Alternative titles; symbols
HGNC Approved Gene Symbol: ACAT1
SNOMEDCT: 124258007, 237953006;
Cytogenetic location: 11q22.3 Genomic coordinates (GRCh38): 11:108,116,705-108,147,603 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 11q22.3 | Alpha-methylacetoacetic aciduria | 203750 | Autosomal recessive | 3 |
The ACAT1 gene encodes mitochondrial acetyl-CoA acetyltransferase, a short-chain-length-specific thiolase (EC 2.3.1.9). Cytosolic acetoacetyl-CoA thiolase is encoded by the ACAT2 gene (100678).
Fukao et al. (1990) cloned and sequenced cDNA encoding the precursor of hepatic mitochondrial acetoacetyl-CoA thiolase. The 427-amino acid precursor had a molecular mass of 45.2 kD. The sequence included a 33-residue leader peptide and a 394-amino acid subunit of the mature enzyme, which had a molecular mass of 41.4 kD. By Northern blotting, they analyzed the T2 gene expression in fibroblasts from 4 patients with 3-ketothiolase deficiency. In all 4 cell lines, the T2 mRNA had the same 1.7-kb transcript as that of the control; however, content was reduced in 2 cell lines and normal in the other 2. Human T2 is a homotetramer of 41-kD subunits.
Yang et al. (2016) reported a mechanism by which the antitumor response of mouse CD8+ T cells can be potentiated by modulating cholesterol metabolism. Inhibiting cholesterol esterification in T cells by genetic ablation or pharmacologic inhibition of ACAT1, a key cholesterol esterification enzyme, led to potentiated effector function and enhanced proliferation of CD8+ but not CD4+ T cells. This was due to the increase in the plasma membrane cholesterol level of CD8+ T cells, which caused enhanced T-cell receptor clustering and signaling as well as more efficient formation of the immunologic synapse. ACAT1-deficient CD8+ T cells were better than wildtype CD8+ T cells at controlling melanoma growth and metastasis in mice. Yang et al. (2016) used the ACAT inhibitor avasimibe, which had been tested in clinical trials for treating atherosclerosis and showed a good human safety profile, to treat melanoma in mice and observed a good antitumor effect. A combined therapy of avasimibe plus an anti-PD1 (600244) antibody showed better efficacy than monotherapies in controlling tumor progression. Yang et al. (2016) concluded that ACAT1, an established target for atherosclerosis, is therefore also a potential target for cancer immunotherapy.
Kano et al. (1991) determined that the ACAT gene spans approximately 27 kb and contains 12 exons.
Using a plasmid clone of an EcoRI genomic fragment of the ACAT1 gene, containing exons 9 to 12, Masuno et al. (1992) assigned the ACAT1 locus to 11q22.3-q23.1 by in situ hybridization.
Matsuda et al. (1996) determined the chromosomal locations of the Atm (607585) and Acat1 genes in mouse, rat, and Syrian hamster by direct R-banding fluorescence in situ hybridization. The 2 genes colocalized to mouse 9C-D, the proximal end of rat 8q24.1, and 12qa4-qa5 of Syrian hamster. The regions in the mouse and rat are homologous to human chromosome 11q. In the study of interspecific backcross mice, no recombinants were found among Atm, Npat (601448), and Acat1.
Cryoelectron Microscopy
Qian et al. (2020) presented the cryoelectron microscopy structure of human ACAT1 as a dimer of dimers. Each protomer consists of 9 transmembrane segments, which enclose a cytosolic tunnel and a transmembrane tunnel that converge at the predicted catalytic site. Evidence from structure-guided mutational analyses suggested that acyl-CoA enters the active site through the cytosolic tunnel, whereas cholesterol may enter from the side through the transmembrane tunnel. Qian et al. (2020) concluded that this structural and biochemical characterization helped to rationalize the preference of ACAT1 for unsaturated acyl chains, and provided insight into the catalytic mechanism of enzymes within the membrane-bound O-acyltransferase (MBOAT) family.
Long et al. (2020) reported a cryoelectron microscopy structure of human ACAT1 in complex with its inhibitor nevanimibe. The ACAT1 holoenzyme is a tetramer that consists of 2 homodimers. Each monomer contains 9 transmembrane helices, 6 of which (TM4-TM9) form a cavity that accommodates nevanimibe and an endogenous acyl-coenzyme A. This cavity also contains a histidine that had been identified as essential for catalytic activity. Long et al. (2020) concluded that their structural data and biochemical analyses provided a physical model to explain the process of cholesterol esterification, as well as details of the interaction between nevanimibe and ACAT1.
In a German boy with 3-ketothiolase deficiency (203750), born of nonconsanguineous parents, Fukao et al. (1991) found compound heterozygosity for 2 mutations in the ACAT1 gene: an A347T mutation (607809.0001) inherited from the mother, and a mutation inherited from the father that abolished expression of the gene. This was apparently the first definition of a mutant ACAT allele.
In a patient (JB) from the Dutch family and 2 patients (JM and IM) from the Chilean family in which 3-ketothiolase deficiency (203750) was first described by Daum et al. (1973), Fukao et al. (1993) identified homozygosity for a splice site and a missense mutation (607809.0006 and 607809.0007, respectively) in the ACAT1 gene.
In a pregnant woman with alpha-methylacetoacetic aciduria (203750), Sewell et al. (1998) identified 2 mutations in exon 11 of the ACAT1 gene: a 3-bp deletion 1033delGAA (607908.0010), which caused deletion of glu345, and a 1-bp insertion (1083insA) (607809.0011), which caused a frameshift and premature termination. Her child inherited only the trinucleotide deletion. Both of her husband's alleles were normal.
In Japanese patients with T2 deficiency, Fukao et al. (1998) found compound heterozygosity for mutations in the ACAT1 gene (see 607809.0012-607809.0014 and 607809.0016).
Fukao et al. (2002) identified and characterized 6 different mutations in the ACAT1 gene responsible for T2 deficiency (see, e.g., Q145E, 607809.0015). In vitro functional expression studies showed that the mutations resulted in various effects, including direct modification of the active site, destruction of the hydrophobic core, removal of a salt bridge with resultant destabilization, destabilization of the homodimer, and reduction of solubility of the molecule.
Fukao et al. (2003) performed in vivo transient expression analysis on 9 mutant T2 cDNAs harboring 1-base substitutions at the initiator methionine codon. They found that all the mutants produced wildtype T2 polypeptide to varying degrees, from 7.4% to 66% as compared with wildtype. They proposed that all 1-base substitutions at the initiator methionine codon in the T2 gene retain some residual T2 activity.
Sakurai et al. (2007) identified 7 novel and 2 previously reported mutations in 6 T2-deficient patients.
In a German boy with 3-ketothiolase deficiency (203750) born of nonconsanguineous parents, Fukao et al. (1991) found compound heterozygosity for 2 mutations in the ACAT1 gene: a G-to-A substitution, resulting in an ala347-to-thr substitution (A347T), inherited from the mother, and a mutation inherited from the father that abolished expression of the gene. Transfection analysis showed that the A347T substitution resulted in instability of the protein. The patient showed normal development until his first ketoacidotic attack at the age of 6 months, following which severe retardation developed. The diagnosis of 3-ketothiolase deficiency was made by urinary organic acid analysis during the attack.
Fukao et al. (1992) studied a Caucasian family reported by Schutgens et al. (1982). The family was unusual in that the father and a son had 3-ketothiolase deficiency (203750). Three mutant alleles of the ACAT1 gene were found. The father was a compound heterozygote: one allele had a 547G-A mutation, resulting in a gly150-to-arg (G150R) substitution, and the other allele had a GT-to-TT transition at the 5-prime splice site of intron 8, causing skipping of exon 8 in the cDNA (607809.0003). The son was also a compound heterozygote: one allele, inherited from his mother, had an AG-to-CG transition at the 3-prime splice site of intron 10, causing skipping of exon 11 of the cDNA (607809.0004), and the other allele derived from the father had the G150R substitution. Another son was an obligatory carrier of the mutant allele causing exon 8 skipping.
For discussion of the splice site mutation in the ACAT1 gene (GT-to-TT transition at the 5-prime splice site of intron 8) that was found in compound heterozygous state in a father and son with 3-ketothiolase deficiency (203750) by Fukao et al. (1992), see 607809.0002.
For discussion of the splice site mutation in the ACAT1 gene (AG-to-CG transition at the 3-prime splice site of intron 10) that was found in compound heterozygous state in a father and son with 3-ketothiolase deficiency (203750) by Fukao et al. (1992), see 607809.0002.
In a patient with 3-ketothiolase deficiency (203750) born in Canada of nonconsanguineous Vietnamese parents, Fukao et al. (1992) found by cDNA analysis with polymerase chain reaction (PCR) that the normal exon 11 sequence was missing and that the parents were carriers of this defect. When PCR-amplified genomic fragments around exon 11 were sequenced, an AG-to-AC mutation was found at the last nucleotide of intron 10, i.e., in the 3-prime splice site. The mutation was presumed to be responsible for exon 11 skipping.
In a patient from the Dutch family in which 3-ketothiolase deficiency (203750) was first described by Daum et al. (1973), Fukao et al. (1993) demonstrated homozygosity for a 4-bp insertion (GCAG), a derived mutation. The primary mutation was an AG/gt to AG/gc transition at the 5-prime splice-junction site in intron 11. An alternative splice site 4 bp downstream was used, which caused a frameshift and replaced 39 C-terminal residues by 70 nonfunctional residues. Fukao et al. (1993) provided a 20-year follow-up on the proband in this family and on the 2 affected sibs in the Chilean family (see 607809.0007) reported by Daum et al. (1973). All had developed normally, had had no recurrence of acute metabolic decompensation since 1973 despite persistent abnormal organic aciduria (2-methyl-3-hydroxybutyrate, 2-methylacetoacetate), and were gainfully employed adults. They completed high school and 1 had attended university.
In the Chilean family in which Daum et al. (1973) first described 3-ketothiolase deficiency (203750), Fukao et al. (1993) demonstrated homozygosity for a mutation in the translation initiation codon of the ACAT1 gene, an ATG-to-AAG transversion (2T-A), resulting in a met1-to-lys (M1K) substitution. By expression analysis, they showed that the mutation severely impaired T2 mRNA translation.
Fukao et al. (1994) reported a Caucasian girl, born to nonconsanguineous parents, in whom the diagnosis of 3-ketothiolase deficiency (203750) was made when she was 3 years old and after multiple ketoacidotic attacks. Her growth and development were normal, and there was no mental retardation. She was found to be a compound heterozygote; the maternal allele had a 1136G-to-T transversion, resulting in a gly379-to-val substitution (G379V) in the thiolase precursor. Cells transfected with cDNA carrying the G379V mutation showed no evidence of restored T2 activity. The paternal allele was associated with exon 8 skipping at the cDNA level. In the paternal allele at the gene level, a C-to-T transition causing a gln272-to-ter (Q272X) change was identified within exon 8, 13 bp from the 5-prime splice site of intron 8. Splicing experiments showed that the exonic mutation caused partial skipping of exon 8. This substitution was thought to alter the secondary structure of T2 pre-mRNA around exon 8 and thus impede normal splicing. They cited a similar situation reported by Steingrimsdottir et al. (1992), who detected aberrant splicing in the HGPRT (308000) gene resulting from a mutation located 13 nucleotides from the 5-prime splice site of intron 8 and causing exon 8 skipping in 90% of HGPRT transcripts.
For discussion of the gln272-to-ter (Q272X) mutation in the ACAT1 gene that was found in compound heterozygous state in a patient with 3-ketothiolase deficiency (203750) by Fukao et al. (1994), see 607809.0008.
Sewell et al. (1998) described a compound heterozygous woman with 3-ketothiolase deficiency (203750) in whom 1 mutation was a 3-bp deletion of nucleotides 1033 to 1035 (GAA), resulting in deletion of glutamic acid at codon 345 (glu345del). The other mutation was a 1-bp insertion of adenine between nucleotides 1083 and 1084 (607809.0011), causing premature termination.
For discussion of the 1-bp insertion in the ACAT1 gene (1083insA) that was found in compound heterozygous state in a patient with 3-ketothiolase deficiency (203750) by Sewell et al. (1998), see 607809.0010.
In a Japanese patient (GK19) with mitochondrial acetoacetyl-Coa thiolase deficiency (203750), Fukao et al. (1998) identified compound heterozygous mutations in the ACAT1 gene: an asn93-to-ser (N93S) substitution on one allele and an ile312-to-thr (I312T; 607809.0013) substitution on the other.
In a Japanese patient (GK19) with mitochondrial acetoacetyl-Coa thiolase deficiency (203750), Fukao et al. (1998) identified compound heterozygous mutations in the ACAT1 gene: an asn93-to-ser (N93S; 607809.0012) substitution on one allele and an ile312-to-thr (I312T) substitution on the other.
In a Japanese patient (GK01) with T2 deficiency (203750), Fukao et al. (1998) identified compound heterozygous mutations in the ACAT1 gene: an ala333-to-pro (A333P) substitution on one allele and a 1-bp deletion (149delC; 607809.0016) on the other.
In a patient with T2 deficiency (203750), Fukao et al. (2002) identified a homozygous 433C-G transversion in the ACAT1 gene, resulting in a gln145-to-glu (Q145E) substitution. In vitro functional expression studies showed that the mutant protein had 15% residual activity at 37 degrees, which increased to 30% at 30 degrees. The findings indicated decreased heat stability of enzyme activity consistent with adverse effects on protein folding or dimerization.
In a Japanese patient (GK01) with T2 deficiency (203750), Fukao et al. (1998) identified compound heterozygous mutations in the ACAT1 gene: an ala333-to-pro (A333P; 607809.0014) substitution on one allele and a 1-bp deletion (149delC) on the other.
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Long, T., Sun, Y., Hassan, A., Qi, X., Li, X. Structure of nevanimibe-bound tetrameric human ACAT1. Nature 581: 339-343, 2020. [PubMed: 32433613] [Full Text: https://doi.org/10.1038/s41586-020-2295-8]
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Qian, H., Zhao, X., Yan, R., Yao, X., Gao, S., Sun, X., Du, X., Yang, H., Wong, C. C. L., Yan, N. Structural basis for catalysis and substrate specificity of human ACAT1. Nature 581: 333-338, 2020. [PubMed: 32433614] [Full Text: https://doi.org/10.1038/s41586-020-2290-0]
Sakurai, S., Fukao, T., Haapalainen, A. M., Zhang, G., Yamada, K., Lilliu, F., Yano, S., Robinson, P., Gibson, M. K., Wanders, R. J. A., Mitchell, G. A., Wierenga, R. K., Kondo, N. Kinetic and expression analyses of seven novel mutations in mitochondrial acetoacetyl-CoA thiolase (T2): identification of a Km mutant and an analysis of the mutational sites in the structure. Molec. Genet. Metab. 90: 370-378, 2007. [PubMed: 17236799] [Full Text: https://doi.org/10.1016/j.ymgme.2006.12.002]
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Yang, W., Bai, Y., Xiong, Y., Zhang, J., Chen, S., Zheng, X., Meng, X., Li, L., Wang, J., Xu, C., Yan, C., Wang, L., and 10 others. Potentiating the antitumour response of CD8+ T cells by modulating cholesterol metabolism. Nature 531: 651-655, 2016. [PubMed: 26982734] [Full Text: https://doi.org/10.1038/nature17412]