N-terminal Ankyrin Repeat Domain Research Articles

Ca2+-Dependent Desensitization of TRPV2 Channels Is Mediated by Hydrolysis of Phosphatidylinositol 4,5-Bisphosphate

TRPV2 is a member of the transient receptor potential family of ion channels involved in chemical and thermal pain transduction. Unlike the related TRPV1 channel, TRPV2 does not appear to bind either calmodulin or ATP in its N-terminal ankyrin repeat domain. In addition, it does not contain a calmodulin-binding site in the distal C-terminal region, as has been proposed for TRPV1. We have found that TRPV2 channels transiently expressed in F-11 cells undergo Ca(2+)-dependent desensitization, similar to the other TRPVs, suggesting that the mechanism of desensitization may be conserved in the subfamily of TRPV channels. TRPV2 desensitization was not altered in whole-cell recordings in the presence of calmodulin inhibitors or on coexpression of mutant calmodulin but was sensitive to changes in membrane phosphatidylinositol 4,5-bisphosphate (PIP(2)), suggesting a role of membrane PIP(2) in TRPV2 desensitization. Simultaneous confocal imaging and electrophysiological recording of cells expressing TRPV2 and a fluorescent PIP(2)-binding probe demonstrated that TRPV2 desensitization was concomitant with depletion of PIP(2). We conclude that the decrease in PIP(2) levels on channel activation underlies a major component of Ca(2+)-dependent desensitization of TRPV2 and may play a similar role in other TRP channels.

Role Of Pip2 On Ca2+-Dependent Desensitization of Trpv2

TRPV2 is a member of the transient receptor potential superfamily of ion channels involved in chemical and thermal pain transduction. Unlike the related TRPV1 channel, TRPV2 does not appear to bind either calmodulin or ATP in its N-terminal ankyrin repeat domain. In addition, it does not contain a calmodulin-binding site in the distal C-terminal region, as has been proposed for TRPV1. Importantly, though, we have found that TRPV2 undergoes Ca2+-dependent desensitization similar to TRPV1, suggesting that the mechanism of desensitization may be conserved in the two channels. To elucidate the molecular mechanism underlying Ca2+-dependent desensitization in TRPV2 we used whole-cell recordings of F-11 cells transiently transfected with TRPV2. We found that prolonged applications of the TRPV2 agonist 2-APB led to nearly complete desensitization of the channel in the presence of extracellular Ca2+. In contrast, no desensitization was observed in the absence of Ca2+. TRPV2 desensitization was not altered in whole-cell recordings in the presence of calmodulin inhibitors or upon co-expression of mutant calmodulin, suggesting that CaM does not play a major role in Ca2+-dependent desensitization of TRPV2. Interestingly, simultaneous confocal imaging and electrophysiological recording of whole cells expressing TRPV2 and a fluorescent PI(4,5)P2 binding probe showed a high degree of temporal correlation between the Ca2+ induced desensitization and depletion of PI(4,5)P2. Thus, Ca2+ influx through TRPV2 is sufficient to trigger a dramatic decrease in PI(4,5)P2 levels, presumably by activating PLC. We propose that the decrease in PI(4,5)P2 levels upon channel activation underlies at least a major component of Ca2+-dependent desensitization of TRPV2.

Heat and Spice: Setting the Sensitivity of TRPV Channels

TRPV channels play key roles in pain, thermo- and mechanosensation, and calcium homeostasis. The six mammalian TRPV channels partition into two groups: TRPV1-4, involved in sensory signaling; and TRPV5 and TRPV6, expressed in the intestinal tract and kidneys and important for calcium homeostasis. We determined the crystal structures of the N-terminal ankyrin repeat domain of TRPV1, TRPV2, TRPV4 and TRPV6. Superficially, the structures are similar, as expected from sequence homology, with six ankyrin repeats and unusually long finger loops.

Differential Regulation of TRPV1, TRPV3, and TRPV4 Sensitivity through a Conserved Binding Site on the Ankyrin Repeat Domain

Transient receptor potential vanilloid (TRPV) channels, which include the thermosensitive TRPV1-V4, have large cytoplasmic regions flanking the transmembrane domain, including an N-terminal ankyrin repeat domain. We show that a multiligand binding site for ATP and calmodulin previously identified in the TRPV1 ankyrin repeat domain is conserved in TRPV3 and TRPV4, but not TRPV2. Accordingly, TRPV2 is insensitive to intracellular ATP, while, as previously observed with TRPV1, a sensitizing effect of ATP on TRPV4 required an intact binding site. In contrast, ATP reduced TRPV3 sensitivity and potentiation by repeated agonist stimulations. Thus, ATP and calmodulin, acting through this conserved binding site, are key players in generating the different sensitivity and adaptation profiles of TRPV1, TRPV3, and TRPV4. Our results suggest that competing interactions of ATP and calmodulin influence channel sensitivity to fluctuations in calcium concentration and perhaps even metabolic state. Different feedback mechanisms likely arose because of the different physiological stimuli or temperature thresholds of these channels.

Solution structure of the inhibitory phosphorylation domain of myosin phosphatase targeting subunit 1

Cell motility, such as smooth muscle contraction and cell migration, is controlled by the reversible phosphorylation of the regulatory light chain of myosin II and other cytoskeletal proteins. Mounting evidence suggests that in smooth muscle cells and other types of cells in vertebrates, myosin phosphatase (MP) plays an important role in controlling the phosphorylation of myosin II as well as other cytoskeletal proteins, including ezrin, moesin, and radixin.1 MP is a holoenzyme consisting of a catalytic subunit of a type-1 Ser/Thr phosphatase (PP1C) delta isoform, a myosin phosphatase targeting subunit 1 (MYPT1), and an accessory subunit M21. In this ternary complex, MYPT1 is responsible for regulating the phosphatase activity.1 A recent X-ray crystallographic study revealed an allosteric interaction between PP1C and the N-terminal ankyrin repeat domain of MYPT1 that confers the substrate specificity of the enzyme.2 MP activity is suppressed when Thr696 or Thr853 of MYPT1 is phosphorylated by various kinases, such as ROCK, ZIPK, ILK, and PAK.1,3 However, it is still unclear how the phosphorylation of MYPT1 inhibits MP activity. The amino acid sequence around Thr696 of MYPT1 is highly conserved among MYPT1 family members including MYPT2 and MBS85. Therefore, structural insights into the inhibitory domain of MYPT1 are expected to provide new clues to fully elucidate the mechanism that controls phosphatase activity via the phosphorylation of MYPT1 or other family members involved in kinase-phosphatase crosstalk in cytoskeletal regulation. Here, we prepared a bacterial recombinant fragment of MYPT1 corresponding to residues 658 to 714, including the phosphorylation site Thr696, and determined its three-dimensional structure through the use of computer-assisted distance geometry and a simulated annealing protocol combined with stable-isotope-aided multi-dimensional NMR techniques.

The ankyrin repeat domain of Huntingtin interacting protein 14 contains a surface aromatic cage, a potential site for methyl‐lysine binding

Huntingtin interacting protein 14 (HIP14), a membrane-bound palmitoyl transferase, palmitoylates a number of neuronal proteins (including Huntingtin) and affects the trafficking, stability, aggregation, and/or functional activity of substrate proteins. HIP14 contains an N-terminal ankyrin repeat domain that may function in its substrate recognition. Sequence analysis suggests that the HIP14 ankyrin repeats share approximately 50% identity with the ankyrin repeats of G9a and G9a-like protein (GLP) histone lysine methyltransferases. The crystal structure of the HIP14 ankyrin repeats reveals a surface aromatic cage, formed by two tryptophans, one tyrosine, and one methionine. The all-hydrophobic cage resembles the tri-methylated lysine binding pocket of the plant homeodomain (PHD) of human BPTF (bromodomain and PHD domain transcription factor) 1. HIP14, a Huntingtin interacting protein 2, is a 633-residue protein, including 7-8 ankyrin repeats in the N-terminal region followed by five predicted transmembrane helices. The protein contains a signature DHHC palmitoyl transferases motif located close to the predicted fourth transmembrane helix 3. Importantly, the ankyrin repeats (a protein-protein interaction domain that may function in substrate recognition) and the DHHC sequence (the hypothetical active site) are both predicted to reside on the cytoplasmic face of the lipid bilayer 4, presumably allowing the substrate recognition and the active site to interact with the same substrate. Posttranslational palmitoylation involves the attachment of the saturated C16 fatty acid palmitate to specific cysteines via a thioester linkage 5-7. HIP14 palmitoylates Huntingtin at cysteine 214 8. Other substrates of HIP14-mediated palmitoylation include SNAP-25 (synaptosome associated protein 25 kDa), PSD-95 (postsynaptic density 95 kDa), GAD-65 (glutamate decarboxylase 65 kDa), and Synaptotagmin I 9. Ankyrin repeats are known to mediate protein-protein interactions 10. Recently we showed that the ankyrin repeat domains of G9a and GLP, two euchromatin associated histone lysine methyltranferases, bind N-terminal histone H3 peptides containing mono- or di-methylated lysine 9 (H3K9me1, me2) via a partial aromatic cage with three tryptophans and one acidic residue 11. Besides the ankyrin repeats of G9a and GLP, other protein domains including the Chromodomain 12, plant homeodomain 1,13-15, and Tudor domain 16, also recognize methylated lysines (Review 17). The common mode of methyl-lysine interactions is via a surface aromatic cage consisting of 2-4 aromatic residues. These aromatic cages are highly selective for methyllysine. In a study of Chromodomain-methyllysine interaction, binding was driven primarily by cation-π interactions (i.e, a methyllysine carries a positive charge), and secondarily by the packing of methyl group(s) against the aromatic ring(s) of the cage, with the hydrophobic effect contributing the least to binding 18. This eliminates the possibility of such cages generically binding hydrophobic residues, and suggests that other methyllysine binding ankyrin repeats could be identified by the presence of a surface aromatic cage.

Structural Basis of Focal Adhesion Localization of LIM-only Adaptor PINCH by Integrin-linked Kinase

The LIM-only adaptor PINCH (the particularly interesting cysteine- and histidine-rich protein) plays a pivotal role in the assembly of focal adhesions (FAs), supramolecular complexes that transmit mechanical and biochemical information between extracellular matrix and actin cytoskeleton, regulating diverse cell adhesive processes such as cell migration, cell spreading, and survival. A key step for the PINCH function is its localization to FAs, which depends critically on the tight binding of PINCH to integrin-linked kinase (ILK). Here we report the solution NMR structure of the core ILK.PINCH complex (28 kDa, K(D) approximately 68 nm) involving the N-terminal ankyrin repeat domain (ARD) of ILK and the first LIM domain (LIM1) of PINCH. We show that the ILK ARD exhibits five sequentially stacked ankyrin repeat units, which provide a large concave surface to grip the two contiguous zinc fingers of the PINCH LIM1. The highly electrostatic interface is evolutionally conserved but differs drastically from those of known ARD and LIM bound to other types of protein domains. Consistently mutation of a hot spot in LIM1, which is not conserved in other LIM domains, disrupted the PINCH binding to ILK and abolished the PINCH targeting to FAs. These data provide atomic insight into a novel modular recognition and demonstrate how PINCH is specifically recruited by ILK to mediate the FA assembly and cell-extracellular matrix communication.

Drosophila Ankyrin 2 Is Required for Synaptic Stability

Synaptic connections are stabilized through transsynaptic adhesion complexes that are anchored in the underlying cytoskeleton. The Drosophila neuromuscular junction (NMJs) serves as a model system to unravel genes required for the structural remodeling of synapses. In a mutagenesis screen for regulators of synaptic stability, we recovered mutations in Drosophila ankyrin 2 (ank2) affecting two giant Ank2 isoforms that are specifically expressed in the nervous system and associate with the presynaptic membrane cytoskeleton. ank2 mutant larvae show severe deficits in the stability of NMJs, resulting in a reduction in overall terminal size, withdrawal of synaptic boutons, and disassembly of presynaptic active zones. In addition, lack of Ank2 leads to disintegration of the synaptic microtubule cytoskeleton. Microtubules and microtubule-associated proteins fail to extend into distant boutons. Interestingly, Ank2 functions downstream of spectrin in the anchorage of synaptic microtubules, providing the cytoskeletal scaffold that is essential for synaptic stability.

Mapping the Binding Site on Small Ankyrin 1 for Obscurin

Small ankyrin 1 (sAnk1), an integral protein of the sarcoplasmic reticulum encoded by the ANK1 gene, binds with nanomolar affinity to the C terminus of obscurin, a giant protein surrounding the contractile apparatus in striated muscle. We used site-directed mutagenesis to characterize the binding site on sAnk1, specifically addressing the role of two putative amphipathic, positively charged helices. We measured binding qualitatively by blot overlay assays and quantitatively by surface plasmon resonance and showed that both positively charged sequences are required for activity. We showed further that substitution of a lysine or arginine with an alanine or glutamate located at the same position along either of the two putative helices has similar inhibitory or stimulatory effects on binding and that the effects of a particular mutation depended on the position of the mutated amino acid in each helix. We modeled the structure of the binding region of sAnk1 by homology with ankyrin repeats of human Notch1, which have a similar pattern of charged and hydrophobic residues. Our modeling suggested that each of the two positively charged sequences forms pairs of amphipathic, anti-parallel alpha-helices flanked by beta-hairpin-like turns. Most of the residues in homologous positions along each helical unit have similar, though not identical, orientations. CD spectroscopy confirmed the alpha-helical content of sAnk1, approximately 33%, predicted by the model. Thus, structural and mutational studies of the binding region on sAnk1 for obscurin suggest that it consists of two ankyrin repeats with very similar structures.

Insights into the Roles of Conserved and Divergent Residues in the Ankyrin Repeats of TRPV Ion Channels

Ion channels are often modulated by intracellular calcium levels. TRPV1, a channel responsible for the burning pain sensation in response to heat, acid or capsaicin, is desensitized at high intracellular calcium concentrations. We recently identified a multiligand-binding site in the N-terminal ankyrin repeat domain (ARD) of TRPV1 that binds ATP and sensitizes the channel. Calcium-calmodulin binds the same site and is necessary for calcium-mediated TRPV1 desensitization. Here, we examine in more detail the conservation of this TRPV1 multiligand-binding site in other species. Furthermore, using sequence analysis, we determine that the unusually twisted shape of the TRPV1-ARD is likely conserved in other TRPV channels, but not in the ARDs of other TRP subfamilies.

Myosin16b: The COOH‐tail region directs localization to the nucleus and overexpression delays S‐phase progression

Rat Myo16a and Myo16b comprise the founding members of class XVI myosin and are characterized by an N-terminal ankyrin repeat domain thought to mediate an association with protein phosphatase 1 catalytic subunits 1alpha and 1gamma. Myo16b is the principal isoform and reveals predominant expression in developing neural tissue. Here, we use COS-7 cells as a model system to develop an understanding of Myo16b function. We find that Myo16b displays predominant localization in the nucleus of cells transitioning through interphase, but is not associated with processes of mitosis. Using a panel of EGFP-Myo16b-expression plasmids in transient transfection studies, we identified the COOH-terminal residues 1616-1912 as necessary and solely sufficient to target Myo16b to the nucleus. We show that the Myo16b-tail region directs localization to a nuclear compartment containing profilin and polymerized actin, which appears to form a three-dimensional meshwork through the depth of the nucleus. Further, we demonstrate that this compartment localizes within euchromatic regions of the genome and contains proliferating cell nuclear antigen (PCNA) and cyclin A, both markers of S-phase of the cell cycle. Cells transiently expressing Myo16b or Myo16b-tail region show limited incorporation of BrdU, delayed progression through S-phase of the cell cycle, and curtailed cellular proliferation.

Structure of the N-terminal Ankyrin Repeat Domain of the TRPV2 Ion Channel

The TRPV ion channels mediate responses to many sensory stimuli including heat, low pH, neuropeptides, and chemical ligands. All TRPV subfamily members contain an intracellular N-terminal ankyrin repeat domain (ARD), a prevalent protein interaction motif. The 1.6-A crystal structure of the TRPV2-ARD, with six ankyrin repeats, reveals several atypical structural features. Repeats one through three display unusually long and flexible fingers with a large number of exposed aromatic residues, whereas repeats five and six have unusually long outer helices. Furthermore, a large counterclockwise twist observed in the stacking of repeats four and five breaks the regularity of the domain, altering the shape of surfaces available for interactions with proteins or other cellular ligands. Both solution studies and crystal packing interactions indicate that the TRPV2-ARD does not form homo-oligomers, suggesting that the ARD of TRPV ion channels may be used for interactions with regulatory factors rather than in promoting tetrameric assembly of the ion channels.

Molecular basis for recognition of 2′,5′-linked oligoadenylates by the N-terminal ankyrin repeat domain of human ribonuclease L

Ribonuclease L (RNase L) is implicated in both the molecular mechanisms of interferon action and the fundamental control of RNA stability in mammalian cells. RNase L is catalytically active only after binding an unusual activator molecule containing a 5'-phosphorylated 2',5'-linked oligoadenylate, [(pp)p(A2'p5')(n)A] (2-5A), in the N-terminal half. Here we report the crystal structure of the N-terminal ankyrin repeat domain (ANK) of human RNase L complexed with the activator 2-5A. The ANK folds into eight ankyrin repeat elements and forms an extended curved structure with a concave surface. The 2-5A molecule is accommodated in the concavity and interacts with ankyrin repeats 2 to 4. Two structurally equivalent 2-5A binding motifs are found at repeats 2 and 4. The molecular basis for 2-5A recognition by RNase L is essential for designing stable 2-5As with a high likelihood of activating RNase L.

Crystallization of the N-Terminal Ankyrin Repeat Domain of the 2-5ADependent Endoribonuclease, RNase L

The N-terminal ankyrin repeat domain of the 2'-5'-linked oligoadenylate (2-5A)-dependent endoribonuclease, RNase L, has been crystallized by the hanging-drop vapor diffusion method in the presence of 2-5 Angstroms. The crystals belong to an orthorhombic space group P2(1)2(1)2(1) with cell dimensions of a = 63.11 Angstroms, b = 73.03 Angstroms, and c = 82.64 Angstroms. There is one molecule per asymmetric unit. The crystals diffract to at least 2.1 Angstroms resolution using synchrotron radiation and are suitable for X-ray structure analysis at high resolution.

Structural basis for recognition of 2',5'-linked oligoadenylates by human ribonuclease L.

An interferon-induced endoribonuclease, ribonuclease L (RNase L), is implicated in both the molecular mechanism of action of interferon and the fundamental control of RNA stability in mammalian cells. RNase L is catalytically active only after binding to an unusual activator molecule containing a 5'-phosphorylated 2',5'-linked oligoadenylate (2-5A), in the N-terminal half. Here, we report the crystal structure of the N-terminal ankyrin repeat domain (ANK) of human RNase L complexed with the activator 2-5A. This is the first structural view of an ankyrin repeat structure directly interacting with a nucleic acid, rather than with a protein. The ANK domain folds into eight ankyrin repeat elements and forms an extended curved structure with a concave surface. The 2-5A molecule is accommodated at a concave site and directly interacts with ankyrin repeats 2-4. Interestingly, two structurally equivalent 2-5A binding motifs are found at repeats 2 and 4. The structural basis for 2-5A recognition by ANK is essential for designing stable 2-5As with a high likelihood of activating RNase L.

The role of integrin-linked kinase (ILK) in cancer progression.

Integrin-linked kinase (ILK) is an intracellular protein, which interacts with the cytoplasmic domains of integrin beta and beta3 subunits. ILK is a 59 kDa protein containing a phosphoinositide phospholipid-binding domain flanked by an N-terminal ankyrin repeat domain and a C-terminal serine/threonine protein kinase domain. Genetic and biochemical evidence have established an essential role of ILK in connecting integrins to the actin cytoskeleton. Apart from integrins, ILK interacts with several adaptor and signaling proteins resulting in its activation and localization to focal adhesion plaques. The kinase activity of ILK is stimulated upon integrin engagement, as well as by growth factors and chemokines in a PI-3Kinase-dependent manner. ILK can mediate the phosphorylation of a variety of intracellular substrates, most notable of which are: protein kinase B (PKB/Akt), glycogen synthase kinase-3 (GSK-3) and myosin light chain. Gain and loss of function strategies have shown that overexpression, and/or constitutive activation of ILK results in oncogenic transformation and progression to invasive and metastatic phenotypes. In addition ILK expression and activity are upregulated in several types of cancers. In this review, we summarize the adaptor and signaling properties ofILK, and also progress in the identification of therapeutic strategies for inhibition of ILK activity.

ILK interactions.

Integrin-linked kinase (ILK*) is a multidomain focal adhesion protein that is critically involved in adhesion of cells to the extracellular matrix (ECM) and signal transduction. The figure shows the interactions involving ILK and other related proteins and the downstream signals these elicit. ILK interacts with the cytoplasmic domains of β integrins (e.g. β1 integrin). Furthermore, it binds with high affinity to PINCH, a focal adhesion protein comprising five LIM domains. The ILK-PINCH binding is mediated by the N-terminal ankyrin (ANK) repeat domain of ILK and the second Zn finger located within the N-terminal-most LIM domain (LIM1) of PINCH. ILK also interacts with CH-ILKBP, an actin-binding focal adhesion protein containing two calponinhomology (CH) domains. Human CH-ILKBP is structurally closely related to rat actopaxin, a paxillin- and actin-binding protein. In addition, ILK can bind to the paxillin LD1 motif. The interaction between ILK and CH-ILKBP is mediated by the C-terminal domain of ILK and the CH2 domain of CH-ILKBP. Simultaneous interactions mediated by the two separate (the N- and C-terminal) domains of ILK result in the formation of a stable PINCH—ILK—CH-ILKBP ternary complex in cells. The formation of this complex facilitates the localization of PINCH, ILK and CH-ILKBP to cell-ECM contact sites, at which they provide a crucial physical connection between transmembrane receptors such as integrins and the actin filaments. This function of the PINCH—ILK—CH-ILKBP complex is probably conserved in organisms ranging from nematodes and insects to humans.FIG1*Abbreviations used: ANK, ankyrin; CH, calponin homology domain; CH-ILKBP, calponin-homology-domain-containing ILK-binding protein; ECM, extracellular matrix; FA, focal adhesion; GSK-3; glycogen synthase kinase 3; ILK, integrin-linked kinase; IRS-1, insulin receptor substrate 1; MAPK, mitogen-activated protein kinase; PAK, p21-activated kinase; PDGF, platelet-derived growth factor; PI3K, phosphoinositide 3-kinase; PtdIns(3,4,5)P3, phosphatidylinositol 3,4,5-trisphosphate; PH, pleckstrin homology domain; PKB, protein kinase B; RTK, receptor tyrosine kinase, SH, Src homology domain; WASP, Wiskott-Aldrich syndrome protein.ILK not only serves as an important molecular scaffold at the cell-ECM adhesion sites but also participates in signal transduction pathways that control cell survival, differentiation, proliferation and gene expression in mammalian cells. Important downstream targets of ILK signaling include PKB/Akt, GSK-3, β-catenin, p44/42 MAP kinases and the myosin light chain. Upstream events that regulate ILK activity include cell-ECM interactions and insulin stimulation, which are probably mediated by P13K. An ILK-associated serine/threonine phosphatase, termed ILKAP, has also been implicated in the regulation of GSK-3 phoshorylation. One of the potential convergence points between cell-adhesion- and growth-factor-mediated signal transduction pathways could be Nck-2, an adaptor protein that contains three N-terminal SH3 domains and one C-terminal SH2 domain. Nck-2 interacts with the LIM4 domain of PINCH through its third SH3 domain. In addition, it can associate with IRS-1 through its multiple SH3 domains and with ligand-activated growth factor receptors such as PDGF receptor β through its SH2 domain. Thus, the interactions mediated by multiple Nck-2 domains could regulate the formation of supramolecular complexes that contain components from both cell-adhesion- and growth-factor-signaling pathways and thereby facilitate communication between them (although the interactions mediated by Nck-2 have been demonstrated experimentally, they are depicted by red double arrows to indicate the hypothetical nature of the function of Nck-2 in such communication). Additional Nck-2-binding proteins include PAK, WASPs and DOCK 180, which are known to play important roles in Cdc42- and Racmediated actin cytoskeleton dynamics. Solid double arrows indicate proteinprotein interactions; dashed double arrows indicate putative intermolecular interactions; open arrows indicate phosphorylation reactions.

Integrin-linked kinase and PINCH: partners in regulation of cell-extracellular matrix interaction and signal transduction.

Integrin-linked kinase (ILK) is a focal adhesion serine/threonine protein kinase that is emerging as a key signaling protein functioning at one of the early convergence points of integrin- and growth factor-signaling pathways. ILK binds to PINCH through the N-terminal ankyrin (ANK) repeat domain and the PINCH binding is crucial for focal adhesion localization of ILK. The ILK-PINCH interaction also connects ILK to Nck-2, an SH2-SH3-containing adaptor protein that interacts with components of growth factor and small GTPase signaling pathways. The kinase activity of ILK is regulated by both cell adhesion and growth factors in a phosphoinositide 3-kinase (PI3K)-dependent manner. ILK phosphorylates downstream targets such as protein kinase B (PKB, also known as Akt) and glycogen synthase kinase 3 (GSK-3) and regulates their activities. Overexpression of ILK in epithelial cells leads to striking morphological changes mimicking epithelial-mesenchymal transition, including upregulation of integrin-mediated fibronectin matrix assembly and downregulation of cell-cell adhesions. Furthermore, ILK regulates nuclear translocation of (beta)-catenin and gene expression, and promotes cell cycle progression and tumor formation. Recent genetic studies in Drosophila melanogaster and Caenorhabditis elegans have shown that lack of expression of ILK or PINCH results in phenotypes resembling those of integrin-null mutants, which demonstrates that ILK and PINCH are indispensable for integrin function during embryonic development.