Alternative titles; symbols
HGNC Approved Gene Symbol: KNSTRN
Cytogenetic location: 15q15.1 Genomic coordinates (GRCh38) : 15:40,382,721-40,394,288 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 15q15.1 | ?Roifman-Chitayat syndrome, digenic | 613328 | Digenic recessive | 3 |
SKAP has a role in kinetochore-microtubule interaction for faithful chromosome segregation (Huang et al., 2012).
By affinity purification with mass spectrometric analysis and yeast 2-hybrid screening to identify HeLa cell proteins that interacted with the essential mitotic kinesin CENPE (117143), followed by PCR of a testis cDNA library, Huang et al. (2012) cloned C15ORF23, which they called SKAP. The deduced 316-amino acid protein has 2 coiled-coil regions in its C-terminal half and a classic SxIP microtubule plus end-binding motif. Database analysis identified SKAP orthologs in mammals, but not in other eukaryotes. Immunohistochemical analysis and immunoelectron microscopic analysis of mitotic HeLa cells colocalized SKAP with CENPE at kinetochores. SKAP localized to the interface between kinetochores and spindle microtubules and appeared to be degraded at the end of mitosis. Western blot analysis detected SKAP at an apparent molecular mass of 32 kD.
Fang et al. (2009) found that SKAP localized to spindle microtubules and kinetochores of HeLa cells during mitosis. Depletion of SKAP did not activate spindle assembly checkpoint, but prolonged metaphase, delayed activation of separase (ESPL1; 604143), increased the number of cells with multiple spindle poles, and decreased the fidelity of chromosome segregation.
Using immunoprecipitation analysis, Huang et al. (2012) found that the coiled-coil region of SKAP interacted with the C terminus of CENPE. Knockdown of SKAP in synchronized HeLa cells via small interfering RNA caused mitotic arrest, with scattering of chromosomes and failure of chromosomes to align at the equator. Recombinant SKAP bound microtubules in vitro with relatively low affinity, and addition of CENPE increased the binding of SKAP to microtubules. Huang et al. (2012) concluded that SKAP interacts with CENPE to link kinetochores to spindle microtubules.
Sharfe et al. (2018) demonstrated that SKAP localized predominantly to microtubules in human T-cell lines. SKAP strongly associated with the microtubule organizing center (MTOC) and colocalized with MAP4 (157132). These findings suggested that SKAP is involved in the regulation of microtubule filament dynamics and remodeling.
Hartz (2012) mapped the C15ORF23 gene to chromosome 15q15.1 based on an alignment of the C15ORF23 sequence (GenBank AK027408) with the genomic sequence (GRCh37).
In 2 sisters, born of consanguineous parents, with Roifman-Chitayat syndrome (ROCHIS; 613328) originally reported by Roifman and Chitayat (2009), Sharfe et al. (2018) identified homozygous loss-of-function mutations in 2 different genes: PIK3CD (602839.0005) and SKAP (KNSTRN; 614718.0001). The mutations, which were found by whole-genome sequencing, segregated with the disorder in the family. Western blot analysis of patient cells showed no detectable PIK3CD or KNSTRN proteins, consistent with a loss of function of both genes. Patient cells showed a near absence of AKT1 (164730) phosphorylation compared to controls, revealing defective PIK3CD function. Detailed in vitro studies showed that patient-derived B and T lymphocytes failed to cluster or aggregate properly, similar to abnormalities noted in SKAP-null cells, suggesting that SKAP deficiency was responsible for this feature. In addition, T cells showed reduced spontaneous migration and inefficient cell-cell contact formation due to limited cell spreading. These abnormalities were associated with aberrant MAP4 (157132) distribution and localized altered microtubule acetylation, which was also attributed to loss of SKAP. Sharfe et al. (2018) concluded that the complex phenotype resulted from the concurrent loss of 2 different genes, each of which contributed to the disease manifestations.
In 2 sisters, born of consanguineous parents, with Roifman-Chitayat syndrome (ROCHIS; 613328) originally reported by Roifman and Chitayat (2009), Sharfe et al. (2018) identified a homozygous 1-bp deletion (c.744delT) in the KNSTRN gene, resulting in a frameshift and premature termination (Leu210fsTer20). The patients were also homozygous for a loss-of-function mutation in the PIK3CD gene (602839.0005). Both mutations, which were found by whole-genome sequencing, segregated with the disorder in the family. Patient cells showed no detectable KNSTRN protein levels, consistent with a loss of function. Patient cells had a near absence of AKT1 (164730) phosphorylation compared to controls, revealing defective PIK3CD function. Detailed in vitro studies showed that patient-derived B and T lymphocytes failed to cluster or aggregate properly, similar to abnormalities noted in SKAP-null cells, suggesting that SKAP deficiency was responsible for this feature. In addition, T cells showed reduced spontaneous migration and inefficient cell-cell contact formation due to limited cell spreading. These abnormalities were associated with aberrant MAP4 (157132) distribution and localized altered microtubule acetylation, which was also attributed to loss of SKAP. Knockdown of SKAP using siRNA in control EBV B cells reduced clustering, again suggesting that SKAP deficiency was responsible for aberrant clustering of patient lymphocytes. Sharfe et al. (2018) concluded that the complex phenotype resulted from the concurrent loss of 2 different genes, each of which contributed to the disease manifestations.
Fang, L., Seki, A., Fang, G. SKAP associates with kinetochores and promotes the metaphase-to-anaphase transition. Cell Cycle 8: 2819-2827, 2009. [PubMed: 19667759] [Full Text: https://doi.org/10.4161/cc.8.17.9514]
Hartz, P. A. Personal Communication. Baltimore, Md. 6/29/2012.
Huang, Y., Wang, W., Yao, P., Wang, X., Liu, X., Zhuang, X., Yan, F., Zhou, J., Du, J., Ward, T., Zou, H., Zhang, J., Fang, G., Ding, X., Dou, Z., Yao, X. CENP-E kinesin interacts with SKAP protein to orchestrate accurate chromosome segregation in mitosis. J. Biol. Chem. 287: 1500-1509, 2012. [PubMed: 22110139] [Full Text: https://doi.org/10.1074/jbc.M111.277194]
Roifman, C. M., Chitayat, D. Combined immunodeficiency, facial dysmorphism, optic nerve atrophy, skeletal anomalies and developmental delay: a new syndrome. Clin. Genet. 76: 449-457, 2009. [PubMed: 19863561] [Full Text: https://doi.org/10.1111/j.1399-0004.2009.01239.x]
Sharfe, N., Karanxha, A., Dadi, H., Merico, D., Chitayat, D., Herbrick, J.-A., Freeman, S., Grinstein, S., Roifman, C. M. Dual loss of p110-delta PI3-kinase and SKAP (KNSTRN) expression leads to combined immunodeficiency and multisystem syndromic features. J. Allergy Clin. Immun. 142: 618-629, 2018. [PubMed: 29180244] [Full Text: https://doi.org/10.1016/j.jaci.2017.10.033]