Transcriptional Activation of Inflammatory Genes: Mechanistic Insight into Selectivity and Diversity.

Acute inflammation, an integral part of host defence and immunity, is a highly conserved cellular response to pathogens and other harmful stimuli. An inflammatory stimulation triggers transcriptional activation of selective pro-inflammatory genes that carry out specific functions such as anti-microbial activity or tissue healing. Based on the nature of inflammatory stimuli, an extensive exploitation of selective transcriptional activations of pro-inflammatory genes is performed by the host to ensure a defined inflammatory response. Inflammatory signal transductions are initiated by the recognition of inflammatory stimuli by transmembrane receptors, followed by the transmission of the signals to the nucleus for differential gene activations. The differential transcriptional activation of pro-inflammatory genes is precisely controlled by the selective binding of transcription factors to the promoters of these genes. Among a number of transcription factors identified to date, NF-κB still remains the most prominent and studied factor for its diverse range of selective transcriptional activities. Differential transcriptional activities of NF-κB are dictated by post-translational modifications, specificities in dimer formation, and variability in activation kinetics. Apart from the differential functions of transcription factors, the transcriptional activation of selective pro-inflammatory genes is also governed by chromatin structures, epigenetic markers, and other regulators as the field is continuously expanding.

Integrin-linked kinase mediates force transduction in cardiomyocytes by modulating SERCA2a/PLN function.

Human dilated cardiomyopathy (DCM) manifests as a profound reduction in biventricular cardiac function that typically progresses to death or cardiac transplantation. There is no effective mechanism-based therapy currently available for DCM, in part because the transduction of mechanical load into dynamic changes in cardiac contractility (termed mechanotransduction) remains an incompletely understood process during both normal cardiac function and in disease states. Here we show that the mechanoreceptor protein integrin-linked kinase (ILK) mediates cardiomyocyte force transduction through regulation of the key calcium regulatory protein sarcoplasmic/endoplasmic reticulum Ca(2+)ATPase isoform 2a (SERCA-2a) and phosphorylation of phospholamban (PLN) in the human heart. A non-oncogenic ILK mutation with a synthetic point mutation in the pleckstrin homology-like domain (ILK(R211A)) is shown to enhance global cardiac function through SERCA-2a/PLN. Thus, ILK serves to link mechanoreception to the dynamic modulation of cardiac contractility through a previously undiscovered interaction with the functional SERCA-2a/PLN module that can be exploited to rescue impaired mechanotransduction in DCM.

Integrin-linked kinase modulates lipopolysaccharide- and Helicobacter pylori-induced nuclear factor κB-activated tumor necrosis factor-α production via regulation of p65 serine 536 phosphorylation.

Integrin-linked kinase (ILK) is a ubiquitously expressed and highly conserved serine-threonine protein kinase that regulates cellular responses to a wide variety of extracellular stimuli. ILK is involved in cell-matrix interactions, cytoskeletal organization, and cell signaling. ILK signaling has also been implicated in oncogenesis and progression of cancers. However, its role in the innate immune system remains unknown. Here, we show that ILK mediates pro-inflammatory signaling in response to lipopolysaccharide (LPS). Pharmacological or genetic inhibition of ILK in mouse embryonic fibroblasts and macrophages selectively blocks LPS-induced production of the pro-inflammatory cytokine tumor necrosis factor α (TNF-α). ILK is required for LPS-induced activation of nuclear factor κB (NF-κB) and transcriptional induction of TNF-α. The modulation of LPS-induced TNF-α synthesis by ILK does not involve the classical NF-κB pathway, because IκB-α degradation and p65 nuclear translocation are both unaffected by ILK inhibition. Instead, ILK is involved in an alternative activation of NF-κB signaling by modulating the phosphorylation of p65 at Ser-536. Furthermore, ILK-mediated alternative NF-κB activation through p65 Ser-536 phosphorylation also occurs during Helicobacter pylori infection in macrophages and gastric cancer cells. Moreover, ILK is required for H. pylori-induced TNF-α secretion in macrophages. Although ILK-mediated phosphorylation of p65 at Ser-536 is independent of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway during LPS stimulation, upon H. pylori infection this event is dependent on the PI3K/Akt pathway. Our findings implicate ILK as a critical regulatory molecule for the NF-κB-mediated pro-inflammatory signaling pathway, which is essential for innate immune responses against pathogenic microorganisms.

Mutation in integrin-linked kinase (ILK(R211A)) and heat-shock protein 70 comprise a broadly cardioprotective complex.

RATIONALE: Integrin-linked kinase (ILK) has been proposed as a novel molecular target that has translational potential in diverse cardiac diseases, since its upregulation promotes a broadly cardioprotective phenotype. However, ILK has been implicated as both a cardioprotective and oncogenic target, which imposes therapeutic constraints that are generally relevant to the translational potential of many kinases. OBJECTIVE: To study the cardioprotective properties of the activation-resistant, non-oncogenic, mutation of ILK (ILK(R211A)) against experimental MI in vivo and Doxorubicin induced apoptosis in vitro and it's relationships to stress induced heat shock proteins. METHODS/RESULTS: The transgenic mouse heart over-expressing a point mutation in the ILK pleckstrin homology (PH) domain (Tg(R211A)) exhibits a highly cardioprotective phenotype based on LAD-ligation-induced MI reduction in vivo, and on protection against doxorubicin (DOX)-induced cardiomyocyte apoptosis when overexpressed in human induced pluripotent stem cell (iPS)-derived cardiomyocytes in vitro. Intriguingly, the degree of cardioprotection seen with the ILK(R211A) mutation exceeded that with the ILK(S343D) mutation. Microarray and immunoprecipitation analyses revealed upregulation of expression levels and specific binding of ILK(WT), ILK(S343D) and ILK(R211A) to both constitutively active heat-shock protein 70 (Hsc70) and inducible Hsp70 in response to MI, and to acute ILK overexpression in iPSC-cardiomyocytes. ILK-mediated cardioprotection was shown to depend upon Hsp70 ATPase activity. CONCLUSIONS: These findings indicate that wild type ILK and the non-oncogenic ILK(R211A) mutation comprise a cardioprotective module with Hsp/c70. These results advance a novel target discovery theme in which kinase mutations can be safely engineered to enhance cardioprotective effects.

Interaction of smoothened with integrin-linked kinase in primary cilia mediates Hedgehog signalling.

Here we report that ILK localizes in the mouse primary cilium, a sensory organelle required for signalling by the Hedgehog (Hh) pathway. Genetic or pharmacological inhibition of ILK blocks ciliary accumulation of the Hh pathway effector smoothened (Smo) and suppresses the induction of Gli transcription factor mRNAs by SHh. Conditional deletion of ILK or Smo also inhibits SHh-driven activation of Gli2 in the embryonic mouse cerebellum. ILK regulation of Hh signalling probably requires the physical interaction of ILK and Smo in the cilium, and we also show selective cilia-associated interaction of ILK with ß-arrestin, a known mediator of Smo-dependent signalling.

Serum concentration of integrin-linked kinase in malignant pleural mesothelioma and after asbestos exposure.

OBJECTIVES: Integrin-linked kinase (ILK) is an intracellular protein implicated in chronic inflammation and neoplastic transformation. In a recently accomplished pilot study, we showed that ILK can be detected in the serum of patients with benign and malignant chest diseases, including malignant pleural mesothelioma (MPM). Interestingly, average serum ILK concentrations were 10 times higher in MPM patients when compared with the rest of the study population, and a diagnostic test solely based on serum ILK concentration could discriminate between MPM and non-MPM with considerable accuracy. This study aimed to investigate whether serum ILK concentration could also be used to discriminate between MPM and asbestos exposure only. METHODS: Using a self-developed sandwich enzyme-linked immunosorbent assay, we measured serum ILK concentrations in 101 MPM patients, and 96 asbestos-exposed, but healthy insulation workers. Seventy-three MPM patients had an epitheloid subtype (72.3%), and 42 had a Stage I or II disease (41.6%). RESULTS: When compared with asbestos-exposed individuals, MPM patients of all clinical stages had significantly higher (mean ± standard deviation, median) serum ILK concentrations (10.7 ± 13.6, median 7 ng/ml vs 3.1 ± 4.6, median 1.4 ng/ml; P < 0.001). Among MPM patients, the serum ILK concentration was significantly higher at advanced disease stages III + IV than at early stages I + II (13.7 ± 15.9, median 8.5 ng/ml vs 6.7 ± 7.8, median 3.5 ng/ml; P = 0.02). Using serum ILK to discriminate between MPM patients and asbestos-exposed individuals yielded an area under the curve of 0.69 (95% confidence interval 0.63-0.76). The corresponding sensitivity and specificity for a cut-off of 4.49 ng/ml ILK are 61.4 and 80.2%, respectively. CONCLUSIONS: These data show significant differences between MPM patients and asbestos-exposed but healthy individuals concerning their serum ILK concentration. Furthermore, since ILK levels are increased in advanced MPM stages in comparison with early MPM stages, we suggest evaluating its potential use as a marker of disease progression in MPM.

ILK induces cardiomyogenesis in the human heart.

BACKGROUND: Integrin-linked kinase (ILK) is a widely conserved serine/threonine kinase that regulates diverse signal transduction pathways implicated in cardiac hypertrophy and contractility. In this study we explored whether experimental overexpression of ILK would up-regulate morphogenesis in the human fetal heart. METHODOLOGY/PRINCIPAL FINDINGS: Primary cultures of human fetal myocardial cells (19-22 weeks gestation) yielded scattered aggregates of cardioblasts positive for the early cardiac lineage marker nk × 2.5 and containing nascent sarcomeres. Cardiac cells in colonies uniformly expressed the gap junction protein connexin 43 (C × 43) and displayed a spectrum of differentiation with only a subset of cells exhibiting the late cardiomyogenic marker troponin T (cTnT) and evidence of electrical excitability. Adenovirus-mediated overexpression of ILK potently increased the number of new aggregates of primitive cardioblasts (p<0.001). The number of cardioblast colonies was significantly decreased (p<0.05) when ILK expression was knocked down with ILK targeted siRNA. Interestingly, overexpression of the activation resistant ILK mutant (ILK(R211A)) resulted in much greater increase in the number of new cell aggregates as compared to overexpression of wild-type ILK (ILK(WT)). The cardiomyogenic effects of ILK(R211A) and ILK(WT) were accompanied by concurrent activation of ß-catenin (p<0.001) and increase expression of progenitor cell marker islet-1, which was also observed in lysates of transgenic mice with cardiac-specific over-expression of ILK(R211A) and ILK(WT). Finally, endogenous ILK expression was shown to increase in concert with those of cardiomyogenic markers during directed cardiomyogenic differentiation in human embryonic stem cells (hESCs). CONCLUSIONS/SIGNIFICANCE: In the human fetal heart ILK activation is instructive to the specification of mesodermal precursor cells towards a cardiomyogenic lineage. Induction of cardiomyogenesis by ILK overexpression bypasses the requirement of proximal PI3K activation for transduction of growth factor- and ß1-integrin-mediated differentiation signals. Altogether, our data indicate that ILK represents a novel regulatory checkpoint during human cardiomyogenesis.

Hedgehog overexpression is associated with stromal interactions and predicts for poor outcome in breast cancer.

Hedgehog (Hh) signaling plays an important role in several malignancies but its clinical significance in breast cancer is unclear. In a cohort of 279 patients with invasive ductal carcinoma of the breast, expression of Hh ligand was significantly associated with increased risk of metastasis, breast cancer-specific death, and a basal-like phenotype. A paracrine signature, encompassing high epithelial Hh ligand and high stromal Gli1, was an independent predictor for overall survival in multivariate analysis. In 2 independent histological progression series (n = 301), Hh expression increased with atypia. Hh ligand overexpression in a mouse model of basal breast cancer increased growth, induced a poorly differentiated phenotype, accelerated metastasis, and reduced survival. A stromal requirement for these effects was supported by the lack of similar Hh-mediated changes in vitro, and by stromal-specific expression of Hh target genes in vivo. Furthermore, inhibition of Hh ligand with a monoclonal antibody (5E1) inhibited tumor growth and metastasis. These data suggest that epithelial-stromal Hh signaling, driven by ligand expression in carcinoma cells, promotes breast cancer growth and metastasis. Blockade of Hh signaling to peritumoral stromal cells may represent a novel therapeutic approach in some basal-like breast cancers.

Detection of integrin-linked kinase in the serum of patients with malignant pleural mesothelioma.

OBJECTIVE: Integrin-linked kinase, which is relevant to neoplastic transformation, is highly expressed in malignant pleural mesothelioma. Recently, detection of integrin-linked kinase in serum of patients with ovarian cancer has been reported. This study asks whether integrin-linked kinase can also be detected in serum of patients with malignant pleural mesothelioma and whether serum level has diagnostic or prognostic relevance for that disease. METHODS: A sandwich enzyme-linked immunosorbent assay was designed to detect integrin-linked kinase and applied to serum samples from 46 patients with malignant pleural mesothelioma, 98 patients with other malignant chest disease, and 23 patients with benign chest disease. Integrin-linked kinase serum concentration and clinical data were correlated statistically. RESULTS: Median serum integrin-linked kinase concentration was significantly higher in malignant pleural mesothelioma (8.89 ng/mL) than in other malignant chest disease (0.66 ng/mL) or benign chest disease (0.78 ng/mL, P < .001). There was no relevant correlation of serum integrin-linked kinase with cell lysis parameters (R(2) < 0.1). Serum integrin-linked kinase concentration greater than 2.48 ng/mL had diagnostic sensitivity of 80%, specificity of 95%, positive predictive value of 85.7%, negative predictive value of 92.7%, and overall accuracy of 91% for distinction between malignant pleural mesothelioma and other diseases. Serum integrin-linked kinase concentration in malignant pleural mesothelioma was independent of histologic subtype or asbestos exposure. There was no statistically significant impact of serum integrin-linked kinase concentration on prognosis. CONCLUSIONS: Integrin-linked kinase can be detected in serum of patients with malignant pleural mesothelioma and may be a diagnostic marker for the disease.

Integrin-linked kinase is a functional Mn2+-dependent protein kinase that regulates glycogen synthase kinase-3ß (GSK-3beta) phosphorylation.

BACKGROUND: Integrin-linked kinase (ILK) is a highly evolutionarily conserved, multi-domain signaling protein that localizes to focal adhesions, myofilaments and centrosomes where it forms distinct multi-protein complexes to regulate cell adhesion, cell contraction, actin cytoskeletal organization and mitotic spindle assembly. Numerous studies have demonstrated that ILK can regulate the phosphorylation of various protein and peptide substrates in vitro, as well as the phosphorylation of potential substrates and various signaling pathways in cultured cell systems. Nevertheless, the ability of ILK to function as a protein kinase has been questioned because of its atypical kinase domain. METHODOLOGY/PRINCIPAL FINDINGS: Here, we have expressed full-length recombinant ILK, purified it to >94% homogeneity, and characterized its kinase activity. Recombinant ILK readily phosphorylates glycogen synthase kinase-3 (GSK-3) peptide and the 20-kDa regulatory light chains of myosin (LC(20)). Phosphorylation kinetics are similar to those of other active kinases, and mutation of the ATP-binding lysine (K220 within subdomain 2) causes marked reduction in enzymatic activity. We show that ILK is a Mn-dependent kinase (the K(m) for MnATP is approximately 150-fold less than that for MgATP). CONCLUSIONS/SIGNIFICANCE: Taken together, our data demonstrate that ILK is a bona fide protein kinase with enzyme kinetic properties similar to other active protein kinases.

The oncogenic and growth-suppressive functions of the integrin-linked kinase are distinguished by JNK1 expression in human cancer cells.

While most reports detail an oncogenic function for the integrin-linked kinase (ILK) in human cancer, few describe a contradictory growth-suppressive function. We previously reported that ILK functions as either a tumor suppressor or an oncogene in rhabdomyosarcoma (RMS), in a manner linked to expression of the c-jun amino terminal kinase-1 (JNK1). However, studies in other tumors are lacking. With the advent of bioavailable small molecule inhibitors of ILK, defining both the function of ILK and biomarkers to predict its behaviour are of critical importance. Here, we studied the role of ILK in a panel of tumor cell lines. We demonstrate that ILK functions as either a growth-promoter or suppressor in numerous tumor cell lines. Further, cell lines in which ILK functioned as a growth suppressor displayed elevated JNK1 expression relative to cells in which ILK functioned as an oncogene. Comparison of endogenous JNK1 and JNK1ß isoform expression levels to the cellular response to ILK overexpression demonstrated that JNK1ß isoforms represent biomarkers differentiating the two functions of ILK. Moreover, RNAi and overexpression-based alteration of JNK1 expression levels was sufficient to switch the function of ILK in both transformed and untransformed cells. These results indicate widespread oncogenic and growth-suppressive functions for ILK in multiple human malignancies and suggest that JNK1 isoforms represent biomarkers for ILK neoplastic activity. These results provide a rationale for stratifying patients to receive ILK kinase inhibitors based on individualized tumor-specific ILK function.

Oncogenic ILK, tumor suppression and all that JNK.

In neoplastic cells, proteins exert either pro or anti-tumorigenic functions. However, some proteins exhibit both properties, commonly dependent on specific aberrations occurring in a tumor-specific context. Recently, we demonstrated that the integrin-linked kinase (ILK), generally characterized as an oncogenic protein kinase, functions as a tumor suppressor protein in vitro and in vivo in the aggressive pediatric tumor, rhabdomyosarcoma (RMS). Other studies have similarly demonstrated both growth and tumor suppressive functions for ILK in normal and transformed tissues. The mechanism of ILK tumor suppression in RMS relies on expression levels of another kinase, the c-jun amino terminal kinase-1 (JNK1). These findings support a model in which ILK tumor suppression is mediated in part by elevated JNK1 expression, and indicate both a rationale for stratification of patients to receive anti-ILK therapies, and a need to better understand the context in which ILK displays its seemingly contradictory functions. This review discusses the complex roles of ILK in tumorigenesis, and offers arguments to harness ILK and JNK signaling as novel targets for anti-cancer therapy.

JNK1 determines the oncogenic or tumor-suppressive activity of the integrin-linked kinase in human rhabdomyosarcoma.

Although most reports describe the protein kinase integrin-linked kinase (ILK) as a proto-oncogene, occasional studies detail opposing functions in the regulation of normal and transformed cell proliferation, differentiation, and apoptosis. Here, we demonstrated that ILK functions as an oncogene in the highly aggressive pediatric sarcoma alveolar rhabdomyosarcoma (ARMS) and as a tumor suppressor in the related embryonal rhabdomyosarcoma (ERMS). These opposing functions hinge on signaling through a noncanonical ILK target, JNK1, to the proto-oncogene c-Jun. RNAi-mediated depletion of ILK induced activation of JNK and its target, c-Jun, resulting in growth of ERMS cells, whereas in ARMS cells, it led to loss of JNK/c-Jun signaling and suppression of growth both in vitro and in vivo. Ectopic expression of the fusion gene characteristic of ARMS (paired box 3-forkhead homolog in rhabdomyosarcoma [PAX3-FKHR]) in ERMS cells was sufficient to convert them to an ARMS signaling phenotype and render ILK activity oncogenic. Furthermore, restoration of JNK1 in ARMS reestablished a tumor-suppressive function for ILK. These findings indicate what we believe to be a novel effector pathway regulated by ILK, provide a mechanism for interconversion of oncogenic and tumor-suppressor functions of a single regulatory protein based on the genetic background of the tumor cells, and suggest a rationale for tailored therapy of rhabdomyosarcoma based on the different activities of ILK.

Integrin-linked kinase in the vascular smooth muscle cell response to injury.

Integrin-mediated interactions between smooth muscle cells (SMCs) and the extracellular matrix regulate cell migration and proliferation during neointimal hyperplasia. Integrin-linked kinase (ILK) is a serine-threonine kinase and scaffolding molecule that acts downstream of integrin receptors to modulate cell adhesion; therefore, we examined ILK function in SMCs during wound repair. Silencing of ILK expression with siRNA in vitro decreased cell adhesion to fibronectin and accelerated both cell proliferation and wound closure in the cell monolayer; it also resulted in the rearrangement of focal adhesions and diminished central actin stress fibers. Akt and GSK3beta are ILK substrates that are important in cell motility; however, ILK siRNA silencing did not attenuate injury-induced increases in Akt and GSK3beta phosphorylation. Following balloon catheter injury of the rat carotid artery in vivo, a dramatic decrease in ILK levels coincided with both the proliferation and migration of SMCs, which leads to the formation of a thickened neointima. Immunostaining revealed decreased ILK levels in the media and deep layers of the neointima, but increased ILK levels in the subluminal layers of the intima. Taken together, these results suggest that ILK functions to maintain SMC quiescence in the normal artery. A decrease in ILK levels after injury may permit SMC migration, proliferation, and neointimal thickening, and its re-expression at the luminal surface may attenuate this process during later stages of the injury response.

Parvin-beta inhibits breast cancer tumorigenicity and promotes CDK9-mediated peroxisome proliferator-activated receptor gamma 1 phosphorylation.

Parvin-beta is a focal adhesion protein downregulated in human breast cancer cells. Loss of Parvin-beta contributes to increased integrin-linked kinase activity, cell-matrix adhesion, and invasion through the extracellular matrix in vitro. The effect of ectopic Parvin-beta expression on the transcriptional profile of MDA-MB-231 breast cancer cells, which normally do not express Parvin-beta, was evaluated. Particular emphasis was placed upon propagating MDA-MB-231 breast cancer cells in three-dimensional culture matrices. Interestingly, Parvin-beta reexpression in MDA-MB-231 cells increased the mRNA expression, serine 82 phosphorylation (mediated by CDK9), and activity of the nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma), and there was a concomitant increase in lipogenic gene expression as a downstream effector of PPARgamma. Importantly, Parvin-beta suppressed breast cancer growth in vivo, with associated decreased proliferation. These data suggest that Parvin-beta might influence breast cancer progression.

Integrin-linked kinase at the heart of cardiac contractility, repair, and disease.

Recent advances in cardiac physiology identify the integrin-linked kinase (ILK) as an essential molecule regulating cardiac growth, contractility, and repair. A key transducer of biochemical signals initiated at the plasma membrane by cell-matrix interactions, ILK now emerges as a crucial player in mechanotransduction by integrins. Animal models have been particularly instructive in dissecting the cardiac functions of ILK and its associated proteins, such as parvins and PINCH, and have clearly established ILK as a major contributor to cardiac health. ILK gene knockouts in mice, flies, and worms result in early embryonic lethality because of cell adhesion defects and cytoskeletal disorganization. Although widely distributed in mammalian tissues, ILK expression is highest in the heart, and cardiac-specific ablation of ILK causes cardiomyopathy and sudden death in mice. ILK protein complexes are found in the sarcomere, which is the basic contractile unit of myocytes. A natural inactivating mutation in the kinase domain of ILK disrupts ILK protein interactions in the sarcomere, causing a contractile defect in the zebrafish heart. The relatively subtle phenotype of mutant ILK hearts, compared with ILK-ablated hearts, suggests multiple cardiac ILK functions. Cardiac-specific expression of ILK in transgenic mice induces a hypertrophic program, pointing to ILK as a proximal regulator of multiple hypertrophic signal transduction pathways. ILK protein interactions may also be important in mediating postinfarct cell migration and myocardial repair.

An essential role for the integrin-linked kinase-glycogen synthase kinase-3 beta pathway during dendrite initiation and growth.

Multiple cues, including growth factors and circuit activity, signal to regulate the initiation and growth of mammalian dendrites. In this study, we have asked how these environmental cues regulate dendrite formation, and in particular, whether dendrite initiation and growth requires integrin-linked kinase (ILK) or its downstream effector, glycogen synthase kinase-3beta (GSK-3beta). In cultured sympathetic neurons, NGF and neuronal depolarization activated ILK and promoted dendrite initiation and growth, and inhibition of ILK (either pharmacologically, with a dominant-negative form of ILK, or by genetic knockdown) reduced depolarization-induced dendrite formation. In sympathetic neurons, ILK phosphorylated and inhibited GSK-3beta, and inhibition of GSK-3beta (either pharmacologically, with dominant-negative GSK-3beta, or by genetic knockdown) caused robust dendrite initiation. GSK-3beta inhibition also caused dendrite initiation in cultured cortical neurons and growth of hippocampal neurons in slice cultures. GSK-3beta functioned downstream of ILK to regulate dendrite formation, because inhibition of GSK-3beta promoted dendrite initiation even when ILK was simultaneously inhibited. Moreover, GSK-3beta promoted dendrite formation in sympathetic neurons by regulating the activity of a key dendrite formation effector, the MAP (microtubule-associated protein) kinase kinase (MEK)-extracellular signal-regulated protein kinase (ERK) pathway. Specifically, inhibition of GSK-3beta led to increased ERK phosphorylation, and inhibition of MEK completely blocked the effects of GSK-3beta inhibition on dendrite initiation and growth. Thus, the ILK-GSK-3beta pathway plays a key role in regulating dendrite formation in developing mammalian neurons.

Overexpression of integrin-linked kinase induces cardiac stem cell expansion.

OBJECTIVE: Recent evidence suggests that the adult heart contains stem cells that are capable of self-renewal as well as multilineage differentiation. However, their inherent capacity for self-renewal is limiting to cell replacement applications. Integrin-linked kinase is a multifunctional protein kinase that activates Wnt target genes implicated in the symmetric replication of embryonic stem cells. METHODS: Primary cultures derived from human fetal cardiac tissue (19-22 weeks' gestation) were grown in serum-free media and evaluated for the presence of cardiac progenitor cells. The effect of integrin-linked kinase was ascertained by adenoviral overexpression. RESULTS: Cultures infected with wild-type integrin-linked kinase yielded a significant (P = .001), approximately 5-fold increase in both the absolute number and the frequency of c-Kit-positive, myosin-negative cells. Cardiospheres, comprised on morphologically homogeneous, anchorage-independent cells, were reproducibly present at days 7 to 10 and formed derivative cardiospheres in multiple passages. Integrin-linked kinase infection of primary cardiac cell cultures resulted in a greater number of primary spheres at each cell density tested, compared with untreated and virus controls (P = .001). Secondary spheres transferred to differentiation medium and 5-aza-deoxycytodine (10 micromol/L) generated cells exhibiting biochemical evidence of differentiation into cardiomyocytes, smooth muscle cells, and endothelial cells. CONCLUSIONS: This study demonstrates that self-renewing cardiospheres generated from human fetal cardiac cells are composed of cells exhibiting the properties of stem cells, including the capacity for self-renewal and multilineage differentiation. Our results suggest that integrin-linked kinase promotes stem cell amplification and can be applied therapeutically to overcome a major limitation in the field of cardiac regenerative medicine.

Integrin-linked kinase expression is elevated in human cardiac hypertrophy and induces hypertrophy in transgenic mice.

BACKGROUND: Although numerous signaling pathways are known to be activated in experimental cardiac hypertrophy, the molecular basis of the hypertrophic response inherent in human heart diseases remains largely unknown. Integrin-linked kinase (ILK) is a multifunctional protein kinase that physically links beta-integrins with the actin cytoskeleton, suggesting a potential mechanoreceptor role. METHODS AND RESULTS: Here, we show a marked increase in ILK protein levels in hypertrophic ventricles of patients with congenital and acquired outflow tract obstruction. This increase in ILK was associated with activation of the Rho family guanine triphosphatases, Rac1 and Cdc42, and known hypertrophic signaling kinases, including extracellular signal-related kinases (ERK1/2) and p70 S6 kinase. Transgenic mice with cardiac-specific expression of a constitutively active ILK (ILK(S343D)) or wild-type ILK (ILK(WT)) 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 (ILK(R211A)) were unable to mount a compensatory hypertrophic response to angiotensin II in vivo. CONCLUSIONS: Taken together, these results identify ILK-regulated signaling as a broadly adaptive hypertrophic response mechanism relevant to a wide range of clinical heart disease.