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PubMed1992

The amino terminus of ADP-ribosylation factor (ARF) is a critical determinant of ARF activities and is a potent and specific inhibitor of protein transport.

Deletion of the amino-terminal 17 residues from human ADP-ribosylation factor (ARF) resulted in a protein ([delta 1-17]mARF1p) devoid of ARF activity but which retained the ability to bind guanine nucleotides with high affinity. Unlike the wild type, the binding of guanine nucleotides to this deletion mutant was found to be independent of added phospholipids. A chimeric protein was produced, consisting of 10% (the amino-terminal 17 amino acids) human ARF1p and 90% ARL1p, an ARF-like protein (55% identical protein sequence) from Drosophila. This chimera was found to have ARF activity, lacking in the parental ARL1 protein. Thus, the amino terminus of ARF1p was shown to be a critical component of ARF activity. A synthetic peptide, derived from the amino terminus of ARF1p, has no ARF activity. Rather, the peptide was found to be a specific inhibitor of ARF activities. This peptide was also found to be a potent and specific inhibitor of both an in vitro intra-Golgi transport assay and the guanosine 5'-3-O-(thio)triphosphate-stimulated accumulation of coated vesicles and buds from Golgi preparations. We conclude that ARF is required for the budding of coated vesicles from the Golgi stacks and serves a regulatory role in protein secretion through the Golgi in eukaryotic cells.

ADP-Ribosylation Factor 1↗
PubMed2001

ADP-ribosylation factors (ARFs) and ARF-like 1 (ARL1) have both specific and shared effectors: characterizing ARL1-binding proteins.

Despite the 40-60% identity between ADP-ribosylation factors (ARFs) and ARF-like (ARL) proteins, distinct functional roles have been inferred from findings that ARLs lack the biochemical or genetic activities characteristic of ARFs. The potential for functional overlap between ARFs and ARLs was examined by comparing effects of expression on intact cells and the ability to bind effectors. Expression of [Q71L]ARL1 in mammalian cells led to altered Golgi structure similar to, but less dramatic than, that reported previously for [Q71L]ARF1. Two previously identified partners of ARFs, MKLP1 and Arfaptin2/POR1, also bind ARL1 but not ARL2 or ARL3. Two-hybrid screens of human cDNA libraries with dominant active mutants of human ARL1, ARL2, and ARL3 identified eight different but overlapping sets of binding partners. Specific interactions between ARL1 and two binding proteins, SCOCO and Golgin-245, are defined and characterized in more detail. Like ARFs and ARL1, the binding of SCOCO to Golgi membranes is rapidly reversed by brefeldin A, suggesting the presence of a brefeldin A-sensitive ARL1 exchange factor. These data reveal a complex network of interactions between GTPases in the ARF family and their effectors and reveal a potential for cross-talk not demonstrated previously.

ADP-Ribosylation Factors↗
PubMed2006

Altered intravenous pharmacokinetics of topotecan in rats with acute renal failure (ARF) induced by uranyl nitrate: do adenosine A1 antagonists (selective/non-selective) normalize the altered topotecan kinetics in ARF?

A series of exploratory investigations with multiple agents was carried out in normal rats and in rats with uranyl nitrate-induced acute renal failure to understand the disposition characteristics of intravenous topotecan (TPT) used as a model substrate. The disposition of TPT was unaltered in normal rats when treated with methotrexate, whereas treatment with probenecid increased the systemic exposure of TPT. In case of uranyl nitrate-induced acute renal failure (UN-ARF) rats, the systemic exposure of TPT was increased when compared with normal rats, whereas in UN-ARF rats treated with probenecid a further reduction in renal clearance of TPT was noted as compared with that of UN-ARF induced rats. Thus, TPT may be involved in the tubular secretory pathway when a passive glomerular filtration pathway for elimination was not possible. The disposition of TPT did not normalize in UN-ARF rats when treated with caffeine, a non-selective adenosine A1 receptor antagonist, whereas the selective adenosine A1 receptor antagonist (1,3-dipropyl-8-phenylxanthine, DPPX) normalized TPT pharmacokinetic disposition by improving renal function. Renal excretion studies demonstrated that CLR improved by almost fivefold following DPPX treatment in ARF rats. In addition, the qualitative stability/metabolism pattern of TPT in liver microsomes prepared from various groups of rats (normal rats, UN-ARF rats, rats treated with DPPX, and UN-ARF rats treated with DPPX) was found to be similar. In summary, using a pharmacokinetic tool as a surrogate, it has been shown that the pharmacokinetic disposition of TPT improved considerably upon treatment with DPPX, a selective adenosine A1 antagonist.

Acute Kidney Injury↗
PubMed2006

Nomenclature for the human Arf family of GTP-binding proteins: ARF, ARL, and SAR proteins.

The Ras superfamily is comprised of at least four large families of regulatory guanosine triphosphate-binding proteins, including the Arfs. The Arf family includes three different groups of proteins: the Arfs, Arf-like (Arls), and SARs. Several Arf family members have been very highly conserved throughout eukaryotic evolution and have orthologues in evolutionally diverse species. The different means by which Arf family members have been identified have resulted in an inconsistent and confusing array of names. This confusion is further compounded by differences in nomenclature between different species. We propose a more consistent nomenclature for the human members of the Arf family that may also serve as a guide for nomenclature in other species.

ADP-Ribosylation Factors↗
PubMed1994

The amino terminus of ADP-ribosylation factor (ARF) 1 is essential for interaction with Gs and ARF GTPase-activating protein.

The role of the amino terminus in the actions of ADP-ribosylation factor 1 (ARF1) was examined by comparing wild type ARF1, a 13-residue NH2-terminal deletion mutant ([delta 13]ARF1), and a 17-residue NH2-terminal deletion mutant ([delta 17]ARF1). The amino-terminal 13 residues of ARF1 are required for cofactor activity in the ADP-ribosylation by cholera toxin when Gs is the substrate. This is in marked contrast to the finding that cofactor activity is the same for wild type and [delta 13]ARF1 when agmatine is substrate (Hong, J.-X., Haun, R. S., Tsai, S.-C., Moss, J., and Vaughan, M. (1994) J. Biol. Chem. 269, 9743-9745). These data support the conclusion that ARF1 interacts with both cholera toxin and Gs and that the amino terminus of ARF1 is required specifically for binding Gs. Surprisingly, this result also clearly revealed that the two principal assays for ARF activity, cofactor activity for cholera toxin using either Gs or agmatine as substrates, used for over 10 years in different laboratories, can yield quite different results. While both NH2-terminal deletion mutants failed to support the ADP-ribosylation of Gs by cholera toxin, [delta 13]ARF1, but not [delta 17]ARF1, inhibited the activity of the wild type protein. The GTPase activity of [delta 13]ARF1 was activated to a small extent by ARF GTPase-activating protein (GAP), whereas that of [delta 17]ARF1 was unaffected. We conclude that residues 14-17 are involved in the interaction of ARF with both cholera toxin and ARF GAP. The co-purifying nucleotides, nucleotide exchange kinetics, and dependence of exchange on phospholipids for the mutant proteins were all different from the wild type ARF1 proteins. The importance of monitoring the nucleotide binding to ARF proteins under the conditions used in the ARF assay and expressing ARF activities as specific activities, normalized to GTP binding sites, particularly when comparisons between different proteins or preparations are made, is discussed.

ADP-Ribosylation Factor 1↗
PubMed1990

Mechanism of activation of cholera toxin by ADP-ribosylation factor (ARF): both low- and high-affinity interactions of ARF with guanine nucleotides promote toxin activation.

Activation of adenylyl cyclase by cholera toxin A subunit (CT-A) results from the ADP-ribosylation of the stimulatory guanine nucleotide binding protein (GS alpha). This process requires GTP and an endogenous guanine nucleotide binding protein known as ADP-ribosylation factor (ARF). One membrane (mARF) and two soluble forms (sARF I and sARF II) of ARF have been purified from bovine brain. Because the conditions reported to enhance the binding of guanine nucleotides by ARF differ from those observed to promote optimal activity, we sought to characterize the determinants influencing the functional interaction of guanine nucleotides with ARF. High-affinity GTP binding by sARF II (apparent KD of approximately 70 nM) required Mg2+, DMPC, and sodium cholate. sARF II, in DMPC/cholate, also enhanced CT-A ADP-ribosyltransferase activity (apparent EC50 for GTP of approximately 50 nM), although there was a delay before achievement of a maximal rate of sARF II stimulated toxin activity. The delay was abolished by incubation of sARF II with GTP at 30 degrees C before initiation of the assay. In contrast, a maximal rate of activation of toxin by sARF II, in 0.003% SDS, occurred without delay (apparent EC50 for GTP of approximately 5 microM). High-affinity GTP binding by sARF II was not detectable in SDS. Enhancement of CT-A ADP-ribosyltransferase activity by sARF II, therefore, can occur under conditions in which sARF II exhibits either a relatively low affinity or a relatively high affinity for GTP. The interaction of GTP with ARF under these conditions may reflect ways in which intracellular membrane and cytosolic environments modulate GTP-mediated activation of ARF.

ADP-Ribosylation Factors↗
PubMed2000

Identification of lysosomal and Golgi localization signals in GAP and ARF domains of ARF domain protein 1.

ADP ribosylation factors (ARFs) are approximately 20-kDa guanine nucleotide-binding proteins that activate cholera toxin and phospholipase D and are critical components of vesicular trafficking pathways. ARF domain protein 1 (ARD1), a member of the ARF superfamily, contains a 46-kDa amino-terminal extension, which acts as a GTPase-activating protein (GAP) with activity towards its ARF domain. When overexpressed, ARD1 was associated with lysosomes and the Golgi apparatus. In agreement with this finding, lysosomal and Golgi membranes isolated from human liver by immunoaffinity contained native ARD1. ARD1, expressed as a green fluorescent fusion protein, was initially associated with the Golgi network and subsequently appeared on lysosomes, suggesting that ARD1 might undergo vectorial transport between the two organelles. Here we show by microscopic colocalization that GAP and ARF domains determine lysosomal and Golgi localization, respectively, consistent with the presence of more than one signal motif. Using truncated ARD1 molecules, expressed as green fluorescent fusion proteins, it was found that the signal for lysosomal localization was present in residues 301 to 402 of the GAP domain. Site-specific mutagenesis demonstrated that the sequence (369)KXXXQ(373) in the GAP domain was responsible for lysosomal localization. Association of ARD1 with the Golgi apparatus required tyrosine-based motifs. A green fluorescent fusion protein containing the QKQQQQF motif was partially associated with lysosomes, suggesting that this motif contains the information sufficient for lysosomal targeting. These results suggest that ARD1 is a multidomain protein with ARF and GAP regions, which contain Golgi and lysosomal localization signals, respectively, that could function in vesicular trafficking.

3T3 Cells↗
PubMed1994

ADP-ribosylation factor (ARF)-like 3, a new member of the ARF family of GTP-binding proteins cloned from human and rat tissues.

The human and rat homologues of a new member of the ADP-ribosylation factor (ARF) family of 21-kDa GTP-binding proteins, termed Arl3, were identified as an expressed sequence tag (human) and as a product of polymerase chain reaction amplification using degenerate probes derived from conserved sequences in members of the ARF family (rat). Alignments of the full-length open reading frames of the human and rat homologues revealed the encoded proteins to be over 97% identical to each other and 43% identical to human ARF1. Northern blots of mRNA from seven human tissues and four rat tissues revealed the presence of a ubiquitous band of about 1 kilobase in length that hybridized with the corresponding Arl3 probes. A number of human tumor cell lines expressed Arl3, as determined by immunoblotting with an Arl-specific antibody, raised against a peptide derived from the human Arl3 sequence. The level of Arl3 expressed in these cell lines was on the order of 0.01% of total cell protein. Purified recombinant human Arl3 was shown to bind guanine nucleotides but lacks ARF activity and intrinsic or ARF GTPase-activating protein-stimulated GTPase activity. In contrast to ARF proteins, the Arl3 protein has reduced dependence on phospholipids and magnesium for guanine nucleotide exchange. Thus, Arl3 is a ubiquitously expressed GTP-binding protein in the ARF family with distinctive biochemical properties consistent with its having unique, but unknown, role(s) in cell physiology.

ADP-Ribosylation Factor 1↗
PubMed2001

Quantitative real-time PCR does not show selective targeting of p14(ARF) but concomitant inactivation of both p16(INK4A) and p14(ARF) in 105 human primary gliomas.

In many human cancers, the INK4A locus is frequently mutated by homozygous deletions. By alternative splicing this locus encodes two non-related tumor suppressor genes, p16(INK4A) and p14(ARF) (p19(ARF) in mice), which regulate cell cycle and cell survival in the retinoblastoma protein (pRb) and p53 pathways, respectively. In mice, the role of p16(INK4A) as the critical tumor suppressor gene at the INK4A locus was challenged when it was found that p19(ARF) only knock-out mice developed tumors, including gliomas. We have analysed the genetic status of the INK4A locus in 105 primary gliomas using both microsatellite mapping (MSM) and quantitative real-time PCR (QRT-PCR). Comparison of the results of the two methods revealed agreement in 67% of the tumors examined. In discordant cases, fluorescence in situ hybridization (FISH) analysis was always found to support QRT-PCR classification. Direct assessment of p14(ARF) exon 1beta, p16(INK4A) exon 1alpha and exon 2 by QRT-PCR revealed 43 (41%) homozygous and eight (7%) hemizygous deletions at the INK4A locus. In 49 (47%) gliomas, both alleles were retained. In addition, QRT-PCR, but not MSM, detected hyperploidy in five (5%) tumors. Deletion of p14(ARF) was always associated with co-deletion of p16(INK4A) and increased in frequency upon progression from low to high grade gliomas. Shorter survival was associated with homozygous deletions of INK4A in the subgroup of glioblastoma patients older than 50 years of age (P=0.025, Anova test single factor, alpha=0.05).

Chromosome Mapping↗
PubMed2004

Alternative reading frame protein (ARF)-independent function of CARF (collaborator of ARF) involves its interactions with p53: evidence for a novel p53-activation pathway and its negative feedback control.

CARF, a collaborator of ARF (alternative reading frame protein), was cloned as a novel ARF-binding protein from a yeast-interaction screen. It potentiated ARF-mediated p53 function, and also caused a moderate increase in p53 activity in the absence of ARF. We herein report the molecular mechanism of ARF-independent function of CARF. By employing a variety of approaches, including overexpression of CARF, its suppression by small interfering RNA and use of protease inhibitors, we demonstrate that: (i) CARF directly interacts with wild-type p53, causing its stabilization and functional activation; and (ii) CARF and p53 levels show an inverse relationship that is instigated by a negative-feedback control via a proteasome-mediated degradation pathway.

Alternative Splicing↗
PubMed2005

INK4-ARF and p53 mutations in metastatic cutaneous squamous cell carcinoma: case report and archival study on the use of Ink4a-ARF and p53 mutation analysis in identification of the corresponding primary tumor.

So far, histopathologic, immunohistochemical and molecular properties of metastatic cutaneous squamous cell carcinomas (CSCCs) are relatively unexplored. In patients with multiple CSCCs, as for instance renal transplant recipients (RTRs), it might prove difficult to identify the primary tumor responsible for metastasis. We report a case of an RTR with multiple CSCCs, one of which metastasized. By using p53 and INK4a-ARF mutation analysis, we identified the responsible primary tumor due to an identical mutation in exon 2 of the INK4a-ARF locus. Archival study yielded 14 cases of metastatic CSCC (present case included). In only 8 of 14 metastases, DNA quality was sufficient to perform PCR reactions. In 7 of 8 metastases, either an INK4a-ARF (6 of 8 cases) and/or p53 (3 of 8 cases) mutation was present. In 6 of 7 cases, the corresponding primary could be identified by an identical mutation in p53 and/or INK4a-ARF. In conclusion, molecular analysis using a combination of p53 and INK4a-ARF mutation analysis can identify the corresponding primary skin tumor in case of CSCC metastases in the majority of cases. This is facilitated by the high frequency of these mutations in metastatic CSCC when compared with frequency spectra reported in the literature in primary CSCCs. The major limitation was formed by insufficient DNA quality in archival tissue.

ADP-Ribosylation Factor 6↗
PubMed2004

Arf-like GTPases: not so Arf-like after all.

ADP-ribosylation factor (Arf) GTP-binding proteins are among the best-characterized members of the Ras superfamily of GTPases, with well-established functions in membrane-trafficking pathways. A recent watershed of genomic and structural information has identified a family of conserved related proteins: the Arf-like (Arl) GTPases. The best-characterized Arl protein, Arl2, regulates the folding of beta tubulin, and recent data suggest that Arl1 and Arf-related protein 1 (ARFRP1) are localized to the trans-Golgi network (TGN), where they function, in part, to regulate the tethering of endosome-derived transport vesicles. Other Arl proteins are localized to the cytosol, nucleus, cytoskeleton and mitochondria, which indicates that Arl proteins have diverse roles that are distinct from the known functions of traditional Arf GTPases.

ADP-Ribosylation Factors↗
PubMed2005

Frequent alteration of p16(INK4a)/p14(ARF) and p53 pathways in the round cell component of myxoid/round cell liposarcoma: p53 gene alterations and reduced p14(ARF) expression both correlate with poor prognosis.

In myxoid/round cell liposarcoma (MLS/RCLS), the presence of a round cell (RC) component has been reported to correlate with a worse prognosis for the patients. However, little is known about the molecular genetic differences between conventional myxoid (MX) components and RC components in this tumour. The aim of this study was to investigate the possible implications of molecular alterations of G1 to S-phase check-point genes, especially in the RC component. We evaluated the immunohistochemical expression of p53, MDM2, p14 and p16 protein and assessed proliferative activities using MIB-1 in 29 RC components and 81 MX components from 90 cases. Mutation of the p53 gene, amplification of the MDM2 gene, homozygous deletion, methylation status and mutation of the p16(INK4a)/p14(ARF) genes were also investigated, using concordant paraffin-embedded and frozen material. The data were analysed together with clinicopathological factors to assess their prognostic implications in MLS/RCLS. Immunohistochemically, the over-expression of p53 protein (p = 0.01366) and the reduced expression of p14 (p < 0.0001) and p16 (p < 0.0001) proteins were significantly more frequently observed in RC components than in MX components. Reduced expression of p14 protein correlated significantly with hypermethylation of the p14(ARF) gene promoter (p = 0.0176) and over-expression of p53 protein (p = 0.00837). By univariate analysis, reduced expression of p14 and p53 missense mutation were found to reduce the rate of survival significantly (p < 0.05). Multivariate analysis, including clinicopathological factors, revealed that tumour site (p = 0.0251), the presence of an RC component (p = 0.0113), high MIB-1 labelling index (p = 0.0005) and p53 missense mutation (p = 0.0036) were adverse prognostic factors. In MLS/RCLS, reduction of p14 protein expression and p53 mutation were related to poor prognosis. Accordingly, the p14(ARF)/p53 pathway may contribute to the presence of an RC component and malignant progression in this tumour.

Adolescent↗
PubMed1999

ADP-ribosylation factor (ARF)-like 4, 6, and 7 represent a subgroup of the ARF family characterization by rapid nucleotide exchange and a nuclear localization signal.

The novel ARF-like GTPase ARL7 is a close relative of ARL4 and ARL6 (71% and 59%) identical amino acids). A striking characteristic of these GTPases is their basic C-terminus which, when fused to the C-terminus of green fluorescent protein (GFP), targets the constructs to the nucleus of transfected COS-7 cells. Full length ARL4 was detected in both nuclear and extranuclear compartments, whereas a construct of ARL4 lacking its C-terminus was excluded from the nucleus. Nucleotide exchange rates of recombinant ARL4, ARL6 and ARL7 were similar and appeared considerably higher than those of other members of the ARF family (ARF1, ARP). It is concluded that ARL4, ARL6 and ARL7 form a subgroup within the ARF family with similar, possibly nuclear, function.

ADP-Ribosylation Factor 1↗
PubMed1997

Nuclear ADP-ribosylation factor (ARF)- and oleate-dependent phospholipase D (PLD) in rat liver cells. Increases of ARF-dependent PLD activity in regenerating liver cells.

Two forms of phospholipase D (PLD) have been found to be present in nuclei isolated from rat hepatocytes by measuring phosphatidylbutanol produced from exogenous radiolabeled phosphatidylcholine in the presence of butanol. In nuclear lysates from either rat liver or ascites hepatoma AH 7974 cells, the PLD activity was markedly stimulated by a recombinant ADP-ribosylation factor (rARF) in the presence of the guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) and phosphatidylinositol 4, 5-bisphosphate. ATP and phorbol-12-myristate 13-acetate had no synergistic effect on this PLD activity. On the other hand, the nuclear PLD was stimulated by unsaturated fatty acids, especially by oleic acid. The ARF-dependent nuclear PLD activity was increased in the S-phase of the regenerating rat liver after partial hepatectomy and also was much higher in AH 7974 cells than in the resting rat liver. In contrast, the levels of the oleate-dependent PLD activity remained constant throughout the cell cycle in liver regeneration. The intranuclear levels of the stimulating proteins of the nuclear PLD activity, e.g. ARF, RhoA, and protein kinase Cdelta increased in the S-phase of the regenerating liver. These results suggested that the nuclear ARF-dependent PLD activity may be associated with cell proliferation.

ADP-Ribosylation Factors↗
PubMed2002

Calcium-regulated exocytosis of dense-core vesicles requires the activation of ADP-ribosylation factor (ARF)6 by ARF nucleotide binding site opener at the plasma membrane.

The ADP ribosylation factor (ARF) GTP binding proteins are believed to mediate cytoskeletal remodeling and vesicular trafficking along the secretory pathway. Here we show that ARF6 is specifically associated with dense-core secretory granules in neuroendocrine PC12 cells. Stimulation with a secretagogue triggers the recruitment of secretory granules to the cell periphery and the concomitant activation of ARF6 by the plasma membrane-associated guanine nucleotide exchange factor, ARF nucleotide binding site opener (ARNO). Expression of the constitutively inactive ARF6(T27N) mutant inhibits secretagogue-dependent exocytosis from PC12 cells. Using a mutant of ARF6 specifically impaired for PLD1 stimulation, we find that ARF6 is functionally linked to phospholipase D (PLD)1 in the exocytotic machinery. Finally, we show that ARNO, ARF6, and PLD1 colocalize at sites of exocytosis, and we demonstrate direct interaction between ARF6 and PLD1 in stimulated cells. Together, these results provide the first direct evidence that ARF6 plays a role in calcium-regulated exocytosis in neuroendocrine cells, and suggest that ARF6-stimulated PLD1 activation at the plasma membrane and consequent changes in membrane phospholipid composition are critical for formation of the exocytotic fusion pore.

ADP-Ribosylation Factor 6↗
PubMed2000

COP I domains required for coatomer integrity, and novel interactions with ARF and ARF-GAP.

We performed a systematic mapping of interaction domains on COP I subunits to gain novel insights into the architecture of coatomer. Using the two-hybrid system, we characterize the domain structure of the alpha-, beta'-, epsilon-COP and beta-, gamma-, delta-, zeta-COP coatomer subcomplexes and identify links between them that contribute to coatomer integrity. Our results demonstrate that the domain organization of the beta-, gamma-, delta-, zeta-COP subcomplex and AP adaptor complexes is related. Through in vivo analysis of alpha-COP truncation mutants, we characterize distinct functional domains on alpha-COP. Its N-terminal WD40 domain is dispensable for yeast cell viability and overall coatomer function, but is required for KKXX-dependent trafficking. The last approximately 170 amino acids of alpha-COP are also non-essential for cell viability, but required for epsilon-COP incorporation into coatomer and maintainance of normal epsilon-COP levels. Further, we demonstrate novel direct interactions of coatomer subunits with regulatory proteins: beta'- and gamma-COP interact with the ARF-GTP-activating protein (GAP) Glo3p, but not Gcs1p, and beta- and epsilon-COP interact with ARF-GTP. Glo3p also interacts with intact coatomer in vitro.

ADP-Ribosylation Factors↗
PubMed2004

An Arf(GFP/GFP) reporter mouse reveals that the Arf tumor suppressor monitors latent oncogenic signals in vivo.

Understanding how the Arf tumor suppressor is activated in response to abnormally elevated mitogenic signaling thresholds is a particularly vexing problem. Studies of a knock-in mouse strain in which sequences encoding green fluorescent protein were substituted for those encoding p19Arf argue that the Arf gene responds to latent oncogenic signals in vivo to eliminate incipient cancer cells.

Animals↗