Disease relevance of Max

• Analysis of the DNA-binding activities of Myc/Max/Mad network complexes during induced differentiation of U-937 monoblasts and F9 teratocarcinoma cells [1].
• Regulation of murine Max (Myn) parallels the regulation of c-Myc in differentiating murine erythroleukemia cells [2].
• An exception is P19 embryonal carcinoma cells, where Mnt is expressed and in a complex with Max, but Myc proteins are not detected [3].
• For this strategy we selected the Heb HLH and Max Zip regions as molecular scaffolds for the randomization process and displayed the two resulting molecular repertoires on lambda phage capsids [4].
• However, cell toxicity was observed only in COLO320 DM and A-431 cells when the HSV-TK gene promoted by the Myc/Max binding sequence was introduced [5].

High impact information on Max

• Mad-Max and mSin3 form ternary complexes in solution that specifically recognize the Mad-Max E box-binding site [6].
• CpG methylation of the recognition site greatly inhibits DNA binding, suggesting that DNA methylation may regulate the c-Myc/Myn complex in vivo [7].
• In 3T3 fibroblasts, Myn mRNA levels are induced several-fold by serum with delayed early kinetics, suggesting regulation by immediate-early gene products [7].
• The three-dimensional structure of the basic/helix-loop-helix/leucine zipper domain of the transcription factor Max complexed with DNA has been determined by X-ray crystallography at 2.9 A resolution [8].
• Essential role for Max in early embryonic growth and development [9].

Biological context of Max

• In addition, Myc/Max heterodimers, but not Max homodimers, bind to the EFII enhancer sequence in vitro [10].
• We suggest that the c-Myc HLH/LZ domain induces apoptosis by specific interaction with cellular factors different to Max [11].
• We have studied the phenotype of dominant-negative mutants of c-Myc and Max in microinjection experiments [11].
• c-Myc and Mad each form heterodimers with Max that bind the same E-box related DNA sequences [12].
• Thus, dMax is a widely expressed, naturally occurring protein, with the capacity to bind most members of the Myc/Max superfamily; dMax has little effect on Inr-mediated repression by c-Myc, but can significantly decrease E-box-mediated events promoting proliferation and cell survival [13].

Anatomical context of Max

• Max mutants with a deleted or mutated basic region inhibited DNA synthesis in serum-stimulated 3T3-L1 mouse fibroblasts [11].
• Using Western blot (immunoblot) and immunoprecipitation analysis, we have identified a variant form of Max protein (16 to 17 kDa), termed dMax, in detergent nuclear extracts of murine B-lymphoma cells, normal B lymphocytes, and NIH 3T3 fibroblasts [14].
• Immunoprecipitation experiments confirmed that Max was also phosphorylated in NIH-3T3 cells, demonstrating that Max phosphorylation may have an important physiological function [15].
• Loss of Max function in the mouse resulted in generalized developmental arrest of both embryonic and extraembryonic tissues at early postimplantation (approximately E5.5-6.5), coincident with loss or dilution of maternal Max stores in the expanding embryo in vivo and in blastocyst outgrowths in vitro [9].
• Max RNA is expressed in quiescent BALB/c 3T3 cells and is modestly increased 3 h after addition of serum to the quiescent cells [16].

Associations of Max with chemical compounds

• In contrast to Myc RNA, Max RNA does not decline immediately upon induction of differentiation of HL60 cells by dimethyl sulfoxide, and only a modest decrease of Max RNA was observed 72 h after induction of differentiation [16].
• The basic helix-loop-helix/leucine zipper region, the casein kinase II phosphorylation sites and the nuclear localization signal sequence are 100% conserved in all vertebrate Max proteins characterized to date [17].
• However, injection of the HSV-TK gene promoted by the Myc/Max binding sequence and aciclovir administration into mice could achieve significant tumor regression only in COLO320 DM and A-431 cells [5].
• A buried salt bridge involving a histidine on the Max LZ and two glutamate residues on the c-Myc LZ is observed at the interface of the heterodimeric LZ [18].

Physical interactions of Max

• Max protein forms specific DNA-binding dimeric complexes with itself and with proteins of the c-myc gene family [19].
• Mnt interacts with Max in vivo and functions as a transcriptional repressor of reporter genes containing promoter-proximal CACGTG sites [3].

Other interactions of Max

• The Myc proteins, as heterodimers with Max protein, have been shown to function as activators of transcription through an E-box DNA-binding element, CACGTG [10].
• c-Myc and Max transregulate the mouse ornithine decarboxylase promoter through interaction with two downstream CACGTG motifs [20].
• Our findings suggest that the precise temporal regulation of Myc/Max/Mad network proteins is critical for determining cellular behavior [21].
• Mga, a dual-specificity transcription factor that interacts with Max and contains a T-domain DNA-binding motif [22].
• In contrast, the p22/Myn-L and p21/Myn-S protein isoforms down-regulate in monophasic fashion [2].

Analytical, diagnostic and therapeutic context of Max

• The past two decades of gene targeting experiments have allowed us to make significant strides towards understanding how the Myc/Max/Mad network influences multiple aspects of cellular behavior during development [23].
• Affinity chromatography confirmed that YY1 associates with c-Myc but not with Max [24].
• By deletion analysis and site-directed mutagenesis, the inhibitory domain was localized to a CKII phosphorylation site in the amino terminus of Max [15].
• Omomyc sequestered Myc in complexes with low DNA binding efficiency, preventing binding to Max and inhibiting Myc transcriptional activator function [25].
• These results suggest that gene therapy using the HSV-TK gene promoted by the Myc/Max binding sequence can be an attractive approach for treatment against tumor cells expressing high levels of c-myc [5].

References