of levels of actin threonine phosphorylation during life cycle of Physarum polycephalum

Calyculin A–induced actin phosphorylation and depolymerization in renal epithelial cells

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