Disease relevance of MITF

• Clinically, primary human melanoma expression microarrays revealed tight nearest neighbor linkage for MITF and BCL2 [1].
• MITF mutations occur in patients with Waardenburg syndrome type 2, a disorder associated with melanocyte abnormalities [2].
• Therefore, hypopigmentation and hearing loss in WS2 are likely to be the results of an anomaly of melanocyte differentiation caused by MITF mutations [3].
• In situ hybridization experiments carried out in the dominant megacolon (DOM:) mouse, confirmed that SOX10 dysfunction impairs MITF: expression as well as melanocytic development and survival [4].
• Heterozygous mutations of PAX3, MITF, or c-kit genes induce Waardenburg syndrome (WS) 1/3, WS 2 or Piebaldism, respectively [5].
• Our findings suggest that strong amplifications of the melanoma oncogene MITF affects patient survival but does not influence tumor chemosensitivity and chemotherapy response [6].

High impact information on MITF

• We further show that PAX3 proteins associated with WS1 in either the paired domain or the homeodomain fail to recognize and transactivate the MITF promoter [3].
• We have previously shown that MITF transactivates the gene for tyrosinase, a key enzyme for melanogenesis, and is critically involved in melanocyte differentiation [3].
• Epistatic relationship between Waardenburg syndrome genes MITF and PAX3 [3].
• Most cloned cells of MITF transfectants exhibited dendritic morphology and expressed melanogenic markers, but such properties were not observed in cells transfected with closely related TFE3 cDNA [2].
• Our findings indicate that MITF is critically involved in melanocyte differentiation [2].

Chemical compound and disease context of MITF

• Expression levels of MITF and CDK2 are tightly correlated in primary melanoma specimens and predict susceptibility to the CDK2 inhibitor roscovitine [7].
• In the present report, using recombinant adenovirus encoding the wild-type or a dominant negative form of MITF, as well as stable cell lines expressing tetracycline inducible wild-type MITF, we reassessed the role of MITF in melanocyte differentiation and in the regulation of melanin synthesis [8].
• We studied a series of 11 cellular neurothekeomas using paraffin immunoperoxidase staining with microphthalmia transcription factor (Mitf), NKI/C3, and S-100 [9].

Biological context of MITF

• MITF transfectants formed foci of morphologically altered cells, which resemble those induced by oncogenes, but did not exhibit malignant phenotypes [2].
• Functional cooperation of MITF with LEF-1 results in synergistic transactivation of the dopachrome tautomerase (DCT) gene promoter, an early melanoblast marker [10].
• Here we show the interaction between the basic helix-loop-helix and leucine-zipper region of microphthalmia-associated transcription factor (MITF) and LEF-1 [10].
• PAX3 has been shown to regulate MITF gene expression [4].
• This difference is consistent with the different structures of the c-RET and MITF enhancers, and the different mechanisms by which Pax3 binds to these enhancers [11].

Anatomical context of MITF

• Here we show that ectopic expression of MITF converts NIH/3T3 fibroblasts into cells with characteristics of melanocytes [2].
• In addition, MITF and TRPM1 mRNA levels were correlated tightly across a series of human melanoma cell lines [12].
• For this purpose, the effect of co-expression of cDNA encoding MITF on MC1R promoter activity in NIH/3T3 cells was studied [13].
• Microphthalmia-associated transcription factor (MITF) regulates the differentiation and development of melanocytes and retinal pigment epithelium and is also responsible for pigment cell-specific transcription of the melanogenesis enzyme genes [14].
• Co-transfection of an expression vector for MITF-M, the MITF isoform specific for pigment cells, or empty control vector with a full-length PKC-beta promoter-CAT (chloramphenicol acetyltransferase) reporter construct (PKC-beta/CAT) into Cos-7 cells showed >60-fold increase in CAT activity [15].

Associations of MITF with chemical compounds

• Genes in the MITF/TFE pathway may therefore also represent valuable therapeutic targets for the treatment of human cancer [16].
• A lysine to arginine mutation abolished MITF (K201R) degradation by hUBC9 in vivo [17].
• Serine 73, which is located in a region rich in proline, glutamic acid, serine, and threonine (PEST), regulates MITF protein stability, since a serine to alanine mutation prevented hUBC9-mediated MITF (S73A) degradation [17].
• These results suggest that hinokitiol-induced ERK phosphorylation reduces MITF and TYR transcription, and mediates the action of hinokitiol on melanogenesis [18].
• The same serine was found to be phosphorylated in vivo, and expression of dominant-negative GSK3beta selectively suppressed the ability of MITF to transactivate the tyrosinase promoter [19].

Physical interactions of MITF

• Microphthalmia-associated transcription factor interacts with LEF-1, a mediator of Wnt signaling [10].
• Mutagenesis reducing the number of MITF binding sites in the promoter of TRPM1 from three to one eliminated the difference in transcriptional activity between the MITF mutants [20].
• The mutated MITF proteins lose their DNA-binding activity and fail to transactivate the promoter of the tyrosinase gene [21].
• These studies define the VMD2 promoter region sufficient to drive RPE-specific expression in the eye, identify positive regulatory regions in vitro, and suggest that MITF as well as other E-box binding factors may act as positive regulators of VMD2 expression [22].
• Tyrosinase, Tyrp1 and Dct promoters contain a motif termed E-box which is bound by the transcription factor Mitf [23].

Enzymatic interactions of MITF

• Using this antibody, we could demonstrate that MITF was rapidly and persistently phosphorylated upon stimulation of primary osteoclasts with RANKL and that phosphorylation of Ser(307) correlated with expression of the target gene tartrate-resistant acid phosphatase [24].

Regulatory relationships of MITF

• In this report, the possibility was examined that MITF might additionally regulate expression of the SILV and MLANA genes [25].
• This prompted examination of whether MITF also might transcriptionally regulate TRPM1 expression [12].
• These data suggest that protein factors that modulate the activity of MITF in melanoma cells repress TYRP1 and presumably other MITF target genes [26].
• Promoter deletion and mutational analyses indicate that SOX10 can activate MITF expression through binding to a region that is evolutionarily conserved between the mouse and human MITF promoters [27].
• Here we show that Mitf can redirect beta-catenin transcriptional activity away from canonical Wnt signaling-regulated genes toward Mitf-specific target promoters to activate transcription [28].
• Gene expression profiling has been used to identify large numbers of target genes [29].
• High throughput sequencing has also been used to identify many new target genes [30].

Other interactions of MITF

• Here we show that PAX3, a transcription factor with a paired domain and a homeodomain, transactivates the MITF promoter [3].
• This study therefore suggests that the MITF/TFE3 family is a new class of nuclear modulators for LEF-1, which may ensure efficient propagation of Wnt signals in many types of cells [10].
• Interaction among SOX10, PAX3 and MITF, three genes altered in Waardenburg syndrome [4].
• Based on these results we conclude that the RCC-associated t(6;11)(p21;q13) translocation leads to a dramatic transcriptional and translational upregulation of TFEB due to promoter substitution, thereby severely unbalancing the nuclear ratios of the MITF/TFE subfamily members [31].
• The promoter activation caused by MITF is dependent on each CATGTG motif of the distal enhancer element, the M box, and the initiator E box of the tyrosinase gene and the TRP-1 M box [32].

Analytical, diagnostic and therapeutic context of MITF

• The TRPM1 promoter contains multiple MITF consensus binding elements that were seen by chromatin immunoprecipitation to be occupied by endogenous MITF within melanoma cells [12].
• MITF knockdown by small interfering RNA (siRNA) in cell culture revealed a strong correlation between MITF and VMD2 mRNA levels [33].
• Analysis using in vivo electroporation with constructs containing mutation of each E-box indicated that expression in native RPE requires both E-boxes, yet in vitro DNA binding studies suggested that MITF binds well to E-box 1 but only minimally to E-box 2 [33].
• The authors tested 15 AMLs with T311 and D5 by immunohistochemistry and a subset of 3 cases by reverse transcription-polymerase chain reaction for their expression of tyrosinase and Mitf mRNA [34].
• The transcription activation domain of microphthalmia transcription factor, tested as a GAL-MITF fusion protein, remained fully functional in these cells, however, and ectopic microphthalmia transcription factor localized normally to the nucleus and bound to the tyrosinase initiator E-box in gel retardation assays [35].

References