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Stress-induced alternative splice forms of MDM2 and MDMX modulate the p53-pathway in distinct ways.

Jacob AG, Singh RK, Comiskey DF, Rouhier MF, Mohammad F, Bebee TW, Chandler DS - PLoS ONE (2014)

Bottom Line: We show here that MDM2-ALT1 is capable of binding full-length MDMX as well as full-length MDM2.Moreover, MDM2-ALT1 expression causes cell cycle arrest in the G1 phase in a p53 and p21 dependent manner, which is consistent with the increased levels of p21.In summary, our study shows that the stress-inducible alternative splice forms MDM2-ALT1 and MDMX-ALT2 are important modifiers of the p53 pathway and present a potential mechanism to tailor the p53-mediated cellular stress response.

View Article: PubMed Central - PubMed

Affiliation: From the Center for Childhood Cancer at the Research Institute at Nationwide Children's Hospital, Columbus, Ohio, United States of America; The Department of Pediatrics, and Molecular, Cellular and Developmental Biology (MCDB) program, The Ohio State University, Columbus, Ohio, United States of America; Center for RNA Biology, Wexner Medical Center, The Ohio State University, Columbus, Ohio, United States of America.

ABSTRACT
MDM2 and MDMX are the chief negative regulators of the tumor-suppressor protein p53 and are essential for maintaining homeostasis within the cell. In response to genotoxic stress and also in several cancer types, MDM2 and MDMX are alternatively spliced. The splice variants MDM2-ALT1 and MDMX-ALT2 lack the p53-binding domain and are incapable of negatively regulating p53. However, they retain the RING domain that facilitates dimerization of the full-length MDM proteins. Concordantly, MDM2-ALT1 has been shown to lead to the stabilization of p53 through its interaction with and inactivation of full-length MDM2. The impact of MDM2-ALT1 expression on the p53 pathway and the nature of its interaction with MDMX remain unclear. Also, the role of the architecturally similar MDMX-ALT2 and its influence of the MDM2-MDMX-p53 axis are yet to be elucidated. We show here that MDM2-ALT1 is capable of binding full-length MDMX as well as full-length MDM2. Additionally, we demonstrate that MDMX-ALT2 is able to dimerize with both full-length MDMX and MDM2 and that the expression of MDM2-ALT1 and MDMX-ALT2 leads to the upregulation of p53 protein, and also of its downstream target p21. Moreover, MDM2-ALT1 expression causes cell cycle arrest in the G1 phase in a p53 and p21 dependent manner, which is consistent with the increased levels of p21. Finally we present evidence that MDM2-ALT1 and MDMX-ALT2 expression can activate subtly distinct subsets of p53-transcriptional targets implying that these splice variants can modulate the p53 tumor suppressor pathway in unique ways. In summary, our study shows that the stress-inducible alternative splice forms MDM2-ALT1 and MDMX-ALT2 are important modifiers of the p53 pathway and present a potential mechanism to tailor the p53-mediated cellular stress response.

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Proposed model: MDM2-ALT1 and MDMX-ALT2 antagonize their full-length counterparts and lead to p53 stabilization.A. Under normal conditions, MDM2 and MDMX function to maintain low levels of p53 (via ubiquitination and subsequent degradation) and curb its transcriptional activity by binding p53. This helps maintain homeostasis and normal cellular functions including cell cycle progression. B. Under genotoxic stress, alternative splice forms MDM2-ALT1 and MDMX-ALT2 interact with the full-length MDM proteins and interfere in their p53-regulatory functions. This leads to the stabilization and upregulation of p53 levels and also the activation of p53 transcriptional targets leading to changes in cell cycle progression.
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pone-0104444-g005: Proposed model: MDM2-ALT1 and MDMX-ALT2 antagonize their full-length counterparts and lead to p53 stabilization.A. Under normal conditions, MDM2 and MDMX function to maintain low levels of p53 (via ubiquitination and subsequent degradation) and curb its transcriptional activity by binding p53. This helps maintain homeostasis and normal cellular functions including cell cycle progression. B. Under genotoxic stress, alternative splice forms MDM2-ALT1 and MDMX-ALT2 interact with the full-length MDM proteins and interfere in their p53-regulatory functions. This leads to the stabilization and upregulation of p53 levels and also the activation of p53 transcriptional targets leading to changes in cell cycle progression.

Mentions: Overall, we present our findings in the following model: under normal conditions when the alternative splice forms such as MDM2-ALT1 and MDMX-ALT2 are absent, their full-length MDM2 and MDMX functional normally to inhibit p53 activity (Fig 5A). However, under DNA damaging conditions and in cancers, the splice variants like MDM2-ALT1 and MDMX-ALT2, or other splice variants as discussed above, interact with and cause altered activity of endogenous MDM2 and MDMX leading to the stabilization of p53 and also act to fine-tune p53 transcriptional activity (Fig 5B).


Stress-induced alternative splice forms of MDM2 and MDMX modulate the p53-pathway in distinct ways.

Jacob AG, Singh RK, Comiskey DF, Rouhier MF, Mohammad F, Bebee TW, Chandler DS - PLoS ONE (2014)

Proposed model: MDM2-ALT1 and MDMX-ALT2 antagonize their full-length counterparts and lead to p53 stabilization.A. Under normal conditions, MDM2 and MDMX function to maintain low levels of p53 (via ubiquitination and subsequent degradation) and curb its transcriptional activity by binding p53. This helps maintain homeostasis and normal cellular functions including cell cycle progression. B. Under genotoxic stress, alternative splice forms MDM2-ALT1 and MDMX-ALT2 interact with the full-length MDM proteins and interfere in their p53-regulatory functions. This leads to the stabilization and upregulation of p53 levels and also the activation of p53 transcriptional targets leading to changes in cell cycle progression.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4126728&req=5

pone-0104444-g005: Proposed model: MDM2-ALT1 and MDMX-ALT2 antagonize their full-length counterparts and lead to p53 stabilization.A. Under normal conditions, MDM2 and MDMX function to maintain low levels of p53 (via ubiquitination and subsequent degradation) and curb its transcriptional activity by binding p53. This helps maintain homeostasis and normal cellular functions including cell cycle progression. B. Under genotoxic stress, alternative splice forms MDM2-ALT1 and MDMX-ALT2 interact with the full-length MDM proteins and interfere in their p53-regulatory functions. This leads to the stabilization and upregulation of p53 levels and also the activation of p53 transcriptional targets leading to changes in cell cycle progression.
Mentions: Overall, we present our findings in the following model: under normal conditions when the alternative splice forms such as MDM2-ALT1 and MDMX-ALT2 are absent, their full-length MDM2 and MDMX functional normally to inhibit p53 activity (Fig 5A). However, under DNA damaging conditions and in cancers, the splice variants like MDM2-ALT1 and MDMX-ALT2, or other splice variants as discussed above, interact with and cause altered activity of endogenous MDM2 and MDMX leading to the stabilization of p53 and also act to fine-tune p53 transcriptional activity (Fig 5B).

Bottom Line: We show here that MDM2-ALT1 is capable of binding full-length MDMX as well as full-length MDM2.Moreover, MDM2-ALT1 expression causes cell cycle arrest in the G1 phase in a p53 and p21 dependent manner, which is consistent with the increased levels of p21.In summary, our study shows that the stress-inducible alternative splice forms MDM2-ALT1 and MDMX-ALT2 are important modifiers of the p53 pathway and present a potential mechanism to tailor the p53-mediated cellular stress response.

View Article: PubMed Central - PubMed

Affiliation: From the Center for Childhood Cancer at the Research Institute at Nationwide Children's Hospital, Columbus, Ohio, United States of America; The Department of Pediatrics, and Molecular, Cellular and Developmental Biology (MCDB) program, The Ohio State University, Columbus, Ohio, United States of America; Center for RNA Biology, Wexner Medical Center, The Ohio State University, Columbus, Ohio, United States of America.

ABSTRACT
MDM2 and MDMX are the chief negative regulators of the tumor-suppressor protein p53 and are essential for maintaining homeostasis within the cell. In response to genotoxic stress and also in several cancer types, MDM2 and MDMX are alternatively spliced. The splice variants MDM2-ALT1 and MDMX-ALT2 lack the p53-binding domain and are incapable of negatively regulating p53. However, they retain the RING domain that facilitates dimerization of the full-length MDM proteins. Concordantly, MDM2-ALT1 has been shown to lead to the stabilization of p53 through its interaction with and inactivation of full-length MDM2. The impact of MDM2-ALT1 expression on the p53 pathway and the nature of its interaction with MDMX remain unclear. Also, the role of the architecturally similar MDMX-ALT2 and its influence of the MDM2-MDMX-p53 axis are yet to be elucidated. We show here that MDM2-ALT1 is capable of binding full-length MDMX as well as full-length MDM2. Additionally, we demonstrate that MDMX-ALT2 is able to dimerize with both full-length MDMX and MDM2 and that the expression of MDM2-ALT1 and MDMX-ALT2 leads to the upregulation of p53 protein, and also of its downstream target p21. Moreover, MDM2-ALT1 expression causes cell cycle arrest in the G1 phase in a p53 and p21 dependent manner, which is consistent with the increased levels of p21. Finally we present evidence that MDM2-ALT1 and MDMX-ALT2 expression can activate subtly distinct subsets of p53-transcriptional targets implying that these splice variants can modulate the p53 tumor suppressor pathway in unique ways. In summary, our study shows that the stress-inducible alternative splice forms MDM2-ALT1 and MDMX-ALT2 are important modifiers of the p53 pathway and present a potential mechanism to tailor the p53-mediated cellular stress response.

Show MeSH
Related in: MedlinePlus