Limits...
Cell wall stress depolarizes cell growth via hyperactivation of RHO1.

Delley PA, Hall MN - J. Cell Biol. (1999)

Bottom Line: Depolarization of the actin cytoskeleton and FKS1 is mediated by the plasma membrane protein WSC1, the RHO1 GTPase switch, PKC1, and a yet-to-be defined PKC1 effector branch.The PKC1-activated mitogen-activated protein kinase cascade is not required for depolarization, but rather for repolarization of the actin cytoskeleton and FKS1.Thus, activated RHO1 can mediate both polarized and depolarized cell growth via the same effector, PKC1, suggesting that RHO1 may function as a rheostat rather than as a simple on-off switch.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.

ABSTRACT
Cells sense and physiologically respond to environmental stress via signaling pathways. Saccharomyces cerevisiae cells respond to cell wall stress by transiently depolarizing the actin cytoskeleton. We report that cell wall stress also induces a transient depolarized distribution of the cell wall biosynthetic enzyme glucan synthase FKS1 and its regulatory subunit RHO1, possibly as a mechanism to repair general cell wall damage. The redistribution of FKS1 is dependent on the actin cytoskeleton. Depolarization of the actin cytoskeleton and FKS1 is mediated by the plasma membrane protein WSC1, the RHO1 GTPase switch, PKC1, and a yet-to-be defined PKC1 effector branch. WSC1 behaves like a signal transducer or a stress-specific actin landmark that both controls and responds to the actin cytoskeleton, similar to the bidirectional signaling between integrin receptors and the actin cytoskeleton in mammalian cells. The PKC1-activated mitogen-activated protein kinase cascade is not required for depolarization, but rather for repolarization of the actin cytoskeleton and FKS1. Thus, activated RHO1 can mediate both polarized and depolarized cell growth via the same effector, PKC1, suggesting that RHO1 may function as a rheostat rather than as a simple on-off switch.

Show MeSH

Related in: MedlinePlus

BCK1 and MPK1 are required for repolarization of the actin cytoskeleton upon heat shock. Wild-type (A–F, JK9-3da), bck1 (G–L, PA109-1c), and mpk1 (M–R, TS45-1a) cells were grown in rich medium at 24°C and shifted to 37°C for 35 and 180 min. Samples were fixed, stained with TRITC-phalloidin, and observed by fluorescence (A, C, E, G, I, K, M, O, and Q) and Nomarski (B, D, F, H, J, L, N, P, and R) microscopy to visualize the actin cytoskeleton and whole cells, respectively.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2164985&req=5

Figure 4: BCK1 and MPK1 are required for repolarization of the actin cytoskeleton upon heat shock. Wild-type (A–F, JK9-3da), bck1 (G–L, PA109-1c), and mpk1 (M–R, TS45-1a) cells were grown in rich medium at 24°C and shifted to 37°C for 35 and 180 min. Samples were fixed, stained with TRITC-phalloidin, and observed by fluorescence (A, C, E, G, I, K, M, O, and Q) and Nomarski (B, D, F, H, J, L, N, P, and R) microscopy to visualize the actin cytoskeleton and whole cells, respectively.

Mentions: The previous findings that mutants defective in MPK1/SLT2 exhibit a depolarized actin cytoskeleton (Mazzoni et al. 1993) and overexpression of MPK1 suppresses the actin polarization defect of a rho1 mutant (Helliwell et al. 1998b) suggested that the PKC1-activated MAP kinase pathway might be required for repolarization. To investigate this further, we examined repolarization of the actin cytoskeleton and FKS1 in bck1 and mpk1 mutants. As described above, the actin cytoskeleton and FKS1 were normally depolarized in bck1 and mpk1 cells shifted to 37°C for 35 min (Fig. 4). However, after 120 min and longer, when the actin cytoskeleton is repolarized in wild-type cells, depolarization of the actin cytoskeleton persisted in most bck1 and mpk1 cells (Fig. 4). A similar effect was obtained when examining FKS1 distribution (data not shown). It is important to note that bck1 and mpk1 mutations in our strain background do not confer a severe temperature sensitive growth defect, as reported for other strain backgrounds, and therefore the persistent depolarization of the actin cytoskeleton and FKS1 cannot be attributed to cell death. Thus, the PKC1-activated MAP kinase cascade is required for repolarization rather than depolarization of cell growth.


Cell wall stress depolarizes cell growth via hyperactivation of RHO1.

Delley PA, Hall MN - J. Cell Biol. (1999)

BCK1 and MPK1 are required for repolarization of the actin cytoskeleton upon heat shock. Wild-type (A–F, JK9-3da), bck1 (G–L, PA109-1c), and mpk1 (M–R, TS45-1a) cells were grown in rich medium at 24°C and shifted to 37°C for 35 and 180 min. Samples were fixed, stained with TRITC-phalloidin, and observed by fluorescence (A, C, E, G, I, K, M, O, and Q) and Nomarski (B, D, F, H, J, L, N, P, and R) microscopy to visualize the actin cytoskeleton and whole cells, respectively.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2164985&req=5

Figure 4: BCK1 and MPK1 are required for repolarization of the actin cytoskeleton upon heat shock. Wild-type (A–F, JK9-3da), bck1 (G–L, PA109-1c), and mpk1 (M–R, TS45-1a) cells were grown in rich medium at 24°C and shifted to 37°C for 35 and 180 min. Samples were fixed, stained with TRITC-phalloidin, and observed by fluorescence (A, C, E, G, I, K, M, O, and Q) and Nomarski (B, D, F, H, J, L, N, P, and R) microscopy to visualize the actin cytoskeleton and whole cells, respectively.
Mentions: The previous findings that mutants defective in MPK1/SLT2 exhibit a depolarized actin cytoskeleton (Mazzoni et al. 1993) and overexpression of MPK1 suppresses the actin polarization defect of a rho1 mutant (Helliwell et al. 1998b) suggested that the PKC1-activated MAP kinase pathway might be required for repolarization. To investigate this further, we examined repolarization of the actin cytoskeleton and FKS1 in bck1 and mpk1 mutants. As described above, the actin cytoskeleton and FKS1 were normally depolarized in bck1 and mpk1 cells shifted to 37°C for 35 min (Fig. 4). However, after 120 min and longer, when the actin cytoskeleton is repolarized in wild-type cells, depolarization of the actin cytoskeleton persisted in most bck1 and mpk1 cells (Fig. 4). A similar effect was obtained when examining FKS1 distribution (data not shown). It is important to note that bck1 and mpk1 mutations in our strain background do not confer a severe temperature sensitive growth defect, as reported for other strain backgrounds, and therefore the persistent depolarization of the actin cytoskeleton and FKS1 cannot be attributed to cell death. Thus, the PKC1-activated MAP kinase cascade is required for repolarization rather than depolarization of cell growth.

Bottom Line: Depolarization of the actin cytoskeleton and FKS1 is mediated by the plasma membrane protein WSC1, the RHO1 GTPase switch, PKC1, and a yet-to-be defined PKC1 effector branch.The PKC1-activated mitogen-activated protein kinase cascade is not required for depolarization, but rather for repolarization of the actin cytoskeleton and FKS1.Thus, activated RHO1 can mediate both polarized and depolarized cell growth via the same effector, PKC1, suggesting that RHO1 may function as a rheostat rather than as a simple on-off switch.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.

ABSTRACT
Cells sense and physiologically respond to environmental stress via signaling pathways. Saccharomyces cerevisiae cells respond to cell wall stress by transiently depolarizing the actin cytoskeleton. We report that cell wall stress also induces a transient depolarized distribution of the cell wall biosynthetic enzyme glucan synthase FKS1 and its regulatory subunit RHO1, possibly as a mechanism to repair general cell wall damage. The redistribution of FKS1 is dependent on the actin cytoskeleton. Depolarization of the actin cytoskeleton and FKS1 is mediated by the plasma membrane protein WSC1, the RHO1 GTPase switch, PKC1, and a yet-to-be defined PKC1 effector branch. WSC1 behaves like a signal transducer or a stress-specific actin landmark that both controls and responds to the actin cytoskeleton, similar to the bidirectional signaling between integrin receptors and the actin cytoskeleton in mammalian cells. The PKC1-activated mitogen-activated protein kinase cascade is not required for depolarization, but rather for repolarization of the actin cytoskeleton and FKS1. Thus, activated RHO1 can mediate both polarized and depolarized cell growth via the same effector, PKC1, suggesting that RHO1 may function as a rheostat rather than as a simple on-off switch.

Show MeSH
Related in: MedlinePlus