Disease relevance of PSCD2

• Murine gammaherpesvirus gammaHV68 is genetically and biologically related to human gammaherpesviruses and herpesvirus saimiri and has been reported to be associated with lymphoproliferative disease in mice (N. P. Sunil-Chandra, J. Arno, J. Fazakerley, and A. A. Nash, Am. J. Pathol. 145:818-826, 1994) [1].
• Three other trial were designed as cross-over studies; the Intergroup Exemestane Study (IES) and the Austrian Breast and Colorectal Cancer Study Group (ABCSG) Trial 8/German ARNO 95 trial compared a crossover from tamoxifen to an aromatase inhibitor versus continued tamoxifen in women who had completed 2 to 3 years of tamoxifen [2].
• Switching of postmenopausal women with endocrine-responsive early breast cancer to anastrozole after 2 years' adjuvant tamoxifen: combined results of ABCSG trial 8 and ARNO 95 trial [3].

High impact information on PSCD2

• Structure of the guanine nucleotide exchange factor Sec7 domain of human arno and analysis of the interaction with ARF GTPase [4].
• Here we characterized a smaller human protein (relative molecular mass 47K) named ARNO, which contains a central Sec7 domain that promotes guanine-nucleotide exchange on ARF1 [5].
• This suggests that a regulatory component which is sensitive to brefeldin A associates with ARNO in vivo, possibly through the amino-terminal coiled-coil [5].
• The a2-isoform is targeted to early endosomes, interacts with ARNO in an intra-endosomal acidification-dependent manner, and disruption of this interaction results in reversible inhibition of endocytosis [6].
• The recruitment of the small GTPase Arf6 and ARNO from cytosol to endosomal membranes is driven by V-ATPase-dependent intra-endosomal acidification [6].

Biological context of PSCD2

• We first determined the genomic structure of the PSCD2 and PRKCG genes, and performed mutation analysis of all exons and exon-intron junctions of the four genes, in the PJS07 family [7].
• Substrate specificity of ARNO-like GEFs for ARF1 depends solely on the Sec7 domain [8].
• Discriminatory aptamer reveals serum response element transcription regulated by cytohesin-2 [9].
• We conclude that the N-terminal coiled-coil and parts of the Sec7 domain of cytohesin-2 are required for serum-mediated transcriptional activation in nonimmune cells, whereas cytohesin-1 is not [9].
• However, a deletion mutant of IPCEF1 that lacks the cytohesin 2 binding site failed to co-migrate with cytohesin 2 to the membrane in stimulated cells [10].

Anatomical context of PSCD2

• Furthermore, based on subcellular fractionation and immunolocalization experiments, we find that ARNO is localized to the plasma membrane in mammalian cells rather than the Golgi [11].
• When expressed in murine 3T3 L1 adipocytes, ARNO tagged using green fluorescent protein (GFP) is localised exclusively in the cytoplasm [12].
• Overexpression of ARP-Q79L, but not of ARP-T31N, in COS-7 cells reduced the fluorescence from co-expressed green fluorescent protein fused with mSec7-1/cytohesin or mSec7-2/ARNO in plasma membranes as detected by deconvolution microscopy [13].
• ARNO but not cytohesin-1 translocation is phosphatidylinositol 3-kinase-dependent in HL-60 cells [14].
• ARNO mutants: DeltaCC-ARNO and CC-ARNO were partially translocated to the membranes while DeltaPH-ARNO and PH-ARNO could not be translocated to the membranes [15].

Associations of PSCD2 with chemical compounds

• ARNO is a guanine nucleotide exchange factor for ADP-ribosylation factor 6 [11].
• Me2SO-differentiated HL-60 cells expressed ARNO and cytohesin-1 isoforms with a diglycine and a triglycine motif in their PH domains, respectively [14].
• The deduced amino acid sequence in PSec7 for the motifs that form the ARF binding site are more than 70% identical to yeast Sec7 and similarly identical to ARNO, the human ARF exchange factor, with correct positioning of the critical glutamic acid residue within the motif region [16].
• PIP2 is strongly stimulatory, indicating that binding of Arno to phospholipids is involved, but in addition, electrostatic interactions between phospholipids and the amino-terminal portion of unmyristoylated ARF1GDP seem to be important [17].
• These data indicate that the unique diglycine motif in the GRP1 PH domain, as opposed to the triglycine in ARNO and cytohesin-1, directs its remarkable PtdIns(3,4,5)P(3) binding selectivity [18].

Physical interactions of PSCD2

• The N-terminal coiled coil domain of the cytohesin/ARNO family of guanine nucleotide exchange factors interacts with the scaffolding protein CASP [19].
• Endogenous beta-arrestin is found in complex with ARNO [20].
• A glutamic finger in the guanine nucleotide exchange factor ARNO displaces Mg2+ and the beta-phosphate to destabilize GDP on ARF1 [21].

Enzymatic interactions of PSCD2

• We have previously shown that ARNO localizes to the plasma membrane in vivo and efficiently catalyzes ARF6 nucleotide exchange in vitro [22].

Co-localisations of PSCD2

• Both DOCK180 and Elmo colocalize extensively with ARNO in migrating MDCK cells [23].

Regulatory relationships of PSCD2

• We report here that in vitro ARNO can stimulate nucleotide exchange on both ARF1 and ARF6 [11].
• Our data strongly suggest that ARNO binds PIP3 in vivo and that this interaction causes a translocation of ARNO to the plasma membrane where it might activate ARF6 and regulate subsequent plasma membrane cycling events [12].
• Here, we show that ARNO is expressed in HL-60 cells and established that granulocytic differentiation induced with Me2SO stimulated cytohesin-1 but not ARNO expression [14].
• Overexpression of wild type ARNO significantly increased insulin-stimulated PLD activity, and mutations in the Sec7 and PH domains, or deletion of the PH or CC domains inhibited the effects of insulin [15].
• In contrast, a similar mutant of the Rac GEF beta-PIX fails to inhibit ARNO-induced Rac activation or motility [23].

Other interactions of PSCD2

• In this system, ARD1-GDP interacted well with cytohesin-1 but very poorly with cytohesin-2 [24].
• It is therefore likely that ARNO functions in plasma membrane events by modulating the activity of ARF6 in vivo [11].
• In agreement, cytohesin-1, but not cytohesin-2, markedly accelerated [(35)S]guanosine 5'-3-O-(thio)triphosphate binding to ARD1 [24].
• These observations collectively suggest that CASP is a scaffolding protein that facilitates the function of at least one member of the cytohesin/ARNO family in response to specific cellular stimuli [19].
• Here, we report crystal structures for dual specificity variants of the Grp1 and ARNO PH domains in either the unliganded form or in complex with the head groups of PtdIns(4,5)P(2) and PtdIns(3,4,5)P(3) [25].

Analytical, diagnostic and therapeutic context of PSCD2

• The interaction of cytohesin 2 and IPCEF1 in mammalian cells was demonstrated by immunoprecipitation [10].
• The crystal structure of ARNO-Sec7 has been solved recently, and a site-directed mutagenesis approach identified a hydrophobic groove and an adjacent hydrophilic loop as the ARF1-binding site [21].
• Furthermore, reverse transcriptase-polymerase chain reaction and immunoreplica analysis indicate that ARNO, a member of the brefeldin A-insensitive ARF-GEF family, is expressed and predominantly localized in the cytosol and in the plasma membrane of chromaffin cells [26].
• By immunofluorescence and cell fractionation, ARNO was found to be mostly cytosolic in HeLa cells [27].
• In contrast, mAbs 5D8, 4C3, 2G8, 6G11, 4C3, 6D4, 7B4 and 6F8 detected both cytohesin-1 and ARNO as monitored by immunoblotting [28].

References