Cancer Research 68, 9608, December 1, 2008. doi: 10.1158/0008-5472.CAN-08-2263
© 2008 American Association for Cancer Research
The ARF Tumor Suppressor Can Promote the Progression of Some Tumors
Olivier Humbey1,
Julia Pimkina1,
Jack T. Zilfou3,
Michal Jarnik2,
Carmen Dominguez-Brauer4,
Darren J. Burgess5,
Christine M. Eischen6 and
Maureen E. Murphy1
Divisions of 1 Medical Sciences and 2 Basic Sciences, Fox Chase Cancer Center, Philadelphia, Pennsylvania; 3 Zilfou Therapeutics, Inc., Allentown, Pennsylvania; 4 University of Illinois at Chicago, Chicago, Illinois; 5 Cold Spring Harbor Laboratory, Cold Spring Harbor, New York; and 6 Vanderbilt University School of Medicine, Nashville, Tennessee
Requests for reprints: Maureen E. Murphy, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111. Phone: 215-728-5684; Fax: 215-728-4333; E-mail: Maureen.Murphy{at}FCCC.edu.
 |
Abstract
|
|---|
p14/p19ARF (ARF) is a tumor suppressor gene that is frequently mutated in human cancer. ARF has multiple tumor suppressor functions, some of which are mediated by signaling to p53. Surprisingly, a significant fraction of human tumors retain persistently high levels of ARF, suggesting that ARF may possess a prosurvival function. We show that ARF protein is markedly up-regulated in cells exposed to nutrient starvation. Cells with silenced ARF show reduced autophagy and reduced viability when placed under conditions of starvation. We show for the first time that ARF silencing can limit the progression of some tumors, such as lymphoma, but not others, such as E1A/Ras-induced tumors. Specifically, myc-driven lymphomas with mutant p53 tend to overexpress ARF; we show that silencing ARF in these tumors greatly impedes their progression. These data are the first to show that ARF can act in a p53-independent manner to promote the progression of some tumors. [Cancer Res 2008;68(23):9608–13]
|
Introduction
|
|---|
The ARF tumor suppressor is best known for its ability to stabilize p53, mediated by inhibition of the p53 ubiquitin ligase MDM2. Additionally, ARF has multiple tumor suppressor functions that are independent of p53: these involve interaction with several proteins with roles in cell proliferation, including nucleophosmin, NIAM, c-myc, E2F-1, DP1, and others (see ref. 1 for review). Despite its multiple growth suppression functions, ARF is inexplicably overexpressed in a significant fraction of human tumors, including up to 50% of Burkitt's lymphomas (2, 3), as well as the majority of tumors with mutant p53 (4). To date, the overwhelming majority of studies on ARF have focused on its tumor suppressor roles, and no groups have addressed the possibility that ARF might promote the survival of a subset of tumors.
A role for ARF in autophagy has recently been discovered. Specifically, a small molecular weight variant of this protein generated by translation from an internal methionine has been shown to localize to mitochondria and induce autophagy (5, 6). More recently, another group has shown that full-length ARF can likewise induce autophagy (7). Autophagy is a process of lysosome-mediated self-digestion that occurs during periods of nutrient deprivation (see ref. 8 for review). This process is necessary for cell survival; following nutrient starvation, proteins and organelles are degraded, and the released amino acids are used for the synthesis of essential proteins. Whereas recent studies have shown that ARF can induce autophagy, the relevance of ARF to starvation-induced autophagy and the significance of this finding to cancer development have not been addressed. In this study, we show that nutrient deprivation leads to significant increases in ARF protein. We show that ARF-mediated autophagy can protect cells from periods of nutrient deprivation. Further, we show that lymphomas with ARF silenced show impaired progression in immunocompromised mice. Our data support the premise that ARF can enhance tumor development under certain circumstances and that some tumors with mutant p53 may retain ARF to promote survival under metabolic stress.
|
Materials and Methods
|
|---|
Cell culture, retroviral infections, and cell viability. Wild-type (wt), p53-null, and p53/ARF double-knockout mouse embryonic fibroblasts (MEF) were cultured as described (9). B-cell lymphomas B2998 and E330 were cultured in RPMI 1640 with 20% heat-inactivated FCS, 55 µmol/L β-mercaptoethanol, and 10 ng/mL interleukin-7 (R&D Systems). Retroviral infection, p53 short hairpins, and short hairpin control vector are described (10). Short hairpin RNA vectors for ARF were generated by PCR amplification of 97-mer DNA oligonucleotides as described (11) and cloned into the LMP vector (12). Oligonucleotide sequences were the following: shARF157, 5'-TGCTGTTGACAGTGAGCGACGCTCTGGCTTTCGTGAACATTAGTGAAGCCACAGATGTAATGTTCACGAAAGCCAGAGCGCTGCCTACTGCCTCGGA-3'; shARF56, 5'-TGCTGTTGACAGTGAGCGATTGGTCACTGTGAGGATTCAGTAGTGAAGCCACAGATGTACTGAATCCTCACAGTGACCAAGTGCCTACTGCCTCGGA-3'.
Unless otherwise indicated, shARF56 was used for all experiments to silence ARF. Cell viability assays were performed using the ViaCount assay and the Guava Personal Cell Analysis machine (Guava Technologies); statistical significance was calculated using the two-sided Student's t test.
Mitochondria isolation, Western analysis, and immunoelectron microscopy. Mitochondria were purified as described (13). Western blotting was performed on 100 µg whole-cell lysate or 20 µg mitochondrial lysate; antisera used were anti-p19ARF (GeneTex), anti-actin (AC15, Sigma), anti-LC3 (Novus), anti-Beclin-1 (Santa Cruz Biotechnology), and anti-p62SQSTM1 (Santa Cruz Biotechnology). For electron microscopy, cells were fixed with 2% glutaraldehyde/2% formaldehyde in cacodylate buffer, fixed in 1% osmium tetroxide, embedded in epoxy resin, and stained with uranyl acetate and lead citrate. The area of autophagosomes was calculated using NIH Image. Immunoelectron microscopy was performed as described (14) and visualized by secondary labeling with protein A-colloidal gold. All samples were viewed in a FEI Tecnai 12 TEM operated at 80 kV.
Long-lived protein degradation assay. Long-lived protein degradation was assayed as described (15). The percentage of long-lived protein degraded was obtained by the following formula: % degradation = (14C counts at time point/sum of 14C counts at each time point + total cell-associated radioactivity) x 100.
Bioluminescent imaging. For xenograft analyses, MEFs were coinfected with retrovirus encoding luciferase along with retroviruses encoding vector, shBec1, shp53, or E1A/Ras before being injected (1 x 106 cells per injection) into severe combined immunodeficient (SCID) mice. E1A, Ras, and luciferase levels were monitored by Western analysis. Before injection, luciferase activity in infected cells was tested and silencing of all genes was confirmed by Western analysis. For biophotonic imaging on the IVIS Spectrum (Xenogen Biosciences), 1% isoflurane/oxygen-anesthetized mice were injected with luciferin (4 mg/animal) into the i.p. cavity. In all cases, the averaged data from each of two independent experiments using three animals for each sample were calculated; caliper measurements of tumors corroborated these analyses. For the lymphoma studies, cells were infected with shControl or shARF four times and selected in 1.5 µg/mL puromycin for 48 h. After 1 wk, cells were resuspended in PBS and 1 x 106 cells were injected into the tail vein of SCID mice. For these studies, the averaged data from each of two independent experiments (three animals per sample) plus SE were calculated and analyzed by the Wilcoxon two-sample test, and P values were combined according to the method of Fisher.
|
Results
|
|---|
ARF plays a role in autophagy induced by nutrient deprivation. ARF expression is negligible in normal nontransformed cells. This gene is also potently repressed by p53; consequently, p53-null MEFs express high levels of ARF (4, 16). To determine the relevance of ARF to starvation-induced autophagy, we exposed p53-null MEFs to nutrient deprivation by incubating them in HBSS, which is amino acid–free and growth factor–free. HBSS incubation led to a rapid (2 hours) and significant up-regulation of ARF protein (Fig. 1A
); this occurred independent of p53 status (Fig. 1B). Data quantitated from several experiments indicate that ARF is up-regulated 
1.6-fold in wt MEFs and 6.5-fold in p53–/– MEFs after 4-hour incubation in HBSS (data not shown). Induction of ARF mRNA by serum starvation has been noted previously (17). However, in response to HBSS, the up-regulation of ARF was not accompanied by an increase in ARF mRNA (data not shown). Further, there were no differences in ARF half-life under these conditions (Fig. 1C). The increase in ARF may be due to enhanced translation of ARF mRNA during nutrient deprivation.
View larger version (40K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1. Nutrient deprivation causes significant up-regulation of ARF along with mitochondrial localization of ARF. A, Western analysis of whole-cell lysate from p53–/– MEFs (passage 3) untreated or incubated in HBSS for the indicated time points (starvation) using antisera to actin (loading control) and ARF. B, Western analysis of MEFs with wt p53 (passage 2) untreated or incubated in HBSS for the indicated time points (starvation) using antisera to actin (loading control) and ARF. C, analysis of the half-life of ARF in untreated and nutrient-deprived cells. p53-null MEFs were untreated (UNT) or incubated for 2 h in HBSS followed by supplementation with complete medium containing 40 µg/µL cycloheximide to halt new protein synthesis. Cells were harvested and analyzed by Western blotting for ARF at the indicated time points; the data depicted are representative of two independent experiments. D, immunoelectron microscopy (Immuno-EM) using ARF antisera followed by protein G-gold in MEFs from the p53 knockout mouse following 2-h treatment with HBSS (starvation). Arrows point to gold particles in mitochondria and nucleoli. Scale bar, 500 nm.
|
|
ARF has been shown to play a role in autophagy via its localization to mitochondria (5). We could find no evidence for ARF localization at mitochondria in unstressed p53-null MEFs (Supplementary Fig. S1A); however, immunoelectron microscopy analyses revealed considerable localization of ARF to mitochondria after 2 hours of nutrient deprivation (Fig. 1D). These data were consistent with Western analyses of purified mitochondria, which showed demonstrable ARF copurifying with mitochondria after 2 hours of HBSS (Supplementary Fig. S1B). Quantitative Western analysis and counting of grains from immunoelectron microscopy indicated that between 5% and 10% of ARF localized to mitochondria following HBSS treatment.
The relevance of ARF up-regulation to starvation-induced autophagy was assessed in p53-null MEFs using a short hairpin to silence this gene (shARF); this hairpin reduces over 90% of ARF protein but does not silence p16ink4a expression (see Fig. 4A for example). In these experiments, the extent of autophagy was assessed by Western analysis for the protein LC3, which becomes processed to a faster-mobility species during autophagy (LC3 II), as well as by autophagosome formation and the analysis of long-lived protein degradation. Infection of p53-null MEFs with a parental retrovirus, or a virus encoding a short hairpin for p53 (which has no target in p53-null cells), did not influence the accumulation of LC3 II following HBSS treatment (Fig. 2A
). Notably, however, ARF silencing in p53-null MEFs led to markedly decreased accumulation of LC3 II following HBSS treatment (Fig. 2A). Moreover, electron microscopy indicated that following HBSS treatment, cells with silenced ARF had fewer, and often smaller, autophagosomes than control cells (Fig. 2B). The area of autophagosome coverage in HBSS-treated cells decreased from 48 ± 5% to 7 ± 2% when ARF was silenced. Consistent with this, silencing ARF in p53-null MEFs reduced the degradation of long-lived proteins in response to HBSS treatment (Fig. 2C). Not surprisingly, this decrease in autophagy was accompanied by a decrease in viability; after 24 hours of nutrient deprivation in HBSS, the majority of p53-null MEFs remained viable, whereas only 30% of cells with silenced ARF were viable at this time point (Fig. 2D). The combined data point to a previously unseen role for ARF in promoting cell survival during metabolic stress.
View larger version (37K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4. Silencing of ARF inhibits lymphoma development. A, bioluminescent imaging of tail vein–injected, luciferase-expressing B2998 B-cell lymphoma cells from the Eµ-myc mouse infected with vector control or two different short hairpins for ARF, shARF157 or shARF56. Most tumor cells track to the lymph nodes and meninges. Results are at day 7 following tail vein injection; equivalent results were obtained at day 14. Data depicted are representative of two independent experiments using three mice for each retrovirus (shControl, shARF157, and shARF56). Middle, Western analysis for p16, ARF, and actin control in infected lymphoma cells from the B2998 lymphoma 48 h after retroviral infection. Right, combined data from two independent experiments using three mice per virus, along with SE. Silencing of ARF, but not infection with short hairpin control vector, reduces tumor volume by 60% (P < 0.01). B, the viability of B2998 cells with silenced ARF is decreased following HBSS treatment for 24 h. Cell viability was determined using the ViaCount assay and the Guava Personal Cell Analysis machine. Columns, averaged results from three independent experiments; bars, SE. The P value reflects comparison between the second and fourth column. C, silencing ARF in B2998 lymphoma cells reduces the steady-state level of autophagy. Western analysis for ARF, actin, and p62SQSTM1 (which is degraded by autophagy) in cells infected with shControl or each of two ARF short hairpins (shARF157 and shARF56). D, silencing ARF in a primary T-cell lymphoma from the p53–/– mouse impedes tumor progression. Results are at day 2 following tail vein injection; equivalent results were obtained at day 4. Results are representative of two independent experiments. Right, Western analysis for ARF and loading control (actin).
|
|
View larger version (68K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2. ARF silencing reduces starvation-induced autophagy and survival. A, Western analysis for LC3 II in p53–/– MEFs following nutrient starvation (HBSS). Cells were infected for 48 h with a short hairpin for p53 (shp53, negative control) or short hairpin for ARF (shARF) and incubated for 2 h in HBSS. Data depicted are representative of three independent experiments; the depicted data were obtained from a single blot that was cropped for optimal data presentation. The difference in LC3 II in unstressed cells in lanes 1 and 3 was not consistent or reproducible from experiment to experiment. B, electron microscopy of p53-null MEFs infected with shp53 (negative control; top) or shARF (bottom) following 2-h incubation in HBSS (starvation). Scale bars, 5 µm (left) and 500 nm (right). C, the degradation of long-lived proteins in p53-null MEFs infected with short hairpin to p53 (negative control; black line) is increased compared with those infected with short hairpin to ARF (shARF; gray line) following starvation in HBSS for 24 h; results are normalized to cell number. X axis, time points of sampling. Data are representative of two independent experiments. D, viability of p53-null cells infected with short hairpin to p53 (MEF p53–/–) or shARF following 24-h treatment with HBSS; equal numbers of viable cells were plated at the 0 time point (1 x 106), and cell viability was determined using the ViaCount assay and the Guava Personal Cell Analysis machine. Columns, averaged results from three independent experiments; bars, SE.
|
|
Tumors without ARF are more sensitive to autophagy inhibition. We next sought to determine whether ARF-mediated autophagy might promote tumor growth. For this analysis, we chose to induce metabolic stress in tumors by silencing Beclin-1, a critical mediator of autophagy. Other groups have found that autophagy inhibition causes tumor regression (18, 19); similarly, we found that silencing Beclin-1 inhibited xenograft tumor development (Supplementary Fig. S2A). Interestingly, we found that the effect of Beclin-1 silencing on tumor growth was influenced by ARF status. For these studies, we created luciferase-expressing transformed MEF cell lines that differed in ARF status (p53-null versus p53/ARF double-knockout MEFs infected with E1A and Ras); these were subjected to Beclin-1 silencing and monitored for tumor development in a xenograft assay. We were able to achieve significant silencing of Beclin-1 in these lines (Fig. 3A
). Bioluminescent imaging indicated that tumors with high ARF (p53 null) were consistently resistant to the growth-suppressive effects of silencing Beclin-1 compared with tumors without ARF (p53/ARF double knockout; Fig. 3B, compare mouse 2A with 3A). Nearly identical results were obtained when we silenced ARF with a short hairpin (shARF; Fig. 3B, compare mouse 2A with 2B). The combined results from two independent experiments using three mice per virus are plotted in Fig. 3C; these data indicate that tumors without ARF are markedly more sensitive to growth inhibition induced by Beclin-1 silencing.
View larger version (25K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3. Tumors without ARF are more sensitive to metabolic stress (silencing of Beclin-1). A, Western analysis of p53-null MEFS (high ARF) and MEFs from the p53/ARF double-knockout mouse (p53/ARF DKO) following infection with short hairpin to silence Beclin-1 (shBec1) for the levels of actin (loading control), ARF, and Beclin-1. B, bioluminescent imaging of xenograft tumors derived from early-passage MEFs from the p53–/– mouse or p53/ARF double knockout stably infected with luciferase virus and then infected with the retroviruses indicated (shARF or shBec) for 48 h. Tumors were imaged after 21 d; equivalent results were seen after 30 d, and all measurements were consistent with caliper measurements. C, analysis of the combined imaging data from two independent experiments depicted in B using three mice for each sample per experiment (six samples total per retrovirus combination). Columns, raw mean of bioluminescence; bars, SE.
|
|
Silencing of ARF inhibits the progression of lymphomas with mutant or no p53. To assess the physiologic relevance of ARF-mediated autophagy to tumor development, we silenced ARF in tumors that overexpress this protein and assessed the effect on tumorigenesis. Toward this end, we used a primary murine B-cell lymphoma cell line (B2998) from the Eµ-myc transgenic mouse that contains mutant p537 and high levels of ARF. We infected this lymphoma cell line with one of two different short hairpins for ARF (shARF157 or shARF56) or a short hairpin control virus (shControl) followed by a luciferase retrovirus. Following confirmation that luciferase activity was equivalent and that ARF was silenced, cells were injected into the tail vein of immunocompromised mice and imaged after 7 days. As depicted in Fig. 4A
, infection with either of two different ARF short hairpins, but not with a short hairpin control, led to markedly impaired lymphoma development. This result was consistent in another lymphoma cell line containing mutant p53 (E330; Supplementary Fig. S2B) and was consistent when tumors were imaged after 7 or 14 days (data not shown). The combined data from two independent experiments using three mice per virus are plotted in Fig. 4A; these data indicate that the inhibition of tumor progression by ARF silencing was reproducible and statistically significant (P < 0.01). Notably, ARF silencing also led to decreased viability of B2998 cells following HBSS treatment (Fig. 4B) and hypoxia (Supplementary Fig. S2C) and to decreased levels of steady-state autophagy, as evidenced by accumulation of p62SQSTM1, which is degraded by autophagy (Fig. 4C). In contrast, ARF silencing did not affect the proliferation of lymphoma cells cultured under nutrient-rich conditions (Supplementary Fig. S2D). To confirm these findings in another cell line, we silenced ARF in a primary T-cell lymphoma from the p53-null mouse; here again, we found that ARF silencing reduced tumor development (Fig. 4D), suggesting that ARF can confer a survival advantage to certain tumors.
|
Discussion
|
|---|
In this article, we provide data indicating that ARF has a previously undiscovered tumor-promoting activity and that this activity may be mediated by its role in starvation-induced autophagy. These data do not discount the ample data indicating that ARF is a tumor suppressor, as all of our studies are performed in cells with mutant or null p53, exposed to metabolic stress. Although some groups have reported that ARF-mediated autophagy is cytotoxic (5–7), we find that ARF is cytoprotective to tumors. This discrepancy may be due to differences in cell types analyzed or the use of transfection and supraphysiologic overexpression of ARF by these other groups. We find that ARF silencing in myc-driven lymphoma cells containing mutant p53 impedes their survival under nutrient-starved conditions and their development as xenografts. These data are the first to indicate that the ARF tumor suppressor has a survival function and further that this survival function may be selected for in certain tumors. It should be noted, however, that this survival function is likely to be tumor type specific; consistent with the data of others (9), we find that ARF silencing enhances the development of E1A/Ras-driven tumors (Fig. 3C). Ras can inhibit autophagy (20), and this may explain why ARF-mediated autophagy has no selective benefit to Ras-driven tumors. The findings described herein have important clinical relevance: autophagy modulators such as chloroquine and rapamycin are currently used in clinical trials for human cancer. Our data suggest that tumors without ARF may be more susceptible to such treatment.
|
Disclosure of Potential Conflicts of Interest
|
|---|
No potential conflicts of interest were disclosed.
|
Acknowledgments
|
|---|
Grant support: NIH grants R01 CA080854 and CA150002 (M.E. Murphy) and Philippe Foundation (O. Humbey).
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
We thank Gerry Zambetti, Scott Lowe, and Shengkan Jin for reagents; Eileen White and Carol Prives for critical reading of the manuscript; and Cory Abate-Shen for communicating results before publication.
|
Footnotes
|
|---|
Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/).
O. Humbey and J. Pimkina contributed equally to this work.
7 C.M. Eischen, unpublished results. 
Received 6/16/08.
Revised 10/13/08.
Accepted 10/14/08.
|
References
|
|---|
- Sherr CJ, Bertwistle D, Den Besten W, et al. p53-dependent and -independent functions of the Arf tumor suppressor. Cold Spring Harb Symp Quant Biol 2005;70:129–37.[Abstract/Free Full Text]
- Basso K, Margolin AA, Stolovitzky G, Klein U, Dalla-Favera R, Califano A. Reverse engineering of regulatory networks in human B cells. Nat Genet 2005;37:382–90.[CrossRef][Medline]
- Eischen CM, Weber JD, Roussel MF, Sherr CJ, Cleveland JL. Disruption of the ARF-Mdm2-p53 tumor suppressor pathway in Myc-induced lymphomagenesis. Genes Dev 1999;13:2658–69.[Abstract/Free Full Text]
- Kamijo T, Weber JD, Zambetti G, Zindy F, Roussel MF, Sherr CJ. Functional and physical interactions of the ARF tumor suppressor with p53 and Mdm2. Proc Natl Acad Sci U S A 1998;95:8292–7.[Abstract/Free Full Text]
- Reef S, Zalckvar E, Shifman O, et al. A short mitochondrial form of p19ARF induces autophagy and caspase-independent cell death. Mol Cell 2006;22:463–75.[CrossRef][Medline]
- Ueda Y, Koya T, Yoneda-Kato N, Kato JY. Small mitochondrial ARF (smARF) is located in both the nucleus and cytoplasm, induces cell death, and activates p53 in mouse fibroblasts. FEBS Lett 2008;582:1459–64.[CrossRef][Medline]
- Abida WM, Gu W. p53-dependent and independent activation of autophagy by ARF. Cancer Res 2008;68:352–7.[Abstract/Free Full Text]
- Jin S, White E. Role of autophagy in cancer: management of metabolic stress. Autophagy 2007;3:28–31.[Medline]
- Weber JD, Jeffers JR, Rehg JE, et al. p53-independent functions of the p19(ARF) tumor suppressor. Genes Dev 2000;14:2358–65.[Abstract/Free Full Text]
- Hemann MT, Fridman JS, Zilfou JT, et al. An epi-allelic series of p53 hypomorphs created by stable RNAi produces distinct tumor phenotypes in vivo. Nat Genet 2003;33:396–400.[CrossRef][Medline]
- Paddison PJ, Cleary M, Silva JM, et al. Cloning of short hairpin RNAs for gene knockdown in mammalian cells. Nat Methods 2004;1:163–7.[CrossRef][Medline]
- Dickins RA, Hemann MT, Zilfou JT, et al. Probing tumor phenotypes using stable and regulated synthetic microRNA precursors. Nat Genet 2005;37:1289–95.[Medline]
- Pietsch EC, Leu JI, Frank A, Dumont P, George DL, Murphy ME. The tetramerization domain of p53 is required for efficient BAK oligomerization. Cancer Biol Ther 2007;6:1576–83.[Medline]
- Tokuyasu KT. Immunochemistry on ultrathin frozen sections. Histochem J 1980;12:381–403.[CrossRef][Medline]
- Pattingre S, Petiot A, Codogno P. Analyses of G-
-interacting protein and activator of G-protein-signaling-3 functions in macroautophagy. Methods Enzymol 2004;390:17–31.[Medline] - Robertson KD, Jones PA. The human ARF cell cycle regulatory gene promoter is a CpG island which can be silenced by DNA methylation and down-regulated by wild-type p53. Mol Cell Biol 1998;18:6457–73.[Abstract/Free Full Text]
- Inoue R, Asker C, Klangby U, Pisa P, Wiman KG. Induction of the human ARF protein by serum starvation. Anticancer Res 1999;19:2939–43.[Medline]
- Amaravadi RK, Yu D, Lum JJ, et al. Autophagy inhibition enhances therapy-induced apoptosis in a Myc-induced model of lymphoma. J Clin Invest 2007;117:326–36.[CrossRef][Medline]
- Carew JS, Nawrocki ST, Kahue CN, et al. Targeting autophagy augments the anticancer activity of the histone deacetylase inhibitor SAHA to overcome Bcr-Abl-mediated drug resistance. Blood 2007;110:313–22.[Abstract/Free Full Text]
- Furuta S, Hidaka E, Ogata A, Yokota S, Kamata T. Ras is involved in the negative control of autophagy through the class I PI3-kinase. Oncogene 2004;23:3898–904.[CrossRef][Medline]
This article has been cited by other articles:
|
|
|
|
 
J. T. Zilfou and S. W. Lowe
Tumor Suppressive Functions of p53
Cold Spring Harb Perspect Biol,
November 1, 2009;
1(5):
a001883 - a001883.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Z. Chen, A. Carracedo, H.-K. Lin, J. A. Koutcher, N. Behrendt, A. Egia, A. Alimonti, B. S. Carver, W. Gerald, J. Teruya-Feldstein, et al.
Differential p53-Independent Outcomes of p19Arf Loss in Oncogenesis
Sci. Signal.,
August 18, 2009;
2(84):
ra44 - ra44.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Pimkina, O. Humbey, J. T. Zilfou, M. Jarnik, and M. E. Murphy
ARF Induces Autophagy by Virtue of Interaction with Bcl-xl
J. Biol. Chem.,
January 30, 2009;
284(5):
2803 - 2810.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Abstract
Introduction
