Alternative titles; symbols
HGNC Approved Gene Symbol: FZR1
Cytogenetic location: 19p13.3 Genomic coordinates (GRCh38) : 19:3,506,311-3,538,334 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 19p13.3 | Developmental and epileptic encephalopathy 109 | 620145 | Autosomal dominant | 3 |
The FZR1 gene encodes a coactivator of the E3 ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C), which regulates mitotic and non-mitotic functions through interactions with proteins involved with ubiquitination and proteasomal degradation. In late mitosis, APC/C-FZR1 activation controls mitotic exit and cell cycle progression, thus regulating DNA replication. This complex also has postmitotic roles in neuronal survival and function (summary by Rodriguez et al., 2019).
Activation of the anaphase-promoting complex (APC) is required for anaphase initiation and for exit from mitosis. Fang et al. (1998) showed that APC is activated during mitosis and G1 by 2 regulatory factors, CDC20 (603618) and HCDH1. These proteins directly bind to APC and activate its cyclin ubiquitination activity. CDC20 confers a strict destruction box (D box) dependence on APC, while HCDH1 shows a much more relaxed specificity for the D box. HCDH1 contains WD40 repeats and is more closely related to yeast CDH1/HCT1 and Xenopus and Drosophila fzr, with which it shows 36%, 96%, and 69% sequence identity, respectively. In HeLa cells, the HCDH1 protein levels remain constant during the cell cycle and may target specific substrates lacking the D box in G1, such as polo-like kinase, for ubiquitination.
By Western blot analysis of a synchronized mouse fibroblast cell line, Listovsky et al. (2004) found that the level of Hcdh reached a minimum in late G1 of the cell cycle. Hcdh was phosphorylated from S phase to mitosis, which inhibited its activation of APC/C. Listovsky et al. (2004) found that Hcdh levels were reduced by degradation in G1 and G0. APC/C-specific degradation depended upon 2 RxxL-type D boxes in the Hcdh sequence and was autoregulated by Hcdh binding to APC/C. Hcdh was not a substrate for APC/C-Cdc20. Listovsky et al. (2004) concluded that autoregulation of HCDH would assure that the level of HCDH is reduced during G1 and G0.
Using crosslinking to stabilize transient interactions between APC/C and its substrates in HeLa cells, Kraft et al. (2005) determined that the D boxes of substrate proteins interacted with the WD40 domain of HCDH and that these interactions were essential for substrate ubiquitination. HCDH specifically crosslinked to the CDC27 (116946) subunit of APC/C. Kraft et al. (2005) hypothesized that the propeller-shaped WD40 domain of HCDH functions as the receptor for D-box substrates, which are recruited to APC/C via the interaction between HCDH and CDC27.
Dube et al. (2005) obtained 3-dimensional models of the human and Xenopus APC. They mapped CDH1 and APC2 (ANAPC2; 606946) to the same side of APC, implying that this is where substrates are ubiquitinated. Dube et al. (2005) identified a large flexible domain in the complex that adopts a different orientation upon CDH1 binding, suggesting that CDH1 may activate the complex both by recruiting substrates and by inducing conformational changes.
Rapid activation of the anaphase-promoting complex (APC/C) that contains the coactivator CDH1 (APC/C(CDH1)) requires early mitotic inhibitor-1 (EMI1; 606013). Using human cell models, Cappell et al. (2018) showed that cell-cycle commitment for this step is mediated by an EMI1-APC/C(CDH1) dual-negative feedback switch, in which EMI1 is both a substrate and an inhibitor of APC/CCDH1. The inactivation switch triggers a transition between a state with low EMI1 levels and high APC/C(CDH1) activity during G1 and a state with high EMI1 levels and low APC/C(CDH1) activity during S and G2. Cell-based analysis, in vitro reconstitution, and modeling data showed that the underlying dual-negative feedback is bistable and represents a robust irreversible switch. Cappell et al. (2018) concluded that mammalian cells commit to the cell cycle by increasing CDK2 (116953) activity and EMI1 mRNA expression to trigger a 1-way APC/C(CDH1) inactivation switch that is mediated by EMI1 transitioning from acting as a substrate of APC/C(CDH1) to being an inhibitor of APC/C(CDH1).
Sequence analysis of a 3.5-Mb contig in human 19p13.3 by the Joint Genome Institute, at the Lawrence Livermore National Laboratory, resulted in the determination of the genomic sequence of the HCDH gene and its tentative mapping to 19p13.3 (GenBank AC005787).
Fang et al. (1998) used the symbol CDH1 for this gene, but that symbol had already been used for the gene encoding cadherin-1 (192090).
In a 4-year-old boy, born of unrelated Spanish parents, with developmental and epileptic encephalopathy-109 (DEE109; 620145), Rodriguez et al. (2019) identified a de novo heterozygous missense mutation in the FZR1 gene (D187G; 603619.0001). In vitro functional studies in HEK293 cells and in cultured mouse cortical cells showed that the mutant protein failed to arrest the cell cycle and caused abnormalities in cell cycle progression, consistent with impaired activation of APC/C and a loss-of-function effect. The patient was part of a cohort of 390 individuals with neurodevelopmental disorders who were screened for mutations in the FZR1 gene through whole-exome sequencing.
In 3 unrelated patients with DEE109, Manivannan et al. (2022) identified de novo heterozygous missense mutations affecting the WD40 domain of the FZR1 gene. One mutation (D187N; 603619.0002) occurred at the same residue as the mutation reported by Rodriguez et al. (2019), whereas the other 2 mutations yielded the same substitution even though the nucleotide changes were different (N333K; 603619.0003 and 603619.0004). The mutations, which were found by exome or panel-based sequencing, were not present in the gnomAD database. Expression of the mutations in HEK293 cells showed that they caused a reduction in FZR1 protein levels by about 40% compared to controls. None of the mutations was able to rescue the abnormal neurodevelopmental phenotype in fzr mutant Drosophila, indicating that they cause a partial loss-of-function effect and are likely hypomorphic alleles.
In Drosophila, Manivannan et al. (2022) found expression of the orthologous fzr gene in larval brains and eye imaginal discs, consistent with a developmental role in these tissues. Loss-of-function mutations in the fzr gene resulted in a rough eye phenotype and defects in ERG responses. Mutant flies showed an aberrant pattern of photoreceptors in the retina, ERG defects indicating abnormalities in synaptic transmission, defects in neuronal patterning in the CNS, and abnormal migration of glial cells. These findings suggested that fzr is involved in the development and function of the fly visual system and likely plays a role in overall neurodevelopment. Homozygosity for a null allele was embryonic lethal.
In a 4-year-old boy, born of unrelated Spanish parents, with developmental and epileptic encephalopathy-109 (DEE109; 620145), Rodriguez et al. (2019) identified a de novo heterozygous c.560A-G transition (c.560A-G, NM_001136198.1) in the FZR1 gene, resulting in an asp187-to-gly (D187G) substitution at a conserved residue in the WD40 domain. The patient was part of a cohort of 390 individuals with neurodevelopmental disorders who were screened for mutations in the FZR1 gene through whole-exome sequencing. Western blot analysis of patient leukocytes and HEK293 cells transfected with the mutation showed that it caused decreased levels of the FZR1 protein compared to controls, suggesting instability of the mutant protein. The mutant protein was confined to the nucleus, whereas wildtype FZR1 localized to the nucleus and also spread to the cytosol. In vitro functional studies in HEK293 cells and in cultured mouse cortical cells showed that the mutant protein failed to arrest the cell cycle and caused abnormalities in cell cycle progression, consistent with impaired activation of APC/C and a loss-of-function effect. The patient was noted to have intrauterine growth retardation and microcephaly, which the authors postulated was due to replicative stress and apoptotic death of neural precursor cells.
In a 17-year-old male (patient 1), born of unrelated Turkish parents, with developmental and epileptic encephalopathy-109 (DEE109; 620145), Manivannan et al. (2022) identified a de novo heterozygous c.559G-A transition (c.559G-A, NM_001136198.1) in the FZR1 gene, resulting in an asp187-to-asn (D187N) substitution at a highly conserved residue in the WD40 domain. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not present in the gnomAD database. Expression of the mutation in HEK293 cells showed that it caused a reduction in FZR1 protein levels by about 40% compared to controls. The D187N mutation was unable to rescue the abnormal neurodevelopmental phenotype in fzr mutant Drosophila, indicating that it causes a partial loss-of-function effect.
In a 15-year-old girl (patient 2), born of unrelated Moroccan parents, with developmental and epileptic encephalopathy-109 (DEE109; 620145), Manivannan et al. (2022) identified a de novo heterozygous c.999C-G transversion (c.999C-G, NM_001136198.1) in the FZR1 gene, resulting in an asn333-to-lys (N333K) substitution at a highly conserved residue in the WD40 domain. The mutation, which was found by targeted sequencing of a panel and confirmed by Sanger sequencing, was not present in the gnomAD database. Expression of the mutation in HEK293 cells showed that it caused a reduction in FZR1 protein levels by about 40% compared to controls. The N333K mutation was unable to rescue the abnormal neurodevelopmental phenotype in fzr mutant Drosophila, indicating that it causes a partial loss-of-function effect.
In a 3-year-old girl (patient 3), born of consanguineous Afghan parents, with developmental and epileptic encephalopathy-109 (DEE109; 620145), Manivannan et al. (2022) identified a de novo heterozygous c.999C-A transversion (c.999C-A, NM_001136198.1) in the FZR1 gene, resulting in an asn333-to-lys (N333K) substitution at highly conserved residue in the WD40 domain. The mutation, which was found by exome sequencing, was not present in the gnomAD database. Expression of the mutation in HEK293 cells showed that it caused a reduction in FZR1 protein levels by about 40% compared to controls. The N333K mutation was unable to rescue the abnormal neurodevelopmental phenotype in fzr mutant Drosophila, indicating that it causes a partial loss-of-function effect. The patient also carried 2 homozygous variants of uncertain significance in the PTPN21 (603271) and TPD52L2 (603747) genes, which may have contributed to the phenotype.
Cappell, S. D., Mark, K. G., Garbett, D., Pack, L. R., Rape, M., Meyer, T. EMI1 switches from being a substrate to an inhibitor of APC/C(CDH1) to start the cell cycle. Nature 558: 313-317, 2018. [PubMed: 29875408] [Full Text: https://doi.org/10.1038/s41586-018-0199-7]
Dube, P., Herzog, F., Gieffers, C., Sander, B., Riedel, D., Muller, S. A., Engel, A., Peters, J.-M., Stark, H. Localization of the coactivator Cdh1 and the cullin subunit Apc2 in a cryo-electron microscopy model of vertebrate APC/C. Molec. Cell 20: 867-879, 2005. [PubMed: 16364912] [Full Text: https://doi.org/10.1016/j.molcel.2005.11.008]
Fang, G., Yu, H., Kirschner, M. W. Direct binding of CDC20 protein family members activates the anaphase-promoting complex in mitosis and G1. Molec. Cell 2: 163-171, 1998. [PubMed: 9734353] [Full Text: https://doi.org/10.1016/s1097-2765(00)80126-4]
Kraft, C., Vodermaier, H. C., Maurer-Stroh, S., Eisenhaber, F., Peters, J.-M. The WD40 propeller domain of Cdh1 functions as a destruction box receptor for APC/C substrates. Molec. Cell 18: 543-553, 2005. [PubMed: 15916961] [Full Text: https://doi.org/10.1016/j.molcel.2005.04.023]
Listovsky, T., Oren, Y. S., Yudkovsky, Y., Mahbubani, H. M., Weiss, A. M., Lebendiker, M., Brandeis, M. Mammalian Cdh1/Fzr mediates its own degradation. EMBO J. 23: 1619-1626, 2004. [PubMed: 15029244] [Full Text: https://doi.org/10.1038/sj.emboj.7600149]
Manivannan, S. N., Roovers, J., Smal, N., Myers, C. T., Turkdogan, D., Roelens, F., Kanca, O., Chung, H.-L., Scholz, T., Hermann, K., Bierhals, T., Caglayan, H. S., Stamberger, H., MAE Working Group of EuroEPINOMICS RES Consortium, Mefford, H., de Jonghe, P., Yamamoto, S., Weckhuysen, S., Bellen, H. J. De novo FZR1 loss-of-function variants cause developmental and epileptic encephalopathies. Brain 145: 1684-1697, 2022. [PubMed: 34788397] [Full Text: https://doi.org/10.1093/brain/awab409]
Rodriguez, C., Sanchez-Moran, I., Alvarez, S., Tirado, P., Fernandez-Mayoralas, D. M., Calleja-Perez, B., Almeida, A., Fernandez-Jaen, A. A novel human Cdh1 mutation impairs anaphase promoting complex/cyclosome activity resulting in microcephaly, psychomotor retardation, and epilepsy. J. Neurochem. 151: 103-115, 2019. [PubMed: 31318984] [Full Text: https://doi.org/10.1111/jnc.14828]