Alternative titles; symbols
HGNC Approved Gene Symbol: MDM4
Cytogenetic location: 1q32.1 Genomic coordinates (GRCh38) : 1:204,516,406-204,558,120 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 1q32.1 | ?Bone marrow failure syndrome 6 | 618849 | Autosomal dominant | 3 |
The MDM4 gene encodes a protein that, along with MDM2 (164785), acts as a negative regulator of transcription factor TP53 (191170) (summary by Toufektchan et al., 2020).
Shvarts et al. (1997) isolated cDNAs encoding MDM4 by screening a human cDNA library from a colonic tumorigenic cell line with a mouse mdmx probe. The human MDM4 gene encodes a 490-amino acid protein containing a RING finger domain and a putative nuclear localization signal. The predicted mass of the protein was 54 kD, while the observed mass was 80 kD, a difference which Shvarts et al. (1997) stated was probably due to phosphorylation or other posttranslational modification. Northern blot analysis revealed a 10-kb mRNA expressed at a high level in thymus and at lower levels in all other tissues tested. A 2.2-kb mRNA was detected in testis. MDM4 protein produced by in vitro translation interacts with p53 (191170) via a binding domain located in the N-terminal region of the MDM4 protein. MDM4 shows significant structural similarity to p53-binding protein MDM2 (164785), an E3 ubiquitin ligase.
Rallapalli et al. (1999) cloned an isoform of Mdm4 containing a 68-bp internal deletion from a mouse fibroblast cell line. The deletion produces a frameshift that results in a 127-amino acid protein consisting only of the p53-binding domain. This short form was detected in all proliferating and transformed rodent and human cell lines tested. When overexpressed, it was more effective than the full-length protein in inhibiting p53-mediated transcriptional activation and induction of apoptosis.
The interaction between MDM2 and p53 is critical for cell viability; loss of Mdm2 causes cell death in vitro and in vivo in a p53-dependent manner. MDM4 has some of the same properties as MDM2, but unlike MDM2, it does not cause nuclear export or degradation of p53. To study MDM4 function in vivo, Parant et al. (2001) deleted the Mdm4 gene in mice. Mdm4-null mice died at 7.5 to 8.5 days postcoitum due to loss of cell proliferation. When Parant et al. (2001) crossed in a p53-null allele, they found that loss of p53 completely rescued the Mdm4 -/- embryonic lethality. Thus, MDM2 and MDM4 are nonoverlapping critical regulators of p53 in vivo. These data defined a new pathway of p53 regulation and raised the possibility that increased MDM4 levels and the resulting inactivation of p53 contribute to the development of human tumors.
Using in vitro ubiquitination assays and small interfering RNA-mediated downregulation of HDMX expression in human cell lines, Linares et al. (2003) determined that HDMX stimulated HDM2 E3 ligase activity and that HDMX was required to keep p53 at low levels under normal growth conditions. HDMX did not function as an E3 on its own, but was active in complex with HDM2. In addition, HDMX stimulated autoubiquitination of HDM2, and HDMX was a substrate for ubiquitination by HDM2.
Pereg et al. (2005) found that treatment of cultured human cells with 3 double-strand break (DSB)-inducing agents led to a marked decrease of endogenously expressed and ectopically expressed HDMX. The decrease reflected proteasome-mediated degradation after polyubiquitination rather than reduced expression. HDMX was phosphorylated on at least 3 sites, ser342, ser367, and ser402, in response to DSBs, and this phosphorylation induced HDM2-mediated ubiquitination of HDMX, followed by its degradation. ATM (607585) was required for HDMX phosphorylation on ser403 in response to DSBs.
Laurie et al. (2006) showed that the tumor surveillance pathway mediated by ARF (see 600160), MDM2 (164785), MDMX, and p53 (191170) is activated after loss of RB1 (614041) during retinogenesis. RB1-deficient retinoblasts undergo p53-mediated apoptosis and exit the cell cycle. Subsequently, amplification of the MDMX gene and increased expression of MDMX protein are strongly selected for during tumor progression as a mechanism to suppress the p53 response in RB1-deficient retinal cells. Laurie et al. (2006) concluded that their data provided evidence that the p53 pathway is inactivated in retinoblastoma and that this cancer does not originate from intrinsically death-resistant cells as previously thought. In addition, Laurie et al. (2006) suggested that their data supported the idea that MDMX is a specific chemotherapeutic target for treating retinoblastoma.
Using overexpression and inhibition studies in human cancer cell lines, Wang et al. (2017) found that miRNA766 (MIR766; 301062) increased p53 protein expression at the posttranscriptional level. MIR766 bound the 3-prime UTR of MDM4 and reduced MDM4 mRNA and protein expression. Wang et al. (2017) concluded that MIR766 induces p53 accumulation and G2/M arrest by directly targeting MDM4.
By fluorescence in situ hybridization, Shvarts et al. (1997) mapped the MDM4 gene to human chromosome 1q32.
Bone Marrow Failure Syndrome 6
In 4 members of a family (NCI-226) with bone marrow failure syndrome-6 (BMFS6; 618849), Toufektchan et al. (2020) identified a heterozygous missense mutation in the RING domain of the MDM4 gene (T454M; 602704.0001). The mutation, which was found by whole-exome sequencing, segregated with the disorder in the family. It was not found in the gnomAD database. Mutations in other candidate genes were excluded, although the proband also carried a heterozygous W203S variant in the TERT gene (187270). The TERT variant was not found in the gnomAD database, but it did not segregate with the disorder in the family; a modifying effect of the TERT variant could not be excluded. In vitro studies showed that the mutant MDM4 protein retained ATP-binding capacity but had altered binding to MDM2. Transfection of the MDM4 mutation into human U2OS cells showed that the mutation caused decreased levels of the mutant protein and defective inhibition of TP53, resulting in abnormal TP53 activation. The carriers of the mutation, who showed considerable phenotypic heterogeneity, were found to carry different additional TP53 polymorphisms known to affect TP53 activity, suggesting that these may have a modifying influence on the disease. These data and studies in mouse models (see ANIMAL MODEL) led Toufektchan et al. (2020) to suggest that mutation in the MDM4 gene results in telomere shortening due to abnormal TP53 activation that disturbs the expression of telomere-related genes.
Associations Pending Confirmation
D'Alessandro et al. (2016) performed whole-exome sequencing in 81 unrelated probands with atrioventricular septal defect (AVSD; see 606215) to identify potential causal variants in a comprehensive set of 112 genes with strong biological relevance to AVSD. A significant enrichment of rare and rare damaging variants was identified in the gene set, compared with controls (odds ratio (OR) 1.52; 95% confidence interval (CI), 1.35-1.71; p = 4.8 x 10(-11)). The enrichment was specific to AVSD probands, compared with a cohort without AVSD with tetralogy of Fallot (OR 2.25; 95% CI, 1.84-2.76; p = 2.2 x 10(-16)). Six genes, including MDM4, were enriched for rare variants in AVSD compared with controls. The findings were confirmed in a replication cohort of 81 AVSD probands. D'Alessandro et al. (2016) concluded that mutations in genes with strong biological relevance to AVSD, including syndrome-associated genes, can contribute to AVSD, even in those with isolated heart disease. Six rare nonsynonymous variants in MDM4 occurred in 7.4% of AVSD cases compared with 1.2% of controls from the Exome Variant Server (EVS) (OR 5.0; p = 3.2x10(-4)). One variant (K324Q) occurred in 5 individuals (minor allele frequency = 0.061), in 1 unaffected autism control, and in 40 EVS individuals (minor allele frequency = 0.0047). Because this single variant occurred with a high frequency in the cohort, genotyping was undertaken in 97 unaffected controls. The K324Q variant was found at a lower frequency in controls (2/97 or 2.1%) compared with AVSD cases (6.1%; p = 0.003). An additional 3 variants were identified in the replication cohort. All probands with MDM4 variants had isolated cardiac disease.
Toufektchan et al. (2020) found that mice homozygous for the T454M mutation in the Mdm4 gene died soon after birth due to respiratory failure. Lung tissue from mutant mice showed a 25% decrease in mean telomere length compared to controls, as well as increased p21 levels, suggesting an increase in Tp53 activity. These findings were also observed in fibroblasts derived from the mutant mice, which showed altered expression of genes involved in telomere biology, such as RTEL1 (608833). Levels of the mutant Mdm4 protein were also decreased, which may have contributed to increased Tp53 activity. Decreasing Tp53 activity rescued the perinatal lethality, also suggesting that the mutant phenotype resulted from abnormal activation of Tp53. Similarly, homozygous T454M mice who were also Tp53 +/- survived the neonatal period, but developed hyperpigmentation of the foot pads and bone marrow hypocellularity, eventually resulting in premature death. Heterozygous T454M mutant mice had no apparent phenotype by age 6 months except for slight hyperpigmentation of the foot pads, However, heterozygous mice were hypersensitive to increases in Tp53 activity, the combination of which resulted in several abnormalities, including heart hypertrophy, thymic hypoplasia, testicular hypoplasia, bone marrow failure, and premature death associated with a 34% decrease in telomere length.
In 4 members of a family (NCI-226) with bone marrow failure syndrome-6 (BMFS6; 618849), Toufektchan et al. (2020) identified a heterozygous C-to-T transition (chr1.204,518,698C-T, ENST00000367182) in the MDM4 gene, resulting in a thr454-to-met (T454M) substitution in the RING domain. The mutation, which was found by whole-exome sequencing, segregated with the disorder in the family. It was not found in the gnomAD database. In vitro studies showed that the mutant MDM4 protein retained ATP-binding capacity but had altered binding to MDM2 (164785). Transfection of the MDM4 mutation into human U2OS cells showed that it resulted in decreased levels of the mutant protein and defective inhibition of TP53, resulting in abnormal TP53 activation.
D'Alessandro, L. C. A., Al Turki, S., Manickaraj, A. K., Manase, D., Mulder, B. J. M., Bergin, L., Rosenberg, H. C., Mondal, T., Gordon, E., Lougheed, J., Smythe, J., Devriendt, K., UK10K Consortium, Bhattacharya, S., Watkins, H., Bentham, J., Bowdin, S., Hurles, M. E., Mital, S. Exome sequencing identifies rare variants in multiple genes in atrioventricular septal defect. Genet. Med. 18: 189-198, 2016. [PubMed: 25996639] [Full Text: https://doi.org/10.1038/gim.2015.60]
Laurie, N. A., Donovan, S. L., Shih, C.-S., Zhang, J., Mills, N., Fuller, C., Teunisse, A., Lam, S., Ramos, Y., Mohan, A., Johnson, D., Wilson, M., Rodriguez-Galindo, C., Quarto, M., Francoz, S., Mendrysa, S. M., Guy, R. K., Marine, J.-C., Jochemson, A. G., Dyer, M. A. Inactivation of the p53 pathway in retinoblastoma. Nature 444: 61-66, 2006. [PubMed: 17080083] [Full Text: https://doi.org/10.1038/nature05194]
Linares, L. K., Hengstermann, A., Ciechanover, A., Muller, S., Scheffner, M. HdmX stimulates Hdm2-mediated ubiquitination and degradation of p53. Proc. Nat. Acad. Sci. 100: 12009-12014, 2003. [PubMed: 14507994] [Full Text: https://doi.org/10.1073/pnas.2030930100]
Parant, J., Chavez-Reyes, A., Little, N. A., Yan, W., Reinke, V., Jochemsen, A. G., Lozano, G. Rescue of embryonic lethality in Mdm4-null mice by loss of Trp53 suggests a nonoverlapping pathway with MDM2 to regulate p53. Nature Genet. 29: 92-95, 2001. [PubMed: 11528400] [Full Text: https://doi.org/10.1038/ng714]
Pereg, Y., Shkedy, D., de Graaf, P., Meulmeester, E., Edelson-Averbukh, M., Salek, M., Biton, S., Teunisse, A. F. A. S., Lehmann, W. D., Jochemsen, A. G., Shiloh, Y. Phosphorylation of Hdmx mediates its Hdm2- and ATM-dependent degradation in response to DNA damage. Proc. Nat. Acad. Sci. 102: 5056-5061, 2005. [PubMed: 15788536] [Full Text: https://doi.org/10.1073/pnas.0408595102]
Rallapalli, R., Strachan, G., Cho, B., Mercer, W. E., Hall, D. J. A novel MDMX transcript expressed in a variety of transformed cell lines encodes a truncated protein with potent p53 repressive activity. J. Biol. Chem. 274: 8299-8308, 1999. [PubMed: 10075736] [Full Text: https://doi.org/10.1074/jbc.274.12.8299]
Shvarts, A., Bazuine, M., Dekker, P., Ramos, Y. F. M., Steegenga, W. T., Merckx, G., van Ham, R. C. A., van der Houven van Oordt, W., van der Eb, A. J., Jochemsen, A. G. Isolation and identification of the human homolog of a new p53-binding protein, Mdmx. Genomics 43: 34-42, 1997. [PubMed: 9226370] [Full Text: https://doi.org/10.1006/geno.1997.4775]
Toufektchan, E., Lejour, V., Durand, R., Giri, N., Draskovic, I., Bardot, B. Laplante, P., Jaber, S., Alter, B. P., Londono-Vallejo, J.-A., Savage, S. A., Toledo, F. Germline mutation of MDM4, a major p53 regulator, in a familial syndrome of defective telomere maintenance. Sci. Adv. 6: eaay3511, 2020. Note: Electronic Article. [PubMed: 32300648] [Full Text: https://doi.org/10.1126/sciadv.aay3511]
Wang, Q., Selth, L. A., Callen, D. F. MiR-766 induces p53 accumulation and G2/M arrest by directly targeting MDM4. Oncotarget 8: 29914-29924, 2017. [PubMed: 28430625] [Full Text: https://doi.org/10.18632/oncotarget.15530]