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PRE-mRNA-PROCESSING FACTOR 4; PRPF4

PRE-mRNA-PROCESSING FACTOR 4; PRPF4

Alternative titles; symbolsPRECURSOR mRNA-PROCESSING FACTOR 4, S. CEREVISIAE, HOMOLOG OF; PRP4HPRP4HGNC Approved Gene Symbol: PRPF4Cytogenetic location: 9q32 ...

Alternative titles; symbols

  • PRECURSOR mRNA-PROCESSING FACTOR 4, S. CEREVISIAE, HOMOLOG OF; PRP4
  • HPRP4

HGNC Approved Gene Symbol: PRPF4

Cytogenetic location: 9q32 Genomic coordinates (GRCh38): 9:113,275,657-113,292,904 (from NCBI)

▼ Description
The removal of introns from nuclear pre-mRNAs occurs on complexes called spliceosomes, which are made up of 4 small nuclear ribonucleoprotein (snRNP) particles and an undefined number of transiently associated splicing factors. PRPF4 is 1 of several proteins that associate with U4 and U6 snRNPs (Gonzalez-Santos et al., 2002).

▼ Cloning and Expression
By screening a HeLa cell cDNA library using degenerate oligonucleotides designed from peptide sequences of PRPF4 purified from HeLa cell nuclear extracts, followed by 5-prime RACE, Lauber et al. (1997) isolated a full-length cDNA encoding PRPF4. The deduced 521-amino acid protein has a calculated molecular mass of about 58.5 kD. By Western blot analysis, PRPF4 showed an apparent molecular mass of about 55 kD. PRPF4 contains 7 WD repeats that cover the entire C-terminal portion of the protein. These repeats are predicted to form a 7-fold beta propeller, like those found in the beta subunits of heterotrimeric G proteins (see 139380).

Horowitz et al. (1997) also cloned PRPF4. They determined that PRPF4 encodes a protein of 522 amino acids and that the endogenous protein shows a molecular mass of about 60 kD.

Using yeast Prp4 to search a sequence database, followed by PCR and cDNA library screening, Wang et al. (1997) cloned PRPF4. The deduced protein contains 520 amino acids.

Chen et al. (2014) evaluated the expression pattern of Prpf4 in a mouse tissue panel and observed expression in all tissues, including lung, kidney, brain, spleen, heart, and liver, as well as neural retinal and retinal pigment epithelium cells.

▼ Mapping
By FISH, Heng et al. (1998) mapped the PRPF4 gene to chromosome 9q31-q33.

▼ Gene Function
Lauber et al. (1997) and Wang et al. (1997) confirmed the presence of PRPF4 in U4/U6-U5 tri-snRNPs and found that PRPF4 associated more tightly with U4/U6 snRNP. Wang et al. (1997) determined that recombinant HPRP3 (607301), produced in E. coli, interacted directly with HPRP4 from HeLa cell nuclear extracts.

Gonzalez-Santos et al. (2002) determined that the central region of HPRP3, but not the N or C termini, is required for HPRP4 binding. They hypothesized that HPRP3 may recruit HPRP4 for the U4/U6 snRNP assembly.

▼ Molecular Genetics
In a 3-generation Chinese family with retinitis pigmentosa (RP70; 615922) and an unrelated Chinese sporadic RP patient, Chen et al. (2014) identified heterozygosity for a missense mutation (P315L; 607795.0001) and an 18-bp deletion (607795.0002) in the PRPF4 gene, respectively. The mutations, which segregated with disease in each family, were not found in controls or in SNP databases. Functional analysis demonstrated that the missense mutation upregulates expression of PRPF4 as well as other tri-snRNP components, whereas the deletion downregulates promoter activity of PRPF4.

▼ Animal Model
Chen et al. (2014) overexpressed prpf4 C944U (corresponding to human PRPF4 P315L) in zebrafish and observed systemic deformities at 4 days postfertilization, including malformed brains, short trunks, cardiac edema, and curved body axis. Although ocular size was normal, the structure of photoreceptors and the inner and outer segments was severely disrupted, and immunostaining revealed decreased reactivity of rhodopsin in zebrafish injected with prpf4 C944U. In addition, expression levels of several important retinal transcripts were decreased, including opn1lw (300822), gnat2 (139340), rs1 (300839), snrpg (603542), prph2b (see 179605), gnb3 (139130), and rho (180380). In contrast, mRNA levels of various splicing factors were upregulated in the mutant zebrafish. In morphant zebrafish in which the orthologous prpf4 gene was silenced, coinjection of prpf4 C944U markedly augmented death rates, from 31% to 81%, consistent with a dominant-negative effect of the mutation.

▼ ALLELIC VARIANTS ( 2 Selected Examples):

.0001 RETINITIS PIGMENTOSA 70
PRPF4, PRO315LEU
In affected members of a 3-generation Chinese family with retinitis pigmentosa (RP70; 615922), Chen et al. (2014) identified heterozygosity for a c.944C-T transition in exon 10 of the PRPF4 gene, resulting in a pro315-to-leu (P315L) substitution at a highly conserved residue in the second blade of the 7 repeated blades of PRPF4. The mutation was not found in unaffected family members, in 400 unrelated controls, or in SNP databases. Quantitative PCR analysis of cultured patient fibroblasts showed 2.83-fold upregulation of PRPF4 expression compared to fibroblasts from an unaffected family member. Both the wildtype and mutant alleles were upregulated, indicating a compensatory response, and increased expression levels of other tri-snRNP components were also observed, including PRPF3 (607301), PRPF6 (613979), PRPF8 (607300), PRPF31 (606419), EFTUD2 (603892), and SART1 (605941). In addition, the non-snRNP factor SC35 (SRSF2; 600813) was markedly increased, displaying a diffuse pattern on confocal microscopy rather than the distinctly speckled pattern seen with wildtype. Overexpression of the P315L mutant in zebrafish triggered systemic deformities primarily affecting the retina, with disruption of photoreceptors and inner and outer segments, as well as decreased reactivity of rhodopsin (180380).

.0002 RETINITIS PIGMENTOSA 70
PRPF4, 18-BP DEL, NT-114
In a 53-year-old Chinese man with retinitis pigmentosa (RP70; 615922), Chen et al. (2014) identified heterozygosity for an 18-bp deletion (c.-114_-97del) in the 5-prime UTR of the PRPF4 gene. The mutation was not found in his unaffected son, in 400 unrelated controls, or in SNP databases. Luciferase assay of the deletion in ARPE19 and 293T cells showed a 66% and 75% decrease in promoter activity, respectively, compared to wildtype PRPF4. Expression of PRPF4 was decreased by approximately 93% in patient blood cells compared to controls.

Tags: 9q32