Disease relevance of RAP1GAP

• Rap1GAP inhibits tumor growth in oropharyngeal squamous cell carcinoma [1].
• Identification of a putative tumor suppressor gene Rap1GAP in pancreatic cancer [2].
• To investigate the mechanism of the GTP-hydrolysis reaction catalyzed by Rap1GAP, a catalytically active fragment was expressed in Escherichia coli and characterized by kinetic and mutagenesis studies [3].
• Using adenovirus, inactivation of Rap1 by expression of rap1GAPII inhibited wound healing [4].
• Rap1-GAP protein was detected in 15/19 subsequently recurring primary melanomas (79%) but only in 32/67 tumors (47%) of patients who remained free of disease (P < 0.05) for at least 6 years [5].

High impact information on RAP1GAP

• Thus, the alpha-subunit of G(i) activates the Ras-ERK/MAPK mitogenic pathway by membrane recruitment of rap1GAPII and reduction of GTP-bound Rap1 [6].
• Here we show that a novel isoform of Rapl GTPase-activating protein, called rap1GAPII, binds specifically to the alpha-subunits of the G(i) family of heterotrimeric G-proteins [6].
• Stimulation of the G(i)-coupled m2-muscarinic receptor translocates rap1GAPII from the cytosol to the membrane and decreases the amount of GTP-bound Rap1 [6].
• Both the cAMP effect and the Epac effect on cell adhesion were abolished by the expression of Rap1-GTPase-activating protein, indicating the involvement of Rap1 in the signaling pathway [7].
• We could detect mRNAs for a new protein most closely related to Rap1GAP and for postsynaptic density-95 discs-large and zona occludens protein 1 (PDZ)-GEF1 and CalDAG-GEFs I and III [8].

Biological context of RAP1GAP

• Structure-function analyses indicate that the first 74 amino-terminal residues of Rap1GAP, a region distinct from the catalytic core domain responsible for the GAP activity toward Rap1, is required for this interaction [9].
• The RAP1GA1 locus for human Rap1-GTPase activating protein 1 maps to chromosome 1p36.1-->p35 [10].
• Using a panel of somatic cell hybrids we have mapped the locus for Rap1-GTPase activating protein 1 (RAP1GA1) to human chromosome 1 [10].
• By mutational analysis, fluorescence titration and stopped-flow kinetic assay, we demonstrate that Rap1GAP provides a catalytic asparagine to stimulate GTP hydrolysis [11].
• Moreover, depletion of p34cdc2 from mitotic extracts abolishes the phosphorylation of Rap1GAP by such lysates [12].

Anatomical context of RAP1GAP

• Introduction of both Rap1GAP and RalGDS-RBD in the megakaryoblastic cell line DAMI strongly reduced basal adhesion to immobilized fibrinogen [13].
• Furthermore, the ability of a cytosolic rap1 GTPase-activating protein to stimulate neutrophil rap1 GTP hydrolysis was not modified by phosphorylation [14].
• We show that p34cdc2 co-immunoprecipitated from mitotic Hela cell lysates with an anti human cyclin B1 antibody, but not from interphasic cell lysates, is able to phosphorylate efficiently wild-type Rap1GAP, but not a mutant in which the putative consensus site for phosphorylation by the cdc2 kinase (serine 484) has been altered [12].
• Cytoplasmic expression of Rap1-GAP has also been observed in the cells of skin appendages and in keratinocytes, particularly in suprabasal layers of the epidermis [5].

Associations of RAP1GAP with chemical compounds

• The putative TSC2 product (tuberin) contains a region of limited homology to the catalytic domain of Rap1GAP [15].
• Rap1GAP does also not supply the crucial glutamine that is missing in Rap proteins at position 61 [3].

Regulatory relationships of RAP1GAP

• In contrast, depressing Rap1 activity by expressing Rap1GAP led to disassembly of these junctions and increased their permeability [16].
• Rap1GAP (for Rap1 GTPase Activating Protein) is an 89 kD protein that highly stimulates the intrinsic GTPase activity of the small GTP binding protein Rap1 [12].

Other interactions of RAP1GAP

• However, overexpression of a RAP1 GTPase-activating protein (RAP1GAP), which efficiently clamped cellular RAP1 in the inactive GDP-bound form, did not affect A(2A)-agonist-mediated MAP kinase stimulation [17].
• In the present study, we showed that SPA-1, a Rap1 GTPase-activating protein (GAP), was bound to a cytoskeleton-anchoring protein AF-6 [18].
• Human genomic clones, which hybridized with both mouse and human SIPA1 cDNA but not with RAP1GAP cDNA, were then isolated [19].
• However, in rap1GAPII-expressing cells, ephrin-B1 did not induce membrane spreading, probably due to instability of the focal complex [20].
• Our results suggest that CD28-mediated Rap1 GTPase-activating protein activation can help explain the augmentation of ERKs during CD28 costimulation [21].

Analytical, diagnostic and therapeutic context of RAP1GAP

• Purification, crystallization and preliminary structural characterization of human Rap1GAP [22].

References