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At least 109 records · Page 6Linked to original sources
PubMed2002

The Arf tumor suppressor gene promotes hyaloid vascular regression during mouse eye development.

A key tumor suppressor mechanism that is disrupted frequently in human cancer involves the ARF and p53 genes. In mouse fibroblasts, the Arf gene product responds to abnormal mitogenic signals to activate p53 and trigger either cell cycle arrest or apoptosis. Recent evidence indicates that Arf also has p53-independent functions that may contribute to its tumor suppressor activity. Using Arf(-/-) and p53(-/-) mice, we have discovered a p53-independent requirement for Arf in the developmental regression of the hyaloid vascular system (HVS) in the mouse eye. Arf is expressed in the vitreous of the eye and is induced before HVS regression in the first postnatal week. In the absence of Arf, failed HVS regression causes a pathological process that resembles persistent hyperplastic primary vitreous, a developmental human eye disease thought to have a genetic basis. These findings demonstrate an essential and unexpected role for Arf during mouse eye development, provide insights into the potential genetic basis for persistent hyperplastic primary vitreous, and indicate that Arf regulates vascular regression in a p53-independent manner. The latter finding raises the possibility that Arf may function as a tumor suppressor at least in part by regulating tumor angiogenesis.

Animals↗
PubMed2001

The human tumor suppressor arf interacts with spinophilin/neurabin II, a type 1 protein-phosphatase-binding protein.

The INK4a gene, one of the most often disrupted loci in human cancer, encodes two unrelated proteins, p16(INK4a) and p14(ARF) (ARF) both capable of inducing cell cycle arrest. Although it has been clearly demonstrated that ARF inhibits cell cycle via p53 stabilization, very little is known about the involvement of ARF in other cell cycle regulatory pathways, as well as on the mechanisms responsible for activating ARF following oncoproliferative stimuli. In search of factors that might associate with ARF to control its activity or its specificity, we performed a yeast two-hybrid screen. We report here that the human homologue of spinophilin/neurabin II, a regulatory subunit of protein phosphatase 1 catalytic subunit specifically interacts with ARF, both in yeast and in mammalian cells. We also show that ectopic expression of spinophilin/neurabin II inhibits the formation of G418-resistant colonies when transfected into human and mouse cell lines, regardless of p53 and ARF status. Moreover, spinophilin/ARF coexpression in Saos-2 cells, where ARF ectopic expression is ineffective, somehow results in a synergic effect. These data demonstrate a role for spinophilin in cell growth and suggest that ARF and spinophilin could act in partially overlapping pathways.

3T3 Cells↗
PubMed1998

ARF is required for maintenance of yeast Golgi and endosome structure and function.

ADP ribosylation factor (ARF) is thought to play a critical role in recruiting coatomer (COPI) to Golgi membranes to drive transport vesicle budding. Yeast strains harboring mutant COPI proteins exhibit defects in retrograde Golgi to endoplasmic reticulum protein transport and striking cargo-selective defects in anterograde endoplasmic reticulum to Golgi protein transport. To determine whether arf mutants exhibit similar phenotypes, the anterograde transport kinetics of multiple cargo proteins were examined in arf mutant cells, and, surprisingly, both COPI-dependent and COPI-independent cargo proteins exhibited comparable defects. Retrograde dilysine-mediated transport also appeared to be inefficient in the arf mutants, and coatomer mutants with no detectable anterograde transport defect exhibited a synthetic growth defect when combined with arf1Delta, supporting a role for ARF in retrograde transport. Remarkably, we found that early and medial Golgi glycosyltransferases localized to abnormally large ring-shaped structures. The endocytic marker FM4-64 also stained similar, but generally larger ring-shaped structures en route from the plasma membrane to the vacuole in arf mutants. Brefeldin A similarly perturbed endosome morphology and also inhibited transport of FM4-64 from endosomal structures to the vacuole. Electron microscopy of arf mutant cells revealed the presence of what appear to be hollow spheres of interconnected membrane tubules which likely correspond to the fluorescent ring structures. Together, these observations indicate that organelle morphology is significantly more affected than transport in the arf mutants, suggesting a fundamental role for ARF in regulating membrane dynamics. Possible mechanisms for producing this dramatic morphological change in intracellular organelles and its relation to the function of ARF in coat assembly are discussed.

ADP-Ribosylation Factors↗
PubMed1999

Crystal structure of the ARF-GAP domain and ankyrin repeats of PYK2-associated protein beta.

ADP ribosylation factors (ARFs), which are members of the Ras superfamily of GTP-binding proteins, are critical components of vesicular trafficking pathways in eukaryotes. Like Ras, ARFs are active in their GTP-bound form, and their duration of activity is controlled by GTPase-activating proteins (GAPs), which assist ARFs in hydrolyzing GTP to GDP. PAPbeta, a protein that binds to and is phosphorylated by the non-receptor tyrosine kinase PYK2, contains several modular signaling domains including a pleckstrin homology domain, an SH3 domain, ankyrin repeats and an ARF-GAP domain. Sequences of ARF-GAP domains show no recognizable similarity to those of other GAPs, and contain a characteristic Cys-X(2)-Cys-X(16-17)-Cys-X(2)-Cys motif. The crystal structure of the PAPbeta ARF-GAP domain and the C-terminal ankyrin repeats has been determined at 2.1 A resolution. The ARF-GAP domain comprises a central three-stranded beta-sheet flanked by five alpha-helices, with a Zn(2+) ion coordinated by the four cysteines of the cysteine-rich motif. Four ankyrin repeats are also present, the first two of which form an extensive interface with the ARF-GAP domain. An invariant arginine and several nearby hydrophobic residues are solvent exposed and are predicted to be the site of interaction with ARFs. Site-directed mutagenesis of these residues confirms their importance in ARF-GAP activity.

ADP-Ribosylation Factors↗
PubMed2000

Association between INK4a-ARF and p53 mutations in skin carcinomas of xeroderma pigmentosum patients.

BACKGROUND: The INK4a-ARF locus encodes two tumor suppressor proteins, p16(INK4a) and p14(ARF), that act through the Rb-CDK4 and p53 pathways, respectively. Data from murine models and sporadic human skin carcinomas implicate p16(INK4a) and p14(ARF) in the development of skin carcinomas. We examined the frequency of INK4a-ARF, p53, and CDK4 mutations in skin carcinomas from patients with xeroderma pigmentosum (XP), a rare autosomal disease that is associated with a defect in DNA repair and that predisposes patients to skin cancer. METHODS: DNA from skin cancers of 28 unrelated XP patients was screened for mutations in p53, INK4a-ARF, and CDK4 coding exons by single-strand conformation polymorphism analysis and automated sequencing. Data were evaluated with the use of the exact unconditional test derived from Fisher's test. All statistical tests were two-sided. RESULTS: Eight of 28 XP-associated tumors had mutations in the INK4a-ARF locus. Three XP-associated tumors had multiple mutations at this locus. In all, 13 mutations in the INK4a-ARF locus were detected in XP-associated tumors, of which seven (54%) were signature UV radiation-induced mutations, i.e., tandem CC : GG-->TT : AA transitions. p53 mutations, mostly of the type induced by UV radiation, were present in 12 tumors (43%). Statistically significant positive associations were found between the frequency of mutations in p53 and in p16(INK4a) (P =.008) and between the frequency of mutations in p53 and in p14(ARF) (P<.001). No mutations were detected within the CDK4 gene. CONCLUSIONS: We have demonstrated for the first time the occurrence of UV radiation-induced mutations in INK4a-ARF in XP-associated skin carcinomas. The simultaneous inactivation of p53 and INK4a-ARF may be linked to the genetic instability caused by XP and could be advantageous for tumor progression.

Africa, Northern↗
PubMed1997

N-myristoylation of Arf proteins in Candida albicans: an in vivo assay for evaluating antifungal inhibitors of myristoyl-CoA: protein N-myristoyltransferase.

Myristoyl-CoA: protein N-myristoyltransferase (Nmt) catalyses the covalent attachment of myristate to the N-terminal glycine of a small subset of cellular proteins produced during vegetative growth of Candida albicans. nmt447D is a mutant NMT allele encoding an enzyme with a Gly447-->ASP substitution and reduced affinity for myristoyl-CoA. Among isogenic NMT/NMT, NMT/ delta nmt and nmt delta/nmt447D strains, only nmt delta/nmt447D cells require myristate for growth on yeast/peptone/dextrose media (YPD) at 24 or 37 degrees C. When switched from YPD/myristate to YPD alone, 60% of the organisms die with 4 h. Antibodies raised against the C-terminal eight residues of Saccharomyces cerevisiae Arf1p were used to probe Western blots of total cellular proteins prepared from these isogenic Candida strains. N-Myristoylation of C. albicans ADP-ribosylation factor (Arf) produced a change in its electrophoretic mobility during SDS-PAGE: the myristoylated species migrated more rapidly than the nonmyristoylated species. In an NMT/nmt delta strain, 100% of the Arf is N-myristoylated based on this mobility shift assay. When exponentially growing nmt delta/nmt447D cells were incubated at 24 degrees C in YPD/myristate, < 25% cellular Arf was nonmyristoylated. In contrast, 2 or 4 h after withdrawal of myristate, > or = 50% of total cellular Arf was nonmyristoylated. This finding suggests that > or = 50% reduction in Arf N-myristoylation is a biochemical marker of a growth-arrested cell. A similar conclusion was made after assaying isogenic S. cerevisiae strains containing various combinations of NMT1, nmt1-451D, ARF1, arf1 delta, ARF2 and arf2 delta alleles and grown at 24-37 degrees C on YPD of YPD/myristate. Peptidomimetic inhibitors of C. albicans Nmt were synthesized based on the N-terminal sequence of an S. cerevisiae Aft. SC-59383 has an IC50 of 1.45 +/- 0.08 microM for purified C. albicans Nmt and is 560-fold selective for the fungal compared to human N-myristoyltransferase. It had an EC50 of 51 +/- 17 and 67 +/- 6 microM, 24 and 48 h after a single administration of the drug to cultures of C. albicans. The Arf gel mobility shift assay indicated that a single dose of 200 microM produced a < 50% reduction in Arf N-myristoylation after 4 h, which is consistent with the fungistatic, but not fungicidal, activity. The effect on Nmt was specific: an enantiomer, SC-59840, had no inhibitory effect on purified C. albicans Nmt (IC50 > 1,000 microM), and 200 microM of the compound produced no detectable reduction in Arf N-myristoylation in vivo. SC-58272, which is related to SC-59383, was a more potent inhibitor in vitro (IC50 0.056 +/- 0.01 microM), but had no growth inhibitory activity and did not produce any detectable reduction in Arf N-myristoylation. These findings highlight the utility of the Arf protein gel mobility shift assay for demonstrating the mechanism-based antifungal activity of SC-59383, a selective inhibitor of C. albicans Nmt.

ADP-Ribosylation Factor 1↗
PubMed2005

Dissection of membrane dynamics of the ARF-guanine nucleotide exchange factor GBF1.

ADP-ribosylation factor (ARF)-facilitated recruitment of COP I to membranes is required for secretory traffic. The guanine nucleotide exchange factor GBF1 activates ARF and regulates ARF/COP I dynamics at the endoplasmic reticulum (ER)-Golgi interface. Like ARF and coatomer, GBF1 peripherally associates with membranes. ADP-ribosylation factor and coatomer have been shown to rapidly cycle between membranes and cytosol, but the membrane dynamics of GBF1 are unknown. Here, we used fluorescence recovery after photobleaching to characterize the behavior of GFP-tagged GBF1. We report that GBF1 rapidly cycles between membranes and the cytosol (t1/2 is approximately 17 +/- 1 seconds). GBF1 cycles faster than GFP-tagged ARF, suggesting that in each round of association/dissociation, GBF1 catalyzes a single event of ARF activation, and that the activated ARF remains on membrane after GBF1 dissociation. Using three different approaches [expression of an inactive (E794K) GBF1 mutant, expression of the ARF1 (T31N) mutant with decreased affinity for GTP and Brefeldin A treatment], we show that GBF1 is stabilized on membranes when in a complex with ARF-GDP. GBF1 dissociation from ARF and membranes is triggered by its catalytic activity, i.e. the displacement of GDP and the subsequent binding of GTP to ARF. Our findings imply that continuous cycles of recruitment and dissociation of GBF1 to membranes are required for sustained ARF activation and COP I recruitment that underlies ER-Golgi traffic.

ADP-Ribosylation Factors↗
PubMed2002

ARF differentially modulates apoptosis induced by E2F1 and Myc.

The ARF tumor suppressor participates in a p53-dependent apoptotic pathway that is stimulated in response to some oncogenic stimuli. The E2F1 transcription factor is a critical downstream target of the Rb tumor suppressor and, when active, can promote proliferation as well as apoptosis. The finding that E2F1 transcriptionally regulates the ARF gene has led to the suggestion that ARF contributes to E2F1-induced apoptosis. Counter to this hypothesis, this study demonstrates not only that ARF is unnecessary for E2F1 to induce apoptosis but also that inactivation of ARF actually enhances the ability of E2F1 to promote apoptosis. Inactivation of ARF also cooperates with E2F1 activity to promote entry into the S phase of the cell cycle. This relationship between ARF and E2F1 is demonstrated in transgenic epidermis in vivo and in mouse embryo fibroblast cultures in vitro. In contrast, the ability of Myc to induce apoptosis is diminished in the absence of ARF. E2F1 induces the accumulation of p53 in the absence of ARF, and this is associated with the phosphorylation of p53 on several residues. These findings demonstrate that ARF is a negative regulator of E2F1 activity and is not required for E2F1-induced apoptosis.

Animals↗
PubMed2004

ARF impedes NPM/B23 shuttling in an Mdm2-sensitive tumor suppressor pathway.

The ARF tumor suppressor is widely regarded as an upstream activator of p53-dependent growth arrest and apoptosis. However, recent findings indicate that ARF can also regulate the cell cycle in the absence of p53. In search of p53-independent ARF targets, we isolated nucleophosmin (NPM/B23), a protein we show is required for proliferation, as a novel ARF binding protein. In response to hyperproliferative signals, ARF is upregulated, resulting in the nucleolar retention of NPM and concomitant cell cycle arrest. The Mdm2 oncogene outcompetes NPM/B23 for ARF binding, and introduction of Mdm2 reverses ARF's p53-independent properties: in vitro, NPM is released from ARF-containing protein complexes, and in vivo S phase progression ensues. ARF induction by oncogenes or replicative senescence does not alter NPM/B23 protein levels but rather prevents its nucleocytoplasmic shuttling without inhibiting rRNA processing. By actively sequestering NPM in the nucleolus, ARF utilizes an additional mechanism of tumor suppression, one that is readily antagonized by Mdm2.

Amino Acid Sequence↗
PubMed2002

INK4a-ARF alterations in liver cell adenoma.

BACKGROUND: The INK4a-ARF (CDKN2A) locus on chromosome 9p21 encodes two tumour suppressor proteins, p16(INK4a) and p14(ARF), whose functions are inactivated in many human cancers. AIMS: To evaluate p14(ARF) and p16(INK4a) alterations in liver cell adenoma. METHODS: After microdissection, DNA from 25 liver cell adenomas and corresponding normal liver tissue were analysed for INK4-ARF inactivation by DNA sequence analysis, methylation specific polymerase chain reaction, restriction enzyme related-polymerase chain reaction (RE-PCR), mRNA expression, microsatellite analysis, and immunohistochemistry. In addition, microdeletion of p14(ARF) and p16(INK4a) were assessed by differential PCR. RESULTS: Methylation of p14(ARF) was found in 3/25 cases (12%) and alterations in p16(INK4a) occurred in 6/25 liver cell adenomas (24%) which correlated with loss of mRNA transcription. We failed to detect microdeletions or specific mutations of both exons. p16(INK4a) methylation appeared in the context of an unmethylated p14(ARF) promoter in six cases. In normal liver tissue, p14(ARF) or p16(INK4a) alterations were not observed. CONCLUSIONS: Our data suggest that p14(ARF) methylation occurs independently of p16(INK4a) alterations in liver cell adenomas. Furthermore, methylation of p14(ARF) and p16(INK4a) may be a result of cell cycle deregulation and does not seem to be a prerequisite of malignancy.

Adenoma, Liver Cell↗
PubMed1999

Studies on the inhibition of endosome fusion by GTPgammaS-bound ARF.

Using a cell free assay, we have previously shown that ARF is not required for endosome fusion but that inhibition of fusion by GTPgammaS is dependent on a cytosolic pool of ARFs. Since ARF is proposed to function in intracellular membrane traffic by promoting vesicle biogenesis, and components of clathrin- and COP-coated vesicles have been localized on endosomal structures, we investigated whether ARF-mediated inhibition of early endosome fusion involves the recruitment or irreversible association of these proteins onto endosomal membranes. We now report that depletion of components of clathrin coated vesicles (clathrin, AP-1 and AP-2) or COPI vesicles (beta COP) does not affect the capacity of GTPgammaS-activated ARF to inhibit endosome fusion. Inhibition of fusion by activated ARF is also independent of endosomal acidification since assays performed in the presence of the vacuolar ATPase inhibitor bafilomycin A1 are equally sensitive to GTPgammaS-bound ARF. Finally, in contrast to reported effects on lysosomes, we demonstrate that ARF-GTPgammaS does not induce endosomal lysis. These combined data argue that sequestration of known coat proteins to membranes by activated ARF is not involved in the inhibition of early endosome fusion and that its capacity to inhibit fusion involves other specific interactions with the endosome surface. These results contrast with the mechanistic action of ARF on intra-Golgi transport and nuclear envelope assembly.

ADP-Ribosylation Factors↗
PubMed2003

Four ARF GAPs in Saccharomyces cerevisiae have both overlapping and distinct functions.

Previous studies in yeast have revealed the presence of four proteins with a conserved, cysteine-rich, ARF GAP domain that share the ability to suppress the conditional growth defect of the arf1-3 mutant. Three of these proteins have been shown previously to be ADP-ribosylation factor (ARF) GTPase-activating proteins (GAPs). We now demonstrate that the fourth also exhibits in vitro ARF GAP activity and correlates the suppressor and ARF GAP activities for all four. Because the four ARF GAP proteins are quite diverse outside the ARF GAP domain, a genetic analysis was undertaken to define the level of functional cross-talk between them. A large number of synthetic defects were observed that point to a high degree of functional overlap among the four ARF GAPs. However, several differences were also noted in the ability of each gene to suppress the synthetic defects of others and in the impact of single or combined deletions on assays of membrane traffic. We interpret these results as supportive evidence for roles of ARF GAPs in a number of distinct, essential cellular processes that include cell growth, protein secretion, endocytosis and cell cycling. The description of the specificities of the ARF GAPs for the different responses is viewed as a necessary first step in dissecting biologically relevant pathways through a functionally overlapping family of signalling proteins.

ADP-Ribosylation Factors↗
PubMed1993

Identification of an ARF type low molecular mass GTP-binding protein in pea (Pisum sativum).

The ARF class of low molecular mass GTP-binding proteins, originally detected as cholera toxin-activated ADP-ribosylation factors (ARF) in mammalian cells, is now known to participate in intracellular membrane vesicle trafficking. We identified a GTP-binding protein in pea plumules which resembles ARF in several respects. Like mammalian ARF, the pea protein had an apparent molecular mass of 21 kDa and was distributed mainly (approximately 97%) in the cytosol, with 1% and 1.5% occurring in the Golgi and microsomal fractions, respectively. In comparison, small GTP-binding proteins in the 26-30 kDa range were enriched in membranous fractions. The 21 kDa protein crossreacted strongly with an ARF class I antibody prepared against a mammalian ARF, but did not crossreact with ARF 5 (of class II) antibodies. An anti-Volvox yptl antibody did not show immunoreactivity to the 21 kDa pea protein, although it crossreacted strongly with a 28 kDa pea plumule protein. Our results strongly suggest that the 21 kDa pea protein is an analog of the ARF protein localized in the cytosol of mammalian cells. As far as we are aware, this is the first observation of an ARF protein in plants.

ADP-Ribosylation Factors↗
PubMed2005

ADP-ribosylation factor domain protein 1 (ARD1), a multifunctional protein with ubiquitin E3 ligase, GAP, and ARF domains.

ADP-ribosylation factor domain protein 1 (ARD1) is a multifunctional protein that belongs to the family of 20-kDa ARF proteins. The ARD1 gene encodes a 64-kDa protein with a structure comprising an 18-kDa ADP-ribosylation factor (ARF) domain at the C-terminus (amino acids 403-574), and a 46-kDa N-terminal domain (amino acids 1-402) that contains, from the translation start site, a RING finger domain, two predicted B-Boxes, and a coiled-coil protein interaction motif, which places it among the TRIM (tripartite motif) or RBCC (RING, B-Box, coiled-coil) protein families. Recombinant ARD1 (amino acids 1-574) or its RING finger domain (amino acids 1-110) produced polyubiquitylated proteins when incubated in vitro with a mammalian E1, an E2 enzyme (UbcH6 or UbcH5a, -5b, or -5c), ATP, and ubiquitin. Via its C-terminal ARF domain, recombinant ARD1 binds guanine nucleotides, through which it can enhance, in a GTP-dependent manner, cholera toxin ADP-ribosyltransferase activity. Unlike ARFs, ARD1, but not its ARF domain, exhibits significant GTPase activity. Hydrolysis of GTP bound to the C-terminal ARF domain was stimulated by addition of the 46-kDa N-terminal domain (amino acids 1-402) via its GTPase activating protein (GAP) activity. The rate of GDP dissociation from the C-terminal ARF domain in ARD1, is slowed by the adjacent 15 amino acids, which act as a GDP-dissociation inhibitor (GDI) domain. Cytohesin-1, known already as a guanine nucleotide-exchange factor (GEF) ARF activator, also specifically activated recombinant human ARD1, via activation of the ARF domain. Overexpressed ARD1 fusion proteins were associated with structures resembling lysosomes and Golgi membranes, as well as the nucleus, in different types of cells, and sequences potentially responsible for the intracellular localizations were identified.

Agmatine↗
PubMed1999

Mutations in human ARF exon 2 disrupt its nucleolar localization and impair its ability to block nuclear export of MDM2 and p53.

The mammalian ARF-INK4a locus uniquely encodes two cell cycle inhibitors by using separate promoters and alternative reading frames. p16INK4a maintains the retinoblastoma protein in its growth suppressive state while ARF stabilizes p53. We report that human ARF protein predominantly localizes to the nucleolus via a sequence within the exon 2-encoded C-terminal domain and is induced to leave the nucleolus by MDM2. ARF forms nuclear bodies with MDM2 and p53 and blocks p53 and MDM2 nuclear export. Tumor-associated mutations in ARF exon 2 disrupt ARF's nucleolus localization and reduce ARF's ability to block p53 nuclear export and to stabilize p53. Our results suggest an ARF-regulated MDM2-dependent p53 stabilization and link the human tumor-associated mutations in ARF with a functional alteration.

ADP-Ribosylation Factors↗
PubMed2003

Arf regulates interaction of GGA with mannose-6-phosphate receptor.

The role of ADP-ribosylation factor (Arf) in Golgi associated, gamma-adaptin homologous, Arf-interacting protein (GGA)-mediated membrane traffic was examined. GGA is a clathrin adaptor protein that binds Arf through its GAT domain and the mannose-6-phosphate receptor through its VHS domain. The GAT and VHS domains interacted such that Arf and mannose-6-phosphate receptor binding to GGA were mutually exclusive. In vivo, GGA bound membranes through either Arf or mannose-6-phosphate receptor. However, mannose-6-phosphate receptor excluded Arf from GGA-containing structures outside of the Golgi. These data are inconsistent with predictions based on the model for Arf's role in COPI veside coat function. We propose that Arf recruits GGA to a membrane and then, different from the current model, 'hands-off' GGA to mannose-6-phosphate receptor. GGA and mannose-6-phosphate receptor are then incorporated into a transport intermediate that excludes Arf.

ADP-Ribosylation Factors↗
PubMed1986

Loss of glomerular responses to vasoconstrictor agents in rabbits recovering from ARF.

Glomerular responses to angiotensin II (AII), arginine vasopressin (AVP), and norepinephrine (NE) were estimated in rabbits recovering from uranium-mediated nephropathy or ischemic acute renal failure (ARF) to examine roles of intraglomerular events in resistance to ARF. Uranyl acetate (UA, 0.8 mg/kg) produced ARF in some animals but did not in others. Rabbits recovering from UA-induced ARF were highly resistant to a rechallenge with a larger dose of the agent (2 mg/kg). Their glomeruli did not respond to AII, AVP and NE in vitro. In animals having not experienced ARF following the initial insult, however, resistance to the rechallenge was lower than in animals recovering from ARF, and the glomerular response to contractile stimuli was well sustained. A two hour clamping of the renal artery induced ARF in uninephrectomized rabbits. These animals were not resistant to an additional ischemia in the recovery phase, despite inhibited glomerular contractile responses to AII. These data indicate a nonspecific inhibition of glomerular responses to contractile stimuli in the recovery phase of ARF. It is unlikely, however, that resistance to ARF can be attributed to the loss of the glomerular contractile response.

Acute Kidney Injury↗
PubMed2005

Regulation of NF-kappaB and p53 through activation of ATR and Chk1 by the ARF tumour suppressor.

The ARF tumour suppressor is a central component of the cellular defence against oncogene activation. In addition to activating p53 through binding Mdm2, ARF possesses other functions, including an ability to repress the transcriptional activity of the antiapoptotic RelA(p65) NF-kappaB subunit. Here we demonstrate that ARF induces the ATR- and Chk1-dependent phosphorylation of the RelA transactivation domain at threonine 505, a site required for ARF-dependent repression of RelA transcriptional activity. Consistent with this effect, ATR and Chk1 are required for ARF-induced sensitivity to tumour necrosis factor alpha-induced cell death. Significantly, ATR activity is also required for ARF-induced p53 activity and inhibition of proliferation. ARF achieves these effects by activating ATR and Chk1. Furthermore, ATR and its scaffold protein BRCA1, but not Chk1, relocalise to specific nucleolar sites. These results reveal novel functions for ARF, ATR and Chk1 together with a new pathway regulating RelA NF-kappaB function. Moreover, this pathway provides a mechanism through which ARF can remodel the cellular response to an oncogenic challenge and execute its function as a tumour suppressor.

Ataxia Telangiectasia Mutated Proteins↗