The gene spans 3.3kb on the plus strand. It is composed of 3exons and duringtranscription itsmRNA is 2343 bp. The encoded protein consists of 161amino acids, is 16.6 KDa and contains a poly-Ala segment from amino acid 39 to 48, ahelix-loop-helix motif from amino acid 65 to 105 and a poly-Pro region from amino acid 118 to 124. This protein is expressed in various tissues.[7]
TheID4 gene is part of the ID gene family. This family is also known as inhibitors of DNA binding protein family and are composed of transcription inhibitory proteins which modulate a number of processes. They aretranscriptional regulators that work by negatively regulating theirbasic helix-loop-helix (bHLH)transcription factors by formingheterodimers. The heterodimer is what inhibits their DNA binding and transcriptional activity.
Transcriptionfactors containing a basic helix-loop-helix (bHLH) motif regulate expression of tissue-specific genes in a number of mammalian and insect systems.DNA-binding activity of the bHLH proteins is dependent on formation of homo- and/or heterodimers.Dominant-negative (antimorph) HLH proteins encoded by Id-related genes, such as ID4, also contain the HLH-dimerization domain but lack theDNA-binding basic domain. Consequently, ID proteins inhibit binding to DNA and transcriptionaltransactivation byheterodimerization with bHLH proteins.[6]
TheID4 gene plays a pivotal role in development and is a key player in many pathways ofembryogenesis andfoetal development. ID4 expression is upregulated in embryogenesis during days 9.5 and 13.5 ofgestation[8] and restricted to specific cells of thecentral andperipheral nervous system.[9] ID4 transcription control has both negative and positive regulatory elements inclusive of novel inhibitory functions.[10]
ID4 is expressed in the central nervous system and is required forG1-S transition and to enhanceproliferation in earlycorticalprogenitors. It is complexly involved in regulating neuralstem cell proliferation and differentiation by inhibiting proliferation of differentiating neurons through enhancement ofRB1-mediated pathways. This is either by direct interaction or through interaction with other molecules of thecell cycle machinery.[13] ID4 also regulates the lateral expansion of the proliferative zone in the developingcortex andhippocampus. This is integral to normal brain size formation. ID4 regulates neural progenitor proliferation and differentiation.[13] Its expression is seen in theneural tube much later than other ID genes.[11]
ID4 was also shown to be involved in the regulation ofcardiacmesoderm function in frog embryos and human embryonic stem cells. Ablation of the ID gene family mouse embryos showed failure of anterior cardiac progenitor specification and the development of heartless embryos. This study also demonstrated that ID4 protein is involved in the regulating cardiac cell fate by a pathway which represses two inhibitors of cardiogenic mesoderm formation (TCF3 andFOXA2) whilst activating inducers (EVX1, GRRP1, andMESP1).[14]
ID4 has been linked to themolecularpathogenicity ofendometriosis. These pathways are still poorly understood. It is thought that ID4 plays a role in the transcription ofHOXA9 andCDKN1A which are known to be associated with endometriosis.
Agenome wide association study revealed over 100 candidate genes associated with endometriosis. Of these, six were shown to have a highly reliable association, of which the ID4 gene was identified. This is thought to be due to an independentsingle nucleotide polymorphism atloci rs7739264 near ID4 onchromosome 6p22.3. ID4 is implicated in the molecular pathogenicity of endometriosis as being differentially expressed between the proliferative, early and mid-secretory phases.[15]
ID4 is not expressed in normalovary andfallopian tubes. It has been shown to be overexpressed in mostprimaryovarian cancers. The ID4 gene is also seen to be overexpressed in mostovarian,endometrial andbreast cancer cell lines.[16] The mechanism behind this is believed to be that ID4 regulates HOXA9 and CDKN1A genes, which are mediators of cell proliferation and differentiation. HOXA genes are known to play a role in the differentiation of fallopian tubes,uterus,cervix andvagina.[17]
The ID4 promoter region has been found to be hypermethylated and its mRNA suppressed inbreast cancer cell lines including that of primary breast cancers. Patients with invasivecarcinomas have shown ID4 expression in their breast cancerspecimens. This has been identified as a significantrisk factor in nodalmetastasis.[22] ID4 is constitutively expressed in normal humanmammary epithelium but found to be suppressed inER positive breast carcinomas and preneoplasticlesions.ER negative carcinomas also show ID4 expression.[23] There is a hypothesis that ID4 acts as a tumour suppressor factory in human breast tissue whereoestrogen is responsible for regulation of ID4 expression in themammary ductal epithelium.[23]
It is unclear whether the ID4 gene plays a role inbladder cancer. ID4 is found on the 6p22.3amplicon which is frequently associated withadvance stage bladder cancer. ID4 has also been shown to be overexpressed in bladder cancer cell lines. This overexpression is equally seen in both normalurothelium which lines theurinary tract inclusive of therenal pelvis,ureters,bladder and parts of theurethra, but also seen in fresh cancer tissues.[24]
ID4 is closely associated withgastric cancer. The ID4promoter region is hypermethylated and infrequently expressed in gastricadenocarcinomas and frequently expressed in gastric cancer cell lines. In contrast, ID4 is highly expressed in normalgastric mucosa. There is an undefined but significant association seen in ID4 promoter hypermethylation (which results in its down regulation) andmicrosatellite instability.[25]
ID4 is not found in normal epitheliums noradenomas ofcolorectal cancer. Hypermethylation of ID4 causes silencing of the gene. This has been identified as a significant independentrisk factor for poorprognosis of colorectal cancer. It is also frequently observed in liver metastases of colorectal cancer specimens.[26]
Rett syndrome is anX linkedneurodevelopment disorder. It is often identified after six to eight months of age in females. In human brain tissue specimens of Rett syndrome patients, the family of ID genes are seen to be significantly increased in expression.[27]
The ID4 gene is also known as DNA-binding protein inhibitor ID-4, Id-4, IDb4, IDB4, Inhibitor of DNA binding 4, Inhibitor of differentiation 4, helix protein 271, Inhibitor of DNA binding 4 HLH Protein, Inhibitor of Differentiation 4, Inhibitor of DNA Binding 4 Dominant Negative Helix-Loop-Helix Protein, Class B Basic Helix-Loop-Helix Protein 27, and BHLHb272.
^"Human PubMed Reference:".National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:".National Center for Biotechnology Information, U.S. National Library of Medicine.
^Pagliuca A, Bartoli PC, Saccone S, Della Valle G, Lania L (Oct 1995). "Molecular cloning of ID4, a novel dominant negative helix-loop-helix human gene on chromosome 6p21.3-p22".Genomics.27 (1):200–3.doi:10.1006/geno.1995.1026.PMID7665172.
^Kobayashi A, Behringer RR (Dec 2003). "Developmental genetics of the female reproductive tract in mammals".Nature Reviews. Genetics.4 (12):969–980.doi:10.1038/nrg1225.PMID14631357.S2CID3345120.
^Bellido M, Aventín A, Lasa A, Estivill C, Carnicer MJ, Pons C, Matías-Guiu X, Bordes R, Baiget M, Sierra J, Nomdedéu JF (September 2003). "Id4 is deregulated by a t(6;14)(p22;q32) chromosomal translocation in a B-cell lineage acute lymphoblastic leukemia".Haematologica.88 (9):994–1001.PMID12969807.
Stewart HJ, Zoidl G, Rossner M, Brennan A, Zoidl C, Nave KA, Mirsky R, Jessen KR (1998). "Helix-loop-helix proteins in Schwann cells: a study of regulation and subcellular localization of Ids, REB, and E12/47 during embryonic and postnatal development".J. Neurosci. Res.50 (5):684–701.doi:10.1002/(SICI)1097-4547(19971201)50:5<684::AID-JNR6>3.0.CO;2-D.PMID9418957.S2CID23855715.
Bellido M, Aventín A, Lasa A, Estivill C, Carnicer MJ, Pons C, Matías-Guiu X, Bordes R, Baiget M, Sierra J, Nomdedéu JF (2004). "Id4 is deregulated by a t(6;14)(p22;q32) chromosomal translocation in a B-cell lineage acute lymphoblastic leukemia".Haematologica.88 (9):994–1001.PMID12969807.
Yu L, Liu C, Vandeusen J, Becknell B, Dai Z, Wu YZ, Raval A, Liu TH, Ding W, Mao C, Liu S, Smith LT, Lee S, Rassenti L, Marcucci G, Byrd J, Caligiuri MA, Plass C (2005). "Global assessment of promoter methylation in a mouse model of cancer identifies ID4 as a putative tumor-suppressor gene in human leukemia".Nat. Genet.37 (3):265–74.doi:10.1038/ng1521.PMID15723065.S2CID515916.
