An Alternative Splice Form of Mdm2 Induces p53-independent Cell Growth and Tumorigenesis

Steinman, Heather Anne; Burstein, Ezra; Lengner, Christopher J.; Gosselin, J.; Pihán, Germán; Duckett, Colin S.; Jones, Stephen N.

doi:10.1074/jbc.m305966200

Cited by 86 publications

(89 citation statements)

References 46 publications

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“…Nutlin-3A and MDM2/MDMX isoforms F Bozzi et al Taken together, these findings predict that the response of WD/DD LPS to Nutlin-3A depends on the amount of the coexpressed MDM2-B isoform. The lower affinity of MDM2-B, which was further confirmed by MD simulations, is keeping with preclinical in vitro and in vivo data 37 and supports the idea that MDM2-B may contribute to the formation of cancer by means of a TP53-independent mechanism. 38 In particular, transduction of MDM2-B into a variety of cell types reveals that MDM2-B promotes TP53-independent cell growth, inhibits apoptosis, and upregulates the RelA subunit of NF k B.…”

Section: Discussionsupporting

confidence: 65%

In vitro and in silico studies of MDM2/MDMX isoforms predict Nutlin-3A sensitivity in well/de-differentiated liposarcomas

Bozzi

Conca

Laurini

et al. 2013

Laboratory Investigation

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The molecular marker of well-differentiated/de-differentiated liposarcomas is MDM2 gene amplification coupled with protein overexpression and wild-type TP53. MDMX is a recently identified MDM2 homolog and its presence in this tumor is unexplored. Our aim was to investigate the role of full-length MDM2 and MDMX proteins and their isoforms in surgical specimens of well-differentiated/de-differentiated liposarcomas in view of Nutlin-3A (a MDM2 inhibitor) treatment. Frozen and matched formalin-fixed, paraffin-embedded material from surgical specimens was examined by means of: (1) fluorescence in situ hybridization to determine MDM2 and MDMX gene copy numbers; (2) RT-PCR and densitometry to analyze alternative splicing forms of mdm2 and mdmx; (3) immunoblotting and immunohistochemistry to assess the corresponding translated proteins; and (4) in vitro and in silico assays to determine their affinity for Nutlin-3A. All these cases showed MDM2 gene amplification with an MDMX disomic pattern. In all cases, the full-length mdm2 transcript was associated with the mdm2-b transcript, with ratios ranging from 0.07 to 5.6, and both were translated into protein; mdmx and mdmx-s were co-transcripted, with ratios ranging from 0.1 to 5.6. MDMX-S was frequently more upregulated than MDMX at both transcriptional and protein level. Each case showed different amounts of mdm2, mdm2-b, mdmx, and mdmx-s transcripts and the corresponding proteins. In vitro assays showed that Nutlin-3A was ineffective against MDM2-B and was unable to disrupt the MDMX/TP53 and MSMX-S/TP53 complexes. Molecular simulations confirmed these in vitro findings by showing that MDM2 has high Nutlin-3A affinity, followed by MDMX-S, MDMX, and MDM2-B. Nutlin-3A is predicted to be a good therapeutic option for well-differentiated/de-differentiated liposarcomas. However, our findings predict heterogeneous responses depending on the relative expression of mdm2, mdm2-b, mdmx, and mdmx-s transcripts and proteins. Well-differentiated/de-differentiated (WD/DD) liposarcomas (LPS) account for 40% of all liposarcomas. With a few exceptions, 1,2 the DD component is defined as a usually abrupt and generally a phenotypic time-dependent transition to a non-lipogenic sarcoma.WD/DD LPS characteristically involve the retroperitoneum and are characterized by a high rate of local recurrences. The inability of even aggressive surgery to obtain negative margins leads to high local failure rates, worsening the long-term prognosis of WD/DD patients and favors the use of multiple treatment modalities albeit with limited benefit. 3,4 The molecular hallmark of WD/DD LPS is MDM2 gene amplification coupled with protein overexpression and wild-type TP53, 5-7 which provides the rationale supporting the therapeutic potential of the MDM2 antagonist Nutlin-3A. MDM2 is an E3 ubiquitin ligase that, in addition to targeting TP53 for proteasomal degradation, blocks TP53

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Section: Discussionsupporting

confidence: 65%

In vitro and in silico studies of MDM2/MDMX isoforms predict Nutlin-3A sensitivity in well/de-differentiated liposarcomas

Bozzi

Conca

Laurini

et al. 2013

Laboratory Investigation

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“…All of these activities are increased by Mdm2's phosphorylation on Ser 166 and are decreased by mutation of this residue (Mayo and Donner, 2001;Ashcroft et al, 2002). Owing to its capacity to abrogate the antiproliferative effects of p53, Mdm2 overexpression is transforming (Ganguli et al, 2000;Moore et al, 2003;Steinman et al, 2004). As many as one-third of soft tissue sarcomas show amplification and/or overexpression of Mdm2, as do a substantial fraction of breast and prostate cancers (Vousden, 2000).…”

Section: Onzin Overexpression Promotes Growth Survival and Transformentioning

confidence: 99%

Onzin, a c-Myc-repressed target, promotes survival and transformation by modulating the Akt–Mdm2–p53 pathway

et al. 2005

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The c-Myc oncoprotein is a general transcription factor whose target genes dictate the c-Myc phenotype. One such target of c-Myc, 'onzin', is normally expressed at high levels in myeloid cells and is dramatically downregulated in response to c-Myc overexpression. We show here that short hairpin interfering RNA-mediated knockdown of endogenous onzin results in a reduced growth rate and a proapoptotic phenotype. In contrast, onzin overexpression in fibroblasts is associated with an increased growth rate, resistance to apoptotic stimuli, loss of the G2/M checkpoint, and tumorigenic conversion. Onzin-overexpressing cells fail to induce p53 in response to apoptotic stimuli and contain higher levels of the active, phosphorylated forms of Akt1 and, more strikingly, of Mdm2. Using yeast two-hybrid and coimmunoprecipitation assays, we show that onzin directly interacts with both proteins. Green fluorescent protein tagging also confirms directly that Akt1 and Mdm2 colocalize with onzin, although the precise subcellular distribution of each protein is dependent on its relative abundance. Collectively, our results identify onzin as a novel regulator of several p53-dependent aspects of the c-Myc phenotype via its dramatic effect on Mdm2. This is reminiscent of the c-Mycp19 ARF -| Mdm2 pathway and might function as a complementary arm to ensure the proper cellular response to oncogenic and/or apoptotic stimuli.

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“…We recently showed, in a panel of pediatric rhabdomyosarcoma tumors, Ͼ90% of the metastatic tumors were positive for MDM2-ALT1 (15). Furthermore, MDM2-ALT1 and MDM2-ALT2 (another MDM2 splice variant frequently observed in tumors) have been shown to accelerate tumorigenesis in in vitro and in vivo studies (15)(16)(17)(18)(19). Indeed, a recent study showed that the expression of splice variant MDM2-ALT1 in colorectal cancer cells considerably increased the tumorigenic properties of these cells by causing the accumulation of mutant p53 (gain-of-function p53 mutants) (19).…”

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confidence: 99%

The Splicing Factor FUBP1 Is Required for the Efficient Splicing of Oncogene MDM2 Pre-mRNA

Jacob

Singh

Mohammad

et al. 2014

Journal of Biological Chemistry

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Background: MDM2 is alternatively spliced into shorter isoforms under DNA damage and in several cancers through unknown mechanisms. Results: FUBP1 inactivation decreases splicing efficiency of an MDM2 minigene and causes exon skipping of endogenous MDM2 under normal conditions. Its overexpression attenuates damage-induced skipping of MDM2 exons. Conclusion: FUBP1 positively regulates efficient MDM2 splicing. Significance: This work uncovers an important mechanism regulating splicing efficiency of the oncogene MDM2.

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An Alternative Splice Form of Mdm2 Induces p53-independent Cell Growth and Tumorigenesis

Cited by 86 publications

References 46 publications

In vitro and in silico studies of MDM2/MDMX isoforms predict Nutlin-3A sensitivity in well/de-differentiated liposarcomas

In vitro and in silico studies of MDM2/MDMX isoforms predict Nutlin-3A sensitivity in well/de-differentiated liposarcomas

Onzin, a c-Myc-repressed target, promotes survival and transformation by modulating the Akt–Mdm2–p53 pathway

The Splicing Factor FUBP1 Is Required for the Efficient Splicing of Oncogene MDM2 Pre-mRNA

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