Alternative titles; symbols
HGNC Approved Gene Symbol: VAC14
SNOMEDCT: 1172584005;
Cytogenetic location: 16q22.1-q22.2 Genomic coordinates (GRCh38) : 16:70,687,439-70,801,158 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 16q22.1-q22.2 | Striatonigral degeneration, childhood-onset | 617054 | Autosomal recessive | 3 |
The content of phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2) in endosomal membranes changes dynamically with fission and fusion events that generate or absorb intracellular transport vesicles. VAC14 is a component of a trimolecular complex that tightly regulates the level of PtdIns(3,5)P2. Other components of this complex are the PtdIns(3,5)P2-synthesizing enzyme PIKFYVE (609414) and the PtdIns(3,5)P2 phosphatase FIG4 (609390). VAC14 functions as an activator of PIKFYVE (Sbrissa et al., 2007).
Human T-cell lymphotropic virus type-1 (HTLV-1) encodes Tax1, a 40-kD protein that plays a key role in viral replication, transformation, and gene regulation. By screening a human Jurkat T-cell cDNA expression library with biologically active Tax1 protein to identify Tax1-binding proteins, Mireskandari et al. (1996) isolated a cDNA encoding VAC14, which they called TRX. The deduced 221-amino acid TRX protein is predominantly hydrophilic in its C-terminal region. Northern blot analysis of human tissues detected a major 3.5-kb TRX transcript in all tissues examined, namely brain, heart, lung, liver, pancreas, kidney, skeletal muscle, and placenta. However, Western blot analysis detected TRX expression only in lymphocytes and lymphocytic-derived cell lines.
Sbrissa et al. (2004) obtained a full-length cDNA clone of human VAC14. The deduced protein contains 782 amino acids. Western blot analysis of human and other mammalian cell lines and of mouse tissues detected VAC14 at an apparent molecular mass of 82 kD. Fractionation and Western blot analysis of HEK293 human embryonic kidney cells revealed endogenous VAC14 in both cytosolic and membrane compartments. Immunohistochemical analysis of transfected COS cells showed that human VAC14 localized predominantly to the perinuclear region and also in more dispersed vesicles.
HEAT repeats contain 2 antiparallel helices connected by a short loop and provide surfaces for protein-protein interactions. Jin et al. (2008) identified 17 HEAT repeats in mouse and human VAC14.
Mireskandari et al. (1996) demonstrated a specific interaction between Tax1 and TRX by coimmunoprecipitation and Far Western blot analyses.
Using immunohistochemical analysis, Sbrissa et al. (2004) showed that human VAC14 colocalized with mouse Pikfyve in the perinuclear region following cotransfection of COS cells. Knockdown of VAC14 expression in HEK293 cells did not alter cell morphology, but it sensitized cells to brief treatment with a weak base, which resulted in formation of cytoplasmic vacuoles and decreased production of PtsIns(3,5)P and PtdIns(5)P by PIKFYVE. Conversely, overexpression of VAC14 in HEK293 cells increased PIKFYVE protein levels and PIKFYVE activity. Reciprocal coimmunoprecipitation studies showed that endogenous Pikfyve and Vac14 interacted directly in rat PC12 cells, and the immunoprecipitates synthesized PtdIns(5)P and PtdIns(3,5)P2. Sbrissa et al. (2004) concluded that VAC14 is an activator of PIKFYVE, and thereby regulates PtdIns(3,5)P2 synthesis and intracellular membrane homeostasis.
Using coimmunoprecipitation analysis, Sbrissa et al. (2007) showed that endogenous PIKFYVE, ARPIKFYVE, and SAC3 (FIG4) formed a stable ternary complex in HEK293 cells and other mammalian cell lines.
Sbrissa et al. (2008) found that ARPIKFYVE interacted with both SAC3 and PIKFYVE and concluded that it is the principal organizer of the PIKFYVE-ARPIKFYVE-SAC3 (PAS) complex.
Gross (2010) mapped the VAC14 to chromosome 16q22.1-q22.2 based on an alignment of the VAC14 sequence (GenBank AK056433) with the genomic sequence (GRCh37).
Jin et al. (2008) mapped the mouse Vac14 gene to chromosome 8.
In 2 unrelated boys with childhood-onset striatonigral degeneration (SNDC; 617054), Lenk et al. (2016) identified compound heterozygous mutations in the VAC14 gene (604632.0001-604632.0004). The mutations, which were found by exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the families. Cultured fibroblasts from both patients showed abnormal vacuolization, consistent with PI(3,5)P2 deficiency, and the abnormalities were rescued after transfection with wildtype VAC14.
Zhang et al. (2007) obtained Vac14-null mice at mendelian ratios, but all died within 2 days of birth due to massive neurodegeneration, particularly in the midbrain and in peripheral sensory neurons. Cell bodies of affected neurons were vacuolated, and empty spaces were found in areas where neurons should have been. Similar vacuoles were found in cultured Vac14-null neurons and fibroblasts. Defects were observed in intracellular trafficking, particularly in retrograde endosome-to-trans-Golgi trafficking. Vac14-null cells showed abnormal accumulation of PI(3)P and reduced levels of PI(3,5)P2 and PI(5)P compared with wildtype cells. Overexpression of human FAB1 reversed the effect of Vac14 deletion in mouse fibroblasts. Zhang et al. (2007) noted that Fig4-null mice and Vac14-null mice show similar defects in PI(3,5)2 synthesis and acquire profound vacuolation in the same types of neurons. They speculated that the neurodegeneration observed in both mouse mutants is due to defects in metabolism of PI(3,5)P2 and/or PI(5)P, and they concluded that VAC14 and FIG4 control FAB1 activity to maintain normal levels of PI(3)P, PI(3,5)P2, and PI(5)P.
Mice homozygous for the spontaneous Ingls (infantile gliosis) mutation exhibit reduced body size and diluted pigmentation. Homozygous Ingls mice die within 3 weeks of birth and histologically show enlarged brain ventricles. Jin et al. (2008) identified Ingls as a missense mutation resulting in substitution of an invariant leu156 with arg within helix B of HEAT repeat 4 in the Vac14 protein. Western blot analysis of Ingls brains revealed normal Vac14 protein abundance, but cultured Ingls fibroblasts showed reduced PtdIns(3,5)P2 levels. Yeast 2-hybrid analysis showed that the leu156-to-arg mutation disrupted interaction of Vac14 with Fab1 (Pikfyve), but not Fig4.
Mutations affecting the conversion of PI3P to the signaling lipid PI(3,5)P2 result in spongiform degeneration of mouse brain and are associated with the human disorders Charcot-Marie-Tooth disease and amyotrophic lateral sclerosis (ALS). Ferguson et al. (2009) reported accumulation of the proteins Lc3II (MAP1LC3A; 601242), p62 (SQSTM1; 601530), and Lamp2 (309060) in neurons and astrocytes of mice with mutations in 2 components of the PI(3,5)P2 regulatory complex, Fig4 (609390) and Vac14. Cytoplasmic inclusion bodies containing p62 and ubiquitinated proteins were present in regions of the mutant brain that underwent degeneration. Colocalization of p62 and LAMP2 in affected cells indicated that formation or recycling of the autolysosome may be impaired. The authors proposed a role for PI(3,5)P2 in autophagy in the mammalian central nervous system and demonstrated that mutations affecting PI(3,5)P2 may contribute to inclusion body disease.
In a boy with childhood-onset striatonigral degeneration (SNDC; 617054), Lenk et al. (2016) identified compound heterozygous mutations in the VAC14 gene: a c.1271G-T transversion (c.1271G-T, NM_018052.3) in exon 11, resulting in a trp424-to-leu (W424L) substitution at a highly conserved residue, and a G-to-A transition in intron 13 (c.1528+1G-A; 604632.0002), resulting in the skipping of exon 13, a frameshift, and premature termination (Ile459ProfsTer4). The mutant splice transcript was likely degraded by nonsense-mediated mRNA. The mutations, which were found by exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. W424L was reported in a single heterozygote in the ExAC database, whereas the splice site mutation was not found in the ExAC database.
For discussion of the G-to-A transition in intron 13 (c.1528+1G-A, NM_018052.3) in the VAC14 gene, resulting in the skipping of exon 13, a frameshift, and premature termination (Ile459ProfsTer4), that was found in compound heterozygous state in a patient with childhood-onset striatonigral degeneration (SNDC; 617054) by Lenk et al. (2016), see 604632.0001.
In a boy with childhood-onset striatonigral degeneration (SNDC; 617054), Lenk et al. (2016) identified compound heterozygous mutations in exon 15 of the VAC14 gene: a c.1744G-T transversion (c.1744G-T, NM_018052.3), resulting in an ala582-to-ser (A582S) substitution, and a c.1748C-T transition, resulting in a ser583-to-leu (S583L; 604632.0004) substitution. The mutations, which were found by exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family and were not found in the ExAC database. Both mutations occurred at highly conserved residues in the domain required for VAC14 dimerization.
For discussion of the c.1748C-T transition (c.1748C-T, NM_018052.3) in the VAC14 gene, resulting in a ser583-to-leu (S583L) substitution, that was found in compound heterozygous state in a patient with childhood-onset striatonigral degeneration (SNDC; 617054) by Lenk et al. (2016), see 604632.0003.
Ferguson, C. J., Lenk, G. M., Meisler, M. H. Defective autophagy in neurons and astrocytes from mice deficient in PI(3,5)P2. Hum. Molec. Genet. 18: 4868-4878, 2009. [PubMed: 19793721] [Full Text: https://doi.org/10.1093/hmg/ddp460]
Gross, M. B. Personal Communication. Baltimore, Md. 2/26/2010.
Jin, N., Chow, C. Y., Liu, L., Zolov, S. N., Bronson, R., Davisson, M., Petersen, J. L., Zhang, Y., Park, S., Duex, J. E., Goldowitz, D., Meisler, M. H., Weisman, L. S. VAC14 nucleates a protein complex essential for the acute interconversion of PI3P and PI(3,5)P2 in yeast and mouse. EMBO J. 27: 3221-3234, 2008. [PubMed: 19037259] [Full Text: https://doi.org/10.1038/emboj.2008.248]
Lenk, G. M., Szymanska, K., Debska-Vielhaber, G., Rydzanicz, M., Walczak, A., Bekiesinska-Figatowska, M., Vielhaber, S., Hallmann, K., Stawinski, P., Buehring, S., Hsu, D. A., Kunz, W. S., Meisler, M. H., Ploski, R. Biallelic mutations of VAC14 in pediatric-onset neurological disease. Am. J. Hum. Genet. 99: 188-194, 2016. [PubMed: 27292112] [Full Text: https://doi.org/10.1016/j.ajhg.2016.05.008]
Mireskandari, A., Reid, R. L., Kashanchi, F., Dittmer, J., Li, W.-B., Brady, J. N. Isolation of a cDNA clone, TRX, encoding a human T-cell lymphotrophic virus type-I Tax1 binding protein. Biochim. Biophys. Acta 1306: 9-13, 1996. [PubMed: 8611628] [Full Text: https://doi.org/10.1016/0167-4781(96)00012-7]
Sbrissa, D., Ikonomov, O. C., Fenner, H., Shisheva, A. ArPIKfyve homomeric and heteromeric interactions scaffold PIKfyve and Sac3 in a complex to promote PIKfyve activity and functionality. J. Molec. Biol. 384: 766-779, 2008. [PubMed: 18950639] [Full Text: https://doi.org/10.1016/j.jmb.2008.10.009]
Sbrissa, D., Ikonomov, O. C., Fu, Z., Ijuin, T., Gruenberg, J., Takenawa, T., Shisheva, A. Core protein machinery for mammalian phosphatidylinositol 3,5-bisphosphate synthesis and turnover that regulates the progression of endosomal transport: novel Sac phosphatase joins the ArPIKfyve-PIKfyve complex. J. Biol. Chem. 282: 23878-23891, 2007. [PubMed: 17556371] [Full Text: https://doi.org/10.1074/jbc.M611678200]
Sbrissa, D., Ikonomov, O. C., Strakova, J., Dondapati, R., Mlak, K., Deeb, R., Silver, R., Shisheva, A. A mammalian ortholog of Saccharomyces cerevisiae Vac14 that associates with and up-regulates PIKfyve phosphoinositide 5-kinase activity. Molec. Cell. Biol. 24: 10437-10447, 2004. [PubMed: 15542851] [Full Text: https://doi.org/10.1128/MCB.24.23.10437-10447.2004]
Zhang, Y., Zolov, S. N., Chow, C. Y., Slutsky, S. G., Richardson, S. C., Piper, R. C., Yang, B., Nau, J. J., Westrick, R. J., Morrison, S. J., Meisler, M. H., Weisman, L. S. Loss of Vac14, a regulator of the signaling lipid phosphatidylinositol 3,5-bisphosphate, results in neurodegeneration in mice. Proc. Nat. Acad. Sci. 104: 17518-17523, 2007. [PubMed: 17956977] [Full Text: https://doi.org/10.1073/pnas.0702275104]