Identification of a domain within MDMX‐S that is responsible for its high affinity interaction with p53 and high‐level expression in mammalian cells

Abstract

The MDMX gene product is related to the MDM2 oncoprotein, both of which interact with the p53 tumor suppressor. A novel transcript of the MDMX gene has been previously identified that has a short internal deletion of 68 base pairs, producing a shift in the reading frame after codon 114, resulting in the inclusion of 13 novel amino acids (after residue 114) followed by a stop codon at amino acid residue 127. This truncated MDMX protein, termed MDMX-S, represents only the p53 binding domain and binds and inactivates p53 better than full-length MDMX or MDM2. Here we show that when expressed in cells, MDMX-S is targeted more efficiently to the nucleus than MDMX. MDMX-S suppresses p53-mediated transcription from a p53 target promoter better than full-length MDMX. The DNA damage inducibility of these p53 responsive promoters was suppressed better by MDMX-S than by MDMX. Analysis of the MDMX-S protein indicated that the 13 novel amino acids at its carboxy terminus was responsible for high affinity binding to p53 in vitro and for high level expression of the protein in cells. Deletion of this 13 amino acid sequence resulted in a protein that was not able to bind p53 and was not able to be expressed well in cells. Taken together, these data point to an important domain within MDMX-S that enables it to function well in vivo to block p53 activity. Published 2003 Wiley-Liss, Inc.

Regulation of constitutive and alternative splicing by PRMT5 reveals a role for Mdm4 pre-mRNA in sensing defects in the spliceosomal machinery

“…Mdm4 undergoes alternative splicing at exon 7 in Prmt5 F/F ER OHT-treated cells, resulting in the production of a shorter MDM4 isoform that has been previously described as MDM4S (Supplemental Fig. S5A; Rallapalli et al 2003;Lenos and Jochemsen 2011). Mdm4 exon 7 is located within a 1-kb genomic region that is highly conserved in vertebrates (as assessed by PhyloP) (Supplemental Fig.…”

MDMX: from bench to bedside

“…It is detected both in untransformed and transformed cells, and its expression is elevated when cells are stimulated to enter S-phase (Rallapalli et al, 1999). Owing to a higher affinity than full-length MDMX for p53 and to its increased nuclear localization, MDMX-S appears to be a very efficient inhibitor of p53 (Rallapalli et al, 1999;Rallapalli et al, 2003). MDMX-S is also more stable than MDMX, possibly because it can no longer interact with MDM2 and is, therefore, protected from MDM2-mediated degradation.…”

Mitochondrial MDM4 (MDMX): An unpredicted role in the p53-mediated intrinsic apoptotic pathway

“…49 (iii) MDM4 oncogenic function might be related to the presence of MDM4 variants, some of which possessing p53 inhibitory activity higher than fl-MDM4. 70,71 (iv) Finally, the MDM4 proapoptotic function might be impaired by gene mutations able to abrogate it. To our knowledge, studies about the mutational status of the MDM4 gene have not been carried out and thus this hypothesis cannot be excluded.…”