Disease relevance of RASGRF1

• We provide here biochemical and functional evidence demonstrating that human immunodeficiency virus type 1 (HIV-1) Vpr mediates G(2) arrest by forming a complex with protein phosphatase 2A (PP2A), an upstream regulator of cdc25 [1].
• Demonstrating the direct oncogenic potential of a cdc25 gene, we identify a gain-of-function mutant allele of the Caenorhabditis elegans gene cdc-25.1 that causes a deregulated proliferation of intestinal cells resulting in hyperplasia, while other aspects of intestinal cell function are retained [2].
• Many PTPs are recognized as potential drug targets; however, inhibitor development has focused only on a small number of enzymes, most notably PTP1B for type II diabetes and obesity, and MKP1 and CDC25 for cancer [3].
• cdc25 cell cycle-activating phosphatases and c-myc expression in human non-Hodgkin's lymphomas [4].
• We now report that the caulibugulones are selective in vitro inhibitors of the Cdc25 family of cell cycle-controlling protein phosphatases compared with either human vaccinia H1-related phosphatase (VHR) or tyrosine phosphatase 1B (PTP1B) [5].

Psychiatry related information on RASGRF1

• Here, we review the function and regulation of CDC25 phosphatases, their involvement in cancer and Alzheimer's disease, and the properties of several recently identified inhibitors [6].

High impact information on RASGRF1

• The PTP superfamily enzymes, which include tyrosine-specific, dual specificity, low-molecular-weight, and Cdc25 phosphatases, are key mediators of a wide variety of cellular processes, including growth, metabolism, differentiation, motility, and programmed cell death [7].
• Induction of G(2)/M phase transition in mitotic and meiotic cell cycles requires activation by phosphorylation of the protein phosphatase Cdc25 [8].
• In Xenopus oocytes, p42 MAPK interacts with hypophosphorylated Cdc25 before meiotic induction [8].
• The mitotic activator Cdc25 is suppressed by checkpoints through inhibitory phosphorylation at Ser287 (Xenopus numbering) and docking of 14-3-3 [9].
• Role for the PP2A/B56delta Phosphatase in Regulating 14-3-3 Release from Cdc25 to Control Mitosis [9].

Chemical compound and disease context of RASGRF1

• H32, a Non-Quinone Sulfone Analog of Vitamin K3, Inhibits Human Hepatoma Cell Growth by Inhibiting Cdc25 and Activating ERK [10].

Biological context of RASGRF1

• Point mutations within the Cdc25 domain that eliminate Ras binding also eliminate ubiquitination, demonstrating that binding to Ras is necessary for ubiquitination of GRF2 [11].
• Induction of rac-guanine nucleotide exchange activity of Ras-GRF1/CDC25(Mm) following phosphorylation by the nonreceptor tyrosine kinase Src [12].
• The cdc25 M-phase inducer: an unconventional protein phosphatase [13].
• In some crystals, the catalytic Cys-430 forms a disulfide bond with the invariant Cys-384, suggesting that Cdc25 may be self-inhibited during oxidative stress [14].
• These findings identify Cdc25, but not Wee1, as a target of the DNA damage checkpoint [15].

Anatomical context of RASGRF1

• We show here that activated ACK1, a nonreceptor tyrosine kinase that belongs to the focal adhesion kinase family, causes tyrosine phosphorylation of Ras-GRF1 [16].
• Our data suggest that creation of a 14-3-3 "sink," consisting of phosphorylated 14-3-3 binding intermediate filament proteins, including keratins, coupled with reduced Cdc25-14-3-3 affinity, contribute to Cdc25 activation [9].
• Key regulatory residues within CDC25 have been mapped and its activity tied both to the initial activation of cyclin-dependent kinases at the centrosome and to DNA damage checkpoints [17].
• The Cdc25 dual-specificity phosphatases control progression through the eukaryotic cell division cycle by activating cyclin-dependent kinases [18].
• In HeLa cells CDC25 mRNA levels are very low in G1 and increase at least 4-fold as cells progress towards M phase [19].

Associations of RASGRF1 with chemical compounds

• The Cdc25 domain possesses guanine nucleotide exchange factor activity and interacts with Ras [11].
• It is a multidomain protein composed of several recognizable sequence motifs in the following order (NH(2) to COOH): pleckstrin homology (PH), coiled-coil, ilimaquinone (IQ), Dbl homology (DH), PH, REM (Ras exchanger motif), PEST/destruction box, Cdc25 [20].
• Ras-GEF activity of Ras-GRF1 is augmented in response to Ca(2+) influx and G protein betagamma subunit (Gbetagamma) stimulation [12].
• The recombinant c-Src protein phosphorylated affinity-purified glutathione S-transferase-tagged Ras-GRF1 in vitro and thereby elicited Rac-GEF activity [12].
• When tsBN2 cells arrested in S phase were incubated at 40 degrees C in the presence of cycloheximide, Cdc25B, but not Cdc25A and C, among a family of dual-specificity phosphatases, Cdc25, was lost coincidentally with the lack of the activation of p34(cdc2)/cyclin B [21].

Physical interactions of RASGRF1

• Pin1 not only binds the mitotic form of Cdc25 on the phosphorylation sites important for its activity in vitro and in vivo, but it also inhibits its activity, offering one explanation for the ability of Pin1 to inhibit mitotic entry [22].
• We have shown previously that in these cells the CDK1/cyclin B complex is inactive and can be reactivated in vitro using recombinant CDC25 phosphatase [23].
• Crkl constitutively binds to the guanine nucleotide-releasing protein, C3G, via direct SH3 domain binding [24].
• Taken together, these data suggest that HABP1 induces morphological changes and modulates the cell cycle by interacting with proteins like CDC 25 through its N-terminal alpha-helix [25].
• PP2A is known to interact genetically in fission yeast with the Wee1 kinase and Cdc25 phosphatase that act on Tyr15 of Cdc2 [26].

Enzymatic interactions of RASGRF1

• CDC25 phosphatases belong to the tyrosine phosphatase family and play a critical role in regulating cell cycle progression by dephosphorylating cyclin-dependent kinases at inhibitory residues [27].
• Our data suggest that Vpr mediates G(2) arrest by enhancing the nuclear import of PP2A and by positively modulating its catalytic activity towards active phosphorylated nuclear cdc25 [1].
• Affinity-purified human GST-cdc25 was able to dephosphorylate and activate cdk2 isolated from interphase cells [28].
• Here we report that upon Etoposide treatment CDC2 is phosphorylated on tyrosine 15 and is dephosphorylated and activated in vitro by recombinant CDC25 phosphatase [29].
• The dual specificity CDC25 phosphatases dephosphorylate two inhibitory phospho-amino acids of cyclin-dependent kinases, a major family of cell cycle regulators [30].

Regulatory relationships of RASGRF1

• Furthermore, Ras-dependent activation of ERK2 by Ras-GRF1 was enhanced following co-expression of activated ACK1 [16].
• In addition, it is likely that other regulatory mechanisms cooperate with the wee1/cdc25 phosphorylation systems to control the action of cdc2 [31].
• Similarly, CDK2 is activated in vitro by dephosphorylation of Y15 and T14 by the phosphatase CDC25 [32].
• CDC25 phosphatases activate cyclin-dependent kinases by removing inhibitory phosphate groups on the molecules and positively regulate the cell cycle progression [33].
• We then describe a simple assay in which we demonstrate that growth of the humanised CDC25A strain is strongly repressed in a CDC25-dependent manner by BN2003, a potent chemical inhibitor of CDC25 belonging to the benzothiazoledione family [34].

Other interactions of RASGRF1

• Stimulation of Ras guanine nucleotide exchange activity of Ras-GRF1/CDC25(Mm) upon tyrosine phosphorylation by the Cdc42-regulated kinase ACK1 [16].
• Ras-GRF1 has been implicated as a Ras-specific guanine nucleotide exchange factor (GEF), which mediates calcium- and muscarinic receptor-triggered signals in the brain [35].
• GRF2 lacking the Cdc25 domain is not ubiquitinated, suggesting that a protein that cannot bind Ras cannot be properly targeted for destruction [11].
• G protein beta gamma subunit-dependent Rac-guanine nucleotide exchange activity of Ras-GRF1/CDC25(Mm) [35].
• In addition, Ras-GRF1 acts as a GEF for Rac when tyrosine-phosphorylated following G protein-coupled receptor stimulation [16].

Analytical, diagnostic and therapeutic context of RASGRF1

• Microinjection of purified cdc25C proteins into living fibroblasts reveals that only the phosphorylated form of cdc25 is highly effective in activating G2 cells into premature prophase in a manner similar to microinjection of purified active p34cdc2 protein kinase [36].
• Mapping of the human C3G gene coding a guanine nucleotide releasing protein for Ras family to 9q34.3 by fluorescence in situ hybridization [37].
• Changes in the expression of cdc25 phosphatases, mitogen-activated protein kinases (MAPKs), and bcl-2 family proteins were detected using Western blot analysis [38].
• Using an original method of sequence analysis, cdc25 proteins from different sources were compared to protein phosphatases [39].
• RT-PCR was used to estimate CDC25 transcript levels [40].

References