An Arabidopsis 14-3-3 protein can act as a transcriptional activator in yeast. (1/1483)

The 14-3-3 proteins are a group of highly conserved and widely distributed eukaryotic proteins with diverse functions. One 14-3-3 protein, AFT1 from Arabidopsis thaliana, was found to be able to activate transcription in yeast. When fused to the DNA-binding domain of a bacterial protein LexA, AFT1 can activate transcription of reporter genes that contain LexA operator sequences in their promoters. Although the in vivo function of AFT1 is not completely known, its similarity to previously identified proteins found in transcription complexes of Arabidopsis and maize suggests that AFT1 and some other 14-3-3 proteins may activate gene expression in other systems as well.  (+info)

Cell adhesion regulates the interaction between the docking protein p130(Cas) and the 14-3-3 proteins. (2/1483)

Integrin ligand binding induces a signaling complex formation via the direct association of the docking protein p130(Cas) (Cas) with diverse molecules. We report here that the 14-3-3zeta protein interacts with Cas in the yeast two-hybrid assay. We also found that the two proteins associate in mammalian cells and that this interaction takes place in a phosphoserine-dependent manner, because treatment of Cas with a serine phosphatase greatly reduced its ability to bind 14-3-3zeta. Furthermore, the Cas-14-3-3zeta interaction was found to be regulated by integrin-mediated cell adhesion. Thus, when cells are detached from the extracellular matrix, the binding of Cas to 14-3-3zeta is greatly diminished, whereas replating the cells onto fibronectin rapidly induces the association. Consistent with these results, we found that the subcellular localization of Cas and 14-3-3 is also regulated by integrin ligand binding and that the two proteins display a significant co-localization during cell attachment to the extracellular matrix. In conclusion, our results demonstrate that 14-3-3 proteins participate in integrin-activated signaling pathways through their interaction with Cas, which, in turn, may contribute to important biological responses regulated by cell adhesion to the extracellular matrix.  (+info)

Protein kinase C mu is negatively regulated by 14-3-3 signal transduction proteins. (3/1483)

Recent studies have documented direct interaction between 14-3-3 proteins and key molecules in signal transduction pathways like Ras, Cbl, and protein kinases. In T cells, the 14-3-3tau isoform has been shown to associate with protein kinase C theta and to negatively regulate interleukin-2 secretion. Here we present data that 14-3-3tau interacts with protein kinase C mu (PKCmu), a subtype that differs from other PKC members in structure and activation mechanisms. Specific interaction of PKCmu and 14-3-3tau can be shown in the T cell line Jurkat by immunocoprecipitiation and by pulldown assays of either endogenous or overexpressed proteins using PKCmu-specific antibodies and GST-14-3-3 fusion proteins, respectively. Using PKCmu deletion mutants, the 14-3-3tau binding region is mapped within the regulatory C1 domain. Binding of 14-3-3tau to PKCmu is significantly enhanced upon phorbol ester stimulation of PKCmu kinase activity in Jurkat cells and occurs via a Cbl-like serine containing consensus motif. However, 14-3-3tau is not a substrate of PKCmu. In contrast 14-3-3tau strongly down-regulates PKCmu kinase activity in vitro. Moreover, overexpression of 14-3-3tau significantly reduced phorbol ester induced activation of PKCmu kinase activity in intact cells. We therefore conclude that 14-3-3tau is a negative regulator of PKCmu in T cells.  (+info)

Akt promotes cell survival by phosphorylating and inhibiting a Forkhead transcription factor. (4/1483)

Survival factors can suppress apoptosis in a transcription-independent manner by activating the serine/ threonine kinase Akt, which then phosphorylates and inactivates components of the apoptotic machinery, including BAD and Caspase 9. In this study, we demonstrate that Akt also regulates the activity of FKHRL1, a member of the Forkhead family of transcription factors. In the presence of survival factors, Akt phosphorylates FKHRL1, leading to FKHRL1's association with 14-3-3 proteins and FKHRL1's retention in the cytoplasm. Survival factor withdrawal leads to FKHRL1 dephosphorylation, nuclear translocation, and target gene activation. Within the nucleus, FKHRL1 triggers apoptosis most likely by inducing the expression of genes that are critical for cell death, such as the Fas ligand gene.  (+info)

Ca2+-induced apoptosis through calcineurin dephosphorylation of BAD. (5/1483)

The Ca2+-activated protein phosphatase calcineurin induces apoptosis, but the mechanism is unknown. Calcineurin was found to dephosphorylate BAD, a pro-apoptotic member of the Bcl-2 family, thus enhancing BAD heterodimerization with Bcl-xL and promoting apoptosis. The Ca2+-induced dephosphorylation of BAD correlated with its dissociation from 14-3-3 in the cytosol and translocation to mitochondria where Bcl-xL resides. In hippocampal neurons, L-glutamate, an inducer of Ca2+ influx and calcineurin activation, triggered mitochondrial targeting of BAD and apoptosis, which were both suppressible by coexpression of a dominant-inhibitory mutant of calcineurin or pharmacological inhibitors of this phosphatase. Thus, a Ca2+-inducible mechanism for apoptosis induction operates by regulating BAD phosphorylation and localization in cells.  (+info)

Fusicoccin, 14-3-3 proteins, and defense responses in tomato plants. (6/1483)

Fusicoccin (FC) is a fungal toxin that activates the plant plasma membrane H+-ATPase by binding with 14-3-3 proteins, causing membrane hyperpolarization. Here we report on the effect of FC on a gene-for-gene pathogen-resistance response and show that FC application induces the expression of several genes involved in plant responses to pathogens. Ten members of the FC-binding 14-3-3 protein gene family were isolated from tomato (Lycopersicon esculentum) to characterize their role in defense responses. Sequence analysis is suggestive of common biochemical functions for these tomato 14-3-3 proteins, but their genes showed different expression patterns in leaves after challenges. Different specific subsets of 14-3-3 genes were induced after treatment with FC and during a gene-for-gene resistance response. Possible roles for the H+-ATPase and 14-3-3 proteins in responses to pathogens are discussed.  (+info)

Maintenance of G2 arrest in the Xenopus oocyte: a role for 14-3-3-mediated inhibition of Cdc25 nuclear import. (7/1483)

Cdc2-cyclin B1 in the G2-arrested Xenopus oocyte is held inactive by phosphorylation of Cdc2 at two negative regulatory sites, Thr14 and Tyr15. Upon treatment with progesterone, these sites are dephosphorylated by the dual specificity phosphatase, Cdc25, leading to Cdc2-cyclin B1 activation. Whereas maintenance of the G2 arrest depends upon preventing Cdc25-induced Cdc2 dephosphorylation, the mechanisms responsible for keeping Cdc25 in check in these cells have not yet been described. Here we report that Cdc25 in the G2-arrested oocyte is bound to 14-3-3 proteins and that progesterone treatment abrogates this binding. We demonstrate that Cdc25, apparently statically localized in the cytoplasm, is actually capable of shuttling in and out of the oocyte nucleus. Binding of 14-3-3 protein markedly reduces the nuclear import rate of Cdc25, allowing nuclear export mediated by a nuclear export sequence present in the N-terminus of Cdc25 to predominate. If 14-3-3 binding to Cdc25 is prevented while nuclear export is inhibited, the coordinate nuclear accumulation of Cdc25 and Cdc2-cyclin B1 facilitates their mutual activation, thereby promoting oocyte maturation.  (+info)

The zeta isoform of 14-3-3 proteins interacts with the third intracellular loop of different alpha2-adrenergic receptor subtypes. (8/1483)

The alpha2-adrenergic receptors (alpha2ARs) are localized to and function on the basolateral surface in polarized renal epithelial cells via a mechanism involving the third cytoplasmic loop. To identify proteins that may contribute to this retention, [35S]Met-labeled Gen10 fusion proteins with the 3i loops of the alpha2AAR (Val217-Ala377), alpha2BAR (Lys210-Trp354), and alpha2CAR (Arg248-Val363) were used as ligands in gel overlay assays. A protein doublet of approximately 30 kDa in Madin-Darby canine kidney cells or pig brain cytosol (alpha2B >/= alpha2C>> alpha2A) was identified. The interacting protein was purified by sequential DEAE and size exclusion chromatography, and subsequent microsequencing revealed that they are the zeta isoform of 14-3-3 proteins. [35S]Met-14-3-3zeta binds to all three native alpha2AR subtypes, assessed using a solid phase binding assay (alpha2A>/=alpha2B> alpha2C), and this binding depends on the presence of the 3i loops. Attenuation of the alpha2AR-14-3-3 interactions in the presence of a phosphorylated Raf-1 peptide corresponding to its 14-3-3 interacting domain (residues 251-266), but not by its non-phosphorylated counterpart, provides evidence for the functional specificity of these interactions and suggests one potential interface for the alpha2AR and 14-3-3 interactions. These studies represent the first evidence for G protein-coupled receptor interactions with 14-3-3 proteins and may provide a mechanism for receptor localization and/or coordination of signal transduction.  (+info)

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