The TRIP4 gene encodes a subunit of the tetrameric ASC-1 transcriptional cointegrator complex. The other subunits include ASCC1 (614215), ASCC2 (614216), and ASCC3 (614217). The complex associates with transcription factors or with nuclear receptors and can bidirectionally affect the link between receptor and transcription machinery, either as corepressor or coactivator. This complex also likely participates in pre-mRNA processing and regulation of splicing (summary by Knierim et al., 2016).

Thyroid hormone receptors (TRs) are hormone-dependent transcription factors that regulate expression of a variety of specific target genes. They must specifically interact with a number of proteins as they progress from their initial translation and nuclear translocation to heterodimerization with retinoid X receptors (RXRs), functional interactions with other transcription factors and the basic transcriptional apparatus, and eventually, degradation. To help elucidate the mechanisms that underlie the transcriptional effects and other potential functions of TRs, Lee et al. (1995) used the yeast interaction trap, a version of the yeast 2-hybrid system, to identify proteins that specifically interact with the ligand-binding domain of rat TR-beta (THRB; 190160). They isolated HeLa cell cDNAs encoding several different TR-interacting proteins (TRIPs), including TRIP4. TRIP4 contains a putative zinc finger motif with an arrangement of cysteines nearly identical to that of the zinc-binding sequence in the adenovirus E1A transactivator.

By screening human cDNA libraries, Kim et al. (1999) cloned full-length TRIP4, which they called ASC1. In addition to the E1A-type zinc finger, the deduced 581-amino acid ASC1 protein contains several potential phosphorylation sites. Northern blot analysis detected a 2.3-kb ASC1 transcript in all human tissues examined. Western blot analysis of fractionated HeLa cells showed that TRIP4 was a predominantly nuclear protein with an apparent molecular mass of 68 kD.

Jung et al. (2002) found that ASC1 purified from HeLa cell nuclear extracts had an apparent molecular mass of about 65 kD by SDS-PAGE. They cloned mouse Asc1 and identified orthologs in several species, including C. elegans. Compared with mouse and human ASC1, C. elegans Asc1 lacks 122 N-terminal amino acids, but it contains the highly conserved zinc finger domain.

Knierim et al. (2016) found ubiquitous expression of the Trip4 gene in mouse embryos. Highest expression was seen in dorsal root ganglia, the paraspinal sympathetic and trigeminal ganglia, and thyroid and submandibular glands, as well as the spinal cord. Expression in the cerebral cortex was comparable to the expression in the spinal cord.

Davignon et al. (2016) found low expression of the Trip4 gene in murine skeletal muscle, particularly axial muscles.

Lee et al. (1995) found that human TRIP4 interacted with rat Thrb only in the presence of thyroid hormone. TRIP4 also showed a ligand-dependent interaction with RXR-alpha (RXRA; 180245), but it did not interact with glucocorticoid receptor (NR3C1; 138040) under any condition. Lee et al. (1995) demonstrated that a chimeric TRIP4 protein was a relatively strong transcriptional activator.

By mutation analysis, Kim et al. (1999) showed that the isolated E1A-type zinc finger domain of ASC1 activated a reporter gene as effectively as the full-length protein. Protein pull-down assays and yeast 2-hybrid analysis showed that the zinc finger domain of ASC1 interacted with the basal transcription factors TBP (600075) and TFIIA (see 600520), the transcription integrators SRC1 (NCOA1; 602691) and CBP (CREBBP; 600140)-p300 (EP300; 602700), and nuclear receptors. Interaction of ASC1 with nuclear receptors was ligand independent in vitro, but inclusion of the nuclear receptor corepressor SMRT (NCOR2; 600848) in the binding reactions resulted in ligand-dependent interaction of ASC1 with nuclear receptors. The relatively strong basal interaction of ASC1 with receptors was further stimulated by ligand in yeast. The zinc finger region of ASC1 formed a ternary complex with CBP, SRC1, and RXRA. ASC1 localized to nuclei of transfected rat fibroblasts in the presence of 9-cis-retinoic acid or when coexpressed with CBP or SRC1. However, ASC1 accumulated in the cytoplasm of serum-starved cells. Kim et al. (1999) concluded that ASC1 may have distinct roles in different coactivator complexes under different cellular conditions.

By transfecting HeLa cells with reporter genes and increasing amounts of ASC1 cDNA, Jung et al. (2002) showed that ASC1 acted as a coactivator for AP1 (see 165160), NF-kappa-B (see 164011), and SRF (see 600589). ASC1 also relieved RXR-mediated repression of AP1 and NF-kappa-B. Size exclusion chromatography revealed that ASC1 eluted in a 650-kD protein complex. Peptide sequencing, followed by database analysis, revealed the presence of 3 other protein in the ASC1 complex: p50 (ASCC1; 614215), p100 (ASCC2; 614216), and p200 (ASCC3; 614217). Cotransfection experiments showed that full-length p100 enhanced ASC1-mediated transactivation of NF-kappa-B and AP1. Domain analysis showed that an N-terminal domain of p200 bound 2 distinct regions of ASC1, including the central zinc finger region.

Gastrin (GAS; 137250) regulates the expression of a variety of genes involved in the control of acid secretion. It also triggers tissue response to damage, infection, and inflammation in cells expressing gastrin receptor (CCKBR; 118445) and, indirectly, in nearby cells via a paracrine mechanism. Almeida-Vega et al. (2009) found that gastrin directly induced upregulation of the antiapoptotic regulator PAI2 (SERPINB2; 173390) in CCKBR-positive cells. CCKBR-positive cells also released IL8 (146930) and prostaglandin E2 into the culture medium in response to gastrin, which resulted in elevated PAI2 expression in cocultured CCKBR-negative cells. IL8 signaling in CCKBR-negative cells upregulated PAI2 via binding of the ASC1 complex to the PAI2 promoter. Prostaglandin E2 independently upregulated PAI2 via RHOA (165390)-dependent signaling that induced binding of MAZ (600999) to the PAI2 promoter. Electrophoretic mobility shift assays and chromatin immunoprecipitation analysis revealed that MAZ and the p50 subunit of the ASC1 complex bound directly to sites in the PAI2 promoter. Mutation of the putative MAZ site in the PAI2 promoter reduced responses to RHOA. Knockdown of the p50 or p65 (TRIP4) subunits of the ASC1 complex via small interfering RNA significantly reduced PAI2 upregulation in response to gastrin.

In immunoprecipitation studies, Knierim et al. (2016) identified CSRP1 (123876) as a binding partner of the ASC1 holocomplex. An interaction with SRF (600589) was not detected.

Gross (2011) mapped the TRIP4 gene to chromosome 15q22.31 based on an alignment of the TRIP4 sequence (GenBank BC012448) and the genomic sequence (GRCh37).

Spinal Muscular Atrophy With Congenital Bone Fractures 1

In 5 patients from 3 unrelated families with spinal muscular atrophy with congenital bone fractures-1 (SMABF1; 616866), Knierim et al. (2016) identified homozygous or compound heterozygous truncating mutations in the TRIP4 gene (604501.0001 and 604501.0002). The mutations in the first 2 families were found by a combination of autozygosity mapping and whole-exome sequencing and confirmed by Sanger sequencing; mutations in the fifth patient from the third family were found by sequencing the TRIP4 gene in 11 unrelated children with a similar disorder. Neither mutation was able to rescue the motor defects in morpholino-knockout zebrafish embryos.

Congenital Muscular Dystrophy, Davignon-Chauveau Type

In 4 patients from a consanguineous French family with Davignon-Chauveau-type congenital muscular dystrophy (MDCDC; 617066), Davignon et al. (2016) identified a homozygous truncating mutation in the TRIP4 gene (W297X; 604501.0003). The mutation, which was found by linkage analysis followed by candidate gene sequencing, segregated with the disorder in the family. Patient cells showed no detectable TRIP4 protein and significantly decreased mRNA, suggesting that the mutation results in nonsense-mediated mRNA decay. Cultured patient-derived muscle cells showed normal proliferation and fusion in early differentiation, but had abnormally thick branching myotubes. Knockdown of the Trip4 gene using siRNA in a murine myoblastic cell line (C2C12) affected late myogenic differentiation and/or myotube growth, manifest as reduced levels of the contractile protein myosin heavy chain, similar to patient cells. Early myogenic differentiation was not affected. The findings indicated that the TRIP4 gene plays a role in late myogenic differentiation and that defects in myotube growth likely contributed to the disorder.

Knierim et al. (2016) found that morpholino knockdown of the trip4 gene in zebrafish embryos resulted in a severe impairment of axonal outgrowth of alpha-motoneurons, as well as impaired formation of the neuromuscular junction and organization of the myotome. Mutant zebrafish showed compromised motor responses.