HGNC Approved Gene Symbol: USP45Cytogenetic location: 6q16.2 Genomic coordinates (GRCh38): 6:99,432,324-99,515,769 (from NCBI)▼ DescriptionUSP45 controls the...
HGNC Approved Gene Symbol: USP45
Cytogenetic location: 6q16.2 Genomic coordinates (GRCh38): 6:99,432,324-99,515,769 (from NCBI)
USP45 controls the cellular DNA damage response by regulating ubiquitylation of the ERCC1 subunit (126380) of the heterodimeric XPF (ERCC4; 133520)-ERCC1 DNA repair endonuclease (Perez-Oliva et al., 2015).
▼ Cloning and Expression
By searching databases for sequences similar to USP family members, followed by PCR analysis, Quesada et al. (2004) cloned human USP45. The predicted protein has an N-terminal zinc finger ubiquitin-binding (ZNF-UBP) domain, followed by a catalytic domain containing the cys box, QQD box, and his box characteristic of USP enzymes. Northern blot analysis detected widespread expression of a 5.0-kb USP45 transcript in human tissues, with highest expression in ovary, spleen, and skeletal muscle.
Perez-Oliva et al. (2015) reported that the 814-amino acid human USP45 protein contains an N-terminal ZNF-UBP domain, followed by a peptidase domain.
Yi et al. (2019) analyzed USP45 mRNA expression in human eye tissues and observed high levels in the optic nerve, sclera, and retina, with relatively low levels in the choroid, lens, and retinal pigment epithelium (RPE). They found a progressive decrease in Usp45 expression during postnatal retinal development in mice, suggesting that USP45 may play a role in early development of the retina. In the human retina, immunostaining showed USP45 localization predominantly in the inner segments of cone photoreceptors and to a lesser extent in the inner segments of rod photoreceptors and the RPE, with weak staining observed in the inner nuclear layer of the peripheral retina. In zebrafish eyes, usp45 was mainly found in the inner segments of photoreceptors, similar to the distribution in the human retina.
Gross (2019) mapped the USP45 gene to chromosome 6q16.2 based on an alignment of the USP45 sequence (GenBank BC150648) with the genomic sequence (GRCh38).
▼ Gene Function
Quesada et al. (2004) showed that recombinant human USP45 could remove ubiquitin from a test protein.
By coimmunoprecipitation and yeast 2-hybrid analyses, Perez-Oliva et al. (2015) found that the N-terminal 61 amino acids of human USP45 interacted with ERCC1. USP45 deubiquitylated ERCC1 both in vitro and in vivo, and association of USP45 with ERCC1 was required for ERCC1 deubiquitylation. USP45 promoted survival of U2OS osteosarcoma cells exposed to DNA-damaging agents and induced DNA damage responses controlled by the ERCC1-XPF endonuclease. USP45 exerted its effects not by stabilizing ERCC1 expression, but by regulating recruitment of ERCC1 to DNA damage sites. USP45 localized to DNA lesions resulting from DNA-damaging agents and controlled repair. Live-cell fluorescence analysis revealed that recruitment of USP45 to damage sites was rapid, transient, and independent of ERCC1-XPF.
In 2 Chinese children with Leber congenital amaurosis (LCA19; 618513), Yi et al. (2019) identified homozygosity for a missense mutation affecting splicing (R312Q; 618439.0001) and a nonsense mutation (K546X; 618439.0002), respectively, in the USP45 gene.
▼ Animal Model
Yi et al. (2019) studied zebrafish larvae treated with an antisense morpholino (MO) oligonucleotide targeting the acceptor splice site between intron 9 and exon 10 of usp45, at a position similar to that of the c.935G-A mutation in human USP45 (618439.0001). By 72 hours postfertilization, 96.25% of MO-treated zebrafish larvae showed a reduction in eye size compared to only 16.25% of controls, and 87.84% of the morphant fish were rescued by injection of wildtype usp45 mRNA. In addition, immunostaining showed significantly fewer green cones in MO-treated zebrafish larvae at 5 days postfertilization compared to controls. The authors concluded that usp45 plays an important role in photoreceptor development. Yi et al. (2019) also observed severely reduced scotopic and photopic electroretinographic responses in homozygous Usp45-knockout mice compared to wildtype mice. Similar to the zebrafish results, immunostaining showed significantly fewer green cones in Usp45 -/- mice at 20 weeks compared to wildtype mice.
▼ ALLELIC VARIANTS ( 2 Selected Examples):
.0001 LEBER CONGENITAL AMAUROSIS 19 (1 patient)
In a 9-year-old Chinese boy (family 1) with Leber congenital amaurosis (LCA19; 618513), Yi et al. (2019) identified homozygosity for a c.935G-A transition (c.935G-A, NM_00108048.1) in the USP45 gene, resulting in an arg312-to-gln (R312Q) substitution, predicted to affect splicing. His unaffected parents were heterozygous for the variant, which was not found in 3,011 in-house probands with other hereditary eye diseases. The authors noted that the mutation was rare, with an overall allele frequency of 0.00008863 in the ExAC database, and stated that no homozygous mutation at this site had previously been reported.
.0002 VARIANT OF UNKNOWN SIGNIFICANCE
This variant is classified as a variant of unknown significance based on a review of the gnomAD database by Hamosh (2019).
In a 3-month-old Chinese girl (family 2) with Leber congenital amaurosis (see 618513), Yi et al. (2019) identified homozygosity for a c.1636A-T transversion (c.1636A-T, NM_00108048.1) in exon 14 of the USP45 gene, resulting in a lys546-to-ter (K546X) substitution. Her unaffected parents were heterozygous for the variant, which was not found in 3,011 in-house probands with other hereditary eye diseases. The authors noted that the c.1636A-T variant was rare, with an overall allele frequency of 0.0005 in the ExAC database; however, Hamosh (2019) found that the K546X mutation was present in 137 of 282,556 alleles and in 2 homozygotes in the gnomAD database (July 24, 2019).