Cancer Research The Future of Cancer Research: Science and Patient Impact 09 AM Call for Abstracts
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Cancer Research Clinical Cancer Research
Cancer Epidemiology Biomarkers & Prevention Molecular Cancer Therapeutics
Molecular Cancer Research Cancer Prevention Research
Cancer Prevention Journals Portal Cancer Reviews Online
Annual Meeting Education Book Meeting Abstracts Online
[Cancer Research 59, 2064-2067, May 1, 1999]
© 1999 American Association for Cancer Research
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Pan, Y.
Right arrow Articles by Haines, D. S.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pan, Y.
Right arrow Articles by Haines, D. S.
[Cancer Research 59, 2064-2067, May 1, 1999]
© 1999 American Association for Cancer Research

Advances in Brief

The Pathway Regulating MDM2 Protein Degradation Can Be Altered in Human Leukemic Cells1

Yi Pan2 and Dale S. Haines2,, 3

Barry Ashbee Leukemia Research Laboratories, Hahnemann University Hospital, Philadelphia, Pennsylvania 19102


   ABSTRACT
Top
 ABSTRACT
Introduction
 Materials and Methods
 Results
 Discussion
 REFERENCES
 
The MDM2 protein regulates the functional activity of the p53 tumor suppressor through direct physical association. Signals that control MDM2 expression are poorly understood but are likely to play an important role in the regulation of p53 activity. We show here that the half-life of MDM2 protein is shorter in proliferating than in quiescent peripheral blood mononuclear cells. We also demonstrate that MDM2 protein half-life is extended in some, but not all, p53 mutant human leukemic cell lines. In at least one of these p53 mutant lines, increased MDM2 protein stability is associated with higher amounts of MDM2 protein. Moreover, we demonstrate that MDM2 protein accumulates to a much greater extent in proteasome inhibitor-treated cells containing unstable MDM2 than in cells possessing stable MDM2. These results demonstrate that MDM2 expression is regulated by events that control the stability of the protein and suggest that the normal regulation of MDM2 turnover can be altered in tumor cell lines.


   Introduction
Top
 ABSTRACT
 Introduction
Materials and Methods
 Results
 Discussion
 REFERENCES
 
The transforming potential of the MDM2 oncoprotein is activated by overexpression (1 , 2) , and high levels of MDM2 protein are present in some human tumor cells (3) . The primary mechanism by which MDM2 overexpression is thought to induce cellular transformation is through its ability to bind to the p53 tumor suppressor and block p53 activity (4) . MDM2 can inhibit p53 activity by binding to the acidic activation domain of p53 (5) and by targeting p53 for degradation via the proteasome (6 , 7) . Because the transforming activity of MDM2 has been attributed to the overproduction of protein (1 , 2) , it is important to understand the mechanisms that regulate MDM2 protein expression and how these mechanisms may be altered in human tumor cells. It is well established that p53 is itself a key regulator of MDM2 transcription (8, 9, 10, 11) . Besides those signals that induce p53 transcriptional activity (e.g., DNA damage), very little is known about other cellular signals that may regulate MDM2 protein expression. In the work presented here, we have investigated how MDM2 protein stability may be differentially regulated in quiescent and growth stimulated human PBMCs.4 We have also examined the possibility that the regulation of MDM2 protein stability may be altered in human leukemic cell lines.


   Materials and Methods
Top
 ABSTRACT
 Introduction
 Materials and Methods
Results
 Discussion
 REFERENCES
 
Cell Culture.
All lines were cultured in RPMI 1640 containing 10% fetal bovine serum and 1% penicillin-streptomycin (Life Technologies, Inc.). The M8166 (T-cell) line possesses wt p53 alleles, whereas the CEM (T-cell), HEL (erythroleukemia), Jurkat (T-cell), MOLT4 (T-cell), and Raji (B-cell) lines possess mutant p53 alleles (12) . PBMCs were isolated with Ficoll-Paque (Pharmacia) according to the manufacturer’s instructions. Quiescent PBMCs were cultured in complete RPMI 1640 and used for studies immediately after isolation from normal donors. To generate a population of actively proliferating T cells, quiescent PBMCs were seeded at 2 x 106 cells/ml in complete RPMI 1640 supplemented with 1% PHA-M (Life Technologies, Inc.). After 3 days, recombinant IL-2 (Sigma) was added into the media to a final concentration of 1 unit/ml. Cells were counted every other day and maintained at 1 x 106 cells/ml in IL-2-containing media. Once cells possessed a doubling time of ~48 h, they were used for the appropriate studies.

Cycloheximide and MG115 Treatment of Cells.
Cells were seeded at 2 x 106 cells/ml in their respective culture medium containing 75 µg/ml of cycloheximide or 10 µM MG115. Cells were harvested at different time points after cycloheximide treatment and pelleted by centrifugation. For Western analysis, cell pellets were stored at -80°C prior to extraction of protein.

Protein Extraction and Western Analysis.
Cells were lysed in TENN buffer [50 mM Tris (pH 7.4), 5 mM EDTA (pH 8.0), 0.5% NP40, and 150 mM NaCl] supplemented with 1 mM phenylmethylsulfonyl fluoride, 2 µg/ml aprotinin, 2 µg/ml leupeptin, 1 µg/ml soy trypsin inhibitor, and 1 µg/ml pepstatin A. Lysates were clarified by centrifugation, and the protein concentration was determined by the Bradford method (Bio-Rad). Samples were then mixed with 4x SDS-PAGE sample loading buffer, boiled, separated on SDS-polyacrylamide gels, and transferred onto nitrocellulose membranes. Blots were probed with 0.5 µg/ml p53 (DO-1; Calbiochem), 3 µg/ml MDM2 (IF2; Calbiochem), and actin (0.1 µ g/ml, Sigma) antibodies as described previously (12) . Signals were visualized by using horseradish peroxidase-conjugated antibodies (sheep anti-mouse for MDM2 and p53, Amersham; goat-anti rabbit for actin, Boehringer Mannheim) and enhanced chemiluminescence (DuPont NEN).

RNA Isolation and RNase Protection.
Total RNA was isolated using RNazol B (Tel-Test, Inc.) as per manufacturer’s instructions. RNase protection using an MDM2 probe that measures the levels of MDM2-P1 and MDM2-P2 transcripts was performed as described previously (12) , except that 7.5 µg of total RNA were used in hybridization reactions.


   Results
Top
 ABSTRACT
 Introduction
 Materials and Methods
 Results
Discussion
 REFERENCES
 
MDM2 and p53 Half-Life Analysis in Quiescent and Growth-stimulated PBMCs.
To determine whether the stability of MDM2 protein may be differentially regulated in quiescent versus proliferating cells, the half-life of MDM2 protein was measured in both untreated and PHA/IL-2-treated PBMCs. Freshly isolated PBMCs from normal individuals are comprised predominantly of quiescent T cells (~ 70%), whereas the treatment of PBMCs with PHA and the culturing of these cells with IL-2 will generate a relatively pure population of cycling T cells. MDM2 protein half-life was measured by determining the level of protein at various time points after treatment with the protein synthesis inhibitor cycloheximide. Interestingly, Fig. 1aCitation shows that the level of MDM2 protein declined much more rapidly in cycloheximide-treated, growth-stimulated cells than in unstimulated cells. The half-life of MDM2 in growth-stimulated cells measured by the method used here (<30 min) is consistent with previous studies that have used radioactive protein labeling methods to measure MDM2 half-life in cell lines (2) . Because cycloheximide may alter the expression of other factors that may regulate MDM2 protein stability, we did attempt to measure MDM2 protein stability by radiolabeling and immunoprecipitation as well. Although we were able to measure MDM2 stability in cycling cells by pulse-chase experiments (the half-life of MDM2 protein was found to be very similar to that measured with cycloheximide in these cells), we could not detect MDM2 protein in quiescent cells after radiolabeling and immunoprecipitation (data not shown). This is most likely due to a very low rate of MDM2 synthesis in quiescent cells (12) . Therefore, we cannot rule out the possibility at this time that MDM2 half-life is also short in quiescent cells and that cycloheximide is altering the expression of factors that may regulate MDM2 stability in these cells.



View larger version (42K):
[in this window]
[in a new window]
  		Fig. 1. MDM2 (A) and p53 (B) half-life in untreated and growth-stimulated PBMCs. PBMCs were obtained from healthy normal individuals and isolated by Ficoll gradients. To generate an active cycling lymphocyte population, PBMCs were stimulated with PHA and then grown in the presence of IL-2 for at least a week until the cells possessed a doubling time of ~48 h. Then, freshly isolated PBMCs and stimulated PBMCs were treated with the protein synthesis inhibitor cycloheximide (at 75 µg/ml) for the indicated period of time. Cells were harvested, extracts were prepared, and the level of either MDM2 (A) or p53 (B) protein was measured by Western blot analysis as described in "Materials and Methods." Blots were also probed with polyclonal antibodies against actin to show equivalent loading of protein.

 
MDM2 can regulate the stability of the p53 tumor suppressor through direct physical association (6 , 7) . To determine whether growth stimulation also modulates p53 protein stability, p53 half-life analysis was performed on untreated and PHA/IL-2-treated PBMCs. Fig. 1bCitation shows that there is not a dramatic difference in the half-life of p53 protein measured in stimulated and unstimulated cells. In fact, p53 stability in cycling T cells may even be slightly longer than that measured in quiescent PBMCs. This result significantly reduces the concern that the difference in MDM2 half-life measured in cycling versus quiescent PBMCs using cycloheximide is due to a difference in the ability of cycloheximide to block protein synthesis in these two cell populations. It also suggests that the rate of p53 protein degradation is not directly coupled to the rate of MDM2 turnover.

The Half-Life of MDM2 Protein Is Extended in Human Leukemic Cells.
The results presented above suggest that MDM2 expression can be regulated by mechanisms controlling MDM2 protein stability. Because MDM2 has oncogenic properties when overexpressed and MDM2 protein levels have been shown to be elevated in a number of different cancers in the absence of increased RNA levels (including in hematological malignancies; Ref. 13 ), we investigated the possibility that alterations in the regulation of MDM2 protein stability may contribute to high levels of MDM2 protein in human tumor cells. We first performed MDM2 Western blot analysis on a series of leukemic cell lines. Although no lines expressed a high level of MDM2 protein (>10-fold above the level of MDM2 protein measured in PHA/IL-2-stimulated PBMCs), we were surprised to find similar amounts of MDM2 protein in wt and mutant p53-containing lines and that the p53 mutant Jurkat line expressed the highest amount of MDM2 protein (Fig. 2a)Citation . This line expressed six times more MDM2 protein (as determined by densitometric analysis) than that measured in PHA/IL-2-stimulated PBMCs.



View larger version (51K):
[in this window]
[in a new window]
  		Fig. 2. MDM2 protein and MDM2-P2 transcript levels in human leukemic cell lines. MDM2 and p53 protein levels were measured as described in "Materials and Methods" from the following cell lines: Lane P, PHA/IL-2-stimulated PBMCs; Lane M1, M8166 T-cell line; Lane M, MOLT4 T-cell line; Lane C, CEM T-cell line; Lane H, HEL erythroleukemia line; Lane J, Jurkat T-cell line; and Lane R, Raji B-cell line. Ponceau S staining of membranes was performed to verify equivalent loading of protein. High levels of p53 protein were measured in lines possessing missense p53 mutations, whereas undetectable levels of p53 protein were present in the Jurkat line harboring a frameshift p53 mutation. B, the levels of MDM2-P1 and MDM2-P2 transcripts was measured in these same lines by RNase protection as described in "Materials and Methods."

 
The expression profile of MDM2 in leukemic lines was not expected, considering that the majority of these lines possess mutant p53 and should possess low amounts of MDM2-P2 transcripts (12) ; p53-regulated transcripts that have been shown to be translated at high efficiencies in vitro and in cells in culture (14 , 15) . To verify the absence of these transcripts in mutant p53 lines, RNase protection analysis was performed. As expected, those lines with mutant p53 did not possess MDM2-P2 transcripts (Fig. 2b)Citation . Fig. 2bCitation also shows that all lines possessed similar amounts of MDM2-P1 transcripts; MDM2 transcripts that are regulated by the p53-independent promoter of the MDM2 gene. These results raise the possibility that MDM2-P2 transcripts are not translated more efficiently in lymphoid cells. However, it is also conceivable that the half-life of MDM2 protein is longer in some of the lines with undetectable amounts of MDM2-P2 transcripts, but expressing higher or similar level of MDM2 protein as wt p53-containing lines. To address this, the half-life of MDM2 protein was measured in several mutant p53 lines. All lines analyzed possessed similar doubling times, and half-life studies were performed with cells in their logarithmic stage of growth. Fig. 3Citation shows that the half-life of MDM2 protein was clearly longer in the HEL, CEM, Jurkat, and MOLT4 lines than in the Raji line or in PHA/IL-2-stimulated PBMCs. It is unlikely that the difference in MDM2 half-life measured in the lines is do to an unequal inhibition of protein synthesis by cycloheximide because this compound was found to inhibit incorporation of [35S]methionine to a similar degree in all lines tested (data not shown).



View larger version (26K):
[in this window]
[in a new window]
  		Fig. 3. MDM2 protein stability in human leukemic cell lines. Human leukemic cell lines were treated with the protein synthesis inhibitor cycloheximide (at 75 µg/ml) for the indicated period of time. Cells were then harvested, extracts were prepared, and the level of MDM2 protein in these extracts was subsequently measured by Western blot analysis. Abbreviations used are the same as those used in the legend of Fig. 4Citation . Ponceau S staining of membranes was performed to verify equivalent loading of protein.

 
MDM2 protein has been shown to be degraded via the proteasome (16) . The longer half-life of MDM2 protein measured in some of these leukemic lines may be attributed to differences in the way MDM2 protein is degraded by the proteasome. To address this hypothesis, the Jurkat (stable MDM2), MOLT4 (stable MDM2), and Raji (unstable MDM2) lines were treated with the proteasome inhibitor MG115 for varying periods of time, and the level of MDM2 protein was measured after treatment. Fig. 4Citation demonstrates a greater fold increase in MDM2 protein levels in the Raji line (~5-fold at the 2-h time point as determined by densitometric analysis) than in either the Jurkat or MOLT4 cell lines (both displaying a 2-fold induction of protein at the 2-h time point). This result supports those presented in Fig. 3Citation that show that the half-life of MDM2 protein is longer in the Jurkat and MOLT4 lines than in the Raji line and suggests that the normal regulation of proteasome-mediated degradation of MDM2 protein can be altered in human leukemic cells.



View larger version (23K):
[in this window]
[in a new window]
  		Fig. 4. MDM2 protein levels in MG115-treated cells harboring stable or unstable MDM2. Cells were treated with the proteasome inhibitor MG115 (final concentration, 10 µm) for the indicated period of time. Western blots using either a monoclonal antibody against MDM2 or polyclonal antibodies against actin were performed on protein extracts prepared from untreated and treated cells as described in "Materials and Methods."

 

   Discussion
Top
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
REFERENCES
 
p53 and MDM2 expression is regulated at multiple levels by mitogenic signals. Growth stimulation of human lymphocytes has previously been shown to induce an overall increase in both p53 RNA and p53 protein (17 , 18) . MDM2 RNA (specifically, those transcripts that are regulated by p53) and MDM2 protein have also been shown to be up-regulated in growth-stimulated cells (12) . We show here that the stability of MDM2 protein is regulated by growth stimulation signals as well. Interestingly, we show that MDM2 protein has a shorter half-life in growth-stimulated PBMCs than in quiescent PBMCs. This may appear to be inconsistent with an overall increase in the amount of MDM2 protein. However, considering that MDM2 expression can be regulated at multiple levels, the increase in MDM2 protein measured in stimulated cells is probably due to the fact that growth stimulation induces a greater fold increase in MDM2 transcription and/or translation than turnover of MDM2 protein.

What could be the functional significance for the differential regulation of p53 and MDM2 expression in quiescent versus proliferating cells? It is probably not a high priority for a nondividing cell to expend energy required for either the synthesis or degradation of proteins involved in controlling damaged-induced cell cycle arrest. However, an actively proliferating cell needs to possess an increased capacity to respond to the potentially harmful effects of cellular damage. One way to increase the capacity for a p53 response is to increase the amount of latent p53. We propose that this is accomplished by events that regulate p53 and MDM2 RNA production (12 , 17 , 18) , as well as MDM2 degradation (see Fig. 1Citation ). The various mechanisms controlling p53 and MDM2 expression are likely to play an important role in generating an optimal ratio of MDM2 and p53 proteins that is needed to maintain high levels of latent p53 protein in actively proliferating cells.

It appears that there are multiple mechanisms that can lead to the overproduction of MDM2 protein in human tumor cells, including MDM2 gene amplification (3) and enhanced translation of MDM2-P2 transcripts (15) . Besides presenting data that suggest that MDM2 protein stability is differentially regulated in quiescent versus active cycling cells, we also present data that suggest that the normal regulation of MDM2 protein turnover mediated by the proteasome can be altered in human tumor cells. The half-life of MDM2 protein was found to be extended in a number of leukemic cell lines, and MDM2 accumulated to a much lesser degree in proteasome inhibitor-treated cells harboring stable MDM2 than in treated cells possessing unstable MDM2. In at least one of these lines (the Jurkat line), the increased stability of MDM2 protein appears to contribute to a high amount of protein (a 6-fold greater amount of protein than that measured in normal cycling lymphocytes). It is therefore possible that alterations in the regulation of MDM2 turnover via the proteasome may be another mechanism that can contribute to the overproduction of MDM2 protein in human tumor cells. It is, however, unlikely that stabilized MDM2 is sufficient for the inhibition of p53 function in the cell lines analyzed here because the p53 gene is mutated in all lines possessing MDM2 with a long half-life. Alternatively spliced variants of MDM2 lacking the p53 binding region have been shown to transform NIH3T3 cells (19) , and overexpression of MDM2 has been documented to alter cell cycle control pathways in p53 null cells in vivo (20) . Recently, it has also been documented that MDM2 overexpression can block the growth-inhibitory activities of TGF-ß1 via a p53-independent mechanism (21) and that p53 null transgenic mice that overexpress MDM2 develop a different spectrum of tumors than mice that are only null for p53 (22) . Moreover, although rare, alterations in both MDM2 and p53 expression have been detected in primary human tumor cells (23) . Therefore, it is conceivable that stabilized MDM2 may provide a selective growth advantage in p53 mutant cells by altering p53-independent growth control pathways. It is, however, possible that alterations in MDM2 turnover do not contribute at all to the transformation process but are a consequence of alterations in other critical growth control molecules that are important in the regulation of MDM2 stability. It has been reported recently that the alternative translation product of the human CDKN2A locus (p14arf) is regulated by p53 and can regulate MDM2 stability (24) . Thus, MDM2 protein stability may be associated with either p53 or p14arf expression status. Interestingly, both the Jurkat (stable MDM2) and Raji (unstable MDM2) lines possess undetectable levels of p14arf protein (25) and harbor mutant p53 alleles. It is therefore likely that the stability of MDM2 will not be associated simply with p53 or p14arf expression status, and that there are other unknown growth control molecules that are important in the regulation of MDM2 stability that are altered in human leukemic cells.

In summary, our results suggest that MDM2 protein expression is regulated by mechanisms controlling the stability of the protein. It will be of interest for future studies to determine whether MDM2 stability is regulated by signals that not only induce proliferation but also inhibit cell growth (i.e., signals that promote senescence, differentiation, and others). Our data also suggest that mechanisms regulating MDM2 stability can be altered in human tumor cell lines. We did perform half-life studies using primary leukemic cells and found that some patients harbor cells possessing MDM2 with a long half-life (data not shown). However, because we could not control for the proliferative rate of tumor cells derived from the various patients (unlike in cell lines), we do not know if the differences in MDM2 stability measured in primary tumors are due to difference in the proliferative rate of the cells or due to alterations in pathways regulating MDM2 stability. More work will obviously be needed to identify the various factors that play a role in the regulation of MDM2 stability, how alterations in these pathways lead to MDM2 stabilization in cell lines, and whether alterations in the regulation of MDM2 stability occur in primary human tumors.


   ACKNOWLEDGMENTS
 
We thank M. Autieri, M. Boyd, and D. George for their critical review of the manuscript.


   FOOTNOTES
 
1 Supported by Grant CA70165 from the National Cancer Institute and by Grant DAMD17-97-1-7169 from the US Army. Back

2 Present address: The Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, 3307 North Broad Street, Philadelphia, PA 19140. Back

3 To whom requests for reprints should be addressed, at The Fels Institute for Cancer and Molecular Biology, Temple University School of Medicine, 3307 North Broad Street, Philadelphia, PA 19140. Phone: (215) 707-5765; Fax: (215) 707-2102; Back

4 The abbreviations used are: PBMC, peripheral blood mononuclear cell; wt, wild type; PHA, phytohemagglutin; IL, interleukin. Back

Received 12/17/98. Accepted 3/19/99.


   REFERENCES
Top
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
 REFERENCES
 

  1. Fakharzadeh S. S., Trusko S. P., George D. L. Tumorigenic potential associated with enhanced expression of a gene that is amplified in a mouse tumor cell line. EMBO J., 19: 1565-1569, 1991.
  2. Finlay C. A. The mdm-2 oncogene can overcome wild-type p53 suppression of transformed cell growth. Mol. Cell. Biol., 13: 301-306, 1993.[Abstract/Free Full Text]
  3. Leach F. S., Tokino T., Meltzer P., Burell M., Oliner J. D., Smith S., Hill D. E., Sidransky D., Kinzler K. W., Vogelstein B. p53 mutation and MDM2 amplification in human soft tissue sarcomas. Cancer Res., 53: 2231-2234, 1993.[Abstract/Free Full Text]
  4. Momand J., Zambetti G. P., Olson D. C., George D., Levine A. J. The mdm-2 oncogene product forms a complex with the p53 protein and inhibits p53-mediated transactivation. Cell, 69: 1237-1245, 1992.[Medline]
  5. Oliner J. D., Pientenpol J. A., Thiagalingam S., Gyuris J., Kinzler K. W., Vogelstein B. Oncoprotein MDM2 conceals the activation domain of tumour suppressor p53. Nature (Lond.), 362: 857-860, 1993.[Medline]
  6. Kubbutat M. H. G., Jones S. N., Vousden K. H. Regulation of p53 stability by MDM2. Nature (Lond.), 387: 299-303, 1997.[Medline]
  7. Haupt Y., Maya R., Kazaz A., Oren M. MDM2 promotes the rapid degradation of p53. Nature (Lond.), 387: 296-299, 1997.[Medline]
  8. Barak Y., Juven T., Haffner R., Oren M. MDM2 expression is induced by wild type p53 activity. EMBO J., 12: 461-468, 1993.[Medline]
  9. Wu X., Bayle J. H., Olson D., Levine A. J. The p53-mdm-2 autoregulatory feedback loop. Genes Dev., 7: 1126-1132, 1993.[Abstract/Free Full Text]
  10. de Oca Luna R. M., Wagner D. S., Lozano G. Rescue of early embryonic lethality in MDM2-deficient mice by deletion of p53. Nature (Lond.), 378: 203-206, 1995.[Medline]
  11. Jones S. N., Roe A. E., Donehower L. A., Bradley A. Rescue of embryonic lethality in MDM2-dificient mice by absence of p53. Nature (Lond.), 378: 206-208, 1995.[Medline]
  12. Bull E. K., Chakrabarty S., Brodsky I., Haines D. S. MDM2–P2 transcript levels predict the functional activity of the p53 tumor suppressor in primary leukemic cells. Oncogene, 16: 2249-2257, 1998.[Medline]
  13. Marks D. I., Vonderheid E. C., Kurz B. W., Bigler R. D., Sinha K., Morgan D. A., Sukman A., Nowell P. C., Haines D. S. Analysis of p53 and MDM2 expression in 18 patients with Sezary syndrome. Br. J. Haematol., 92: 890-899, 1996.[Medline]
  14. Barak Y., Gottlieb E., Juven-Gershon T., Oren M. Regulation of MDM2 expression by p53: alternative promoters produce transcripts with nonidentical translation potential. Genes Dev., 8: 1739-1749, 1994.[Abstract/Free Full Text]
  15. Landers J. E., Cassel S. L., George D. L. Translational enhancement of MDM2 oncogene expression in human tumor cells containing a stabilized wild-type p53 protein. Cancer Res., 57: 3562-3568, 1997.[Abstract/Free Full Text]
  16. Cahng Y. C., Lee Y. S., Tejima T., Tananka K., Omura S., Heintz N. H., Mitsui J. MDM2 and bax, downstream mediators of the p53 response, are degraded by the uniquitin-proteasome pathway. Cell Growth Differ., 9: 79-84, 1998.[Abstract]
  17. Mercer W. E., Baserga R. Expression of the p53 protein during the cell cycle of human peripheral blood lymphocytes. Exp. Cell Res., 160: 31-46, 1985.[Medline]
  18. Calabretta B., Kaczmarek L., Selleri L., Torelli G., Ming P. M., Ming S. C., Mercer W. E. Growth-dependent expression of human Mr 53,000 tumor antigen messenger RNA in normal and neoplastic cells. Cancer Res., 46: 5738-5742, 1986.[Abstract/Free Full Text]
  19. Sigalas I., Calver A. H., Anderson J. J., Neal D. E., Lunec J. Alternatively spliced MDM2 transcripts with loss of p53 binding domain sequences: transforming ability and frequent detection in human cancer. Nat. Med., 2: 912-917, 1996.[Medline]
  20. Lundgren K., Montes de Oca Luna R., McNeill Y. B., Emerick E. P., Spencer B., Barfield C. R., Lozano G., Rosenberg M. P., Finlay C. A. Targeted expression of MDM2 uncouples S phase from mitosis and inhibits mammary gland development independent of p53. Genes Dev., 11: 714-725, 1997.[Abstract/Free Full Text]
  21. Sun P., Dong P., Dai K., Hannon G. J., Beach D. p53-independent role of MDM2 in TGF-ß1 resistance. Science (Washington DC), 282: 2270-2272, 1998.[Abstract/Free Full Text]
  22. Jones S. N., Hancock A. R., Vogel H., Donehower L. A., Bradley A. Overexpression of MDM2 in mice reveals a p53-independent role for MDM2 in tumorigenesis. Proc. Natl. Acad. Sci. USA, 95: 15608-15612, 1998.[Abstract/Free Full Text]
  23. Cordon-Cardo C., Latres C., Drodnjak M., Olivia M. R., Pollack D., Woodruff J. M., Marechal V., Chen J., Brennan M. F., Levine A. J. Molecular abnormalities of MDM2 and p53 genes in adult soft tissue sarcomas. Cancer Res., 54: 794-799, 1994.[Abstract/Free Full Text]
  24. Stott F. J., Bates S., James M. C., McConnell B. B., Starborg M., Brookes S., Palmero I., Ryan K., Hara E., Vousden K. H., Peters G. The alternative product from the human CDKN2A locus, p14(ARF), participates in a regulatory feedback loop with p53 and MDM2. EMBO J., 17: 5001-5014, 1998.[Medline]
  25. Della Valle V., Duro D., Bernard O., Larsen C-J. The human protein p19arf is not detected in hemopoietic human lines that abundantly express the alternative B transcript of the p16INK4A/MTS gene. Oncogene, 15: 2475-2481, 1997.[Medline]



This article has been cited by other articles:


Home page
 J. Biol. Chem.Home page
J. Feng, R. Tamaskovic, Z. Yang, D. P. Brazil, A. Merlo, D. Hess, and B. A. Hemmings
Stabilization of Mdm2 via Decreased Ubiquitination Is Mediated by Protein Kinase B/Akt-dependent Phosphorylation
J. Biol. Chem., August 20, 2004; 279(34): 35510 - 35517.
[Abstract] [Full Text] [PDF]

Home page
 Clin. Cancer Res.Home page
Z. Zhang, H. Wang, G. Prasad, M. Li, D. Yu, J. A. Bonner, S. Agrawal, and R. Zhang
Radiosensitization by Antisense Anti-MDM2 Mixed-Backbone Oligonucleotide in in Vitro and in Vivo Human Cancer Models
Clin. Cancer Res., February 15, 2004; 10(4): 1263 - 1273.
[Abstract] [Full Text] [PDF]

Home page
 Mol. Cell. Biol.Home page
J. Garriga, S. Bhattacharya, J. Calbo, R. M. Marshall, M. Truongcao, D. S. Haines, and X. Grana
CDK9 Is Constitutively Expressed throughout the Cell Cycle, and Its Steady-State Expression Is Independent of SKP2
Mol. Cell. Biol., August 1, 2003; 23(15): 5165 - 5173.
[Abstract] [Full Text] [PDF]

Home page
 J. Biol. Chem.Home page
Y. Peng, L. Chen, C. Li, W. Lu, S. Agrawal, and J. Chen
Stabilization of the MDM2 Oncoprotein by Mutant p53
J. Biol. Chem., February 23, 2001; 276(9): 6874 - 6878.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Pan, Y.
Right arrow Articles by Haines, D. S.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pan, Y.
Right arrow Articles by Haines, D. S.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Cancer Research Clinical Cancer Research
Cancer Epidemiology Biomarkers & Prevention Molecular Cancer Therapeutics
Molecular Cancer Research Cancer Prevention Research
Cancer Prevention Journals Portal Cancer Reviews Online
Annual Meeting Education Book Meeting Abstracts Online