Alternative titles; symbols
HGNC Approved Gene Symbol: TJP2
SNOMEDCT: 1295517006;
Cytogenetic location: 9q21.11 Genomic coordinates (GRCh38): 9:69,121,264-69,255,208 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 9q21.11 | Cholestasis, progressive familial intrahepatic 4 | 615878 | Autosomal recessive | 3 |
| Hypercholanemia, familial 1 | 607748 | Autosomal recessive | 3 |
The TJP2 gene encodes tight junction protein-2, which belongs to a family of membrane-associated guanylate kinase (MAGUK) homologs involved in the organization of epithelial and endothelial intercellular junctions. TJPs bind to the cytoplasmic C termini of junctional transmembrane proteins, such as claudins (CLDN1; 603718), and link them to the actin cytoskeleton (summary by Itoh et al., 1999).
By exon trapping, Duclos et al. (1994) isolated TJP2, which they designated X104, within the Friedreich ataxia (229300) critical region on chromosome 9q. The deduced 1,116-amino acid protein contains a partially conserved 20-residue motif repeated 4 times. TJP2 shares similarity with several ribonuclear proteins and shares about 38% identity with the human RD protein (154040) over a 122-amino acid region rich in arginine and aspartic acid. Northern blot analysis detected a 5.0-kb transcript expressed at similar levels in all tissues tested. RT-PCR revealed alternative splicing by frame-shift exon skipping.
Beatch et al. (1996) cloned canine Zo2 and compared it to human ZO2. The canine and human proteins share 87% amino acid identity. ZO2 contains 3 N-terminal PDZ domains, an SH3 domain, a MAGUK region, and a proline-rich C terminus. PDZ domains 1 and 2 are separated by a basic region containing 22% arginine residues. The canine sequence has 3 potential in-frame start codons.
Chlenski et al. (2000) identified 2 isoforms of ZO2, ZO2A and ZO2C, that are transcribed from separate promoters. ZO2C lacks an N-terminal 23-amino acid peptide present in ZO2A. Chlenski et al. (2000) also identified an alternatively spliced transcript with in-frame skipping of exons 20 and 21, resulting in a protein that lacks 147 amino acids in the C-terminal region. Northern blot analysis revealed expression of 1 or both of the A and C isoforms in all tissues examined. ZO2A was expressed at high levels in heart and brain and at lower levels in all other tissues examined. ZO2C was highly expressed in kidney, pancreas, heart, and placenta, but not in brain and skeletal muscle, which expressed only ZO2A. Expression of ZO2A was markedly downregulated in several breast adenocarcinomas and breast cancer cell lines and in pancreatic adenocarcinoma of the ductal type.
Using in vitro assays and immunoprecipitation studies, Itoh et al. (1999) showed that the mouse Tjp1 (601009), Tjp2, and Tjp3 (612689) PDZ1 domains interacted with the C-terminal cytoplasmic domains of Cldn1 (603718) through Cldn8 (611231). The mouse Tjp3 PDZ2 domain interacted with Tjp1, but showed no evidence of interaction with Tjp2. Itoh et al. (1999) concluded that Tjp3 may be recruited to the claudin-positive tight junctions through interactions with Tjp1 or claudin family members.
Using several mammalian cDNA constructs and kidney cell lines, Traweger et al. (2003) determined that nuclear Zo2 directly interacts with the DNA-binding protein scaffold attachment factor B (SAFB; 602895). In vivo coimmunoprecipitations and yeast 2-hybrid assays determined that PDZ domain 1 of Zo2 associates with the C-terminal portion of Safb. The 2 proteins also colocalized in nuclei of transfected epithelial cells. Laser confocal microscopy and epifluorescent analysis revealed Zo2 in endothelial cells and in porcine kidney cells, particularly in response to heat shock.
In the mouse inner ear, Walsh et al. (2010) found that Tjp2 expression decreased rapidly between E16.5 and age 1 week to a level in adult mice that was approximately 50% of the level at birth (P0). At E16.5 and P0, immunohistochemical studies showed Tjp2 was localized most prominently in cochlear membranes connecting hair cells and supporting cells, as well as in membranes connecting the cells of the vestibular system. The localization was punctate and most concentrated at membrane boundaries, as expected for junctional staining. Within the hair cell, Tjp2 was localized both at the apical edge, associated with tight junctions, and also along the basolateral side. Tjp2 also showed lesser expression in both the cytoplasm and nucleus, presumably reflecting a role in signal transduction.
Using yeast 2-hybrid, pull-down, and coimmunoprecipitation assays, Lechuga et al. (2010) showed that ZASP (617677) interacted with ZO2. Mutation analysis revealed that the interaction required the PDZ-binding motif in ZASP and the third PDZ domain of ZO2. ZASP overexpression in MDCK cells resulted in increased cyclin D1 (CCND1; 168461) expression, suggesting that ZASP blocks the inhibitory activity of ZO2 on the cyclin D1 promoter.
Chlenski et al. (2000) determined that the TJP2 gene contains 25 exons and spans more than 90 kb.
Duclos et al. (1994) mapped the TJP2 gene telomeric to the Friedreich ataxia critical region on chromosome 9q13-q21. TJP2 lies about 70 kb centromeric to the X123 gene (607710) and is transcribed in the centromere-to-telomere direction.
In connection with the mapping of the gene responsible for familial hypercholanemia, Carlton et al. (2003) by inference mapped the TJP2 gene to 9q12-q13.
Gross (2017) mapped the TJP2 gene to chromosome 9q21.11 based on an alignment of the TJP2 sequence (GenBank AF489824) with the genomic sequence (GRCh38).
Familial Hypercholanemia
In 6 unrelated children of Amish descent (families 1-6) with familial hypercholanemia (FHCA1; 607748), Carlton et al. (2003) identified a homozygous missense mutation in the TJP2 gene (V48A; 607709.0001). The mutation, which was found by a combination of linkage analysis and candidate gene sequencing, segregated with the disorder in 3 families. In vitro studies showed that the V48A mutation decreased the binding of TJP2 to several ligands, including claudins (see, e.g., CLND1, 603718). Carlton et al. (2003) hypothesized that in individuals homozygous for the V48A mutation, bile acids enter bile and then leak through tight junctions in the biliary tract into plasma. This results in increased serum and lower biliary and intestinal bile concentrations. One individual with familial hypercholanemia studied by Carlton et al. (2003) and found to be homozygous for the TJP2 V48A mutation and heterozygous for a BAAT mutation (M76V; 602938.0001) had a nasofrontal encephalocele and facial dysmorphism. 'Polychaetoid,' the postulated functional ortholog of TJP2 in D. melanogaster, is involved in dorsal closure, a process that is probably analogous to neural-tube closure. Hence, TJP2 may also have a role in neurulation.
Autosomal Dominant Deafness 51
In affected members of a large Jewish family with autosomal dominant deafness-51 (DFNA51; 613558), Walsh et al. (2010) identified a tandem inverted duplication of the pericentromeric region of chromosome 9 spanning positions 71,705,804 to 71,974,823 for a size of approximately 269 kb. The duplication included the entire locus for the tight junction protein TJP2, which spans positions 71,788,971 to 71,870,124. The distal breakpoint occurred in intron 2 of the FAM189A2 gene (607710). However, there was no evidence of a mutant FAM189A2 transcript and no correlation of genotype with expression of full-length FAM189A2 in the family, leading the authors to focus their studies on duplication of TJP2. No mutations in the TJP2 gene were found; the sequence of the gene in affected individuals was wildtype. Studies of mouse tissues showed that Tjp2 is developmentally regulated in the inner ear. Studies of DFNA51 patient lymphoblasts showed that endogenous levels of TJP2 were increased approximately 2-fold, consistent with overexpression of the gene resulting from the inverted duplication. This overexpression was associated with decreased amounts of phosphorylated GSK3B (605004), indicating increased GSK3B activity. Increased GSK3B activity makes cells more susceptible to apoptosis. Specific analysis of apoptosis-related genes in patient lymphoblasts showed a shift in expression of BCL2 (151430) family genes, such as BID (601997), BCL2L1 (600039), and TSPO (109610) that would favor apoptosis. Walsh et al. (2010) hypothesized that TJP2 overexpression would increase the susceptibility of inner ear cells to apoptosis, leading to progressive hearing loss.
Hilgert et al. (2008) reported a Guatemalan family with autosomal dominant nonsyndromic hearing loss. Genomewide linkage analysis showed linkage to the DFNA36 (606705) locus on chromosome 9q with a maximum lod score of 4.44. However, no pathogenic mutations were identified in the TMC1 gene (606706). Instead, a putative asp924-to-val (D924V) variant, was identified in the TJP2 gene (607709) on chromosome 9q12-q13. This variant was not identified in 207 control samples, was located in a conserved residue, and was predicted to have decreased stability by bioinformatic analysis. No other TJP2 mutations were found in 26 additional small families segregating deafness. Hilgert et al. (2008) noted that the D924V variant in TJP2 could not be shown conclusively to be causative of deafness in the Guatemalan family, and suggested that this family may indeed have had a mutation outside of the coding region of the TMC1 gene or in another gene in this region.
Progressive Familial Intrahepatic Cholestasis 4
In 12 patients from 8 families with progressive familial intrahepatic cholestasis-4 (PFIC4; 615878), Sambrotta et al. (2014) identified homozygous mutations in the TJP2 gene (see, e.g., 607709.0002-607709.0005). The mutations were identified by a combination of whole-exome sequencing and targeted sequencing of genes known to be associated with cholestasis. The variants were confirmed by Sanger sequencing and filtered against the dbSNP, 1000 Genomes Project, and Exome Sequencing Project databases. All mutations were predicted to abolish protein translation, consistent with a complete loss of function. The patients showed onset of severe progressive liver disease in early childhood, necessitating liver transplant in 9 patients. Liver biopsy tissue available from several patients revealed a lack of TJP2 protein expression. Patient liver tissue showed decreased localization of CLDN1 (603718) at tight junctions, although protein levels were normal; these findings suggested abnormal localization of CLDN1 in the absence of TJP2. Expression and localization of CLDN2 (300520) was normal. Transmission electron microscopy showed that the tight junctions between adjacent hepatocytes and biliary canaliculi in liver tissue were elongated and lacked the densest part of the zona occludens. Sambrotta et al. (2014) noted that homozygous loss of Zo2 in mice is embryonic lethal (Xu et al., 2008), indicating interspecies differences, and concluded that the lack of redundancy in humans must be restricted to the liver.
Zhou et al. (2015) reported 2 patients with neonatal-onset cholestasis who had developed hepatocellular carcinoma. One, found to have hepatocellular carcinoma at age 26 months, was compound heterozygous for mutations in TJP2 (607709.0006; 607709.0007); the other, who developed hepatocellular carcinoma at age 19 months, was homozygous for a frameshift mutation (607709.0008).
Xu et al. (2008) found that homozygous loss of Zo2 in mice was embryonic lethal, resulting in death shortly after implantation due to an arrest in early gastrulation. The findings indicated nonredundancy for Zo2 in the mouse.
In 6 unrelated children (families 1-6) of Old Order Amish descent in Lancaster County, Pennsylvania, with familial hypercholanemia (FHCA1; 607748), Carlton et al. (2003) identified a homozygous c.143T-C transition in the TJP2 gene, predicted to result in a val48-to-ala (V48A) substitution at a conserved residue in the N-terminal PDZ domain. The mutation, which was found by a combination of linkage analysis and candidate gene sequencing, segregated with the disorder in the families. Three unaffected sibs were also homozygous for the mutation, consistent with incomplete penetrance. The mutation was not present in 190 control chromosomes from Caucasian individuals, but was present in 7 (7%) of 104 control chromosomes from Lancaster County Old Order Amish individuals, suggesting a high population frequency. In vitro studies showed that the V48A mutation decreased the binding of TJP2 to several ligands, including claudins (see, e.g., CLND1, 603718). Liver tissue from 1 patient had greater tight junction depth and permeability compared to controls, suggesting poor anchoring of scaffolding proteins. Carlton et al. (2003) hypothesized that in individuals homozygous for the V48A mutation, bile acids enter bile and then leak through tight junctions in the biliary tract into plasma. This results in increased serum and lower biliary and intestinal bile concentrations. In 5 children from 2 further Amish families (families 7 and 8) with a similar bile acid disorder, Carlton et al. (2003) identified homozygosity for the TJP2 V48A mutation and heterozygosity for a BAAT M76V mutation (602938.0001), which is involved in conjugation of bile acids and may have contributed to the phenotype.
In a patient, born of consanguineous parents, with progressive familial intrahepatic cholestasis-4 (PFIC4; 615878), Sambrotta et al. (2014) identified a homozygous 4-bp deletion (c.766_769delGCCT) in exon 5 of the TJP2 gene, resulting in a frameshift and premature termination (Ala256ThrfsTer54).
In 2 sibs, born of consanguineous parents, with progressive familial intrahepatic cholestasis (PFIC4; 615878), Sambrotta et al. (2014) identified a homozygous 1-bp deletion (c.885delC) in exon 5 of the TJP2 gene, resulting in a frameshift and premature termination (Ser296AlafsTer15).
In 2 sibs, born of consanguineous parents, with progressive familial intrahepatic cholestasis (PFIC4; 615878), Sambrotta et al. (2014) identified a homozygous 1-bp deletion (c.1361delC) in exon 9 of the TJP2 gene, resulting in a frameshift and premature termination (Ala454GlyfsTer60).
In 2 sibs, born of consanguineous parents, with progressive familial intrahepatic cholestasis (PFIC4; 615878), Sambrotta et al. (2014) identified a homozygous A-to-G transition in intron 13 of the TJP2 gene (c.1992-2A-G), resulting in a splice site mutation and premature termination (Arg664SerfsTer2).
In a patient with progressive familial intrahepatic cholestasis-4 (PFIC4; 615878), Zhou et al. (2015) identified compound heterozygous mutations in TJP2: a splice site mutation (c.2668-1G-T, NM_004817.3) and a frameshift mutation (607709.0007). The patient had had neonatal onset of intermittent jaundice and presented with liver failure at 26 months of age. Numerous hepatic masses were present and were shown to be moderately differentiated hepatocellular carcinoma. TJP2 expression was not immunohistochemically demonstrable and claudin-1 (603718) expression was markedly decreased.
Hamosh (2016) noted that the c.2668-1G-T variant was not found in the ExAC or Exome Variant Server databases on January 12, 2016.
In a patient with progressive familial intrahepatic cholestasis-4 (PFIC4; 615878) who presented with liver failure at 26 months of age, Zhou et al. (2015) identified a duplication of a T at nucleotide c.2438 of the TJP2 gene (c.2438dupT, NM_004817.3) resulting in an asparagine-to-glutamine substitution at codon 814 with a frameshift downstream (Asn814Glnfs). This mutation occurred in compound heterozygosity with a splice site mutation (607709.0006).
Hamosh (2016) noted that the c.2438dupT variant was not found in the ExAC or Exome Variant Server databases on January 12, 2016.
In a patient with progressive familial intrahepatic cholestasis-4 (PFIC4; 615878), Zhou et al. (2015) identified homozygosity for a 1-bp deletion (c.817delG, NM_004817.3) in the TJP2 gene, resulting in a frameshift (A273fs). The mutation was identified by whole-exome sequencing and confirmed by Sanger sequencing. Each parent was heterozygous for the mutation. The patient was a 6-month-old Caucasian male who was referred for persistent cholestasis following hepatoportoenterostomy for presumed biliary atresia. He was found to have cholestatic hepatitis; follow-up at age 19 months showed a right liver lobe mass with rising serum alpha-fetoprotein (AFP; 104150), prompting liver transplantation. The explanted liver was cirrhotic with multiple cholestatic nodules and a single well-encapsulated 2-cm tumor that diffusely expressed AFP and glypican-3 (300037). A central region of well-differentiated hepatocellular carcinoma was found. TJP2 expression was absent and claudin-1 (603718) expression was markedly decreased in nontumor liver.
Hamosh (2016) noted that the c.817delG variant was not found in the ExAC or Exome Variant Server databases on January 12, 2016.
Beatch, M., Jesaitis, L. A., Gallin, W. J., Goodenough, D. A., Stevenson, B. R. The tight junction protein ZO-2 contains three PDZ (PSD-95/discs-large/ZO-1) domains and an alternatively spliced region. J. Biol. Chem. 271: 25723-25726, 1996. [PubMed: 8824195] [Full Text: https://doi.org/10.1074/jbc.271.42.25723]
Carlton, V. E. H., Harris, B. Z., Puffenberger, E. G., Batta, A. K., Knisely, A. S., Robinson, D. L., Strauss, K. A., Shneider, B. L., Lim, W. A., Salen, G., Morton, D. H., Bull, L. N. Complex inheritance of familial hypercholanemia with associated mutations in TJP2 and BAAT. Nature Genet. 34: 91-96, 2003. [PubMed: 12704386] [Full Text: https://doi.org/10.1038/ng1147]
Chlenski, A., Ketels, K. V., Korovaitseva, G. I., Talamonti, M. S., Oyasu, R., Scarpelli, D. G. Organization and expression of the human zo-2 gene (tjp-2) in normal and neoplastic tissues. Biochim. Biophys. Acta 1493: 319-324, 2000. [PubMed: 11018256] [Full Text: https://doi.org/10.1016/s0167-4781(00)00185-8]
Duclos, F., Rodius, F., Wrogemann, K., Mandel, J.-L., Koenig, M. The Friedreich ataxia region: characterization of two novel genes and reduction of the critical region to 300 kb. Hum. Molec. Genet. 3: 909-914, 1994. [PubMed: 7951235] [Full Text: https://doi.org/10.1093/hmg/3.6.909]
Gross, M. B. Personal Communication. Baltimore, Md. 6/1/2017.
Hamosh, A. Personal Communication. Baltimore, Md. 1/12/2016.
Hilgert, N., Alasti, F., Dieltjens, N., Pawlik, B., Wollnik, B., Uyguner, O., Delmaghani, S., Weil, D., Petit, C., Danis, E., Yang, T., Pandelia, E., Petersen, M. B., Goossens, D., Favero, J. D., Sanati, M. H., Smith, R. J. H., Van Camp, G. Mutation analysis of TMC1 identifies four new mutations and suggests an additional deafness gene at loci DFNA36 and DFNB7/11. Clin. Genet. 74: 223-232, 2008. [PubMed: 18616530] [Full Text: https://doi.org/10.1111/j.1399-0004.2008.01053.x]
Itoh, M., Furuse, M., Morita, K., Kubota, K., Saitou, M., Tsukita, S. Direct binding of three tight junction-associated MAGUKs, ZO-1, ZO-2, and ZO-3, with the COOH termini of claudins. J. Cell Biol. 147: 1351-1363, 1999. [PubMed: 10601346] [Full Text: https://doi.org/10.1083/jcb.147.6.1351]
Lechuga, S., Alarcon, L., Solano, J., Huerta, M., Lopez-Bayghen, E., Gonzalez-Mariscal, L. Identification of ZASP, a novel protein associated to zona occludens-2. Exp. Cell Res. 316: 3124-3139, 2010. [PubMed: 20868680] [Full Text: https://doi.org/10.1016/j.yexcr.2010.09.008]
Sambrotta, M., Strautnieks, S., Papouli, E., Rushton, P., Clark, B. E., Parry, D. A., Logan, C. V., Newbury, L. J., Kamath, B. M., Ling, S., Grammatikopoulos, T., Wagner, B. E., and 11 others. Mutations in TJP2 cause progressive cholestatic liver disease. Nature Genet. 46: 326-328, 2014. [PubMed: 24614073] [Full Text: https://doi.org/10.1038/ng.2918]
Traweger, A., Fuchs, R., Krizbai, I. A., Weiger, T. M., Bauer, H.-C., Bauer, H. The tight junction protein ZO-2 localizes to the nucleus and interacts with the heterogeneous nuclear ribonucleoprotein scaffold attachment factor-B. J. Biol. Chem. 278: 2692-2700, 2003. [PubMed: 12403786] [Full Text: https://doi.org/10.1074/jbc.M206821200]
Walsh, T., Pierce, S. B., Lenz, D. R., Brownstein, Z., Dagan-Rosenfeld, O., Shahin, H., Roeb, W., McCarthy, S., Nord, A. S., Gordon, C. R., Ben-Neriah, Z., Sebat, J., Kanaan, M., Lee, M. K., Frydman, M., King, M.-C., Avraham, K. B. Genomic duplication and overexpression of TJP2/ZO-2 leads to altered expression of apoptosis genes in progressive nonsyndromic hearing loss DFNA51. Am. J. Hum. Genet. 87: 101-109, 2010. [PubMed: 20602916] [Full Text: https://doi.org/10.1016/j.ajhg.2010.05.011]
Xu, J., Kausalya, P. J., Phua, D. C. Y., Ali, S. M., Hossain, Z., Hunziker, W. Early embryonic lethality of mice lacking ZO-2, but not ZO-3, reveals critical and nonredundant roles for individual zonula occludens proteins in mammalian development. Molec. Cell Biol. 28: 1669-1678, 2008. [PubMed: 18172007] [Full Text: https://doi.org/10.1128/MCB.00891-07]
Zhou, S., Hertel, P. M., Finegold, M. J., Wang, L., Kerkar, N., Wang, J., Wong, L.-J. C., Plon, S. E., Sambrotta, M., Foskett, P., Niu, Z., Thompson, R. J., Knisely, A. S. Hepatocellular carcinoma associated with tight-junction protein 2 deficiency. Hepatology 62: 1914-1916, 2015. [PubMed: 25921221] [Full Text: https://doi.org/10.1002/hep.27872]