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PubMed2002

Human p14(ARF)-mediated cell cycle arrest strictly depends on intact p53 signaling pathways.

The tumor suppressor ARF is transcribed from the INK4a/ARF locus in partly overlapping reading frames with the CDK inhibitor p16(Ink4a). ARF is able to antagonize the MDM2-mediated ubiquitination and degradation of p53, leading to either cell cycle arrest or apoptosis, depending on the cellular context. However, recent data point to additional p53-independent functions of mouse p19(ARF). Little is known about the dependency of human p14(ARF) function on p53 and its downstream genes. Therefore, we analysed the mechanism of p14(ARF)-induced cell cycle arrest in several human cell types. Wild-type HCT116 colon carcinoma cells (p53(+/+)p21(CIP1+/+) 14-3-3sigma(+/+)), but not p53(-/-) counterparts, underwent G(1) and G(2) cell cycle arrest following infection with a p14(ARF)-adenovirus. In p21(CIP1-/-) cells, p14(ARF) did not induce G(1) or G(2) arrest, while 14-3-3sigma(-/-) counterparts were mainly arrested in G(1), pointing to essential roles of p21(CIP1) in G(1) and G(2) arrest and cooperative roles of p21 and 14-3-3sigma in ARF-mediated G(2) arrest. Our data demonstrate a strict p53 and p21(CIP1) dependency of p14(ARF)-induced cell cycle arrest in human cells.

14-3-3 Proteins↗
PubMed2004

Loss of one allele of ARF rescues Mdm2 haploinsufficiency effects on apoptosis and lymphoma development.

The tumor suppressor p19ARF inhibits Mdm2, which restricts the activity of p53. Complicated feedback and control mechanisms regulate ARF, Mdm2, and p53 interactions. Here we report that ARF haploinsufficiency completely rescued the p53-dependent effects of Mdm2 haploinsufficiency on B-cell development, survival, and transformation. In contrast to Mdm2+/- B cells, Mdm2+/- B cells deficient in ARF were similar to wild-type B cells in their rates of growth and apoptosis and activation of p53. Consequently, the profoundly reduced numbers of B cells in Mdm2+/-Emu-myc transgenic mice were restored to normal levels in ARF+/-Mdm2+/-Emu-myc transgenics. Additionally, ARF+/-Mdm2+/-Emu-myc transgenics developed lymphomas at rates analogous to those observed for wild-type Emu-myc transgenics, demonstrating that loss of one allele of ARF rescued the protracted lymphoma latency in Mdm2+/-Emu-myc transgenics. Importantly, in ARF+/-Mdm2+/-Emu-myc transgenic lymphomas, p53 was inactivated at the frequency observed in lymphomas of wild-type Emu-myc transgenics. Collectively, these results support a model whereby the stoichiometry of Mdm2 and ARF controls apoptosis and tumor development, which should have significant implications in the treatment of malignancies that have inactivated ARF.

ADP-Ribosylation Factor 1↗
PubMed2003

Elevated serum levels of the type I and type II receptors for tumor necrosis factor-alpha as predictive factors for ARF in patients with septic shock.

BACKGROUND: Acute renal failure (ARF), a common and serious complication in patients with septic shock, has high mortality. Recent data suggest that proinflammatory cytokines may contribute to sepsis-associated ARF. METHODS: To examine the role of proinflammatory cytokines, we evaluated 537 patients enrolled in the placebo arm of the Norasept II study, of whom 112 patients (20%) developed ARF. RESULTS: By univariate analysis, the following factors were significantly associated with the development of ARF: male sex, younger age, increased heart rate, higher Acute Physiology and Chronic Health Evaluation II score, oliguria, increased blood urea nitrogen level, increased serum creatinine (Scr) level, decreased arterial pH, and increased serum potassium level. Although there were no statistically significant differences in serum levels of tumor necrosis factor-alpha (TNF-alpha) or interleukin-6 between patients with and without ARF, elevated serum levels of the two soluble TNF-alpha receptors (S-TNF-RI and S-TNF-RII) were strongly associated with the development of ARF (S-TNF-RI, 25 +/- 16 versus 18 +/- 13 ng/mL; P = 0.00006; S-TNF-RII, 25 +/- 21 versus 18 +/- 17 ng/mL; P = 0.0007). Using forward stepwise regression analysis, elevated S-TNF-R level remained an independent predictor for ARF, even when we limited our analysis to patients with Scr levels of 1.4 mg/dL or less (< or =124 micromol/L) at study entry, suggesting that decreased renal clearance of S-TNF-R alone cannot account for this association. Elevated S-TNF-R level also was an independent predictor of mortality among patients developing ARF. CONCLUSION: S-TNF-R level is an independent predictor for the development of ARF and mortality. We speculate that elevated S-TNF-R levels may reflect a more intense inflammatory response.

Acute Kidney Injury↗
PubMed1979

The diagnosis of acute renal failure (ARF) following cardiac surgery with cardio-pulmonary bypass.

The diagnostic value of renal concentrating capacity expressed as free water clearance (CH2O), in comparison with other routine criteria for the early identification of acute renal failure (ARF), was evaluated in 1,203 adult patients undergoing cardiac surgical procedures. On the basis of the appearance of pathologic CH2O values in the range of -20 to 0 ml/hour or more positive, reversible or irreversible ARF was observed in 90 (= 7.5%) of our patients. Mortality in the presence of ARF was 47%; total ARF mortality was 3.5%. CH2O was pathologic for the first time on an average of 1.6 days after operation. In contrast, routine ARF criteria reported in the literature, such as serum urea and creatinine at varying substrate levels or oliguria, allowed diagnosis 1 to 5.5 days later. Moreover, these parameters only partially and less frequently met the criteria for ARF at the different levels. Likewise, the incidence of ARF decreased to a minimum of 1.7% and the total ARF mortality to 1.3%, depending on the severity of the criteria used. Altogether, the occurrence of pathologic CH2O values proved to be the earliest, most frequent and most reliable criterion for the recognition of ARF following cardiac surgery with cardiac-pulmonary bypass.

Acute Kidney Injury↗
PubMed2005

The hepatitis C virus alternate reading frame (ARF) and its family of novel products: the alternate reading frame protein/F-protein, the double-frameshift protein, and others.

The hepatitis C virus (HCV) has an alternate reading frame (ARF) that overlaps the core protein gene. The overlapping reading frame distinguishes HCV from all of its known viral relatives, with the possible exception of GB virus B (GBV-B). The ARF is expressed during natural HCV infections and stimulates specific immune responses. Like several essential genes in other viruses (e.g., the human immunodeficiency virus polymerase) the ARF lacks an in-frame AUG start codon, suggesting that its expression involves unusual translation-level events. In vitro studies indicate that ribosomal frameshifting may be one of several processes that can lead to translation of the ARF. Frameshifting yields chimeric proteins that have segments encoded in the core gene covalently attached to amino acids encoded in the ARF. A consistent nomenclature for the ARF's protein products has yet to be established. We propose that all proteins that contain amino acids encoded in the + 1 ARF be called alternate reading frame proteins (ARFPs) and that specific ARFPs, such as the ARFP/F-protein, the double-frameshift protein, and the short form of core + 1, be designated as follows: ARFP/F (ARFP/F-protein), ARFP/DF (double-frameshift), and ARFP/S (short form of core + 1). The roles of ARFPs in the HCV life cycle are not yet known. There is a significant possibility that ARFPs may be responsible for some of the effects attributed to the core protein, given that most studies seeking to define the function of the core protein have employed materials likely to contain a combination of the core protein and ARFPs. The observed effects of the core protein include the induction of liver cancer, transformation of cells, and alterations of immune responses. This article reviews the discovery of ARF, describes the RNA structural elements involved in core/ARF gene expression, discusses possible functions of ARFPs, and considers the potential usefulness of ARFPs in vaccines. The HCV ARF is the focus of a new and rapidly expanding area of research, and the results of many ongoing studies are currently available in abstract form only. The preliminary nature of investigations that have not yet been reviewed by peers is noted in the text.

Animals↗
PubMed2001

Differential effects of p19(Arf) and p16(Ink4a) loss on senescence of murine bone marrow-derived preB cells and macrophages.

Establishment of cell lines from primary mouse embryo fibroblasts depends on loss of either the Arf tumor suppressor or its downstream target, the p53 transcription factor. Mouse p19(Arf) is encoded by the Ink4a-Arf locus, which also specifies a second tumor suppressor protein, the cyclin D-dependent kinase inhibitor p16(Ink4a). We surveyed bone marrow-derived cells from wild-type, Ink4a-Arf-null, or Arf-null mice for their ability to bypass senescence during continuous passage in culture. Unlike preB cells from wild-type mice, those from mice lacking Arf alone could be propagated indefinitely when placed onto stromal feeder layers engineered to produce IL-7. The preB cell lines remained diploid and IL-7-dependent and continued to express elevated levels of p16(Ink4a). By contrast, Arf-null bone marrow-derived macrophages that depend on colony-stimulating factor-1 for proliferation and survival in culture initially grew at a slow rate but gave rise to rapidly and continuously growing, but still growth factor-dependent, variants that ceased to express p16(Ink4a). Wild-type bone marrow-derived macrophages initially expressed both p16(Ink4a) and p19(Arf) but exhibited an extended life span when p16(Ink4a) expression was extinguished. In all cases, gene silencing was accompanied by methylation of the Ink4a promoter. Therefore, whereas Arf loss alone appears to be the major determinant of establishment of murine fibroblast and preB cell lines in culture, p16(Ink4a) provides an effective barrier to immortalization of bone marrow-derived macrophages.

3T3 Cells↗
PubMed2003

Arf tumor suppressor promoter monitors latent oncogenic signals in vivo.

Induction of the Arf tumor suppressor gene by elevated thresholds of mitogenic signals activates a p53-dependent transcriptional response that triggers either growth arrest or apoptosis, thereby countering abnormal cell proliferation. Conversely, Arf inactivation is associated with tumor development. Expression of Arf in tissues of adult mice is difficult to detect, possibly because its induction leads to the arrest or elimination of incipient tumor cells. We replaced coding sequences of exon 1beta of the mouse cellular Arf gene with a cDNA encoding GFP, thereby producing Arf-null animals in which GFP expression is driven by the intact Arf promoter. The Arf promoter was induced in several biologic settings previously shown to elicit mouse p19Arf expression. Inactivation of Arf in this manner led to the outgrowth of tumor cells expressing GFP, thereby providing direct evidence that the Arf promoter monitors latent oncogenic signals in vivo.

Animals↗
PubMed2006

A novel nuclear interactor of ARF and MDM2 (NIAM) that maintains chromosomal stability.

The ARF tumor suppressor signals through p53 and other poorly defined anti-proliferative pathways to block carcinogenesis. In a search for new regulators of ARF signaling, we discovered a novel nuclear protein that we named NIAM (nuclear interactor of ARF and MDM2) for its ability to bind both ARF and the p53 antagonist MDM2. NIAM protein is normally expressed at low to undetectable levels in cells because of, at least in part, MDM2-mediated ubiquitination and proteasomal degradation. When reintroduced into cells, NIAM activated p53, caused a G1 phase cell cycle arrest, and collaborated with ARF in an additive fashion to suppress proliferation. Notably, NIAM retains growth inhibitory activity in cells lacking ARF and/or p53, and knockdown experiments revealed that it is not essential for ARF-mediated growth inhibition. Thus, NIAM and ARF act in separate anti-proliferative pathways that intersect mechanistically and suppress growth more effectively when jointly activated. Intriguingly, silencing of NIAM accelerated chromosomal instability, and microarray analyses showed reduced NIAM mRNA expression in numerous primary human tumors. This study identifies a novel protein with tumor suppressor-like behaviors and functional links to ARF-MDM2-p53 signaling.

Adenocarcinoma↗
PubMed2002

ADP-ribosylation factor (ARF) interaction is not sufficient for yeast GGA protein function or localization.

Golgi-localized gamma-ear homology domain, ADP-ribosylation factor (ARF)-binding proteins (GGAs) facilitate distinct steps of post-Golgi traffic. Human and yeast GGA proteins are only ~25% identical, but all GGA proteins have four similar domains based on function and sequence homology. GGA proteins are most conserved in the region that interacts with ARF proteins. To analyze the role of ARF in GGA protein localization and function, we performed mutational analyses of both human and yeast GGAs. To our surprise, yeast and human GGAs differ in their requirement for ARF interaction. We describe a point mutation in both yeast and mammalian GGA proteins that eliminates binding to ARFs. In mammalian cells, this mutation disrupts the localization of human GGA proteins. Yeast Gga function was studied using an assay for carboxypeptidase Y missorting and synthetic temperature-sensitive lethality between GGAs and VPS27. Based on these assays, we conclude that non-Arf-binding yeast Gga mutants can function normally in membrane trafficking. Using green fluorescent protein-tagged Gga1p, we show that Arf interaction is not required for Gga localization to the Golgi. Truncation analysis of Gga1p and Gga2p suggests that the N-terminal VHS domain and C-terminal hinge and ear domains play significant roles in yeast Gga protein localization and function. Together, our data suggest that yeast Gga proteins function to assemble a protein complex at the late Golgi to initiate proper sorting and transport of specific cargo. Whereas mammalian GGAs must interact with ARF to localize to and function at the Golgi, interaction between yeast Ggas and Arf plays a minor role in Gga localization and function.

ADP-Ribosylation Factors↗
PubMed2002

Casein kinase I regulates membrane binding by ARF GAP1.

ARF GAP1, a 415-amino acid GTPase activating protein (GAP) for ADP-ribosylation factor (ARF) contains an amino-terminal 115-amino acid catalytic domain and no other recognizable features. Amino acids 203-334 of ARF GAP1 were sufficient to target a GFP-fusion protein to Golgi membranes in vivo. When overexpressed in COS-1 cells, this protein domain inhibited protein transport between the ER and Golgi and, in vitro, competed with the full-length ARF GAP1 for binding to membranes. Membrane binding by ARF GAP1 in vitro was increased by a factor in cytosol and this increase was inhibited by IC261, an inhibitor selective for casein kinase Idelta (CKIdelta), or when cytosol was treated with antibody to CKIdelta. The noncatalytic domain of ARF GAP1 was phosphorylated both in vivo and in vitro by CKI. IC261 blocked membrane binding by ARF GAP1 in vivo and inhibited protein transport in the early secretory pathway. Overexpression of a catalytically inactive CKIdelta also inhibited the binding of ARF GAP1 to membranes and interfered with protein transport. Thus, a CKI isoform is required for protein traffic through the early secretory pathway and can modulate the amount of ARF GAP1 that can bind to membranes.

ADP-Ribosylation Factors↗
PubMed2000

Characterization of the murine p19(ARF) promoter CpG island and its methylation pattern in primary lymphomas.

The INK4a/ARF locus encodes two different proteins involved in cell cycle control. Both molecules, p16(INK4a) and p19(ARF), inhibit cell cycle progression and have been shown to act as tumor suppressors in a variety of models. Their expression is controlled by separate promoters responding to different stimuli and they therefore show independent transcriptional regulation. We have cloned and characterized a 2.5 kb region upstream of the murine p19(ARF) gene to determine the role of DNA methylation in suppressing p19(ARF) transcription in a wide panel of murine primary T cell lymphomas. This region contains a DNA fragment with the characteristics of a CpG island similar to those described for the murine p16(INK4a) and p15(INK4b) genes. Expression of p19(ARF) is decreased in a significant number (20%) of the murine lymphomas analyzed. Overexpression of the p19(ARF) transcript is also frequent, suggesting alterations in molecules of the retinoblastoma or p53 pathways that are involved in p19(ARF) regulation. Although hypermethylation of the INK4a and INK4b promoters is frequently involved in murine lymphomas, the p19(ARF) CpG island is infrequently methylated in the murine primary lymphomas studied in this work. Since loss of p19(ARF) expression cannot be explained as the result of homozygous deletions or hypermethylation of the ARF gene, other regulatory mechanisms seem to be altered in these malignancies.

Animals↗
PubMed1999

Genetic interactions in yeast between Ypt GTPases and Arf guanine nucleotide exchangers.

Two families of GTPases, Arfs and Ypt/rabs, are key regulators of vesicular transport. While Arf proteins are implicated in vesicle budding from the donor compartment, Ypt/rab proteins are involved in the targeting of vesicles to the acceptor compartment. Recently, we have shown a role for Ypt31/32p in exit from the yeast trans-Golgi, suggesting a possible function for Ypt/rab proteins in vesicle budding as well. Here we report the identification of a new member of the Sec7-domain family, SYT1, as a high-copy suppressor of a ypt31/32 mutation. Several proteins that belong to the Sec7-domain family, including the yeast Gea1p, have recently been shown to stimulate nucleotide exchange by Arf GTPases. Nucleotide exchange by Arf GTPases, the switch from the GDP- to the GTP-bound form, is thought to be crucial for their function. Sec7p itself has an important role in the yeast secretory pathway. However, its mechanism of action is not yet understood. We show that all members of the Sec7-domain family exhibit distinct genetic interactions with the YPT genes. Biochemical assays demonstrate that, although the homology between the members of the Sec7-domain family is relatively low (20-35%) and limited to a small domain, they all can act as guanine nucleotide exchange factors (GEFs) for Arf proteins, but not for Ypt GTPases. The Sec7-domain of Sec7p is sufficient for this activity. Interestingly, the Sec7 domain activity is inhibited by brefeldin A (BFA), a fungal metabolite that inhibits some of the Arf-GEFs, indicating that this domain is a target for BFA. These results demonstrate that the ability to act as Arf-GEFs is a general property of all Sec7-domain proteins in yeast. The genetic interactions observed between Arf GEFs and Ypt GTPases suggest the existence of a Ypt-Arf GTPase cascade in the secretory pathway.

ADP-Ribosylation Factors↗
PubMed2000

Adenovirus-mediated p14(ARF) gene transfer in human mesothelioma cells.

BACKGROUND: The p14(ARF) protein encoded by the INK4a/ARF locus promotes degradation of the MDM2 protein and thus prevents the MDM2-mediated inhibition of p53. Homozygous deletion of the INK4a/ARF locus is common in human mesothelioma and may result in the loss of p14(ARF) and the inactivation of p53. We designed this study to evaluate the biologic and potential therapeutic roles of p14(ARF) expression in mesothelioma cells. METHODS AND RESULTS: We constructed Adp14, an adenoviral vector carrying human p14(ARF) complementary DNA, and used it to transfect human mesothelioma cell lines H28, H513, H2052, and MSTO-211H. Overexpression of p14(ARF) led to increased amounts of p53 and the p21(WAF) proteins and dephosphorylation of the retinoblastoma protein. The growth rate of mesothelioma cells was inhibited markedly by infection with Adp14 compared with mock infection or infection with a control adenovirus vector, AdCtrl. Overexpression of p14(ARF) induced G(1)-phase cell cycle arrest and apoptotic cell death. Cytotoxicity assays showed that Adp14 had a statistically significantly (P =.002) greater effect on colon cancer (HCT116) cell lines containing two copies of the wild-type p53 gene than on p53-null cells, suggesting that functional p53 is a critical determinant of p14(ARF)-mediated cytotoxicity. CONCLUSIONS: The transfection of p14(ARF) into mesothelioma cells led to the overexpression of p14(ARF), which resulted in G(1)-phase arrest and apoptotic cell death. These results suggest that this gene therapy-based approach may be of use in the treatment of mesothelioma.

Adenoviridae↗
PubMed2004

Pathogenesis of persistent hyperplastic primary vitreous in mice lacking the arf tumor suppressor gene.

PURPOSE: Persistent hyperplastic primary vitreous (PHPV) is an idiopathic developmental eye disease associated with failed involution of the hyaloid vasculature. The present work addressed the pathogenesis of PHPV in a mouse model that replicates many aspects of the human disease. METHODS: Ophthalmoscopic and histologic analyses documented pathologic processes in eyes of mice lacking the Arf gene compared with Ink4a-deficient and wild-type control animals. Immunohistochemical staining, in situ hybridization, and RT-PCR demonstrated the expression of relevant gene products. Arf gene expression was determined by in situ hybridization using wholemounts of wild-type mouse eyes and by immunofluorescence staining for green fluorescent protein (GFP) in Arf(+/GFP) heterozygous knock-in mouse eyes. RESULTS: Abnormalities in Arf(-/-) mice mimicked those found in patients with severe PHPV. The mice had microphthalmia; fibrovascular, retrolental tissue containing retinal pigment epithelial cells and remnants of the hyaloid vascular system; posterior lens capsule destruction with lens degeneration and opacity; and severe retinal dysplasia and detachment. Eyes of mice lacking the overlapping Ink4a gene were normal. Arf was selectively expressed in perivascular cells within the vitreous of the postnatal eye. Cells composing the retrolental mass in Arf(-/-) mice expressed the Arf promoter. The remnant hyaloid vessels expressed Flk-1. Its ligand, vascular endothelial growth factor (Vegf), was expressed in the retrolental tissue and the adjacent dysplastic neuroretina. CONCLUSIONS: Arf(-/-) mice have features that accurately mimic severe PHPV. In the HVS, Arf expression in perivascular cells may block their accumulation or repress Vegf expression to promote HVS involution and prevent PHPV.

Animals↗
PubMed2002

p14(ARF) nuclear overexpression in aggressive B-cell lymphomas is a sensor of malfunction of the common tumor suppressor pathways.

p14(ARF), the alternative product from the human INK4a/ARF locus, antagonizes Hdm2 and mediates p53 activation in response to oncogenic stimuli. An immunohistochemical study of p14(ARF) expression in 74 samples of aggressive B-cell lymphomas was performed, demonstrating an array of different abnormalities. A distinct nucleolar expression pattern was detected in nontumoral tissue and a subset of lymphomas (50/74). In contrast, a group of cases (8/74) showed absence of p14(ARF) expression, dependent either on promoter hypermethylation or gene loss. Additionally, 16 out of 74 cases displayed an abnormal nuclear p14(ARF) overexpression not confined to the nucleoli, as confirmed by confocal microscopy, and that was associated with high levels of p53 and Hdm2. A genetic study of these cases failed to show any alteration in the p14(ARF) gene, but revealed the presence of p53 mutations in over 50% of these cases. An increased growth fraction and a more aggressive clinical course, with a shortened survival time, also characterized the group of tumors with p14(ARF) nuclear overexpression. Moreover, this p14(ARF) expression pattern was more frequent in tumors displaying accumulated alterations in the p53, p16(INK4a), and p27(KIP1) tumor supressors. These observations, together with the consideration of the central role of p14(ARF) in cell cycle control, suggest that p14(ARF) abnormal nuclear overexpression is a sensor of malfunction of the major cell cycle regulatory pathways, and consequently a marker of a high tumor aggressivity.

Biomarkers, Tumor↗
PubMed2003

The guanine nucleotide exchange factor ARNO mediates the activation of ARF and phospholipase D by insulin.

BACKGROUND: Phospholipase D (PLD) is involved in many signaling pathways. In most systems, the activity of PLD is primarily regulated by the members of the ADP-Ribosylation Factor (ARF) family of GTPases, but the mechanism of activation of PLD and ARF by extracellular signals has not been fully established. Here we tested the hypothesis that ARF-guanine nucleotide exchange factors (ARF-GEFs) of the cytohesin/ARNO family mediate the activation of ARF and PLD by insulin. RESULTS: Wild type ARNO transiently transfected in HIRcB cells was translocated to the plasma membrane in an insulin-dependent manner and promoted the translocation of ARF to the membranes. 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. Sec7 domain mutants of ARNO did not facilitate the ARF translocation. 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. CONCLUSIONS: Small ARF-GEFs of the cytohesin/ARNO family mediate the activation of ARF and PLD by the insulin receptor.

ADP-Ribosylation Factors↗
PubMed2006

Involvement of a guanine nucleotide-exchange protein, ARF-GEP100/BRAG2a, in the apoptotic cell death of monocytic phagocytes.

We previous identified adenosine 5'-diphosphate-ribosylation factor (ARF)-guanine nucleotide-exchange protein, 100 kDa (GEP(100)), as a novel GEP with a molecular size of approximately 100 kDa, which preferentially activates ARF6. In this study, we examined the effect of ARF-GEP(100) on monocytic cell apoptosis. Overexpression of ARF-GEP(100) in PMA-differentiated human monocyte-macrophage-like U937 cells and mouse macrophage RAW264.7 cells induced apoptotic cell death, which was detected by morphological changes (chromatin condensation, nucleus fragmentation, and shrinking of cytoplasm), annexin V-staining, and TUNEL assay. It is interesting that a mutant lacking the Sec7 domain, which is responsible for ARF activation, was able to induce apoptosis of the target cells to the level of that of a wild-type ARF-GEP(100). Furthermore, ARF-GEP(100)-silencing experiments indicated that the TNF-alpha-induced apoptosis was significantly suppressed among ARF-GEP(100)-depressed cells. These observations apparently suggest that ARF-GEP(100) is involved in the induction of apoptosis in monocytic phagocytes, possibly independent of ARF activation.

Animals↗
PubMed1999

Tumor spectrum in ARF-deficient mice.

The p19ARF product of the INK4a/ARF locus is induced in response to potentially oncogenic hyperproliferative signals and activates p53 by interfering with its negative regulator, Mdm2. Mice lacking ARF are highly prone to tumor development, and in this study, 80% of these animals spontaneously developed tumors and died within their first year of life. Mice that were heterozygous for ARF also developed tumors after a longer latency, whereas their wild-type littermates did not. In heterozygotes, tumor formation was accompanied by loss of the residual ARF allele and/or lack of ARF mRNA expression, implying that ARF can act as a canonical "two-hit" tumor suppressor gene. Tumors occurred earlier in life in ARF-null animals that were neonatally irradiated or given dimethylbenzanthrene, and several animals treated with carcinogen simultaneously developed multiple forms of malignancy arising from distinct cell lineages. Although p53-null mice primarily develop lymphomas and fibrosarcomas, the frequency of these two tumor types was inverted in ARF-null animals, with undifferentiated sarcomas predominating in a 3:2 ratio; 28% of ARF-null animals developed carcinomas and tumors of the nervous system, which have been rarely observed in untreated p53-null mice. The longer latency of tumor formation in ARF-null versus p53-null mice, therefore, appears to enable a broader spectrum of tumors to emerge.

9,10-Dimethyl-1,2-benzanthracene↗