Phosphorylation-dependent regulation of nuclear localization and functions of integrin-linked kinase

Integrin-linked kinase-frizzled 7 interaction maintains cancer stem cells to drive platinum resistance in ovarian cancer

BACKGROUND

Platinum-based chemotherapy regimens are a mainstay in the management of ovarian cancer (OC), but emergence of chemoresistance poses a significant clinical challenge. The persistence of ovarian cancer stem cells (OCSCs) at the end of primary treatment contributes to disease recurrence. Here, we hypothesized that the extracellular matrix protects CSCs during chemotherapy and supports their tumorigenic functions by activating integrin-linked kinase (ILK), a key enzyme in drug resistance.

METHODS

TCGA datasets and OC models were investigated using an integrated proteomic and gene expression analysis and examined ILK for correlations with chemoresistance pathways and clinical outcomes. Canonical Wnt pathway components, pro-survival signaling, and stemness were examined using OC models. To investigate the role of ILK in the OCSC-phenotype, a novel pharmacological inhibitor of ILK in combination with carboplatin was utilized in vitro and in vivo OC models.

RESULTS

In response to increased fibronectin secretion and integrin β1 clustering, aberrant ILK activation supported the OCSC phenotype, contributing to OC spheroid proliferation and reduced response to platinum treatment. Complexes formed by ILK with the Wnt receptor frizzled 7 (Fzd7) were detected in tumors and correlated with metastatic progression. Moreover, TCGA datasets confirmed that combined expression of ILK and Fzd7 in high grade serous ovarian tumors is correlated with reduced response to chemotherapy and poor patient outcomes. Mechanistically, interaction of ILK with Fzd7 increased the response to Wnt ligands, thereby amplifying the stemness-associated Wnt/β-catenin signaling. Notably, preclinical studies showed that the novel ILK inhibitor compound 22 (cpd-22) alone disrupted ILK interaction with Fzd7 and CSC proliferation as spheroids. Furthermore, when combined with carboplatin, this disruption led to sustained AKT inhibition, apoptotic damage in OCSCs and reduced tumorigenicity in mice.

CONCLUSIONS

This "outside-in" signaling mechanism is potentially actionable, and combined targeting of ILK-Fzd7 may lead to new therapeutic approaches to eradicate OCSCs and improve patient outcomes.

PMM2 controls ERα levels and cell proliferation in ESR1 Y537S variant expressing breast cancer cells

PURPOSE

Metabolic reprogramming in breast cancer (BC) subtypes offers potential personalized treatment targets. Estrogen receptor α (ERα)-positive BC patients undergoing endocrine therapy (ET) can develop ET-resistant metastatic disease. Specific mutations, like Y537S in ERα, drive uncontrolled cell proliferation. Targeting mutant receptor levels shows promise for inhibiting growth in metastatic BC expressing ERα variants. Additionally, metabolic reprogramming occurs in ERα Y537S mutant cells. Consequently, we conducted a screen to identify metabolic proteins reducing intracellular levels of ERα Y537S and inhibiting cell proliferation.

METHODS

Nine metabolic proteins were identified in a siRNA-based screen, with phosphomannose mutase 2 (PMM2) showing the most promise. We measured the impact of PMM2 depletion on ERα stability and cell proliferation in ERα Y537S mutant cells. Additionally, we tested the effect of PMM2 reduction on the hyperactive phenotype of the mutant and its proliferation when combined with metastatic BC treatment drugs.

RESULTS

PMM2 emerged as a significant target due to its correlation with better relapse-free survival, overexpression in ERα-positive tumors, and its elevation in ERα Y537S-expressing cells. Depletion of PMM2 induces degradation of ERα Y537S, inhibits cell proliferation, and reduces ERα signaling. Notably, reducing PMM2 levels re-sensitizes ERα Y537S-expressing cells to certain ET drugs and CDK4/CDK6 inhibitors. Mechanistically, depletion of PMM2 leads to a reduction in ESR1 mRNA levels, resulting in decreased ERα receptor protein expression. Furthermore, the reduction of PMM2 decreases FOXA1 levels, which plays a crucial role in ERα regulation.

CONCLUSIONS

Our findings establish PMM2 as an innovative therapeutic target for metastatic BC expressing the ERα Y537S variant, offering alternative strategies for managing and treating this disease.

Integrin-linked kinase-frizzled 7 interaction maintains cancer stem cells to drive platinum resistance in ovarian cancer

Background

Platinum-based chemotherapy regimens are a mainstay in the management of ovarian cancer (OC), but emergence of chemoresistance poses a significant clinical challenge. The persistence of ovarian cancer stem cells (OCSCs) at the end of primary treatment contributes to disease recurrence. Here, we hypothesized that the extracellular matrix protects CSCs during chemotherapy and supports their tumorigenic functions by activating integrin-linked kinase (ILK), a key enzyme in drug resistance.

Methods

TCGA datasets and OC models were investigated using an integrated proteomic and gene expression analysis and examined ILK for correlations with chemoresistance pathways and clinical outcomes. Canonical Wnt pathway components, pro-survival signaling, and stemness were examined using OC models. To investigate the role of ILK in the OCSC-phenotype, a novel pharmacological inhibitor of ILK in combination with carboplatin was utilized in vitro and in vivo OC models.

Results

In response to increased fibronectin (FN) secretion and integrin β1 clustering, aberrant ILK activation supported the OCSC phenotype, contributing to OC spheroid proliferation and reduced response to platinum treatment. Complexes formed by ILK with the Wnt receptor frizzled 7 (Fzd7) were detected in tumors and showed a strong correlation with metastatic progression. Moreover, TCGA datasets confirmed that combined expression of ILK and Fzd7 in high grade serous ovarian tumors is correlated with reduced response to chemotherapy and poor patient outcomes. Mechanistically, interaction of ILK with Fzd7 increased the response to Wnt ligands, thereby amplifying the stemness-associated Wnt/β-catenin signaling. Notably, preclinical studies showed that the novel ILK inhibitor compound 22 (cpd-22) alone disrupted ILK interaction with Fzd7 and CSC proliferation as spheroids. Furthermore, when combined with carboplatin, this disruption led to sustained AKT inhibition, apoptotic damage in OCSCs and reduced tumorigenicity in mice.

Conclusions

This "outside-in" signaling mechanism is potentially actionable, and combined targeting of ILK-Fzd7 may represent a new therapeutic strategy to eradicate OCSCs and improve patient outcomes.

Proteomics profiling and lysine malonylation analysis in primary Sjogren's syndrome

Primary Sjogren's Syndrome (pSS) is a chronic autoimmune disease, with unclear pathogenies. Lysine-malonylation (Kmal) as a novel post-translational modification (PTMs) was found associated with metabolic, immune, and inflammatory processes. For purpose of investigating the proteomic profile and functions of kmal in pSS, liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based analysis and bioinformatics analysis are performed based on twenty-eight pSS patients versus twenty-seven healthy controls (HCs). A total of 331 down-regulated proteins and 289 up-regulated proteins are observed in differentially expressed proteins (DEPs) of pSS. We discover the expression of transforming growth factor beta-1 (TGFB1) and CD40 ligand downregulate which enriches in the inflammatory associated pathway. Expression of signal transducer and activator of transcription 1-alpha/beta (STAT1) show upregulation and enrich in type I interferon signaling pathway and IL-27-mediated signaling pathway. In differentially malonylated proteins (DMPs) of pSS, we identify 3 proteins are down-regulated in 7 sites and 18 proteins are up-regulated in 19 sites. Expression of malonylated integrin-linked kinase (ILK) significantly enrich in the focal adhesion pathway. Together, our data provide evidence that downregulation of TGFB1 and CD40LG play a critical role in the inflammatory process of pSS, while upregulation of STAT1 may be associated with IL-27 immunity and pSS immune dysfunction. Moreover, kmal modification at the kinase domain of ILK may destabilize ILK that thus contributing to pSS pathogenies by regulating the focal adhesion pathway. SIGNIFICANCE: Our research offered the first characterization of Kmal, a newly identified form of lysine acylation in pSS, as well as proteomic data on individuals with pSS. In this study, we found that several key DMPs were associated with focal adhesion pathway, which contributes to the development of pSS. The present results provide an informative dataset for the future exploration of Kmal in pSS.

Protein posttranslational modifications in health and diseases: Functions, regulatory mechanisms, and therapeutic implications

Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.

Targeting P21-Activated Kinase-1 for Metastatic Prostate Cancer

Metastatic prostate cancer (mPCa) has limited therapeutic options and a high mortality rate. The p21-activated kinase (PAK) family of proteins is important in cell survival, proliferation, and motility in physiology, and pathologies such as infectious, inflammatory, vascular, and neurological diseases as well as cancers. Group-I PAKs (PAK1, PAK2, and PAK3) are involved in the regulation of actin dynamics and thus are integral for cell morphology, adhesion to the extracellular matrix, and cell motility. They also play prominent roles in cell survival and proliferation. These properties make group-I PAKs a potentially important target for cancer therapy. In contrast to normal prostate and prostatic epithelial cells, group-I PAKs are highly expressed in mPCA and PCa tissue. Importantly, the expression of group-I PAKs is proportional to the Gleason score of the patients. While several compounds have been identified that target group-I PAKs and these are active in cells and mice, and while some inhibitors have entered human trials, as of yet, none have been FDA-approved. Probable reasons for this lack of translation include issues related to selectivity, specificity, stability, and efficacy resulting in side effects and/or lack of efficacy. In the current review, we describe the pathophysiology and current treatment guidelines of PCa, present group-I PAKs as a potential druggable target to treat mPCa patients, and discuss the various ATP-competitive and allosteric inhibitors of PAKs. We also discuss the development and testing of a nanotechnology-based therapeutic formulation of group-I PAK inhibitors and its significant potential advantages as a novel, selective, stable, and efficacious mPCa therapeutic over other PCa therapeutics in the pipeline.

The role of Actopaxin in tumor metastasis

Actopaxin is a newly discovered focal adhesions (FAs) protein, actin-binding protein and pseudopodia-enriched molecule. It can not only bind to a variety of FAs proteins (such as Paxillin, ILK and PINCH) and non-FAs proteins (such as TESK1, CdGAP, β2-adaptin, G3BP2, ADAR1 and CD29), but also participates in multiple signaling pathways. Thus, it plays a crucial role in regulating important processes of tumor metastasis, including matrix degradation, migration, and invasion, etc. This review covers the latest progress in the structure and function of Actopaxin, its interaction with other proteins as well as its involvement in regulating tumor development and metastasis. Additionally, the current limitations for Actopaxin related studies and the possible research directions on it in the future are also discussed. It is hoped that this review can assist relevant researchers to obtain a deep understanding of the role that Actopaxin plays in tumor progression, and also enlighten further research and development of therapeutic approaches for the treatment of tumor metastasis.

Tissue transglutaminase activates integrin-linked kinase and β-catenin in ovarian cancer

Ovarian cancer (OC) is the most lethal gynecological cancer. OC cells have high proliferative capacity, are invasive, resist apoptosis, and tumors often display rearrangement of extracellular matrix (ECM) components, contributing to accelerated tumor progression. The multifunctional protein tissue transglutaminase (TG2) is known to be secreted in the tumor microenvironment (TME), where it interacts with fibronectin (FN) and the cell surface receptor β1 integrin. However, the mechanistic role of TG2 in cancer cell proliferation is unknown. Here, we demonstrate TG2 directly interacts with and facilitates the phosphorylation and activation of the integrin effector protein integrin-linked kinase (ILK) at Ser246. We show TG2 and p-Ser246-ILK form a complex that is detectable in patient-derived OC primary cells grown on FN-coated slides. In addition, we show co-expression of TGM2 and ILK correlates with poor clinical outcome. Mechanistically, we demonstrate TG2-mediated ILK activation causes phosphorylation of glycogen synthase kinase-3α/β (GSK-3α/β), allowing β-catenin nuclear translocation and transcriptional activity. Furthermore, inhibition of TG2 and ILK using small molecules, neutralizing antibodies, or shRNA-mediated knockdown block cell adhesion to the FN matrix, as well as the Wnt receptor response to the Wnt-3A ligand, and ultimately, cell adhesion, growth, and migration. In conclusion, we demonstrate TG2 directly interacts with and activates ILK in OC cells and tumors, and define a new mechanism which links ECM cues with β-catenin signaling in OC. These results suggest a central role of TG2/FN/integrin clusters in ECM rearrangement and indicate downstream effector ILK may represent a potential new therapeutic target in OC.

Cell Surface Engineering Enables Surfaceome Profiling

Cell surface proteins (CSPs) are vital molecular mediators for cells and their extracellular environment. Thus, understanding which CSPs are displayed on cells, especially in different cell states, remains an important endeavor in cell biology. Here, we describe the integration of cell surface engineering with radical-mediated protein biotinylation to profile CSPs. This method relies on the prefunctionalization of cells with cholesterol lipid groups, followed by sortase-catalyzed conjugation with an APEX2 ascorbate peroxidase enzyme. In the presence of biotin-phenol and H₂O₂, APEX2 catalyzes the formation of highly reactive biotinyl radicals that covalently tag electron-rich residues within CSPs for subsequent streptavidin-based enrichment and analysis by quantitative mass spectrometry. While APEX2 is traditionally used to capture proximity-based interactomes, we envisioned using it in a "baitless" manner on cell surfaces to capture CSPs. We evaluate this strategy in light of another CSP labeling method that relies on the presence of cell surface sialic acid. Using the APEX2 strategy, we describe the CSPs found in three mammalian cell lines and compare CSPs in adherent versus three-dimensional pancreatic adenocarcinoma cells.

The Expression of PPAR Pathway-Related Genes Can Better Predict the Prognosis of Patients with Colon Adenocarcinoma

The postoperative survival time and quality of life of patients with colon adenocarcinoma (COAD) varies widely. In order to make accurate decisions after surgery, clinicians need to distinguish patients with different prognostic trends. However, we still lack effective methods to predict the prognosis of COAD patients. Accumulated evidences indicated that the inhibition of peroxisome proliferator-activated receptors (PPARs) and a portion of their target genes were associated with the development of COAD. Our study found that the expression of several PPAR pathway-related genes were linked to the prognosis of COAD patients. Therefore, we developed a scoring system (named PPAR-Riskscore) that can predict patients' outcomes. PPAR-Riskscore was constructed by univariate Cox regression based on the expression of 4 genes (NR1D1, ILK, TNFRSF1A, and REN) in tumor tissues. Compared to typical TNM grading systems, PPAR-Riskscore has better predictive accuracy and sensitivity. The reliability of the system was tested on six external validation datasets. Furthermore, PPAR-Riskscore was able to evaluate the immune cell infiltration and chemotherapy sensitivity of each tumor sample. We also combined PPAR-Riskscore and clinical features to create a nomogram with greater clinical utility. The nomogram can help clinicians make precise treatment decisions regarding the possible long-term survival of patients after surgery.

Integrin-Linked Kinase Reduces H3K9 Trimethylation to Enhance Herpes Simplex Virus 1 Replication

Histone modifications control the lytic gene expression of herpes simplex virus 1 (HSV-1). The heterochromatin mark, trimethylation of histone H3 on lysine (K) 9 (H3K9me3), is detected on HSV-1 genomes at early phases of infection to repress viral gene transcription. However, the components and mechanisms involved in the process are mostly unknown. Integrin-linked kinase (ILK) is activated by PI3K to phosphorylate Akt and promote several RNA virus infections. Akt has been shown to enhance HSV-1 infection, suggesting a pro-viral role of ILK in HSV-1 infection that has not been addressed before. Here, we reveal that ILK enhances HSV-1 replication in an Akt-independent manner. ILK reduces the accumulation of H3K9me3 on viral promoters and replication compartments. Notably, ILK reduces H3K9me3 in a manner independent of ICP0. Instead, we show an increased binding of H3K9 methyltransferase SUV39H1 and corepressor TRIM28 on viral promoters in ILK knockdown cells. Knocking down SUV39H1 or TRIM28 increases HSV-1 lytic gene transcription in ILK knockdown cells. These results show that ILK antagonizes SVU39H1- and TRIM28-mediated repression on lytic gene transcription. We further demonstrate that ILK knockdown reduces TRIM28 phosphorylation on serine 473 and 824 in HSV-1-infected cells, suggesting that ILK facilitates TRIM28 phosphorylation to abrogate its inhibition on lytic gene transcription. OSU-T315, an ILK inhibitor, suppresses HSV-1 replication in cells and mice. In conclusion, we demonstrate that ILK decreases H3K9me3 on HSV-1 DNA by reducing SUV39H1 and TRIM28 binding. Moreover, our results suggest that targeting ILK could be a broad-spectrum antiviral strategy for DNA and RNA virus infections, especially for DNA viruses controlled by histone modifications.

Indoxyl sulfate- and P-cresol-induced monocyte adhesion and migration is mediated by integrin-linked kinase-dependent podosome formation

Cardiovascular disease is an important cause of death in patients with chronic kidney disease (CKD). Protein-bound uremic toxins, such as p-cresyl and indoxyl sulfate (IS), are poorly removed during hemodialysis, leading to vascular endothelial dysfunction and leukocyte extravasation. These processes can be related to dynamic adhesion structures called podosomes. Several studies have indicated the role of integrin-linked kinase (ILK) in the accumulation of integrin-associated proteins in podosomes. Here, we investigated the involvement of ILK and podosome formation in the adhesion and extravasation of monocytes under p-cresol (pc) and IS exposure. Incubation of THP-1 human monocyte cells with these toxins upregulated ILK kinase activity. Together, both toxins increased cell adhesion, podosome formation, extracellular matrix degradation, and migration of THP-1 cells, whereas ILK depletion with specific small interfering RNAs suppressed these processes. Interestingly, F-actin colocalized with cortactin in podosome cores, while ILK was colocalized in podosome rings under toxin stimulation. Podosome Wiskott-Aldrich syndrome protein (WASP)-interacting protein (WIP) and AKT protein depletion demonstrated that monocyte adhesion depends on podosome formation and that the ILK/AKT signaling pathway is involved in these processes. Ex vivo experiments showed that both toxins induced adhesion and podosome formation in leukocytes from wild-type mice, whereas these effects were not observed in leukocytes of conditional ILK-knockdown animals. In summary, under pc and IS stimulation, monocytes increase podosome formation and transmigratory capacity through an ILK/AKT signaling pathway-dependent mechanism, which could lead to vascular injury. Therefore, ILK could be a potential therapeutic target for the treatment of vascular damage associated with CKD.

An enzyme involved in organizing structural proteins into protrusions of the cell membrane helps facilitate the movement of white blood cells that occurs in chronic kidney disease and can lead to cardiovascular damage. Laura Calleros from the University of Alcalá, Madrid, Spain, and colleagues showed how toxic metabolites that build up in the bloodstream as kidneys fail induce the activity of an enzyme called integrin-linked kinase (ILK). This enzyme in turn spurs white blood cells to form protrusions called podosomes that make the cells more mobile, enabling them to move out of blood vessels and into surrounding tissues where they can cause inflammation -mediated injury. ILK inactivation reversed these effects. Therapies that target the enzyme could therefore help limit the cardiovascular complications of chronic kidney disease.

Integrin-linked kinase (ILK): the known vs. the unknown and perspectives

Integrin-linked kinase (ILK) is a multifunctional molecular actor in cell-matrix interactions, cell adhesion, and anchorage-dependent cell growth. It combines functions of a signal transductor and a scaffold protein through its interaction with integrins, then facilitating further protein recruitment within the ILK-PINCH-Parvin complex. ILK is involved in crucial cellular processes including proliferation, survival, differentiation, migration, invasion, and angiogenesis, which reflects on systemic changes in the kidney, heart, muscle, skin, and vascular system, also during the embryonal development. Dysfunction of ILK underlies the pathogenesis of various diseases, including the pro-oncogenic activity in tumorigenesis. ILK localizes mostly to the cell membrane and remains an important component of focal adhesion. We do know much about ILK but a lot still remains either uncovered or unclear. Although it was initially classified as a serine/threonine-protein kinase, its catalytical activity is now questioned due to structural and functional issues, leaving the exact molecular mechanism of signal transduction by ILK unsolved. While it is known that the three isoforms of ILK vary in length, the presence of crucial domains, and modification sites, most of the research tends to focus on the main isoform of this protein while the issue of functional differences of ILK2 and ILK3 still awaits clarification. The activity of ILK is regulated on the transcriptional, protein, and post-transcriptional levels. The crucial role of phosphorylation and ubiquitylation has been investigated, but the functions of the vast majority of modifications are still unknown. In the light of all those open issues, here we present an extensive literature survey covering a wide spectrum of latest findings as well as a past-to-present view on controversies regarding ILK, finishing with pointing out some open questions to be resolved by further research.

Group I PAKs in myelin formation and repair of the central nervous system: what, when, and how

p21-activated kinases (PAKs) are a family of cell division control protein 42/ras-related C3 botulinum toxin substrate 1 (Cdc42/Rac1)-activated serine/threonine kinases. Group I PAKs (PAK1-3) have distinct activation mechanisms from group II PAKs (PAK4-6) and are the focus of this review. In transformed cancer cells, PAKs regulate a variety of cellular processes and molecular pathways which are also important for myelin formation and repair in the central nervous system (CNS). De novo mutations in group I PAKs are frequently seen in children with neurodevelopmental defects and white matter anomalies. Group I PAKs regulate virtually every aspect of neuronal development and function. Yet their functions in CNS myelination and remyelination remain incompletely defined. Herein, we highlight the current understanding of PAKs in regulating cellular and molecular pathways and discuss the status of PAK-regulated pathways in oligodendrocyte development. We point out outstanding questions and future directions in the research field of group I PAKs and oligodendrocyte development.

Kinases of the Focal Adhesion Complex Contribute to Cardiomyocyte Specification

Differentiation of pluripotent stem cells to cardiomyocytes is influenced by culture conditions including the extracellular matrices or similar synthetic scaffolds on which they are grown. However, the molecular mechanisms that link the scaffold with differentiation outcomes are not fully known. Here, we determined by immunofluorescence staining and mass spectrometry approaches that extracellular matrix (ECM) engagement by mouse pluripotent stem cells activates critical components of canonical wingless/integrated (Wnt) signaling pathways via kinases of the focal adhesion to drive cardiomyogenesis. These kinases were found to be differentially activated depending on type of ECM engaged. These outcomes begin to explain how varied ECM composition of in vivo tissues with development and in vitro model systems gives rise to different mature cell types, having broad practical applicability for the design of engineered tissues.

Integrin-Linked Kinase (ILK) Plays an Important Role in the Laminin-Dependent Development of Dorsal Root Ganglia during Chicken Embryogenesis

Integrin-linked kinase (ILK) is mainly localized in focal adhesions where it interacts and modulates the downstream signaling of integrins affecting cell migration, adhesion, and survival. The interaction of dorsal root ganglia (DRG) cells, being part of the peripheral nervous system (PNS), with the extracellular matrix (ECM) via integrins is crucial for proper PNS development. A few studies have focused on ILK’s role in PNS development, but none of these have focused on chicken. Therefore, we decided to investigate ILK’s role in the development of Gallus gallus domesticus’s DRG. First, using RT-PCR, Western blotting, and in situ hybridization, we show that ILK is expressed in DRG. Next, by immunocytochemistry, we show ILK’s localization both intracellularly and on the cell membrane of DRG neurons and Schwann cell precursors (SCPs). Finally, we describe ILK’s involvement in multiple aspects of DRG development by performing functional experiments in vitro. IgG-mediated interruption of ILK’s action improved DRG neurite outgrowth, modulated their directionality, stimulated SCPs migration, and impacted growth cone morphology in the presence of laminin-1 or laminin-1 mimicking peptide IKVAV. Taken together, our results show that ILK is important for chicken PNS development, probably via its exposure to the ECM.

Integrin Linked Kinase (ILK) and its Role in Liver Pathobiology

Integrin linked kinase (ILK) is a vital signaling protein ubiquitously expressed throughout the body. It binds to intracellular integrins to help promote signaling related to cell adhesion, apoptosis, proliferation, migration, and a plethora of other common cellular functions. In this review, ILKs role in the liver is detailed. Studies have shown ILK to be a major participant in hepatic ECM organization, liver regeneration, insulin resistance, and hepatocellular carcinoma.

PAK1 inhibition reduces tumor size and extends the lifespan of mice in a genetically engineered mouse model of Neurofibromatosis Type 2 (NF2)

Neurofibromatosis Type II (NF2) is an autosomal dominant cancer predisposition syndrome in which germline haploinsufficiency at the NF2 gene confers a greatly increased propensity for tumor development arising from tissues of neural crest derived origin. NF2 encodes the tumor suppressor, Merlin, and its biochemical function is incompletely understood. One well established function of Merlin is as a negative regulator of group A serine/threonine p21 activated kinases (PAKs). In these studies we explore the role of PAK1 and its closely related paralog, PAK2, both pharmacologically and genetically, in Merlin deficient Schwann cells and in a genetically engineered mouse model (GEMM) that develops spontaneous vestibular and spinal schwannomas. We demonstrate that PAK1 and PAK2 are both hyper activated in Merlin deficient murine schwannomas. In preclinical trials, a pan Group A PAK inhibitor, FRAX-1036, transiently reduced PAK1 and PAK2 phosphorylation in vitro, but had insignificant efficacy in vivo. NVS-PAK1-1, a PAK1 selective inhibitor, had a greater but still minimal effect on our GEMM phenotype. However, genetic ablation of Pak1 but not Pak2 reduced tumor formation in our NF2 GEMM. Moreover, germline genetic deletion of Pak1 was well tolerated while conditional deletion of Pak2 in Schwann cells resulted in significant morbidity and mortality. These data support the further development of PAK1-specific small molecule inhibitors and the therapeutic targeting of PAK1 in vestibular schwannomas and argue against PAK1 and PAK2 existing as functionally redundant protein isoforms in Schwann cells.

Chemical carcinogen-induced rat mammary carcinogenesis is a potential model of p21-activated kinase positive female breast cancer

The p21-activated kinase 1 (PAK1) gene encodes a serine/threonine kinase that is overexpressed in a subset of human breast carcinomas with poor prognosis. The laboratory rat (Rattus norvegicus) orthologous gene is located at Mammary carcinoma susceptibility 3 (Mcs3) QTL on rat chromosome 1. We used quantitative PCR to determine effects of Mcs3 genotype and 7,12-dimethylbenz(a)anthracene (DMBA) exposure on Pak1 expression. There was no effect of Mcs3 genotype; however, there was a 3.5-fold higher Pak1 level in DMBA-exposed mammary glands (MGs) than in unexposed glands (P < 0.05). Sequence variants in Pak1 exons did not alter amino acid sequence between Mcs3-susceptible and -resistant strains. Protein expression of PAK1/Pak1 in human breast carcinomas and DMBA-exposed rat mammary glands was detected using immunohistochemistry (IHC). Rat mammary glands from 12-wk-old females unexposed to DMBA were negative for Pak1, whereas 24% of carcinogen-exposed mammary glands from age-matched females stained positive for Pak1. The positive mammary glands exposed to carcinogen had no pathological signs of disease. Human breast carcinomas, used as comparative controls, had a 22% positivity rats. This was consistent with other human breast cancer studies of PAK1 expression. Similar frequencies of human/rat PAK1/Pak1 expression in female breast carcinomas and carcinogen-induced rat mammary glands, showing no visible pathogenesis of disease, suggests aberrant PAK1 expression is an early event in development of some breast cancers. Laboratory rats will be a useful experimental organism for comparative studies of Pak1-mediated mechanisms of breast carcinogenesis. Future studies of PAK1 as a diagnostic marker of early breast disease are warranted.

P21-Activated Kinase 1: Emerging biological functions and potential therapeutic targets in Cancer

The p21-Activated kinase 1 (PAK1), a member of serine-threonine kinases family, was initially identified as an interactor of the Rho GTPases RAC1 and CDC42, which affect a wide range of processes associated with cell motility, survival, metabolism, cell cycle, proliferation, transformation, stress, inflammation, and gene expression. Recently, the PAK1 has emerged as a potential therapeutic target in cancer due to its role in many oncogenic signaling pathways. Many PAK1 inhibitors have been developed as potential preclinical agents for cancer therapy. Here, we provide an overview of essential roles that PAK1 plays in cancer, including its structure and autoactivation mechanism, its crucial function from onset to progression to metastasis, metabolism, immune escape and even drug resistance in cancer; endogenous regulators; and cancer-related pathways. We also summarize the reported PAK1 small-molecule inhibitors based on their structure types and their potential application in cancer. In addition, we provide overviews on current progress and future challenges of PAK1 in cancer, hoping to provide new ideas for the diagnosis and treatment of cancer.

The identification of nuclear αvβ3 integrin in ovarian cancer: non-paradigmal localization with cancer promoting actions

Nuclear translocation of transmembrane proteins was reported in high-grade serous ovarian cancer (HGSOC), a highly aggressive gynecological malignancy. Although the membrane receptor αvβ3 integrin is amply expressed in HGSOC and involved in disease progression, its nuclear localization was never demonstrated. Nuclear αvβ3 was explored in HGSOC cells (OVCAR3, KURAMOCHI, and JHOS4), nuclear localization signal (NLS) modified β3 OVCAR3, Chinese hamster ovaries (CHO-K1) and human embryonic kidney (HEK293) before/after transfections with β3/β1 integrins. We used the ImageStream technology, Western blots (WB), co immunoprecipitations (Co-IP), confocal immunofluorescence (IF) microscopy, flow cytometry for cell counts and cell cycle, wound healing assays and proteomics analyses. Fresh/archived tumor tissues were collected from nine HGSOC patients and normal ovarian and fallopian tube (FT) tissues from eight nononcological patients and assessed for nuclear αvβ3 by WB, confocal IF microscopy and immunohistochemistry (IHC). We identified nuclear αvβ3 in HGSOC cells and tissues, but not in normal ovaries and FTs. The nuclear integrin was Tyr 759 phosphorylated and functionally active. Nuclear αvβ3 enriched OVCAR3 cells demonstrated induced proliferation and oncogenic signaling, intact colony formation ability and inhibited migration. Proteomics analyses revealed a network of nuclear αvβ3-bound proteins, many of which with key cancer-relevant activities. Identification of atypical nuclear localization of the αvβ3 integrin in HGSOC challenges the prevalent conception that the setting in which this receptor exerts its pleiotropic actions is exclusively at the cell membrane. This discovery proposes αvβ3 moonlighting functions and may improve our understanding of the molecular basis of ovarian cancer pathogenesis.

Downstream Effectors of ILK in Cisplatin-Resistant Ovarian Cancer

Despite good responses to first-line treatment with platinum-based combination chemotherapy, most ovarian cancer patients will relapse and eventually develop platinum-resistant disease with poor prognosis. Although reports suggest that integrin-linked kinase (ILK) is a potential target for ovarian cancer treatment, identification of ILK downstream effectors has not been fully explored. The purpose of this study was to investigate the molecular and biological effects of targeting ILK in cisplatin-resistant ovarian cancer. Western blot analysis showed that phosphorylation levels of ILK were higher in cisplatin-resistant compared with cisplatin-sensitive ovarian cancer cells. Further immunohistochemical analysis of ovarian cancer patient samples showed a significant increase in phosphorylated ILK levels in the tumor tissue when compared to normal ovarian epithelium. Targeting ILK by small-interfering RNA (siRNA) treatment reduced cisplatin-resistant cell growth and invasion ability, and increased apoptosis. Differential gene expression analysis by RNA sequencing (RNA-Seq) upon ILK-siRNA transfection followed by Ingenuity Pathway Analysis (IPA) and survival analysis using the Kaplan-Meier plotter database identified multiple target genes involved in cell growth, apoptosis, invasion, and metastasis, including several non-coding RNAs. Taken together, results from this study support ILK as an attractive target for ovarian cancer and provide potential ILK downstream effectors with prognostic and therapeutic value.

UNC5C‑knockdown enhances the growth and metastasis of breast cancer cells by potentiating the integrin α6/β4 signaling pathway

Unc‑5 Netrin Receptor C (UNC5C) is a netrin‑1 dependence receptor that mediates the induction of apoptosis in the absence of netrin‑1. The present study found that UNC5C is heterogeneously expressed in breast cancer cell lines. By knocking down UNC5C in SK‑BR‑3 and ZR‑75‑30 cells and overexpressing UNC5c in MDA‑MB‑231 cells, it was demonstrated that UNC5C exerts an inhibitory effect on the growth and metastasis of breast cancer cells. The mechanism involved a UNC5C‑knockdown‑induced enhancement of matrix metalloproteinase (MMP)3, MMP7, MMP9 and MMP10 expression via activation of the PI3K/AKT, ERK and p38 MAPK signaling pathways. Notably, UNC5C directly interacted with integrin α6, which is involved in the growth and metastasis of breast cancer cells. Additionally, UNC5C‑knockdown enhanced the phosphorylation of FAK and SRC, which are key kinases in the netrin‑1/Unc5C and netrin‑1/integrin α6/β4 signaling pathways. This suggests that netrin‑1 functions as an integrator for both the netrin‑1/Unc5C and netrin‑1/integrin α6/β4 signaling pathways. UNC5C‑knockdown potentiated netrin‑1/integrin α6/β4 signaling. Given that UNC5C‑knockdown inhibited integrin‑liked protein kinase phosphorylation at Thr‑173, at least in SK‑BR‑3 cells, this may be an inhibitory phosphorylation site rather than activating phosphorylation site for relaying integrin signaling.

Integrin-Linked Kinase Is Involved In the Proliferation and Invasion of Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is an aggressive type of cancer with high mortality rate in China, largely due to its high invasive and metastatic potential. The purposes of this study are to investigate the potential molecular mechanisms behind the aggressive nature of ESCC and search for new prognostic biomarkers. By employing the quantitative proteomic based strategy, we compared the proteomic profile between three ESCC samples and paired adjacent tissues. After bioinformatics analysis, four candidate proteins were validated in thirteen paired patient samples. Further validation of the key candidate, integrin-linked kinase (ILK), was carried out in one hundred patient samples. The specific inhibitor compound 22 (cpd22) was used to assess the influence of ILK to ESCC cell motility and invasiveness by applying wound-healing and transwell assay. Western blot analysis was performed to elucidate the signaling pathways involved in ILK-mediated ESCC invasion. Total 236 proteins were identified by proteomic analysis. Bioinformatics analysis suggested a key role of the collagen/integrin/ILK signaling pathway during ESCC progression. Further validation indicated that ILK is overexpressed in ESCC tissues and is correlated with poor patient prognosis. Inhibition of ILK kinase activity suppresses proliferation and blocks invasion and migration of ESCC cells. Signaling pathway analysis revealed that ILK regulates AKT phosphorylation on Ser473 but not GSK-3β on Ser9 to promote proliferation and motility of ESCC cells. In conclusion, our results indicated that ILK may play a crucial role in ESCC invasion and metastasis and may serve as a prognostic biomarker and therapeutic target for ESCC.

Studying the ShcD and ERK interaction under acute oxidative stress conditions in melanoma cells

The newly identified melanoma-associated adaptor ShcD was found to translocate to the nucleus upon hydrogen peroxide treatment. Therefore, the aim of this study was to identify the ShcD network in melanoma cells under oxidative stress. LC-MS/MS and GFP-trap were performed to study the ShcD phosphorylation status during acute severe oxidative stress. ShcD was found to be phosphorylated at threonine-159 (Thr159) in response to 5 mM H₂O₂ treatment. The GPS 2.1 phosphorylation prediction program predicted that the Thr159Pro motif, housed in the N-terminus of the ShcD-CH2 domain, is a potential phosphorylation site for MAPKs (ERK, JNK or p38). Co-immunoprecipitation experiments revealed that ShcD mainly interacts with ERK in B16 and MM138 melanoma cells under both hydrogen peroxide-untreated and -treated conditions. Moreover, ShcD interacts with both phosphorylated and un-phosphorylated ERK, although the interaction between ShcD and phospho-ERK was primarily observed after H₂O₂ treatment. A MEK inhibitor (U0126) enhanced the interaction between ShcD and unphosphorylated ERK under oxidative stress conditions. Furthermore, Thr159 was mutated to either alanine (A) or glutamic acid (E) to study whether the threonine phosphorylation state influences the ShcD/ERK interaction. Introducing the T159E mutation obliterated the ShcD/ERK interaction. To identify the functional impact of the ShcD/ERK interaction on cell survival signalling under oxidative stress conditions, caspase 3/7 assays and 7AAD cell death assays were used. The ShcD/ERK interaction promoted anti-survival signalling upon exposure to hydrogen peroxide, while U0126 treatment reduced death signalling. Our data also showed that the death signalling initiated by the ShcD/ERK interaction was accompanied by p21 phosphorylation. In summary, these data identified ShcD, via its interaction with ERK, as a proapoptotic protein under oxidative stress conditions.

Inhibition of PAK1 alleviates cerulein-induced acute pancreatitis via p38 and NF-κB pathways

Acute pancreatitis is a life-threatening disease accompanied by systemic inflammatory response. NF-κB and p38 signal pathways are activated in AP induced by cerulein. And PAKs are multifunctional effectors of Rho GTPases with kinase activity. In the present study, the function of P21-activated kinase 1 (PAK1) in AP was investigated, and found that PAK1 was up-regulated in pancreas of AP mice model, and led to NF-κB and p38 pathway activation. PAK1 inhibition by shRNA or small molecule inhibitor FRAX597 decreased NF-κB and p38 activity, also alleviated the pathological damage in the pancreas of AP mice model, including decreasing the amylase and lipase levels in serum, decreasing the levels of tumor necrosis factor-α, interleukin-6, and interleukin-1β in AP. These results suggested that PAK1 inhibition protects against AP by inhibiting NF-κB and p38 pathways, and indicated that PAK1 is a potential therapy to alleviate AP patients in clinic, and these need to be explored further.

Binding mechanism of caffeic acid and simvastatin to the integrin linked kinase for therapeutic implications: a comparative docking and MD simulation studies

Integrin linked kinase (ILK) is a Ser/Thr kinase, which regulates various integrin mediated signaling pathways, and is involved in cell adhesion, migration and differentiation. Alteration in the ILK is responsible for abnormal functioning of the cell system, which may lead to the cancer progression and metastasis. Caffeic acid (CA) and simvastatin are used as antioxidant and possess anticancer properties. Thus, inhibiting the kinase activity of ILK by CA and simvastatin may be implicated in the cancer therapy. In this study, we have performed molecular docking followed by 100 ns MD simulations to understand the interaction mechanism of ILK protein with the CA and simvastatin. Average potential energy was found to be highest in case of ILK-CA complex (-770,949 kJ/mol). Binding free energy was found to be higher in case of simvastatin than CA. Our results indicate that simvastatin binds more effectively to the active pocket of ILK. We further performed MTT assay to understand its anticancer potential. Simvastatin shows the IC₅₀ values for HepG2 and MCF-7 as 19.18 ± 0.12 and 13.84 ± 0.22 µM, respectively. However, the IC₅₀ value of CA on HepG2 and MCF-7 was reported as 175.50 ± 1.44 and 144.90 ± 1.53 µM, respectively. Our study provides a deeper insight into the binding mechanism of simvastatin and CA to ILK, which further opens a promising channel for their implications in cancer therapy.

Substratum stiffness tunes proliferation downstream of Wnt3a in part by regulating integrin-linked kinase and frizzled-1

The Wnt/β-catenin pathway controls a variety of cellular behaviors, aberrant activation of which are associated with tumor progression in several types of cancer. The same cellular behaviors are also affected by the mechanical properties of the extracellular matrix (ECM) substratum, which induces signaling through integrins and integrin-linked kinase (ILK). Here, we examined the role of substratum stiffness in the regulation of cell proliferation downstream of Wnt3a. We found that treatment with Wnt3a increased proliferation of cells cultured on stiff substrata, with compliances characteristic of breast tumors, but not of cells on soft substrata, with compliances comparable to that of normal mammary tissue. Depleting ILK rendered cells unresponsive to Wnt3a on both substrata. Ectopic expression of ILK permitted Wnt3a to induce proliferation of cells on both microenvironments, although proliferation on soft substrata remained lower than that on stiff substrata. We further showed that ILK regulates expression of the Wnt receptor frizzled-1 (Fzd1), suggesting the presence of a positive feedback loop between Wnt3a, ILK and Fzd1. These findings suggest that tissue mechanics regulates the cellular response to Wnt under physiological and pathological microenvironmental conditions.This article has an associated First Person interview with the first author of the paper.

Physical Confirmation and Comparative Genomics of the Rat Mammary carcinoma susceptibility 3 Quantitative Trait Locus

Human breast and rat mammary cancer susceptibility are complex phenotypes where complete sets of risk associated loci remain to be identified for both species. We tested multiple congenic rat strains to physically confirm and positionally map rat Mammary carcinoma susceptibility 3 (Mcs3)-a mammary cancer resistance allele previously predicted at Rattus norvegicus chromosome 1 (RNO1). The mammary cancer susceptible Wistar Furth (WF) strain was the recipient, and the mammary cancer resistant Copenhagen (Cop) strain was the RNO1-segment donor for congenics. Inbred WF females averaged 6.3 carcinogen-induced mammary carcinomas per rat. Two WF.Cop congenic strains averaged 2.8 and 3.4 mammary carcinomas per rat, which confirmed Mcs3 as an independently acting allele. Two other WF.Cop congenic strains averaged 6.6 and 8.1 mammary carcinomas per rat, and, thus, did not contain Mcs3 Rat Mcs3 was delimited to 27.8 Mb of RNO1 from rs8149408 to rs105131702 (RNO1:143700228-171517317 of RGSC 6.0/rn6). Human genetic variants with p values for association to breast cancer risk below 10^-7 had not been reported for Mcs3 orthologous loci; however, human variants located in Mcs3-orthologous regions with potential association to risk (10^-7 < p < 10^-3) were listed in some population-based studies. Further, rat Mcs3 contains sequence orthologous to human 11q13/14-a region frequently amplified in female breast cancer. We conclude that Mcs3 is an independently acting mammary carcinoma resistance allele. Human population-based, genome-targeted association studies interrogating Mcs3 orthologous loci may yield novel breast cancer risk associated variants and genes.

Insights into the Structure, Function, and Ion-Mediated Signaling Pathways Transduced by Plant Integrin-Linked Kinases

Kinases facilitate detection of extracellular signals and set in motion cellular responses for plant adaptation and survival. Some of the energy utilized for kinase signal processing is produced through the activity of ion transporters. Additionally, the synergy between cellular ions and signal transduction influences plant response to pathogens, and their growth and development. In plants, the signaling elements that connect cell wall and membrane sensors with ion homeostasis and transport-mediated processes are largely unknown. Current research indicates that plant Integrin-Linked Kinases (ILKs), a subfamily Raf-like MAP2K Kinases, may have evolved to fulfill this role. In this review, we explore new findings on plant ILKs placing a particular focus on the connection between ILKs proteins unique structural features and ILKs functions. The ankyrin repeat motifs and the kinase domains of ILKs in Arabidopsis and land plants lineage, respectively, are analyzed and discussed as potential determinants of ILKs' metal ion cofactor specificity and their enzymatic and interaction activities. Further, ILKs regulation through gene expression, subcellular localization, and ions and ion transporters is reviewed in the context of recent studies. Finally, using evidence from literature and interactomics databanks, we infer ILKs-dependent cellular pathways and highlight their potential in transmitting multiple types of signals originating at the interface between the cell wall and plasma membrane.

Structure, biochemistry, and biology of PAK kinases

PAKs, p21-activated kinases, play central roles and act as converging junctions for discrete signals elicited on the cell surface and for a number of intracellular signaling cascades. PAKs phosphorylate a vast number of substrates and act by remodeling cytoskeleton, employing scaffolding, and relocating to distinct subcellular compartments. PAKs affect wide range of processes that are crucial to the cell from regulation of cell motility, survival, redox, metabolism, cell cycle, proliferation, transformation, stress, inflammation, to gene expression. Understandably, their dysregulation disrupts cellular homeostasis and severely impacts key cell functions, and many of those are implicated in a number of human diseases including cancers, neurological disorders, and cardiac disorders. Here we provide an overview of the members of the PAK family and their current status. We give special emphasis to PAK1 and PAK4, the prototypes of groups I and II, for their profound roles in cancer, the nervous system, and the heart. We also highlight other family members. We provide our perspective on the current advancements, their growing importance as strategic therapeutic targets, and our vision on the future of PAKs.

The Novel Small Molecule Inhibitor, OSU-T315, Suppresses Vestibular Schwannoma and Meningioma Growth by Inhibiting PDK2 Function in the AKT Pathway Activation

Activation of PKB/AKT signaling, which requires PDK1 and PDK2 function, drives Vestibular Schwannoma (VS) and meningioma growth. PDK2 function is defined as a molecule that phosphorylates AKT-Ser473. Integrin-Linked Kinase (ILK) functions as PDK2 in PKB/AKT activation in many cancers; therefore, we hypothesized that OSU-T315, a small molecule ILK inhibitor, will inhibit the ILK-PDK2 function in PKB/AKT signaling activation in VS and meningioma cell growth. OSU-T315 decreased cell viability at IC50 < 2μM in VS (HEI193) and meningioma (Ben-Men-1) cell lines, in primary cells at < 3.5μM, while in normal primary Schwann cells at 7.1μM. OSU-T315 inhibits AKT signaling by decreasing phosphorylation at AKT-Ser473, AKT-Thr308, ILK-Ser246 and ILK-Thr173. In addition, OSU-T315 affected the phosphorylation or expression levels of AKT downstream proliferation effectors as well as autophagy markers. Flow cytometry shows that OSU-T315 increased the percentage of cells arrested at G2/M for both, HEI193 (39.99%) and Ben-Men-1 (26.96%) cells, compared to controls (21.54%, 8.47%). Two hours of OSU-T315 treatment increased cell death in both cell lines (34.3%, 9.1%) versus untreated (12.1%, 8.1%). Though longer exposure increased cell death in Ben-Men-1, TUNEL assays showed that OSU-T315 does not induce apoptosis. OSU-T315 was primarily cytotoxic for HEI193 and Ben-Men-1 inducing a dysregulated autophagy. Our studies suggest that OSU-T315 has translational potential as a chemotherapeutic agent against VS and meningioma.

PAKs in Human Cancer Progression: From Inception to Cancer Therapeutic to Future Oncobiology

Since the initial recognition of a mechanistic role of p21-activated kinase 1 (PAK1) in breast cancer invasion, PAK1 has emerged as one of the widely overexpressed or hyperactivated kinases in human cancer at-large, allowing the PAK family to make in-roads in cancer biology, tumorigenesis, and cancer therapeutics. Much of our current understanding of the PAK family in cancer progression relates to a central role of the PAK family in the integration of cancer-promoting signals from cell membrane receptors as well as function as a key nexus-modifier of complex, cytoplasmic signaling network. Another core aspect of PAK signaling that highlights its importance in cancer progression is through PAK's central role in the cross talk with signaling and interacting proteins, as well as PAK's position as a key player in the phosphorylation of effector substrates to engage downstream components that ultimately leads to the development cancerous phenotypes. Here we provide a comprehensive review of the recent advances in PAK cancer research and its downstream substrates in the context of invasion, nuclear signaling and localization, gene expression, and DNA damage response. We discuss how a deeper understanding of PAK1's pathobiology over the years has widened research interest to the PAK family and human cancer, and positioning the PAK family as a promising cancer therapeutic target either alone or in combination with other therapies. With many landmark findings and leaps in the progress of PAK cancer research since the infancy of this field nearly 20 years ago, we also discuss postulated advances in the coming decade as the PAK family continues to shape the future of oncobiology.

PARVA promotes metastasis by modulating ILK signalling pathway in lung adenocarcinoma

α-parvin (PARVA) is known to be involved in the linkage of integrins, regulation of actin cytoskeleton dynamics and cell survival. However, the role that PARVA plays in cancer progression remains unclear. Here, using a lung cancer invasion cell line model and expression microarrays, we identify PARVA as a potential oncogene. The overexpression of PARVA increased cell invasion, colony-forming ability and endothelial cell tube formation. By contrast, knockdown of PARVA inhibited invasion and tube formation in vitro. Overexpression of PARVA also promoted tumorigenicity, angiogenesis and metastasis in in vivo mouse models. To explore the underlying mechanism, we compared the expression microarray profiles of PARVA-overexpressing cells with those of control cells to identify the PARVA-regulated signalling pathways. Pathway analysis showed that eight of the top 10 pathways are involved in invasion, angiogenesis and cell death. Next, to identify the direct downstream signalling pathway of PARVA, 371 significantly PARVA-altered genes were analysed further using a transcription factor target model. Seven of the top 10 PARVA-altered transcription factors shared a common upstream mediator, ILK. Lastly, we found that PARVA forms a complex with SGK1 and ILK to enhance the phosphorylation of ILK, which led to the phosphorylation of Akt and GSK3β. Notably, the inactivation of ILK reversed PARVA-induced invasion. Taken together, our findings imply that PARVA acts as an oncogene by activating ILK, and that this activation is followed by the activation of Akt and inhibition of GSK3β. To our knowledge, this is the first study to characterize the role of PARVA in lung cancer progression.

An increase in integrin-linked kinase non-canonically confers NF-κB-mediated growth advantages to gastric cancer cells by activating ERK1/2

Background

Increased activity or expression of integrin-linked kinase (ILK), which regulates cell adhesion, migration, and proliferation, leads to oncogenesis. We identified the molecular basis for the regulation of ILK and its alternative role in conferring ERK1/2/NF-κB-mediated growth advantages to gastric cancer cells.

Results

Inhibiting ILK with short hairpin RNA or T315, a putative ILK inhibitor, abolished NF-κB-mediated the growth in the human gastric cancer cells AGS, SNU-1, MKN45, and GES-1. ILK stimulated Ras activity to activate the c-Raf/MEK1/2/ERK1/2/ribosomal S6 kinase/inhibitor of κBα/NF-κB signaling by facilitating the formation of the IQ motif-containing GTPase-activating protein 1 (IQGAP1)–Ras complex. Forced enzymatic ILK expression promoted cell growth by facilitating ERK1/2/NF-κB signaling. PI3K activation or decreased PTEN expression prolonged ERK1/2 activation by protecting ILK from proteasome-mediated degradation. C-terminus of heat shock cognate 70 interacting protein, an HSP90-associated E3 ubiquitin ligase, mediated ILK ubiquitination to control PI3K- and HSP90-regulated ILK stabilization and signaling. In addition to cell growth, the identified pathway promoted cell migration and reduced the sensitivity of gastric cancer cells to the anticancer agents 5-fluorouracil and cisplatin. Additionally, exogenous administration of EGF as well as overexpression of EGFR triggered ILK- and IQGAP1-regulated ERK1/2/NF-κB activation, cell growth, and migration.

Conclusion

An increase in ILK non-canonically promotes ERK1/2/NF-κB activation and leads to the growth of gastric cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-014-0069-3) contains supplementary material, which is available to authorized users.

Distinct regulatory effect of the p34SEI-1 oncoprotein on cancer metastasis in HER2/neu-positive and -negative cells

The p34(SEI-1) oncoprotein is involved in a transcriptional regulation, cell cycle regulation, apoptosis, development and many other important cellular functions. Our present study suggests that p34(SEI-1) can promote metastasis by enhancing migration and invasion of cancer cells. Consistently, p34(SEI-1) expression was found to be increased as the tumor invasiveness progressed in human breast tissues. p34(SEI-1) may promote cancer metastasis by activating the PI3K/AKT signaling pathway. In this process, p34(SEI-1) activates two different serine/threonine kinases, AKT or ILK, depending on the expression status of HER2/neu oncogene. In HER2/neu suppressed cancer cells, p34(SEI-1) promoted metastasis mainly by activating AKT via phosphorylation of the 473 serine residue. In HER2/neu expressing cancer cells, p34(SEI-1) overexpression downregulates HER2/neu expression, leading to the activation of another crucial serine/threonine kinase ILK due to phosphorylation of the 178 threonine residue instead of AKT. These results suggest that p34(SEI-1) affects cancer metastasis by regulating two different signaling pathways depending on the HER2/neu expression level, in which AKT and ILK modulation can be stimulated by p34(SEI-1) overexpression.

Purification and SAXS analysis of the integrin linked kinase, PINCH, parvin (IPP) heterotrimeric complex

The heterotrimeric protein complex containing the integrin linked kinase (ILK), parvin, and PINCH proteins, termed the IPP complex, is an essential component of focal adhesions, where it interacts with many proteins to mediate signaling from integrin adhesion receptors. Here we conduct a biochemical and structural analysis of the minimal IPP complex, comprising full-length human ILK, the LIM1 domain of PINCH1, and the CH2 domain of α-parvin. We provide a detailed purification protocol for IPP and show that the purified IPP complex is stable and monodisperse in solution. Using small-angle X-ray scattering (SAXS), we also conduct the first structural characterization of IPP, which reveals an elongated shape with dimensions 120×60×40 Å. Flexibility analysis using the ensemble optimization method (EOM) is consistent with an IPP complex structure with limited flexibility, raising the possibility that inter-domain interactions exist. However, our studies suggest that the inter-domain linker in ILK is accessible and we detect no inter-domain contacts by gel filtration analysis. This study provides a structural foundation to understand the conformational restraints that govern the IPP complex.

Integrins and small GTPases as modulators of phagocytosis

Phagocytosis is the mechanism whereby cells engulf large particles. This process has long been recognized as a critical component of the innate immune response, which constitutes the organism's defense against microorganisms. In addition, phagocytic internalization of apoptotic cells or cell fragments plays important roles in tissue homeostasis and remodeling. Phagocytosis requires target interactions with receptors on the plasma membrane of the phagocytic cell. Integrins have been identified as important mediators of particle clearance, in addition to their well-established roles in cell adhesion, migration and mechanotransduction. Indeed, these ubiquitously expressed proteins impart phagocytic capacity to epithelial, endothelial and mesenchymal cell types. The importance of integrins in particle internalization is emphasized by the ability of microbial and viral pathogens to exploit their signaling pathways to invade host cells, and by the wide variety of disorders that arise from abnormalities in integrin-dependent phagocytic uptake.

Trop-2 inhibits prostate cancer cell adhesion to fibronectin through the β1 integrin-RACK1 axis

Trop-2 is a transmembrane glycoprotein upregulated in several human carcinomas, including prostate cancer (PrCa). Trop-2 has been suggested to regulate cell-cell adhesion, given its high homology with the other member of the Trop family, Trop-1/EpCAM, and its ability to bind the tight junction proteins claudin-1 and claudin-7. However, a role for Trop-2 in cell adhesion to the extracellular matrix has never been postulated. Here, we show for the first time that Trop-2 expression in PrCa cells correlates with their aggressiveness. Using either shRNA-mediated silencing of Trop-2 in cells that endogenously express it, or ectopic expression of Trop-2 in cells that do not express it, we show that Trop-2 inhibits PrCa cell adhesion to fibronectin (FN). In contrast, expression of another transmembrane receptor, α(v) β(5) integrin, does not affect cell adhesion to this ligand. We find that Trop-2 does not modulate either protein or activation levels of the prominent FN receptors, β(1) integrins, but acts through increasing β(1) association with the adaptor molecule RACK1 and redistribution of RACK1 to the cell membrane. As a result of Trop-2 expression, we also observe activation of Src and FAK, known to occur upon β(1) -RACK1 interaction. These enhanced Src and FAK activities are not mediated by changes in either the activity of IGF-IR, which is known to bind RACK1, or IGF-IR's ability to associate with β(1) integrins. In summary, our data demonstrate that the transmembrane receptor Trop-2 is a regulator of PrCa cell adhesion to FN through activation of the β(1) integrin-RACK1-FAK-Src signaling axis.

ILK: a pseudokinase in the center stage of cell-matrix adhesion and signaling

Integrin-linked kinase (ILK) is a widely expressed and evolutionally conserved component of cell-extracellular matrix (ECM) adhesions. Although initially named as a kinase, ILK contains an unusual pseudoactive site that is incapable of catalyzing phosphorylation. Instead, ILK acts as a central component of a heterotrimer (the PINCH-ILK-parvin complex) at ECM adhesions mediating interactions with a large number of proteins via multiple sites including its pseudoactive site. Through higher level protein-protein interactions, this scaffold links integrins to the actin cytoskeleton and catalytic proteins and thereby regulates focal adhesion assembly, cytoskeleton organization and signaling. This review summarizes recent advances in our understanding of the structure and functions of the PINCH-ILK-parvin complex, and discusses emerging new features of the molecular mechanisms by which it regulates diverse cellular, physiological and pathological processes.

Modularity and functional plasticity of scaffold proteins as p(l)acemakers in cell signaling

Cells coordinate and integrate various functional modules that control their dynamics, intracellular trafficking, metabolism and gene expression. Such capacity is mediated by specific scaffold proteins that tether multiple components of signaling pathways at plasma membrane, Golgi apparatus, mitochondria, endoplasmic reticulum, nucleus and in more specialized subcellular structures such as focal adhesions, cell-cell junctions, endosomes, vesicles and synapses. Scaffold proteins act as "pacemakers" as well as "placemakers" that regulate the temporal, spatial and kinetic aspects of protein complex assembly by modulating the local concentrations, proximity, subcellular dispositions and biochemical properties of the target proteins through the intricate use of their modular protein domains. These regulatory mechanisms allow them to gate the specificity, integration and crosstalk of different signaling modules. In addition to acting as physical platforms for protein assembly, many professional scaffold proteins can also directly modify the properties of their targets while they themselves can be regulated by post-translational modifications and/or mechanical forces. Furthermore, multiple scaffold proteins can form alliances of higher-order regulatory networks. Here, we highlight the emerging themes of scaffold proteins by analyzing their common and distinctive mechanisms of action and regulation, which underlie their functional plasticity in cell signaling. Understanding these mechanisms in the context of space, time and force should have ramifications for human physiology and for developing new therapeutic approaches to control pathological states and diseases.

Protein kinase Cα and integrin-linked kinase mediate the negative axon guidance effects of Sonic hedgehog

In addition to its role as a morphogen, Sonic hedgehog (Shh) has also been shown to function as a guidance factor that directly acts on the growth cones of various types of axons. However, the noncanonical signaling pathways that mediate the guidance effects of Shh protein remain poorly understood. We demonstrate that a novel signaling pathway consisting of protein kinase Cα (PKCα) and integrin-linked kinase (ILK) mediates the negative guidance effects of high concentration of Shh on retinal ganglion cell (RGC) axons. Shh rapidly increased Ca(2+) level and activated PKCα and ILK in the growth cones of RGC axons. By in vitro kinase assay, PKCα was found to directly phosphorylate ILK on threonine-173 and -181. Inhibition of PKCα or expression of a mutant ILK with the PKCα phosphorylation sites mutated (ILK-DM), abolished the Shh-induced macropinocytosis, growth cone collapse and repulsive axon turning. In vivo, expression of a dominant negative PKCα or ILK-DM disrupted RGC axon pathfinding at the optic chiasm but not the projection toward the optic disk, supporting that this signaling pathway plays a specific role in Shh-mediated negative guidance effects.

Palmitoylation regulates 17β-estradiol-induced estrogen receptor-α degradation and transcriptional activity

The estrogen receptor-α (ERα) is a transcription factor that regulates gene expression through the binding to its cognate hormone 17β-estradiol (E2). ERα transcriptional activity is regulated by E2-evoked 26S proteasome-mediated ERα degradation and ERα serine (S) residue 118 phosphorylation. Furthermore, ERα mediates fast cell responses to E2 through the activation of signaling cascades such as the MAPK/ERK and phosphoinositide-3-kinase/v-akt murine thymoma viral oncogene homolog 1 pathways. These E2 rapid effects require a population of the ERα located at the cell plasma membrane through palmitoylation, a dynamic enzymatic modification mediated by palmitoyl-acyl-transferases. However, whether membrane-initiated and transcriptional ERα activities integrate in a unique picture or represent parallel pathways still remains to be firmly clarified. Hence, we evaluated here the impact of ERα palmitoylation on E2-induced ERα degradation and S118 phosphorylation. The lack of palmitoylation renders ERα more susceptible to E2-dependent degradation, blocks ERα S118 phosphorylation and prevents E2-induced ERα estrogen-responsive element-containing promoter occupancy. Consequently, ERα transcriptional activity is prevented and the receptor addressed to the nuclear matrix subnuclear compartment. These data uncover a circuitry in which receptor palmitoylation links E2-dependent ERα degradation, S118 phosphorylation, and transcriptional activity in a unique molecular mechanism. We propose that rapid E2-dependent signaling could be considered as a prerequisite for ERα transcriptional activity and suggest an integrated model of ERα intracellular signaling where E2-dependent early extranuclear effects control late receptor-dependent nuclear actions.

A central multifunctional role of integrin-linked kinase at muscle attachment sites

Integrin-linked kinase (ILK) is an essential component of a multiprotein complex that links actin to the plasma membrane. Here, we have used a genetic approach to examine the molecular interactions that are essential for the assembly of this ILK-containing complex at Drosophila muscle attachment sites (MASs). We show that, downstream of integrins, talin plays a decisive role in the recruitment of three proteins: ILK, PINCH and paxillin. The accumulation of ILK at MASs appears to follow an amplification mechanism, suggesting that numerous binding sites are generated by minimal levels of the upstream integrin and talin effectors. This property suggests that ILK functions as an essential hub in the assembly of its partner proteins at sites of integrin adhesion. We found that PINCH stability, and its subcellular localization at MASs, depends upon ILK function, but that ILK stability and localization is not dependent upon PINCH. An in vivo structure-function analysis of ILK demonstrated that each ILK domain has sufficient information for its independent recruitment at embryonic MASs, whereas at later developmental stages only the kinase domain was effectively recruited. Our data strengthen the view that the ILK complex is assembled sequentially at sites of integrin adhesion by employing multiple molecular interactions, which collectively stabilize the integrin-actin link.

Fibronectin and beta-catenin act in a regulatory loop in dermal fibroblasts to modulate cutaneous healing

β-Catenin is an important regulator of dermal fibroblasts during cutaneous wound repair. However, the factors that modulate β-catenin activity in this process are not completely understood. We investigated the role of the extracellular matrix in regulating β-catenin and found an increase in β-catenin-mediated Tcf-dependent transcriptional activity in fibroblasts exposed to various extracellular matrix components. This occurs through an integrin-mediated GSK3β-dependent pathway. The physiologic role of this mechanism was demonstrated during wound repair in extra domain A-fibronectin-deficient mice, which exhibited decreased β-catenin-mediated signaling during the proliferative phase of healing. Extra domain A-fibronectin-deficient mice have wounds that fail at a lower tensile strength and contain fewer fibroblasts compared with wild type mice. This phenotype was rescued by genetic or pharmacologic activation of β-catenin signaling. Because fibronectin is a transcriptional target of β-catenin, this suggests the existence of a feedback loop between these two molecules that regulates dermal fibroblast cell behavior during wound repair.

Phosphorylation and interaction of myopodin by integrin-link kinase lead to suppression of cell growth and motility in prostate cancer cells

Myopodin is a tumor-suppressor gene that suppresses growth of prostate and urothelial carcinomas. However, the mechanism of myopodin tumor-suppressor activity or signaling that leads to activation of myopodin remains unclear. In this report, we showed that the N-terminus of myopodin binds integrin-linked kinase (ILK) both in vivo and in vitro. An ILK interaction motif of 78 amino acids (amino acids 82-157) was identified in the N-terminus region of myopodin. Induction of ILK-dependent kinase activity by integrin α7 led to phosphorylation of myopodin both in vivo and in vitro. Knocking down ILK dramatically reduced the inhibition of cell growth and motility mediated by myopodin. A mutant of myopodin lacking the ILK interaction motif is inactive in suppressing the growth and motility of PC3 cells. As a result, this study showed a novel and critical signaling pathway that leads to activation of myopodin.

Integrin-linked kinase: not so 'pseudo' after all

Integrin-linked kinase (ILK) is a highly evolutionarily conserved intracellular protein that was originally identified as an integrin-interacting protein, and extensive genetic and biochemical studies have shown that ILK expression is vital during both embryonic development and tissue homeostasis. At the cellular and tissue levels, ILK regulates signaling pathways for cell adhesion-mediated cell survival (anoikis), apoptosis, proliferation and mitosis, migration, invasion, and vascularization and tumor angiogenesis. ILK also has central roles in cardiac and smooth-muscle contractility, and ILK dysregulation causes cardiomyopathies in humans. ILK protein levels are increased in several human cancers and often the expression level predicts poor patient outcome. Abundant evidence has accumulated suggesting that, of the diverse functions of ILK, some may require kinase activity whereas others depend on protein-protein interactions and are, therefore, independent of kinase activity. However, the past several years have seen an ongoing debate about whether ILK indeed functions as a protein serine/threonine kinase. This debate centers on the atypical protein kinase domain of ILK, which lacks some amino-acid residues thought to be essential for phosphotransferase activity. However, similar deficiencies are present in the catalytic domains of other kinases now known to possess protein kinase activity. Numerous studies have shown that ILK phosphorylates peptide substrates in vitro, corresponding to ILK-mediated phosphorylations in intact cells, and a recent report characterizing in vitro phosphotransferase activity of highly purified, full-length ILK, accompanied by detailed enzyme kinetic analyses, shows that, at least in vitro, ILK is a bona fide protein kinase. However, several genetic studies suggest that, not all biological functions of ILK require kinase activity, and that it can function as an adaptor/scaffold protein. Here, we review evidence for and against ILK being an active kinase, and provide a framework for strategies to further analyze the kinase and adaptor functions of ILK in different cellular contexts.

Detachment-mediated resistance to TRAIL-induced apoptosis is associated with stimulation of the PI3K/Akt pathway in fetal and adenocarcinoma epithelial colon cells

The resistance of transformed epithelial cells to a detachment-induced apoptosis (anoikis) can significantly affect their susceptibility to anticancer therapy. We showed that detachment of both fetal (FHC) and adenocarcinoma (HT-29) human colon epithelial cells resulted in the activation of the pro-survival Akt pathway, and significant changes in integrin-linked kinase (ILK) and focal adhesive kinase (FAK) phosphorylation. We demonstrated a detachment-induced and PI3K/Akt-mediated resistance to apoptotic effects of TRAIL, which was not associated with any changes in the cell surface TRAIL death receptor levels. Instead, a modulation of downstream intracellular signaling events was suggested to be involved. Our results may have important implications for optimization of new strategies in treatment of cancers at different stages of development.