Alternative titles; symbols
HGNC Approved Gene Symbol: MAX
Cytogenetic location: 14q23.3 Genomic coordinates (GRCh38): 14:65,006,101-65,102,695 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 14q23.3 | {Pheochromocytoma, susceptibility to} | 171300 | Autosomal dominant | 3 |
| Polydactyly-macrocephaly syndrome | 620712 | Autosomal dominant | 3 |
The MAX protein is the most conserved dimerization component of the MYC (190080)-MAX-MXD1 (600021) network of basic helix-loop-helix leucine zipper (bHLHZ) transcription factors that regulate cell proliferation, differentiation, and apoptosis. While heterodimerization of MAX with MYC activates and mediates its transcription and transforming activity, heterodimerization of MAX with MXD1 family members antagonize MYC-dependent cell transformation by transcriptional repression of the same E-box target DNA sequences. The conservation of the MAX sequence is particularly high in the bHLHZ domain, which is involved in protein-protein interactions and DNA binding (Nair and Burley, 2003; Comino-Mendez et al., 2011).
Wagner et al. (1992) demonstrated that 2 species of RNA hybridized specifically to a MAX cDNA probe in all human and murine cell lines tested. The steady-state level of MAX RNA, unlike that of MYC, was not significantly modulated with respect to proliferation or differentiation. Unlike MYC RNA, MAX RNA was relatively stable with a half-life of more than 3 hours, and therefore it did not exhibit the characteristic short half-life of RNAs encoded by most immediate early genes. The predicted tertiary structure of MAX closely resembles that of MYC, and it was on the basis of the basic/helix-loop-helix/leucine-zipper (bHLHZ) homology that Prendergast et al. (1991) cloned the cDNA encoding MAX.
Comino-Mendez et al. (2011) stated that the 160-amino acid MAX protein contains an N-terminal bHLHZ domain and 6 casein kinase II phosphorylation sites.
The complete structure of the MAX gene was reported by Blackwood and Eisenman (1991).
Comino-Mendez et al. (2011) noted that the MAX gene contains 5 exons.
By fluorescence in situ chromosomal hybridization, Wagner et al. (1992) demonstrated that the MAX gene is located on chromosome 14q23. This region of chromosome 14 is involved in deletions in B-cell chronic lymphocytic leukemia and malignant lymphomas and in the 12;14 translocation in uterine leiomyomas. Gilladoga et al. (1992) similarly mapped the MAX gene to chromosome 14q22-q24 by isotopic in situ hybridization and to mouse chromosome 12 in region D.
Zervos et al. (1995) described MXI2 (600289), a protein that interacts with the MAX protein.
Grandori et al. (1996) identified DDX18 (606355) as a direct in vivo target of Myc and Max and hypothesized that Myc may exert its effects on cell behavior through proteins that affect RNA structure and metabolism.
By microarray analysis, Suzuki et al. (2016) showed identified Max as a suppressor of germ cell-related genes, as deletion of Max led to elevated expression of meiosis-related genes in mouse embryonic stem cells (ESCs). Immunocytochemical analysis revealed meiosis-like cytologic changes in Max-null ESCs. Apoptosis was a prominent phenotype of Max-null ESCs and was, at least in part, due to induction of meiosis-like changes, as treatment with vitamin C significantly accelerated apoptosis and was accompanied by elevated expression of Stra8 (609987). These observations implied that a substantial portion of meiotic-like Max-null ESCs were eliminated at early stages before proceeding to more advanced stages of meiosis. Further analysis revealed that meiosis-like changes in Max-null ESCs occurred without passing through the primordial germ cell state, as mutant ESCs directly acquired features reminiscent of meiosis I phase. Inhibitor analysis suggested that meiosis-related changes in mutant ESCs depended on retinoid, as retinoic acid (RA) was essential for induction of Stra8 expression and deletion of Max sensitized ESCs to the RA-mediated change. Mechanistically, Max was a component of an atypical PRC1 (603484) complex (PRC1.6) that directly bound meiosis-related genes and repressed their expression in ESCs. Max depletion impaired PRC1.6 function and liberated those genes from Max-dependent repression. In agreement with the in vitro results, immunohistochemical analysis revealed that meiosis in mice was coupled with downregulation of Max expression in vivo. Max knockdown also induced meiosis-like cytologic changes in mouse induced pluripotent stem cells (iPSCs), but not in mouse embryonic fibroblasts and NIH3T3 cells, indicating that meiosis-related changes due to Max deficiency were specific to germ and pluripotent cells.
Nair and Burley (2003) determined the x-ray structures of the bHLHZ domains of MYC-MAX and MAD (600021)-MAX heterodimers bound to their common DNA target, the enhancer box (E box) hexanucleotide (5-prime-CACGTG-3-prime), at 1.9- and 2.0-angstrom resolution, respectively. E-box recognition by these 2 structurally similar transcription factor pairs determines whether a cell will divide and proliferate (MYC-MAX) or differentiate and become quiescent (MAD-MAX). Deregulation of MYC has been implicated in the development of many human cancers, including Burkitt lymphoma, neuroblastomas, and small cell lung cancers. Both quasisymmetric heterodimers resemble the symmetric MAX homodimer, albeit with marked structural differences in the coiled-coil leucine zipper regions that explain preferential homo- and heteromeric dimerization of these 3 evolutionarily related DNA-binding proteins. The MYC-MAX heterodimer, but not its MAD-MAX counterpart, dimerizes to form a bivalent heterotetramer, explaining how MYC can upregulate expression of genes with promoters bearing widely separated E boxes.
Pheochromocytoma
Using exome sequencing in 3 unrelated families with bilateral pheochromocytoma (171300), Comino-Mendez et al. (2011) identified 3 different heterozygous germline mutations in the MAX gene (154950.0001-154950.0003) that segregated with the disease. A follow-up study of 59 patients with pheochromocytoma identified 5 additional mutations (see, e.g., 154950.0004-154950.0005). Studies of tumor tissue showed a lack of full-length MAX protein and loss of heterozygosity (LOH) of the MAX allele, which resulted from paternal uniparental disomy (UPD) and loss of the maternal allele. This LOH constituted the somatic second hit of the Knudson hypothesis. The paternal origin of the mutated allele detected in 6 families suggested preferential paternal transmission of the disease (p = 0.031). In addition, 2 children who inherited the mutation from their mother and 2 obligate carriers from another family did not develop tumors, further supporting this theory. Eight of 12 cases had bilateral tumors, and 3 of 8 probands had metastases at diagnosis. Overall, the findings indicated that MAX acts as a classic tumor suppressor gene. Normal lymphocytes from patients showed absence of methylation of the MAX promoter and biallelic expression of MAX, which ruled out an imprinting-mediated effect on MAX expression. Comino-Mendez et al. (2011) pointed to the study of Hopewell and Ziff (1995), who showed loss of Max repression ability in rat pheochromocytoma cells, suggesting that MAX mutations can lead to deregulation of oncogenic MYC.
Polydactyly-Macrocephaly Syndrome
In 3 unrelated children with polydactyly-macrocephaly syndrome (PDMCS; 620712), Harris et al. (2024) identified heterozygosity for the same de novo missense mutation in the MAX gene (R60Q; 154950.0006). The variant was not found in the dbSNP (build 153) or gnomAD databases, but had been identified 56 times as a somatic mutation in tumor tissue in the COSMIC database. Functional analysis demonstrated that the R60Q mutant forms an activating DNA complex with c-Myc (MYC; 190080) more readily than wildtype MAX, likely increasing transcriptional activity.
The designation MAX came from MYC associated factor X (Eisenman, 1994). The murine homolog of MAX is referred to as Myn (Prendergast et al., 1991).
Hopewell and Ziff (1995) showed that a functional Max protein is not expressed in the rat adrenal pheochromocytoma cell line PC12 due to a mutant form of Max lacking the C terminus. The mutant protein was incapable of repressing transcription from an E-box element. Reintroduction of Max into PC12 cells resulted in repression of E-box-dependent transcription and a reduction in growth rate. The ability of these cells to divide, differentiate, and apoptose in the absence of Max demonstrated for the first time that these processes can occur via Max- and possibly Myc-independent mechanisms.
Shen-Li et al. (2000) found that Max -/- mice underwent embryonic lethality, whereas Max +/- were indistinguishable from wildtype with respect to weight, size, activity, fecundity, and life span. Analysis of harvested embryos showed that Max deficiency was associated with generalized developmental arrest soon after implantation, and developmentally arrested embryos were reduced in size and exhibited widespread cytologic degeneration with minimal apoptosis. Max was expressed during early cleavage stages of development in wildtype mice, and lethality of Max -/- embryos likely took place when developing embryos experienced their first burst in growth on embryonic days 5 and 6.
In a 46-year-old woman with bilateral malignant pheochromocytoma (171300), Comino-Mendez et al. (2011) identified a heterozygous 1A-G transition in exon 1 of the MAX gene, resulting in a met1-to-val (M1V) substitution in the initiation codon. Heterozygosity for the mutation was also found in her 29-year-old brother, who had a unilateral nonmalignant pheochromocytoma, as well as in 2 of her unaffected children. The mutation was not found in 750 control chromosomes. Studies of tumor tissue showed a lack of full-length MAX protein and loss of heterozygosity (LOH) of the MAX allele, which resulted from paternal UPD and loss of the maternal allele. The findings indicated that MAX acts as a classic tumor suppressor gene.
In 4 affected members of a large family with autosomal dominant inheritance of bilateral nonmalignant pheochromocytoma (171300) with onset between 28 and 35 years of age, Comino-Mendez et al. (2011) identified a heterozygous 223C-T transition in exon 4 of the MAX gene, resulting in an arg75-to-ter (R75X) substitution. One unaffected family member also carried the mutation, which was not found in 750 control chromosomes. Studies of tumor tissue showed a lack of full-length MAX protein and LOH of the MAX allele, which resulted from paternal UPD and loss of the maternal allele.
In a 32-year-old man with bilateral malignant pheochromocytoma (171300), Comino-Mendez et al. (2011) identified a heterozygous G-to-A transition in intron 4 of the MAX gene (295+1G-A), resulting in a splice site mutation and skipping of exon 4. Family history revealed a deceased brother and niece with unilateral pheochromocytoma. The mutation was not found in 750 control chromosomes. Studies of the tumor tissue showed a lack of full-length MAX protein and LOH of the MAX allele, which resulted from paternal UPD and loss of the maternal allele.
In a young man with bilateral nonmalignant pheochromocytoma (171300), Comino-Mendez et al. (2011) identified a heterozygous 97C-T transition in exon 3 of the MAX gene, resulting in an arg33-to-ter (R33X) substitution. Tumor tissue showed LOH of maternal chromosome 14q.
In a 47-year-old woman with bilateral nonmalignant pheochromocytoma (171300), Comino-Mendez et al. (2011) identified a heterozygous 1-bp deletion (185delA) in exon 4 of the MAX gene, resulting in a frameshift and premature termination. Tumor tissue showed LOH of maternal chromosome 14q.
In 3 unrelated children with polydactyly-macrocephaly syndrome (PDMCS; 620712), Harris et al. (2024) identified heterozygosity for the same de novo c.179G-A transition (c.179G-A, NM_002382.5) in exon 4 of the MAX gene, resulting in an arg60-to-gln (R60Q) substitution at a highly conserved residue within the bHLHZ domain. The variant was not present in the dbSNP (build 153) or gnomAD databases, but had been identified 56 times as a somatic mutation in tumor tissue in the COSMIC database. Analysis of transfected HEK293 cells revealed increased transcription and protein levels of CCND2 (123833) with the mutant compared to wildtype MAX. Further analysis demonstrated that the bHLHZ domain of the R60Q mutant disfavored the formation of the repressive homodimeric E-box complex, and partitioned as a heterodimer and specific activating DNA complex with c-Myc (MYC; 190080) more readily than wildtype MAX, likely increasing transcriptional activity. RNA-seq analysis showed broad transcriptional dysregulation in the presence of the R60Q mutant compared to wildtype MAX.
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Comino-Mendez, I., Gracia-Aznarez, F. J., Schiavi, F., Landa, I., Leandro-Garcia, L. J., Leton, R., Honrado, E., Ramos-Medina, R., Caronia, D., Pita, G., Gomez-Grana, A., de Cubas, A. A., and 17 others. Exome sequencing identifies MAX mutations as a cause of hereditary pheochromocytoma. Nature Genet. 43: 663-667, 2011. [PubMed: 21685915] [Full Text: https://doi.org/10.1038/ng.861]
Eisenman, R. N. Personal Communication. Seattle, Wash. 7/27/1994.
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Harris, E. L., Roy, V., Montagne, M., Rose, A. M. S., Livesey, H., Reijnders, M. R. F., Hobson, E., Sansbury, F. H., Willemsen, M. H., Pfundt, R., Warren, D., Long, V., Carr, I. M., Brunner, H. G., Sheridan, E. G., Firth, H. V., Lavigne, P., Poulter, J. A. A recurrent de novo MAX p.Arg60Gln variant causes a syndromic overgrowth disorder through differential expression of c-Myc target genes. Am. J. Hum. Genet. 111: 119-132, 2024. [PubMed: 38141607] [Full Text: https://doi.org/10.1016/j.ajhg.2023.11.010]
Hopewell, R., Ziff, E. B. The nerve growth factor-responsive PC12 cell line does not express the Myc dimerization partner Max. Molec. Cell Biol. 15: 3470-3478, 1995. [PubMed: 7791753] [Full Text: https://doi.org/10.1128/MCB.15.7.3470]
Nair, S. K., Burley, S. K. X-ray structures of Myc-Max and Mad-Max recognizing DNA: molecular bases of regulation by proto-oncogenic transcription factors. Cell 112: 193-205, 2003. [PubMed: 12553908] [Full Text: https://doi.org/10.1016/s0092-8674(02)01284-9]
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Shen-Li, H., O'Hagan, R. C., Hou, H., Horner, J. W., Lee, H. W., DePinho, R. A. Essential role for Max in early embryonic growth and development. Genes Dev. 14: 17-22, 2000. [PubMed: 10640271]
Suzuki, A., Hirasaki, M., Hishida, T., Wu, J., Okamura, D., Ueda, A., Nishimoto, M., Nakachi, Y., Mizuno, Y., Okazaki, Y., Matsui, Y., Izpisua Belmonte, J. C., Okuda, A. Loss of MAX results in meiotic entry in mouse embryonic and germline stem cells. Nature Commun. 7: 11056, 2016. [PubMed: 27025988] [Full Text: https://doi.org/10.1038/ncomms11056]
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Zervos, A. S., Faccio, L., Gatto, J. P., Kyriakis, J. M., Brent, R. Mxi2, a mitogen-activated protein kinase that recognizes and phosphorylates Max protein. Proc. Nat. Acad. Sci. 92: 10531-10534, 1995. [PubMed: 7479834] [Full Text: https://doi.org/10.1073/pnas.92.23.10531]