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Mnt-Max to Myc-Max complex switching regulates cell cycle entry.

Walker W, Zhou ZQ, Ota S, Wynshaw-Boris A, Hurlin PJ - J. Cell Biol. (2005)

Bottom Line: Here, we show that c-Myc induction during cell cycle entry leads to a transient decrease in Mnt-Max complexes and a transient switch in the ratio of Mnt-Max to c-Myc-Max on shared target genes.Mnt overexpression suppressed cell cycle entry and cell proliferation, suggesting that the ratio of Mnt-Max to c-Myc-Max is critical for cell cycle entry.These results demonstrate that Mnt-Myc antagonism plays a fundamental role in regulating cell cycle entry and proliferation.

View Article: PubMed Central - PubMed

Affiliation: Shriners Hospitals for Children, Portland, OR 97201, USA.

ABSTRACT
The c-Myc oncoprotein is strongly induced during the G0 to S-phase transition and is an important regulator of cell cycle entry. In contrast to c-Myc, the putative Myc antagonist Mnt is maintained at a constant level during cell cycle entry. Mnt and Myc require interaction with Max for specific DNA binding at E-box sites, but have opposing transcriptional activities. Here, we show that c-Myc induction during cell cycle entry leads to a transient decrease in Mnt-Max complexes and a transient switch in the ratio of Mnt-Max to c-Myc-Max on shared target genes. Mnt overexpression suppressed cell cycle entry and cell proliferation, suggesting that the ratio of Mnt-Max to c-Myc-Max is critical for cell cycle entry. Furthermore, simultaneous Cre-Lox mediated deletion of Mnt and c-Myc in mouse embryo fibroblasts rescued the cell cycle entry and proliferative block caused by c-Myc ablation alone. These results demonstrate that Mnt-Myc antagonism plays a fundamental role in regulating cell cycle entry and proliferation.

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Analysis of cell cycle (S-phase) entry after acute deletion of Mnt and Mnt plus c-Myc. (a) Tritiated thymidine incorporation (counts/minute) were determined at the indicated times after serum stimulation of immortal MEFs made quiescent by confluence arrest and serum deprivation. (b) Quantitative real-time RT-PCR analysis of Cyclin D2, E2F2, ODC, and Cyclin E1 gene expression after serum stimulation. Both tritiated thymidine and RT-PCR experiments were performed in triplicate and SDs are shown.
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fig7: Analysis of cell cycle (S-phase) entry after acute deletion of Mnt and Mnt plus c-Myc. (a) Tritiated thymidine incorporation (counts/minute) were determined at the indicated times after serum stimulation of immortal MEFs made quiescent by confluence arrest and serum deprivation. (b) Quantitative real-time RT-PCR analysis of Cyclin D2, E2F2, ODC, and Cyclin E1 gene expression after serum stimulation. Both tritiated thymidine and RT-PCR experiments were performed in triplicate and SDs are shown.

Mentions: Finally, the relationship between Mnt and c-Myc specifically in the context of cell cycle entry was examined after AdCre-mediated deletion of Mnt, c-Myc, and Mnt plus c-Myc in primary MEF cell lines. Whereas ablation of c-Myc completely blocked the ability of MEFs to enter S-phase, MEFs in which c-Myc and Mnt were simultaneously ablated incorporated tritiated thymidine with kinetics similar to control AdCre-infected MEFs (Fig. 7 a). Consistent with the observed rescue of cell cycle entry kinetics, deletion of Mnt rescued the depressed RNA levels of the Cyclin D2, E2F2, ODC, and Cyclin E caused by c-Myc deletion (Fig. 7 b). Interestingly, Gadd45a, a target of c-Myc repression was up-regulated during cell cycle entry in the absence of c-Myc, but its regulation MEFs deficient for both Mnt and c-Myc was similar to that observed in wild-type cells (Fig. S2, available at http://www.jcb.org/cgi/content/full/jcb.200411013/DC1). However, other putative targets of Myc repression were not similarly affected (Fig. S2).


Mnt-Max to Myc-Max complex switching regulates cell cycle entry.

Walker W, Zhou ZQ, Ota S, Wynshaw-Boris A, Hurlin PJ - J. Cell Biol. (2005)

Analysis of cell cycle (S-phase) entry after acute deletion of Mnt and Mnt plus c-Myc. (a) Tritiated thymidine incorporation (counts/minute) were determined at the indicated times after serum stimulation of immortal MEFs made quiescent by confluence arrest and serum deprivation. (b) Quantitative real-time RT-PCR analysis of Cyclin D2, E2F2, ODC, and Cyclin E1 gene expression after serum stimulation. Both tritiated thymidine and RT-PCR experiments were performed in triplicate and SDs are shown.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171929&req=5

fig7: Analysis of cell cycle (S-phase) entry after acute deletion of Mnt and Mnt plus c-Myc. (a) Tritiated thymidine incorporation (counts/minute) were determined at the indicated times after serum stimulation of immortal MEFs made quiescent by confluence arrest and serum deprivation. (b) Quantitative real-time RT-PCR analysis of Cyclin D2, E2F2, ODC, and Cyclin E1 gene expression after serum stimulation. Both tritiated thymidine and RT-PCR experiments were performed in triplicate and SDs are shown.
Mentions: Finally, the relationship between Mnt and c-Myc specifically in the context of cell cycle entry was examined after AdCre-mediated deletion of Mnt, c-Myc, and Mnt plus c-Myc in primary MEF cell lines. Whereas ablation of c-Myc completely blocked the ability of MEFs to enter S-phase, MEFs in which c-Myc and Mnt were simultaneously ablated incorporated tritiated thymidine with kinetics similar to control AdCre-infected MEFs (Fig. 7 a). Consistent with the observed rescue of cell cycle entry kinetics, deletion of Mnt rescued the depressed RNA levels of the Cyclin D2, E2F2, ODC, and Cyclin E caused by c-Myc deletion (Fig. 7 b). Interestingly, Gadd45a, a target of c-Myc repression was up-regulated during cell cycle entry in the absence of c-Myc, but its regulation MEFs deficient for both Mnt and c-Myc was similar to that observed in wild-type cells (Fig. S2, available at http://www.jcb.org/cgi/content/full/jcb.200411013/DC1). However, other putative targets of Myc repression were not similarly affected (Fig. S2).

Bottom Line: Here, we show that c-Myc induction during cell cycle entry leads to a transient decrease in Mnt-Max complexes and a transient switch in the ratio of Mnt-Max to c-Myc-Max on shared target genes.Mnt overexpression suppressed cell cycle entry and cell proliferation, suggesting that the ratio of Mnt-Max to c-Myc-Max is critical for cell cycle entry.These results demonstrate that Mnt-Myc antagonism plays a fundamental role in regulating cell cycle entry and proliferation.

View Article: PubMed Central - PubMed

Affiliation: Shriners Hospitals for Children, Portland, OR 97201, USA.

ABSTRACT
The c-Myc oncoprotein is strongly induced during the G0 to S-phase transition and is an important regulator of cell cycle entry. In contrast to c-Myc, the putative Myc antagonist Mnt is maintained at a constant level during cell cycle entry. Mnt and Myc require interaction with Max for specific DNA binding at E-box sites, but have opposing transcriptional activities. Here, we show that c-Myc induction during cell cycle entry leads to a transient decrease in Mnt-Max complexes and a transient switch in the ratio of Mnt-Max to c-Myc-Max on shared target genes. Mnt overexpression suppressed cell cycle entry and cell proliferation, suggesting that the ratio of Mnt-Max to c-Myc-Max is critical for cell cycle entry. Furthermore, simultaneous Cre-Lox mediated deletion of Mnt and c-Myc in mouse embryo fibroblasts rescued the cell cycle entry and proliferative block caused by c-Myc ablation alone. These results demonstrate that Mnt-Myc antagonism plays a fundamental role in regulating cell cycle entry and proliferation.

Show MeSH