The Ras Guanine Nucleotide Exchange Factor CDC25Mm Is Present at the Synaptic Junction

Sturani, E.; Abbondio, Adele; Branduardi, Paola; Ferrari, Cristina; Zippel, Renata; Martegani, Enzo; Vanoni, Marco; Denis-Donini, S.

doi:10.1006/excr.1997.3660

Cited by 62 publications

(39 citation statements)

References 37 publications

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“…In this regard, it is worth mentioning that Mattingly (16) has recently reported from in vivo and in vitro experiments that phosphorylation of serine 916 was in part dependent on PKA. Phosphorylation of CDC25Mm by PKA has been shown in our work to take place in the neuronal tissue, using synaptosomal membranes from mouse brain that contain PKA, PKC, and CaMKII (24,25). It is interesting to note that, in fibroblasts overexpressing CDC25Mm, the in vitro phosphorylation of CDC25Mm was decreased by 50%, following in vivo phosphorylation with PKA.…”

Section: Discussionmentioning

confidence: 52%

“…We previously showed by subcellular fractionation of mouse brain that CDC25Mm is associated with synaptosomal membranes and is enriched in postsynaptic densities (25). Synaptosomal membranes contain PKA, PKC, and CaMKII (24,25), and, under conditions allowing the activity of the different kinases, it is possible to identify endogenous physiological substrates (24).…”

Section: Resultsmentioning

confidence: 99%

“…Synaptosomal membranes contain PKA, PKC, and CaMKII (24,25), and, under conditions allowing the activity of the different kinases, it is possible to identify endogenous physiological substrates (24). To investigate whether CDC25Mm is phosphorylated by PKA in its physiological environment, mouse brain synaptosomal membranes were isolated and incubated in a kinase assay in the presence of [␥- neuronal tissue, whereas other kinases (calcium/calmodulindependent and protein kinase C) are much less active toward this protein.…”

Section: Resultsmentioning

confidence: 99%

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Sites of Phosphorylation by Protein Kinase A in CDC25Mm/GRF1, a Guanine Nucleotide Exchange Factor for Ras

Baouz

Jacquet

Accorsi

et al. 2001

Journal of Biological Chemistry

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Activation of the neuronal Ras GDP/GTP exchange factor (GEF) CDC25Mm/GRF1 is known to be associated with phosphorylation of serine/threonine. To increase our knowledge of the mechanism involved, we have analyzed the ability of several serine/threonine kinases to phosphorylate CDC25Mm in vivo and in vitro. We could demonstrate the involvement of cAMP-dependent protein kinase (PKA) in the phosphorylation of CDC25Mm in fibroblasts overexpressing this RasGEF as well as in mouse brain synaptosomal membranes. In vitro, PKA was found to phosphorylate multiple sites on purified CDC25Mm, in contrast to protein kinase C, calmodulin kinase II, and casein kinase II, which were virtually inactive. Eight phosphorylated serines and one threonine were identified by mass spectrometry and Edman degradation. Most of them were clustered around the Ras exchanger motif/PEST motifs situated in the C-terminal moiety (residues 631-978) preceding the catalytic domain. Ser 745 and Ser 822 were the most heavily phosphorylated residues and the only ones coinciding with PKA consensus sequences. Substitutions S745D and S822D showed that the latter mutation strongly inhibited the exchange activity of CDC25Mm on Ha-Ras. The multiple PKA-dependent phosphorylation sites on CDC25Mm suggest a complex regulatory picture of this RasGEF. The results are discussed in the light of structural and/or functional similarities with other members of this RasGEF family.

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Section: Discussionmentioning

confidence: 52%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Sites of Phosphorylation by Protein Kinase A in CDC25Mm/GRF1, a Guanine Nucleotide Exchange Factor for Ras

Baouz

Jacquet

Accorsi

et al. 2001

Journal of Biological Chemistry

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“…In mammalian cells two classes of ras-speci®c GEF have been identi®ed. One class is mostly brain-speci®c and has been called CDC25 Mm , Ras Grf, hGRF55 by various groups (Martegani et al, 1992;Shou et al, 1992;Schweigho er et al, 1993;Wei et al, 1993Wei et al, , 1994Sturani et al, 1997). The other class is expressed ubiquitously and is called Sos Buday and Downward, 1993;Guerrero et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

A dominant negative RAS-specific guanine nucleotide exchange factor reverses neoplastic phenotype in K-ras transformed mouse fibroblasts

et al. 2000

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Ras proteins are small GTPases playing a pivotal role in cell proliferation and di erentiation. Their activation state depends on the competing action of GTPase Activating Proteins (GAP) and Guanine nucleotide Exchange Factors (GEF). A tryptophan residue (Trp1056 in CDC25 Mm -GEF), conserved in all rasspeci®c GEFs identi®ed so far has been previously shown to be essential for GEF activity. Its substitution with glutamic acid results in a catalytically inactive mutant, which is able to e ciently displace wild-type GEF from p21 ras and to originate a stable ras/GEF binary complex due to the reduced a nity of the nucleotide-free ras/ GEF complex for the incoming nucleotide. We show here that this`ras-sequestering property' can be utilized to attenuate ras signal transduction pathways in mouse ®broblasts transformed by oncogenic ras. In fact overexpression of the dominant negative GEF W1056E in stable transfected cells strongly reduces intracellular ras´GTP levels in k-ras transformed ®broblasts. Accordingly, the transfected ®broblasts revert to wild-type phenotype on the basis of morphology, cell cycle and anchorage independent growth. The reversion of the transformed phenotype is accompanied by DNA endoreduplication. The possible use of dominant negative ras-speci®c GEFs as a tool to down-regulate tumor growth is discussed.

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“…53 A significant amount of GRF proteins are also found in the cell soma of neurons, some of which are associated with the endoplasmic reticulum. 54 At this membrane site, GRFs may be activated by signals distinct from those occurring in the plasma membrane, such as those from G protein receptors.…”

Section: Structural Organization and Biochemical Functionsmentioning

confidence: 99%

Regulation of Neuronal Function by Ras-GRF Exchange Factors

Feig

2011

Genes & Cancer

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Ras-GRF1 (GRF1) and Ras-GRF2 (GRF2) constitute a family of guanine nucleotide exchange factors (GEFs). The main isoforms, p140-GRF1 and p135-GRF2, have 2 GEF domains that give them the capacity to activate both Ras and Rac GTPases in response to signals from a variety of neurotransmitter receptors. GRF1 and GRF2 proteins are found predominantly in adult neurons of the central nervous system, although they can also be detected in a limited number of other tissues. p140-GRF1 and p135-GRF2 contain calcium/calmodulin-binding IQ domains that allow them to act as calcium sensors to mediate the actions of NMDA-type and calcium-permeable AMPA-type glutamate receptors. p140-GRF1 also mediates the action of dopamine receptors that signal through cAMP. Although p140-GRF1 and p135-GRF2 have similar functional domains, studies of GRF knockout mice show that they can play strikingly different roles in regulating MAP kinase family members, neuronal synaptic plasticity, specific forms of learning and memory, and behavioral responses to psychoactive drugs. In addition, the function of GRF proteins may vary in different regions of the brain. Alternative splice variants yielding smaller GRF1 gene isoforms with fewer functional domains also exist; however, their distinct roles in neurons have not been revealed. Continuing studies of these proteins should yield important insights into the biochemical basis of brain function as well as novel concepts to explain how complex signal transduction proteins, like Ras-GRFs, integrate multiple upstream signals into specific downstream outputs to control brain function.

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The Ras Guanine Nucleotide Exchange Factor CDC25Mm Is Present at the Synaptic Junction

Cited by 62 publications

References 37 publications

Sites of Phosphorylation by Protein Kinase A in CDC25Mm/GRF1, a Guanine Nucleotide Exchange Factor for Ras

Sites of Phosphorylation by Protein Kinase A in CDC25Mm/GRF1, a Guanine Nucleotide Exchange Factor for Ras

A dominant negative RAS-specific guanine nucleotide exchange factor reverses neoplastic phenotype in K-ras transformed mouse fibroblasts

Regulation of Neuronal Function by Ras-GRF Exchange Factors

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