Disruption of FRNK expression by gene targeting of the intronic promoter within the focal adhesion kinase gene

Identification of a novel type of focal adhesion remodelling via FAK/FRNK replacement, and its contribution to cancer progression

Numerous studies have investigated the various cellular responses against genotoxic stress, including those mediated by focal adhesions. We here identified a novel type of focal adhesion remodelling that occurs under genotoxic stress conditions, which involves the replacement of active focal adhesion kinase (FAK) with FAK-related non-kinase (FRNK). FRNK stabilized focal adhesions, leading to strong cell-matrix adhesion, and FRNK-depleted cells were easily detached from extracellular matrix upon genotoxic stress. This remodelling occurred in a wide variety of cells. In vivo, the stomachs of Frnk-knockout mice were severely damaged by genotoxic stress, highlighting the protective role of FRNK against genotoxic stress. FRNK was also found to play a vital role in cancer progression, because FRNK depletion significantly inhibited cancer dissemination and progression in a mouse cancer model. Furthermore, in human cancers, FRNK was predominantly expressed in metastatic tissues and not in primary tissues. We hence conclude that this novel type of focal adhesion remodelling reinforces cell adhesion and acts against genotoxic stress, which results in the protection of normal tissues, but in turn facilitates cancer progression.

The oncogenic PI3K-induced transcriptomic landscape reveals key functions in splicing and gene expression regulation

The PI3K pathway regulates proliferation, survival, and metabolism and is frequently activated across human cancers. A comprehensive elucidation of how this signaling pathway controls transcriptional and co-transcriptional processes could provide new insights into the key functions of PI3K signaling in cancer. Here, we undertook a transcriptomic approach to investigate genome-wide gene expression and transcription factor (TF) activity changes, as well as splicing and isoform usage dynamics, downstream of PI3K. These analyses uncovered widespread alternatively spliced (AS) isoforms linked to proliferation, metabolism, and splicing in PIK3CA mutant cells, which were reversed by inhibition of PI3Kα. Analysis of paired tumor biopsies from PIK3CA-mutated breast cancer patients undergoing treatment with PI3Kα inhibitors identified widespread splicing alterations that affect specific isoforms in common with the preclinical models, and these alterations, namely PTK2/FRNK and AFMID isoforms, were validated as functional drivers of cancer cell growth or migration. Mechanistically, isoform-specific splicing factors mediated PI3K-dependent RNA splicing. Treatment with splicing inhibitors rendered breast cancer cells more sensitive to the PI3Kα inhibitor alpelisib, resulting in greater growth inhibition than alpelisib alone. This study provides the first comprehensive analysis of widespread splicing alterations driven by oncogenic PI3K in breast cancer. The atlas of PI3K-mediated splicing programs establishes a key role for the PI3K pathway in regulating splicing, opening new avenues for exploiting PI3K signaling as a therapeutic vulnerability in breast cancer.

Focal adhesion kinase-related non-kinase ameliorates liver fibrosis by inhibiting aerobic glycolysis via the FAK/Ras/c-myc/ENO1 pathway

BACKGROUND

Hepatic stellate cell (HSC) hyperactivation is a central link in liver fibrosis development. HSCs perform aerobic glycolysis to provide energy for their activation. Focal adhesion kinase (FAK) promotes aerobic glycolysis in cancer cells or fibroblasts, while FAK-related non-kinase (FRNK) inhibits FAK phosphorylation and biological functions.

AIM

To elucidate the effect of FRNK on liver fibrosis at the level of aerobic glycolytic metabolism in HSCs.

METHODS

Mouse liver fibrosis models were established by administering CCl₄, and the effect of FRNK on the degree of liver fibrosis in the model was evaluated. Transforming growth factor-β1 was used to activate LX-2 cells. Tyrosine phosphorylation at position 397 (pY397-FAK) was detected to identify activated FAK, and the expression of the glycolysis-related proteins monocarboxylate transporter 1 (MCT-1) and enolase1 (ENO1) was assessed. Bioinformatics analysis was performed to predict putative binding sites for c-myc in the ENO1 promoter region, which were validated with chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays.

RESULTS

The pY397-FAK level was increased in human fibrotic liver tissue. FRNK knockout promoted liver fibrosis in mouse models. It also increased the activation, migration, proliferation and aerobic glycolysis of primary hepatic stellate cells (pHSCs) but inhibited pHSC apoptosis. Nevertheless, opposite trends for these phenomena were observed after exogenous FRNK treatment in LX-2 cells. Mechanistically, the FAK/Ras/c-myc/ENO1 pathway promoted aerobic glycolysis, which was inhibited by exogenous FRNK.

CONCLUSION

FRNK inhibits aerobic glycolysis in HSCs by inhibiting the FAK/Ras/c-myc/ ENO1 pathway, thereby improving liver fibrosis. FRNK might be a potential target for liver fibrosis treatment.

Integrin αvβ3 Engagement Regulates Glucose Metabolism and Migration through Focal Adhesion Kinase (FAK) and Protein Arginine Methyltransferase 5 (PRMT5) in Glioblastoma Cells

Metabolic reprogramming promotes glioblastoma cell migration and invasion. Integrin αvβ3 is one of the major integrin family members in glioblastoma multiforme cell surface mediating interactions with extracellular matrix proteins that are important for glioblastoma progression. The role of αvβ3 integrin in regulating metabolic reprogramming and its mechanism of action have not been determined in glioblastoma cells. Integrin αvβ3 engagement with osteopontin promotes glucose uptake and aerobic glycolysis, while inhibiting mitochondrial oxidative phosphorylation. Blocking or downregulation of integrin αvβ3 inhibits glucose uptake and aerobic glycolysis and promotes mitochondrial oxidative phosphorylation, resulting in decreased migration and growth in glioblastoma cells. Pharmacological inhibition of focal adhesion kinase (FAK) or downregulation of protein arginine methyltransferase 5 (PRMT5) blocks metabolic shift toward glycolysis and inhibits glioblastoma cell migration and invasion. These results support that integrin αvβ3 and osteopontin engagement plays an important role in promoting the metabolic shift toward glycolysis and inhibiting mitochondria oxidative phosphorylation in glioblastoma cells. The metabolic shift in cell energy metabolism is coupled to changes in migration, invasion, and growth, which are mediated by downstream FAK and PRMT5 in glioblastoma cells.

Myeloid-derived tissue-type plasminogen activator promotes macrophage motility through FAK, Rac1, and NF-κB pathways

Macrophage accumulation is one of the hallmarks of progressive kidney disease. Tissue-type plasminogen activator (tPA) is known to promote macrophage infiltration and renal inflammation during chronic kidney injury. However, the underlying mechanism remains largely unknown. We examined the role of tPA in macrophage motility in vivo by tracking fluorescence-labeled bone marrow-derived macrophages, and found that tPA-deficient mice had markedly fewer infiltrating fluorescence-labeled macrophages than the wild-type (WT) mice. Experiments in bone marrow chimeric mice further demonstrated that myeloid cells are the main source of endogenous tPA that promotes macrophage migration. In vitro studies showed that tPA promoted macrophage motility through its CD11b-mediated protease-independent function; and focal adhesion kinase (FAK), Rac-1, and NF-κB were indispensable to tPA-induced macrophage migration as either infection of FAK dominant-negative adenovirus or treatment with a Rac-1-specific inhibitor or NF-κB inhibitor abolished the effect of tPA. Moreover, ectopic FAK mimicked tPA and induced macrophage motility. tPA also activated migratory signaling in vivo. The accumulation of phospho-FAK-positive CD11b macrophages in the obstructed kidneys from WT mice was clearly attenuated in tPA knockout mice, which also displayed lower Rac-1 activity than their WT counterparts. Therefore, our results indicate that myeloid-derived tPA promotes macrophage migration through a novel signaling cascade involving FAK, Rac-1, and NF-κB.

FAK-related nonkinase is a multifunctional negative regulator of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease whose underlying molecular mechanisms are largely unknown. Herein, we show that focal adhesion kinase-related nonkinase (FRNK) plays a key role in limiting the development of lung fibrosis. Loss of FRNK function in vivo leads to increased lung fibrosis in an experimental mouse model. The increase in lung fibrosis is confirmed at the histological, biochemical, and physiological levels. Concordantly, loss of FRNK function results in increased fibroblast migration and myofibroblast differentiation and activation of signaling proteins that drive these phenotypes. FRNK-deficient murine lung fibroblasts also have an increased capacity to produce and contract matrix proteins. Restoration of FRNK expression in vivo and in vitro reverses these profibrotic phenotypes. These data demonstrate the multiple antifibrotic actions of FRNK. More important, FRNK expression is down-regulated in human IPF, and down-regulation of FRNK in normal human lung fibroblasts recapitulates the profibrotic phenotype seen in FRNK-deficient cells. The effect of loss and gain of FRNK in the experimental model, when taken together with its down-regulation in human IPF, suggests that FRNK acts as an endogenous negative regulator of lung fibrosis by repressing multiple profibrotic responses.

Germline deletion of FAK-related non-kinase delays post-natal cardiomyocyte mitotic arrest

The cardiomyocyte phenotypic switch from a proliferative to terminally differentiated state impacts normal heart development and pathologic myocardial remodeling, yet the signaling mechanisms that regulate this vital process are incompletely understood. Studies from our lab and others indicate that focal adhesion kinase (FAK) is a critical regulator of cardiac growth and remodeling and we found that expression of the endogenous FAK inhibitor, FAK-related non kinase (FRNK) coincided with postnatal cardiomyocyte arrest. Mis-expression of FRNK in the embryonic heart led to pre-term lethality associated with reduced cardiomyocyte proliferation and led us to speculate that the postnatal FRNK surge might be required to promote quiescence in this growth promoting environment. Herein, we provide strong evidence that endogenous FRNK contributes to post-mitotic arrest. Depletion of FRNK promoted DNA synthesis in post-natal day (P) 10 hearts accompanied by a transient increase in DNA content and multi-nucleation by P14, indicative of DNA replication without cell division. Interestingly, a reduction in tri- and tetra-nucleated cardiomyocytes, concomitant with an increase in bi-nucleated cells by P21, indicated the possibility that FRNK-depleted cardiomyocytes underwent eventual cytokinesis. In support of this conclusion, Aurora B-labeled central spindles (a hallmark of cytokinesis) were observed in tetra-nucleated P20 FRNK(-/-) but not wt cardiomyocytes, while no evidence of apoptosis was observed. Moreover, hearts from FRNK null mice developed ventricular enlargement that persisted until young adulthood which resulted from myocyte expansion rather than myocyte hypertrophy or interstitial growth. These data indicate that endogenous FRNK serves an important role in limiting DNA synthesis and regulating the un-coupling between DNA synthesis and cytokinesis in the post-natal myocardium.

Role of FRNK tyrosine phosphorylation in vascular smooth muscle spreading and migration

AIMS

Focal adhesion kinase (FAK) and its autonomously expressed, C-terminal inhibitor FAK-related non-kinase (FRNK), are important regulators of vascular smooth muscle cell (VSMC) spreading and migration. However, the mechanisms of FRNK-mediated inhibition of FAK-dependent signalling are not fully defined. The aim of this study was to determine the potential role of FRNK tyrosine phosphorylation in regulating these processes.

METHODS AND RESULTS

Rat carotid arteries were balloon-injured and FAK and FRNK expression and phosphorylation were examined by immunocytochemistry, immunoprecipitation, and western blotting with total and phosphospecific antibodies. FAK and FRNK expression increased four- and nine-fold, respectively, in alpha-smooth muscle actin-positive VSMCs of injured arteries when compared with contralateral control arteries, and the upregulated FRNK was phosphorylated at residues Y168 and Y232. In A7r5 cells (an embryonic rat VSMC line), endogenously expressed FRNK was also phosphorylated at Y168 and Y232 under basal conditions, and Y168/Y232 phosphorylation increased in response to angiotensin II treatment. When overexpressed in A7r5 cells and adult rat aortic smooth muscle cells (RASM), wild-type (wt) GFP-tagged FRNK was also phosphorylated at residues Y168 and Y232, and GFP-wtFRNK inhibited cell spreading and migration. Mutation of GFP-FRNK at Y168 (GFP-Y168F-FRNK) abrogated FRNK-mediated inhibition of cell spreading and migration, but did not affect its localization in VSMC focal adhesions or its ability to inhibit FAK tyrosine phosphorylation.

CONCLUSION

Phosphorylation of Y168 on FRNK may represent a novel mechanism by which FRNK inhibits cell spreading and migration in VSMCs.

Transient expression of FRNK reveals stage-specific requirement for focal adhesion kinase activity in cardiac growth

Focal adhesion kinase (FAK) is strongly activated by integrins and growth factors and is essential for embryonic development. We previously showed that the C terminus of FAK is expressed as a separate protein termed FAK-related nonkinase (FRNK) in a smooth muscle cell-selective fashion and that FRNK functions to buffer FAK-dependent signals. We now show that FRNK is also transiently expressed in the neonatal myocardium, with peak levels occurring 5 to 7 days postnatal, just before cell cycle withdrawal. Using novel mouse models, we demonstrate that cardiac-selective expression of FRNK (leading to inhibition of FAK) starting at embryonic day 10.5 leads to a severe ventricular noncompaction defect associated with reduced cardiomyocyte proliferation. Remarkably, postnatal expression of nearly identical levels of FRNK is well tolerated and does not affect viability or anabolic cardiac growth. Nonetheless, FRNK expression in the adult heart does attenuate pathological cardiac hypertrophy following aortic banding, confirming and extending our previous data that this compensatory response is blunted in FAK null hearts. Our mechanistic studies in cultured neonatal cardiomyocytes reveal that FRNK expression induces p38/p27(kip)-dependent cell cycle withdrawal and attenuates extracellular signal-regulated kinase-dependent hypertrophic growth. These findings indicate that dynamic expression of FRNK in the neonatal heart may function to promote cardiomyocyte quiescence in an environment that is particularly rich in growth factors and growth promoting extracellular matrices.

Focal adhesion kinase (FAK)-related non-kinase inhibits myofibroblast differentiation through differential MAPK activation in a FAK-dependent manner

Transforming growth factor (TGF)-beta1 induces fibroblast transdifferentiation to myofibroblasts, a process that requires the involvement of integrin-mediated signaling and focal adhesion kinase (FAK). FAK-related non-kinase (FRNK) is known for its role in inhibiting integrin-mediated cell migration; however, its role in myofibroblast differentiation has not been defined. Here, we report that FRNK abrogates TGF-beta1-induced myofibroblast differentiation in vitro and in vivo. TGF-beta1 can induce alpha-smooth muscle actin (alpha-SMA) expression in the presence or absence of FAK; however, TGF-beta1-induced alpha-SMA expression is reduced (approximately 73%) in FAK-deficient fibroblasts. Although both ERK and p38 MAPK activation is required for maximal TGF-beta1-induced alpha-SMA expression, ERK is the major signaling intermediate in cells that express FAK. In contrast, p38 MAPK is the dominant mediator of TGF-beta1-induced alpha-SMA expression in FAK-deficient cells. FRNK overexpression blocks TGF-beta1-induced ERK or p38 MAPK activation in the presence, and surprisingly, in the absence of FAK. The loss of FRNK was tested in vivo during experimentally induced pulmonary fibrosis in mice. FRNK knock-out mice have a greater increase in alpha-SMA-expressing cells in response to a pulmonary fibrotic stimulus in vivo, as compared with congenic wild type mice. This is the first time that FRNK loss has been shown to modify the pathobiology in any animal disease model. Together, the data demonstrate that FRNK negatively regulates myofibroblast differentiation in vitro and in vivo. These data further suggest that modulation FRNK expression may be a novel avenue for therapeutic intervention in tissue fibrosis.

CRNK gene transfer improves function and reverses the myosin heavy chain isoenzyme switch during post-myocardial infarction left ventricular remodeling

PYK2 is a Ca(2+)-dependent, nonreceptor protein tyrosine kinase that is involved in the induction of left ventricular hypertrophy (LVH) and its transition to heart failure. We and others have previously investigated PYK2's function in vitro using cultured neonatal and adult rat ventricular myocytes as model systems. However, the function of PYK2 in the in vivo adult heart remains unclear. Here we evaluate the effect of PYK2 inhibition following myocardial infarction (MI) using adenoviral (Adv) overexpression of the C-terminal domain of PYK2, known as CRNK. First we demonstrate that CRNK functions as a dominant-negative inhibitor of PYK2-dependent signaling, presumably by displacing PYK2 from focal adhesions and costameres. Then, male Sprague-Dawley rats (~300 g) underwent permanent left anterior descending coronary artery ligation. One wk post-MI, either Adv-GFP (n=34) or Adv-CRNK (n=28) was administered (10(10) pfu, 0.1 ml) via catheter-based, Optison-mediated gene transfer. LV structure and function were evaluated by echocardiography 1 and 3 wk after gene transfer, and LV tissue was analyzed by real-time RT-PCR and Western blotting. CRNK overexpression was readily detected by Western blotting 1 wk following gene transfer. Adv-CRNK improved overall survival (P=0.03; Logrank Test) and LV fractional shortening (23+/-2% vs. 31+/-2% for Adv-GFP vs. Adv-CRNK infected animals, respectively; P<0.05). Whereas MI hearts exhibited increased beta-, and decreased alpha-myosin heavy chain (MHC) mRNA expression characteristic of LVH, Adv-CRNK reversed the MHC isoenzyme switch (3.3+/-1.4 fold increase in alpha MHC; 0.4+/-0.1 fold decrease in beta MHC; P<0.05 for both). In summary, CRNK gene transfer improves survival, increases LV function, and alters MHC gene expression suggesting an attenuation of LV remodeling post-MI.