Alternative titles; symbols
HGNC Approved Gene Symbol: ILK
Cytogenetic location: 11p15.4 Genomic coordinates (GRCh38): 11:6,603,774-6,610,870 (from NCBI)
ILK is a serine-threonine protein kinase that associates with the cytoplasmic domain of beta integrins and acts as a proximal receptor kinase regulating integrin-mediated signal transduction (Melchior et al., 2002).
Transduction of extracellular matrix signals through integrins influences intracellular and extracellular functions, and appears to require interaction of integrin cytoplasmic domains with cellular proteins. Using a 2-hybrid screen, Hannigan et al. (1996) isolated from a placenta cDNA library a gene that interacts with the cytoplasmic domain of beta-1 integrin (135630). The gene, designated integrin-linked kinase (ILK), encodes a predicted 451-amino acid protein with an apparent molecular mass of 59 kD based on SDS-PAGE. Northern blot analysis showed that the 1.8-kb ILK mRNA is widely expressed. The ILK protein is a serine/threonine protein kinase with 4 ankyrin-like repeats.
Melchior et al. (2002) cloned the human ILK gene. The deduced 452-amino acid protein has 4 N-terminal ankyrin repeats, followed by a pleckstrin homology domain and a C-terminal kinase catalytic domain composed of 11 subdomains.
By immunofluorescence analysis on cryosections of wildtype mouse hearts, White et al. (2006) detected ILK protein in a pattern consistent with that of the Z-bands and costameres of cardiomyocytes.
Melchior et al. (2002) determined that the ILK gene contains 13 exons and spans 9.0 kb. The ATG codon is located within exon 2. Intron 2 is more than 3.6 kb long and has an Alu-like repeat sequence. The promoter region has characteristics typical of housekeeping genes, such as high GC content, the presence of CpG islands, lack of TATA and CAAT boxes, and the presence of multiple transcription initiation start sites.
Hannigan et al. (1997) mapped the ILK gene to 11p15.5-p15.4 by fluorescence in situ hybridization.
Hannigan et al. (1996) found that ILK coimmunoprecipitated with beta-1 integrin from cell lysates, and that overexpression of ILK disrupted cell architecture and inhibited adhesion to integrin substrates, while inducing anchorage-independent growth in epithelial cells, suggesting that ILK regulates integrin-mediated signal transduction.
Leung-Hagesteijn et al. (2001) showed that human ILKAP (618909) interacted directly with ILK and inhibited its kinase activity and ILK-mediated signal transduction in HEK293 cells. ILKAP phosphatase activity was not required for interaction with ILK, but it was required for inhibition. ILKAP inhibited ILK-mediated phosphorylation of GSK3-beta (GSK3B; 605004) at ser9, thereby selectively inhibiting beta-catenin (CTNNB1; 116806)-LEF1 (153245) transactivation.
By knockout of the ILK gene in human embryonic kidney cells and mouse macrophages, Troussard et al. (2003) showed that ILK is essential for regulation of AKT (see AKT1; 164730) activity. ILK knockout had no effect on phosphorylation of AKT on thr308, but resulted in almost complete inhibition of phosphorylation on ser473, causing significant inhibition of AKT activity accompanied by significant stimulation of apoptosis. ILK knockout also suppressed phosphorylation of GSK3B on ser9 and cyclin D1 (168461) expression. Troussard et al. (2003) concluded that ILK is an essential upstream regulator of AKT activation.
Fukuda et al. (2003) found that PINCH1 (LIMS1; 602567) and ILK are essential for prompt HeLa cell spreading and motility following passage, and that they are crucial for cell survival. While ILK depletion reduced AKT phosphorylation on ser473, PINCH1 depletion reduced AKT phosphorylation on both ser473 and thr308. PINCH1 also regulated ILK protein levels. Fukuda et al. (2003) concluded that PINCH1 is an obligate partner of ILK and both are indispensable for proper control of cell shape change, motility, and survival.
Bock-Marquette et al. (2004) demonstrated that the G-actin sequestering peptide thymosin beta-4 (300159) promoted myocardial and endothelial cell migration in the embryonic heart and retained this property in postnatal cardiomyocytes. Survival of embryonic and postnatal cardiomyocytes in culture was also enhanced by thymosin beta-4. Thymosin beta-4 formed a functional complex with PINCH1 and ILK, resulting in activation of the survival kinase AKT, also known as protein kinase B. After coronary artery ligation in mice, thymosin beta-4 treatment resulted in upregulation of Ilk and Akt activity in the heart, enhanced early myocyte survival, and improved cardiac function. Bock-Marquette et al. (2004) concluded that thymosin beta-4 promotes cardiomyocyte migration, survival, and repair.
Kumar et al. (2004) showed that endogenous ILKAP selectively regulated GSK3-beta signaling by inhibiting ILK-mediated phosphorylation of GSK3-beta at ser9 in LNCaP prostate carcinoma cells. However, ILKAP did not affect phosphorylation of the ILK target PKB (AKT1) and ILK-PKB signaling. ILKAP inhibition of ILK-mediated signaling was independent of PTEN (601728).
Lu et al. (2006) demonstrated a marked increase in ILK protein levels in hypertrophic ventricles of patients with congenital and acquired outflow tract obstruction. The increase in ILK was associated with the activation of Rho family guanine triphosphatases, RAC1 (602048) and CDC42 (116952), and known hypertrophic signaling kinases, including extracellular signal-related kinases, such as ERK1/2 (see 601795) and p70-S6-kinase (RPS6KB1; 608938). Transgenic mice with cardiac-specific expression of a constitutively active or wildtype ILK exhibited a compensated ventricular hypertrophic phenotype and displayed an activation profile of guanine triphosphatases and downstream protein kinases concordant with that seen in human hypertrophy. In contrast, transgenic mice with cardiomyocyte-restricted expression of a kinase-inactive ILK were unable to mount a compensatory hypertrophic response to angiogensin II (see 106150) in vivo. Lu et al. (2006) concluded that ILK-regulated signaling represents a broadly adaptive hypertrophic response mechanism relevant to a wide range of clinical heart disease.
Using a forward genetic screen in zebrafish to identify novel genes required for myocardial function, Knoll et al. (2007) identified the lost-contact (loc) mutant, which has a nonsense mutation in the ilk gene. The loc/ilk mutant is associated with a severe defect in cardiomyocytes and endothelial cells that leads to severe myocardial dysfunction.
Nakrieko et al. (2008) found that ILKAP interacted with ILK and induced export of ILK from the nucleus in human keratinocytes. ILKAP-stimulated nuclear export of ILK was dependent on ILKAP phosphatase activity and was mediated by CRM1 (XPO1; 602559).
In primary cultures of human fetal myocardial cells, Traister et al. (2012) observed that adenovirus-mediated overexpression of ILK potently increased the number of new aggregates of primitive cardioblasts. The number of cardioblast colonies was significantly decreased when ILK expression was knocked down with ILK-targeted siRNA. Overexpression of an activation-resistant ILK mutant, R211A, resulted in a much greater increase in the number of new cell aggregates compared to wildtype. The cardiomyogenic effects of both wildtype and mutant ILK were accompanied by concurrent activation of beta-catenin and increased expression of progenitor cell marker islet-1 (ISL1; 600366), which was also observed in lysates of transgenic mice with cardiac-specific overexpression of the R211A mutant and wildtype ILK. Endogenous ILK expression was shown to increase in concert with those of cardiomyogenic markers during directed cardiomyogenic differentiation in human embryonic stem cells. Traister et al. (2012) concluded that ILK represents a regulatory checkpoint in human cardiomyogenesis.
For discussion of mutation in the ILK gene as a cause of dilated cardiomyopathy (CMD; see 115200), see (602366.0001).
Sakai et al. (2003) found that embryonic mice lacking Ilk expression died at the periimplantation stage due to failure of epiblast polarization and cavitation. The impaired epiblast polarization was associated with abnormal F-actin accumulation at sites of integrin attachment to the basement membrane zone. Likewise, Ilk-deficient fibroblasts showed abnormal F-actin aggregates associated with impaired cell spreading and delayed formation of stress fibers and focal adhesions. Ilk-deficient fibroblasts also had diminished proliferation rates. The proliferation defect was not due to absent or reduced Ilk-mediated phosphorylation of Akt or Gsk3b. Expression of mutant Ilk lacking kinase activity and/or paxillin (602505) binding in Ilk-deficient fibroblasts rescued cell spreading, F-actin organization, focal adhesion formation, and proliferation.
Friedrich et al. (2004) found that endothelial cell-specific deletion of Ilk in mice conferred placental insufficiency with decreased labyrinthine vascularization, and yielded no viable offspring. Deletion of Ilk in zebrafish resulted in marked patterning abnormalities of the vasculature and was similarly lethal. Phenotypic rescue of Ilk-deficient mouse lung endothelial cells with wildtype Ilk, but not by a constitutively active mutant of Akt, suggested that regulation of endothelial cell survival by ILK is independent of AKT.
The recessive 'main squeeze' (msq) mutation in zebrafish is embryonic lethal due to heart failure. Bendig et al. (2006) found that stretch-responsive genes, such as atrial natriuretic factor (ANF; 108780) and Vegf (192240), were downregulated in msq mutant hearts. Through positional cloning, they found that heart failure in msq mutants was due to a point mutation in the Ilk gene. In normal hearts, Ilk specifically localized to costameres and sarcomeric Z discs. The msq mutation reduced Ilk kinase activity and disrupted binding of Ilk to the Z disc adaptor protein beta-parvin (PARVB; 608121). In msq mutant embryos, heart failure could be suppressed by expression of Ilk or constitutively active forms of Akt and Vegf. Antisense-mediated abrogation of zebrafish beta-parvin phenocopied the msq phenotype.
White et al. (2006) performed targeted ablation of Ilk expression in the mouse heart and observed spontaneous cardiomyopathy and heart failure by 6 weeks of age. The murine symptoms reflected classic human symptoms of dilated cardiomyopathy (CMD; see 115200), with labored breathing, lack of strength, and sudden death; postmortem examination revealed grossly enlarged hearts in all animals, with dramatically dilated left ventricular chambers and evidence of fibrosis on histology. Immunofluorescence analysis of frozen heart sections from the mutant mice revealed loss of Ilk from the sarcolemma, resulting in disaggregation of adjacent cardiomyocytes within the heart tissue; trichrome staining confirmed the dramatic disaggregation in mutant mice compared to the compact arrangement of cardiomyocytes in controls. Deletion of Ilk was associated with disruption of adhesion signaling through the beta-1 integrin (135630)/Fak (PTK2; 600758) complex, and loss of Ilk was accompanied by a reduction in cardiac Akt (164730) phosphorylation, which normally provides a protective response against stress. White et al. (2006) suggested that ILK plays a central role in protecting the mammalian heart against cardiomyopathy and failure.
Lange et al. (2009) showed that mice carrying point mutations in the proposed autophosphorylation site of the putative kinase domain and in the pleckstrin homology domain of Ilk are normal. In contrast, mice with point mutations in the conserved lysine residue of the potential ATP-binding site of the kinase domain, which mediates Ilk binding to alpha-parvin (608120), die owing to renal agenesis. Similar renal defects occur in alpha-parvin-null mice. Lange et al. (2009) concluded that their results provided genetic evidence that the kinase activity of Ilk is dispensable for mammalian development; however, an interaction between Ilk and alpha-parvin is critical for kidney development.
Moik et al. (2013) stated that substitution of val386 and thr387 with glycine in mouse Ilk disrupts interaction of Ilk with paxillin and reduces localization of Ilk at focal adhesions. They found that expression of these mutations in mice caused a defect in vasculogenesis and was embryonic lethal. The substitutions decreased Ilk protein stability, and mutant fibroblasts showed impaired migration.
This variant is classified as a variant of unknown significance because its contribution to dilated cardiomyopathy (see 115200) has not been confirmed.
In a Caucasian man with severe dilated cardiomyopathy who had been diagnosed at 54 years of age and had an ejection fraction of only 25%, Knoll et al. (2007) identified heterozygosity for a 785C-T transition in the ILK gene, resulting in an ala262-to-val (A262V) substitution at a highly conserved residue in a proline-rich region of the ILK kinase domain. In vitro kinase assay revealed a 63% reduction in kinase activity for the A262V variant compared to wildtype. Immunohistochemistry on a myocardial biopsy sample from the patient showed a significant loss of endothelial cells.
Bendig, G., Grimmler, M., Huttner, I. G., Wessels, G., Dahme, T., Just, S., Trano, N., Katus, H. A., Fishman, M. C., Rottbauer, W. Integrin-linked kinase, a novel component of the cardiac mechanical stretch sensor, controls contractility in the zebrafish heart. Genes Dev. 20: 2361-2372, 2006. [PubMed: 16921028] [Full Text: https://doi.org/10.1101/gad.1448306]
Bock-Marquette, I., Saxena, A., White, M. D., DiMaio, J. M., Srivastava, D. Thymosin beta-4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature 432: 466-472, 2004. [PubMed: 15565145] [Full Text: https://doi.org/10.1038/nature03000]
Friedrich, E. B., Liu, E., Sinha, S., Cook, S., Milstone, D. S., MacRae, C. A., Mariotti, M., Kuhlencordt, P. J., Force, T., Rosenzweig, A., St-Arnaud, R., Dedhar, S., Gerszten, R. E. Integrin-linked kinase regulates endothelial cell survival and vascular development. Molec. Cell. Biol. 24: 8134-8144, 2004. [PubMed: 15340074] [Full Text: https://doi.org/10.1128/MCB.24.18.8134-8144.2004]
Fukuda, T., Chen, K., Shi, X., Wu, C. PINCH-1 is an obligate partner of integrin-linked kinase (ILK) functioning in cell shape modulation, motility, and survival. J. Biol. Chem. 278: 51324-51333, 2003. [PubMed: 14551191] [Full Text: https://doi.org/10.1074/jbc.M309122200]
Hannigan, G. E., Bayani, J., Weksberg, R., Beatty, B., Pandita, A., Dedhar, S., Squire, J. Mapping of the gene encoding the integrin-linked kinase, ILK, to human chromosome 11p15.5-p15.4. Genomics 42: 177-179, 1997. [PubMed: 9177792] [Full Text: https://doi.org/10.1006/geno.1997.4719]
Hannigan, G. E., Leung-Hagesteijn, C., Fitz-Gibbon, L., Coppolino, M. G., Radeva, G., Filmus, J., Bell, J. C., Dedhar, S. Regulation of cell adhesion and anchorage-dependent growth by a new beta-1-integrin-linked protein kinase. Nature 379: 91-96, 1996. [PubMed: 8538749] [Full Text: https://doi.org/10.1038/379091a0]
Knoll, R., Postel, R., Wang, J., Kratzner, R., Hennecke, G., Vacaru, A. M., Vakeel, P., Schubert, C., Murthy, K., Rana, B. K., Kube, D., Knoll, G., and 17 others. Laminin-alpha-4 and integrin-linked kinase mutations cause human cardiomyopathy via simultaneous defects in cardiomyocytes and endothelial cells. Circulation 116: 515-525, 2007. [PubMed: 17646580] [Full Text: https://doi.org/10.1161/CIRCULATIONAHA.107.689984]
Kumar, A. S., Naruszewicz, I., Wang, P., Leung-Hagesteijn, C., Hannigan, G. E. ILKAP regulates ILK signaling and inhibits anchorage-independent growth. Oncogene 23: 3454-3461, 2004. [PubMed: 14990992] [Full Text: https://doi.org/10.1038/sj.onc.1207473]
Lange, A., Wickstrom, S. A., Jakobson, M., Zent, R., Sainio, K., Fassler, R. Integrin-linked kinase is an adaptor with essential functions during mouse development. Nature 461: 1002-1106, 2009. [PubMed: 19829382] [Full Text: https://doi.org/10.1038/nature08468]
Leung-Hagesteijn, C., Mahendra, A., Naruszewicz, I., Hannigan, G. E. Modulation of integrin signal transduction by ILKAP, a protein phosphatase 2C associating with the integrin-linked kinase, ILK1. EMBO J. 20: 2160-2170, 2001. [PubMed: 11331582] [Full Text: https://doi.org/10.1093/emboj/20.9.2160]
Lu, H., Fedak, P. W. M., Dai, X., Du, C., Zhou, Y.-Q., Henkelman, M., Mongroo, P. S., Lau, A., Yamabi, H., Hinek, A., Husain, M., Hannigan, G., Coles, J. G. Integrin-linked kinase expression is elevated in human cardiac hypertrophy and induces hypertrophy in transgenic mice. Circulation 114: 2271-2279, 2006. [PubMed: 17088456] [Full Text: https://doi.org/10.1161/CIRCULATIONAHA.106.642330]
Melchior, C., Kreis, S., Janji, B., Kieffer, N. Promoter characterization and genomic organization of the gene encoding integrin-linked kinase 1. Biochim. Biophys. Acta 1575: 117-122, 2002. [PubMed: 12020826] [Full Text: https://doi.org/10.1016/s0167-4781(02)00247-6]
Moik, D., Bottcher, A., Makhina, T., Grashoff, C., Bulus, N., Zent, R., Fassler, R. Mutations in the paxillin-binding site of integrin-linked kinase (ILK) destabilize the pseudokinase domain and cause embryonic lethality in mice. J. Biol. Chem. 288: 18863-18871, 2013. [PubMed: 23658024] [Full Text: https://doi.org/10.1074/jbc.M113.470476]
Nakrieko, K.-A., Vespa, A., Mason, D., Irvine, T. S., D'Souza, S. J. A., Dagnino, L. Modulation of integrin-linked kinase nucleo-cytoplasmic shuttling by ILKAP and CRM1. Cell Cycle 7: 2157-2166, 2008. [PubMed: 18635968] [Full Text: https://doi.org/10.4161/cc.7.14.6241]
Sakai, T., Li, S., Docheva, D., Grashoff, C., Sakai, K., Kostka, G., Braun, A., Pfeifer, A., Yurchenco, P. D., Fassler, R. Integrin-linked kinase (ILK) is required for polarizing the epiblast, cell adhesion, and controlling actin accumulation. Genes Dev. 17: 926-940, 2003. [PubMed: 12670870] [Full Text: https://doi.org/10.1101/gad.255603]
Traister, A., Aafaqi, S., Masse, S., Dai, X., Li, M., Hinek, A., Nanthakumar, K., Hannigan, G., Coles, J. G. ILK induces cardiomyogenesis in the human heart. PloS One 7: e37802, 2012. Note: Electronic Article. [PubMed: 22666394] [Full Text: https://doi.org/10.1371/journal.pone.0037802]
Troussard, A. A., Mawji, N. M., Ong, C., Mui, A., St.-Arnaud, R., Dedhar, S. Conditional knock-out of integrin-linked kinase demonstrates an essential role in protein kinase B/Akt activation. J. Biol. Chem. 278: 22374-22378, 2003. [PubMed: 12686550] [Full Text: https://doi.org/10.1074/jbc.M303083200]
White, D. E., Coutu, P., Shi, Y.-F., Tardif, J.-C., Nattel, S., St. Arnaud, R., Dedhar, S., Muller, W. J. Targeted ablation of ILK from the murine heart results in dilated cardiomyopathy and spontaneous heart failure. Genes Dev. 20: 2355-2360, 2006. [PubMed: 16951252] [Full Text: https://doi.org/10.1101/gad.1458906]