FAK-related Nonkinase Research Articles

Abstract LB431: Direct comparison of focal adhesion kinase (FAK) therapeutic modalities in cancer: Kinase, FAT, and PROTAC

Abstract Introduction: Focal Adhesion Kinase (FAK) is a multifunctional non-receptor tyrosine kinase and scaffolding protein that has emerged as a potential therapeutic target for the treatment of cancer due to its upregulation and role in cancer cell survival. However, it remains unknown which cancer types are most susceptible to FAK modulation or the best pharmacological strategy to target FAK. FAK is endogenously regulated by an alternative transcript termed FAK-related non-kinase (FRNK), which inhibits FAK through the Focal Adhesion Targeting (FAT) domain. Current FAK-kinase inhibitors that block the catalytic site have shown limited efficacy in multiple Phase I/II clinical trials. FAK-degrading PROTACs have also shown inadequate induction of antiproliferative effects despite successful protein degradation. However, we have shown promising results with our novel FAK-FAT inhibitors, which target the scaffolding function of FAK to induce anoikis and inhibit proliferation in cancer cells. A direct comparison of these different FAK modulators in various cancer types has yet to be performed, creating a significant gap in understanding the best approach for targeted FAK inhibition for the treatment of cancer. Methods: The Broad Institute’s Cancer Dependency Map (DepMap) was utilized to select a cancer cell line cohort based on dependency on FAK for survival. Four cancer types, including breast, brain, lung, and skin cancers were selected based on the correlation of FAK expression for survival and previous literature evidence for dependency on FAK. Three FAK-dependent and one FAK-independent cell lines per cancer type were selected for a total of 16 cancer cell lines. Genetic adenoviral constructs that block the FAK-FAT domain (Ad-FRNK) and knockdown FAK levels (shRNA) were utilized to investigate the role of FAK in cancer cell survival. These constructs were used as they recapitulate the pharmacological strategy of our FAK-FAT inhibitor UA-2012 and FAK degrading PROTACs, respectively. Results: Cell viability was significantly decreased in 10/13 FAK-dependent cell lines after transduction with either adFRNK or FAK targeting shRNAs, six of which showed a statically significant decrease in cell viability upon transduction with adFRNK compared to shRNAs. No cell lines showed a greater response to FAK shRNAs compared to adFRNK. We then evaluated the ability of the FAK kinase inhibitor Defactinib, FAK degrading PROTAC BI-3663, and our novel FAK-FAT domain inhibitor UA-2012 to induce cancer cell death. Overall, FAK-FAT domain inhibition with UA-2012 resulted in the most potent reduction in viability of FAK-dependent cells, particularly in skin and breast cancer cell lines. Treatment with Defactinib resulted in low IC50 values regardless of FAK, and PROTAC BI-3663 displayed minimal effects with high IC50 values often above 200 µM despite successful protein degradation. Conclusion: This data suggests that the FAK-FAT domain may be the major modulator of FAK-mediated survival in breast and skin cancer cells. Citation Format: Lauren Reyes, Ruchi Khatiwala, Timothy Marlowe. Direct comparison of focal adhesion kinase (FAK) therapeutic modalities in cancer: Kinase, FAT, and PROTAC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB431.

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.

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

BACKGROUNDHepatic 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.AIMTo elucidate the effect of FRNK on liver fibrosis at the level of aerobic glycolytic metabolism in HSCs.METHODSMouse 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.RESULTSThe 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.CONCLUSIONFRNK 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.

Effects of FRNK on activation and migration of hepatic stellate cells

Objective: To investigate the effect of focal adhesion kinase related non kinase (FRNK) on the activation and migration of hepatic stellate cells (HSCs). Methods: Human liver tissue was divided into healthy control group and fibrosis group from March 2019 to September 2019 in Affiliated Hospital of Guizhou Medical University. C57BL/6 mice were divided into wild type (WT) and FRNK gene knockout type (FRNK-/-) groups. The liver fibrosis model was established with carbon tetrachloride (CCl4). After that, FRNK gene overexpression (Ad-FRNK) was constructed with adenovirus vector. HE and Masson staining were used to evaluate the pathological changes and fiber deposition of liver tissue. Western blot was used to detect the expression of PY397-FAK and α-SMA protein. Mouse primary HSCs were extracted, and the effect of FRNK on HSCs migration was detected by wound healing, activation of Rac and Rho was detected by Western blot. Results: The expression of PY397-FAK protein in human liver tissue with hepatic fibrosis was significantly higher than that in healthy control group (0.88±0.09 vs. 0.73±0.09). FRNK was significantly lower than that in control group(0.68±0.09 vs. 0.79±0.11). After animal model was set up, the degree of liver fibrosis in FRNK-/-mice (153±13)% was more serious than that in WT (100%) group. The expression of PY397-FAK and α-SMA protein was significantly elevated (2.50±0.23 vs. 0.75±0.09, 1.46±0.20 vs. 0.92±0.10). After FRNK gene was re-expressed (100%), the degree of liver fibrosis was mainly reversed [(74±6)%], and the expression of PY397-FAK and α-SMA was accordingly decreased(0.68±0.11 vs. 1.12±0.19,0.68±0.10 vs. 0.85±0.06). In vitro, FRNK inhibited the migration of HSCs [WT∶FRNK-/-∶Ad-FRNK,(339±49)%∶(580±53)%∶(259±33)%] and the activation of Rac and Rho proteins (Rac: 0.54±0.07 vs. 0.91±0.10 vs. 0.77±0.12,Rho:0.45±0.05 vs. 0.64±0.06 vs. 0.53±0.07), all P<0.01. Conclusions: FRNK can inhibit the activation and migration of HSCs which contributed to liver fibrosis. The potential mechanism is related to down regulation of PY397-FAK and inhibition of Rac and Rho activation.

Increased expression of FAK isoforms as potential cancer biomarkers in ovarian cancer.

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that is expressed in most human cell types (example: Epithelial cells, fibroblasts and endothelial), it serves a key role in the control of cell survival, proliferation and motility. The abnormal expression of FAK has been associated with poor prognosis in cancer, including ovarian cancer. However, although FAK isoforms with specific molecular and functional properties have been characterized, there are a limited number of published studies that examine FAK isoforms in ovarian cancer. The aim of the present study was to analyze the expression level of FAK and its isoforms in ovarian cancer. The expression of FAK kinase and focal adhesion targeting (FAT) domains was determined with immunohistochemistry in healthy ovary, and serous and mucinous cystadenoma, borderline tumor and carcinoma samples. Additionally, the expression of FAK and its isoforms were investigated in three ovarian cancer-derived cell lines with western blotting and reverse transcription-semi-quantitative polymerase chain reaction. An increased expression of FAK kinase domain was determined in serous tumor samples and was associated with advancement of the lesion. FAK kinase domain expression was moderate-to-low in mucinous tumor samples. The expression of the FAK FAT domain in tumor samples was reduced, compared with healthy ovary samples; however, the FAT domain was localized to the cellular nucleus. Expression of alternative transcripts FAK°, FAK28,6 and FAK28 was determined in all three cell lines investigated. In conclusion, FAK kinase and FAT domains are differentially expressed among ovarian tumor types. These results indicated the presence of at least two isoforms of FAK (FAK and the putative FAK-related non-kinase) in tumor tissue, which is supported by the cells producing at least three FAK alternative transcripts. These results may support the use of FAK and its isoforms as biomarkers for ovarian cancer.

Therapeutic Potential of Focal Adhesion Kinase Inhibition in Small Cell Lung Cancer.

Small cell lung cancer (SCLC) has a poor prognosis. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase regulating cell proliferation, survival, migration, and invasion, which is overexpressed and/or activated in several cancers, including SCLC. We wanted to determine whether FAK contributes to SCLC aggressive behavior. We first evaluated the effect of FAK small-molecule inhibitor PF-573,228 in NCI-H82, NCI-H146, NCI-H196, and NCI-H446 SCLC cell lines. PF-573,228 (0.1-5 μmol/L) inhibited FAK activity by decreasing phospho-FAK (Tyr397), without modifying total FAK expression. PF-573,228 decreased proliferation, decreased DNA synthesis, induced cell-cycle arrest in G2-M phases, and increased apoptosis in all cell lines. PF-573,228 also decreased motility in adherent cell lines. To make sure that these effects were not off-target, we then used a genetic method to inhibit FAK in NCI-H82 and NCI-H446, namely stable transduction with FAK shRNA and/or FAK-related nonkinase (FRNK), a splice variant lacking the N-terminal and kinase domains. Although FAK shRNA transduction decreased total and phospho-FAK (Tyr397) expression, it did not affect proliferation, DNA synthesis, or progression through cell cycle. However, restoration of FAK-targeting (FAT) domain (attached to focal adhesion complex where it inhibits pro-proliferative proteins such as Rac-1) by FRNK transduction inhibited proliferation, DNA synthesis, and induced apoptosis. Moreover, although FAK shRNA transduction increased active Rac1 level, FRNK reexpression in cells previously transduced with FAK shRNA decreased it. Therefore, FAK appears important in SCLC biology and targeting its kinase domain may have a therapeutic potential, while targeting its FAT domain should be avoided to prevent Rac1-mediated protumoral activity.

Inhibiting focal adhesion kinase (FAK) blocks IL-4 induced VCAM-1 expression and eosinophil recruitment in vitro and in vivo.

Leukocyte recruitment plays a critical role during both normal inflammation and chronic inflammatory diseases, and ongoing studies endeavor to better understand the complexities of this process. Focal adhesion kinase (FAK) is well known for its role in cancer, yet it also has been shown to regulate aspects of neutrophil and B16 melanoma cell recruitment by rapidly influencing endothelial cell focal adhesion dynamics and junctional opening. Recently, we found that FAK related non-kinase (FRNK), a protein that is often used as a FAK dominant negative, blocked eosinophil transmigration by preventing the transcription of vascular cell adhesion molecule-1 (VCAM-1) and eotaxin-3 (CCL26). Surprisingly, the blocking occurred even in the absence of endogenous FAK. To better understand the role of FAK in leukocyte recruitment, we used a FAK-specific inhibitor (PF-573228) and determined the effect on IL-4 induced eosinophil recruitment in vitro and in vivo. PF-573228 prevented the expression of VCAM-1 and CCL26 expression in IL-4-stimulated human endothelial cells in vitro. As a result, eosinophil adhesion and transmigration were blocked. PF-572338 also prevented IL-4-induced VCAM-1 expression in vivo. Using brightfield intravital microscopy, we found that PF-573228 decreased leukocyte rolling flux, adhesion, and emigration. We specifically examined eosinophil recruitment in vivo by using an eosinophil-GFP reporter mouse and found PF-573228 attenuated eosinophil emigration. This study reveals that a FAK inhibitor influences inflammation through its action on eosinophil recruitment.

Syndecan-2 cytoplasmic domain up-regulates matrix metalloproteinase-7 expression via the protein kinase Cγ–mediated FAK/ERK signaling pathway in colon cancer

The syndecan family of heparan sulfate proteoglycans contributes to cell adhesion and communication by serving as co-receptors for cell signaling and extracellular matrix molecules. Syndecan-2 is located at the cell surface, and we previously reported that it induces matrix metalloproteinase-7 (MMP-7) expression in colon cancer cells. However, the underlying regulatory mechanisms are unknown. Here, we report that overexpression of syndecan-2 in HT-29 colon cancer cells increases the phosphorylation of focal adhesion kinase (FAK) and ERK in parallel with up-regulated MMP-7 expression, but a syndecan-2 mutant lacking the cytoplasmic domain showed significant reductions in these effects. Consistent with this observation, FAK inhibition via FAK-related non-kinase expression or inhibition of ERK with the ERK1/2 inhibitor SCH772984 diminished the syndecan-2-mediated up-regulation of MMP-7. Activation of PKC enhanced syndecan-2-mediated MMP-7 expression, whereas inhibition of PKC had the opposite effect. Of note, the exogenous expression of syndecan-2 triggered localization of PKCγ to the membrane. Expression of syndecan-2 harboring a phosphomimetic (S198E) mutation of the variable region of the cytoplasmic domain enhanced MMP-7 expression and FAK phosphorylation. Finally, experimental suppression of shedding of the syndecan-2 extracellular domain did not significantly affect the syndecan-2-mediated up-regulation of MMP-7 in the early period after syndecan-2 overexpression. Taken together, these findings suggest that syndecan-2's cytoplasmic domain up-regulates MMP-7 expression in colon cancer cells via PKCγ-mediated activation of FAK/ERK signaling.

Regulation of Focal Adhesion Kinase through a Direct Interaction with an Endogenous Inhibitor.

Focal adhesion kinase (FAK) plays a key role in integrin and growth factor signaling pathways. FAK-related non-kinase (FRNK) is an endogenous inhibitor of FAK that shares its primary structure with the C-terminal third of FAK. FAK S910 phosphorylation is known to regulate FAK protein-protein interactions, but the role of the equivalent site on FRNK (S217) is unknown. Here we determined that S217 is highly phosphorylated by ERK in cultured rat aortic smooth muscle cells. Blocking phosphorylation by mutation (S217A) greatly increased FRNK inhibitory potency, resulting in strong inhibition of FAK autophosphorylation at Y397 and induction of smooth muscle cell apoptosis. FRNK has been proposed to compete for FAK anchoring sites in focal adhesions, but we did not detect displacement of FAK by WT-FRNK or superinhibitory S217A-FRNK. Instead, we found FRNK interacted directly with FAK, and this interaction is markedly strengthened for the superinhibitory S217A-FRNK. The results suggest that FRNK limits growth and survival signaling pathways by binding directly to FAK in an inhibitory complex, and this inhibition is relieved by phosphorylation of FRNK at S217.

Focal Adhesion Kinase Regulatory Interactions Quantified by TIRF-FRET

Focal adhesion kinase related non-kinase (FRNK) is an inhibitor of focal adhesion kinase (FAK)-dependent cell growth, survival, and migration pathways. In vascular smooth muscle cells, both FAK and FRNK are upregulated after vascular injury, suggesting balanced stimulation and inhibition of growth during recovery. Here we propose a novel mechanism by which FRNK can inhibit FAK: direct binding of FRNK to FAK forming an inhibitory complex within focal adhesions. This hypothesis is supported by co-immunoprecipitation of FAK and FRNK. In addition, total internal reflection fluorescence (TIRF)-mode fluorescence resonance energy transfer (FRET) measurements suggest that FRNK binds directly to FAK within focal adhesions of live vascular smooth muscle cells. We hypothesized that this interaction might be regulated by serine phosphorylation of FRNK S217, a site we found to be basally highly phosphorylated at S217 by extracellular signal-regulated kinase 1/2 (ERK). To determine the significance of S217 phosphorylation, we generated a non-phosphorylatable mutant FRNK by mutating S217 to alanine. S217A-FRNK exhibited significantly higher amounts of FRET compared to wild type FRNK, suggesting increased interaction with FAK. Progressive acceptor photobleaching analysis revealed that the FRNK-FAK complex consisted of FRNK and multiple FAK proteins in a high order hetero-oligomer. To determine the functional role of the proposed regulatory site we performed an apoptosis assay using flow cytometry. S217A FRNK was a much more potent inducer of apoptosis in vascular smooth muscle cells compared to wild type FRNK. Additionally, we determined that S217A FRNK was a more potent inhibitor of FAK signaling by examining FAK Y397 phosphorylation. We conclude that dephosphorylation of FRNK at S217 during response to injury results in increased FRNK-FAK complex formation, thereby inhibiting FAK signaling.

Focal adhesion kinase (FAK) and mechanical stimulation negatively regulate the transition of airway smooth muscle tissues to a synthetic phenotype.

The effects of mechanical forces and focal adhesion kinase (FAK) in regulating the inflammatory responses of airway smooth muscle (ASM) tissues to stimulation with interleukin (IL)-13 were investigated. Canine tracheal tissues were subjected to different mechanical loads in vitro, and the effects of mechanical load on eotaxin secretion and inflammatory signaling pathways in response to IL-13 were determined. Eotaxin secretion by tissues in response to IL-13 was significantly inhibited in muscles maintained at a higher (+) load compared with those at a lower (-) load as assessed by ELISA, and Akt activation was also reduced in the higher (+) loaded tissues. Conversely the (+) mechanical load increased activation of the focal adhesion proteins FAK and paxillin in the tissues. The role of FAK in regulating the mechanosensitive responses was assessed by overexpressing FAK-related nonkinase in the tissues, by expressing the FAK kinase-dead mutant FAK Y397F, or by treating tissues with the FAK inhibitor PF-573228. FAK inactivation potentiated Akt activity and increased eotaxin secretion in response to IL-13. FAK inhibition also suppressed the mechanosensitivity of Akt activation and eotaxin secretion. In addition, FAK inactivation suppressed smooth muscle myosin heavy chain expression induced by the higher (+) mechanical load. The results demonstrate that the imposition of a higher mechanical load on airway smooth muscle stimulates FAK activation, which promotes the expression of the differentiated contractile phenotype and suppresses the synthetic phenotype and the inflammatory responses of the muscle tissue.

Novel Mechanisms of FRNK Inhibition of FAK in Vascular Smooth Muscle Cells

The nonreceptor protein tyrosine kinase focal adhesion kinase (FAK) is an important regulator of growth and migration in smooth muscle cells that acts as a kinase and a scaffolding protein. FAK-related nonkinase (FRNK) is an endogenously expressed truncated form of FAK that inhibits FAK signaling through an unknown mechanism. Traditionally, FRNK has been thought to inhibit FAK by displacing it from focal adhesion binding sites. We propose an additional parallel mechanism wherein FRNK binds directly to FAK, inhibiting downstream signaling. Initial co-immunoprecipitation experiments suggested FAK and FRNK interact. We quantified fluorescence resonance energy transfer (FRET) from FAK to FRNK using acceptor photobleaching and fluorescence lifetime measurements. Both approaches used total internal reflection fluorescence (TIRF) microscopy for selective illumination. Acceptor photo-bleaching experiments indicated 5.2±1.2% FRET between CER-FRNK and YFP-FAK. Fluorescence lifetime FRET experiments revealed 8.6±0.9% FRET between GFP-FAK and mCherry-FRNK. Furthermore, we show that FAK and FRNK localize to specific locations within focal adhesions. FRNK appears to be localized preferentially towards the proximal side of the focal adhesion. We hypothesize that this polarization is induced by strain on the focal adhesion from the attached actin stress fiber. Lastly, we have identified a phosphorylation site on FRNK, serine at position 217, that appears to regulate FRNK inhibition. A phosphomimetic mutant with serine 217 mutated to aspartic acid reduced FAK Y397 (activation site) phosphorylation by approximately 50% compared to wild type. The phosphomimetic mutant tagged with mCherry exhibited reduced FRET with GFP-FAK (5.4 ± 0.8) compared to wild type FRNK (8.6 ± 0.9%) suggesting decreased FAK binding or an altered conformation of the FAK/FRNK regulatory complex. We conclude that FRNK regulates FAK through a direct inhibitory interaction, and the inhibitory potency of FRNK is modulated by phosphorylation of serine 217.

FRNK negatively regulates IL-4-mediated inflammation.

Focal adhesion kinase (FAK)-related nonkinase (PTK2 isoform 6 in humans, hereafter referred to as FRNK) is a cytoskeletal regulatory protein that has recently been shown to dampen lung fibrosis, yet its role in inflammation is unknown. Here, we show for the first time that expression of FRNK negatively regulates IL-4-mediated inflammation in a human model of eosinophil recruitment. Mechanistically, FRNK blocks eosinophil accumulation, firm adhesion and transmigration by preventing transcription and protein expression of VCAM-1 and CCL26. IL-4 activates STAT6 to induce VCAM-1 and CCL26 transcription. We now show that IL-4 also increases GATA6 to induce VCAM-1 expression. FRNK blocks IL-4-induced GATA6 transcription but has little effect on GATA6 protein expression and no effect on STAT6 activation. FRNK can block FAK or Pyk2 signaling and we, thus, downregulated these proteins using siRNA to determine whether signaling from either protein is involved in the regulation of VCAM-1 and CCL26. Knockdown of FAK, Pyk2 or both had no effect on VCAM-1 or CCL26 expression, which suggests that FRNK acts independently of FAK and Pyk2 signaling. Finally, we found that IL-4 induces the late expression of endogenous FRNK. In summary, FRNK represents a novel mechanism to negatively regulate IL-4-mediated inflammation.

Mechanisms of FRNK Inhibition of FAK in Vascular Smooth Muscle Cells

The nonreceptor protein tyrosine kinase focal adhesion kinase (FAK) is an important regulator of growth and migration in smooth muscle cells that acts as a kinase and a scaffolding protein. FAK-related nonkinase (FRNK) is an endogenously expressed truncated form of FAK that inhibits FAK signaling through an unknown mechanism. Traditionally, FRNK has been thought to inhibit FAK by displacing it from focal adhesion binding sites. We propose an additional parallel mechanism wherein FRNK binds directly to FAK, inhibiting downstream signaling. Initial co-immunoprecipitation experiments suggested FAK and FRNK interact. We quantified fluorescence resonance energy transfer (FRET) from FAK to FRNK using acceptor photobleaching and fluorescence lifetime measurements. Both approaches used total internal reflection fluorescence (TIRF) microscopy for selective illumination. Acceptor photo-bleaching experiments indicated 5.2±1.2% FRET between CER-FRNK and YFP-FAK. Fluorescence lifetime FRET experiments revealed 8.6±0.9% FRET between GFP-FAK and mCherry-FRNK. Furthermore, we show that FAK and FRNK localize to specific locations within focal adhesions. FRNK appears to be localized preferentially towards the proximal side of the focal adhesion. We hypothesize that this polarization is induced by strain on the focal adhesion from the attached actin stress fiber. Lastly, we have identified a phosphorylation site on FRNK, serine at position 217, that appears to regulate FRNK inhibition. A phosphomimetic mutant with serine 217 mutated to aspartic acid reduced FAK Y397 (activation site) phosphorylation by approximately 50% compared to wild type. The phosphomimetic mutant tagged with mCherry exhibited reduced FRET with GFP-FAK (5.4 ± 0.8) compared to wild type FRNK (8.6 ± 0.9%) suggesting decreased FAK binding or an altered conformation of the FAK/FRNK regulatory complex. We conclude that FRNK regulates FAK through a direct inhibitory interaction, and the inhibitory potency of FRNK is modulated by phosphorylation of serine 217.

RacGAP1-driven focal adhesion formation promotes melanoma transendothelial migration through mediating adherens junction disassembly

Melanoma cell migration across vascular endothelial cells is an essential step of tumor metastasis. Here, we provide evidence that RacGAP1, a cytokinesis-related Rho GTPase-activating protein, contributed to this process. Depletion of RacGAP1 with RacGAP1-targeting siRNA or overexpression of RacGAP1 mutant (T249A) attenuated melanoma cell transendothelial migration and concomitant changes of adherens junctions. In addition, RacGAP1 promoted the activations of RhoA, FAK, paxillin and triggered focal adhesion formation and cytoskeletal rearrangement. By overexpressing FAK-related non-kinase (FRNK) in endothelium, we showed that RacGAP1 mediated endothelial barrier function loss and melanoma transmigration in a focal adhesion-dependent manner. These results suggest that endothelial RacGAP1 may play critical roles in pathogenic processes of cancer by regulating endothelial permeability.

Focal adhesion kinase (FAK)‐related non‐kinase (FRNK) negatively regulates eosinophil recruitment (146.4)

Focal adhesion kinase (FAK)‐related non‐kinase (FRNK) is an independently expressed protein containing the C‐terminal domain of FAK. A recent study showed that FRNK negatively regulates lung fibrosis. In this study we asked if FRNK could negatively regulate human eosinophil recruitment in response to IL‐4. Exogenous expression of FRNK blocked &gt;90% of eosinophil firm adhesion and transmigration to IL‐4‐stimulated endothelial cells (HUVEC) under flow conditions. FRNK blocked eosinophil recruitment by preventing the transcription and translation of VCAM‐1 and eotaxin‐3 (CCL26), two proteins we previously showed were critical for eosinophil recruitment. GATA6 has been shown to regulate VCAM‐1 in response to TNF, but its role in IL‐4‐mediated VCAM‐1 expression is not known. We found the IL‐4 increased GATA6 expression and down‐regulating GATA6 with siRNA blocked VCAM‐1 expression and function. Expressing FRNK in HUVEC prevented GATA6 upregulation by IL‐4 suggesting that FRNK blocks VCAM‐1 expression through its actions on GATA6. FRNK can act directly by binding to target molecules or indirectly by displacing FAK at focal adhesions and blocking FAK’s kinase activity. To determine if FRNK was acting through FAK, we down‐regulated FAK with siRNA and found that knocking down FAK had no effect on GATA6, VCAM‐1 or CCL26 expression. These data suggest that FRNK acts independent of FAK to negatively regulate eosinophil recruitment.Grant Funding Source: Supported by the Canadian Institutes of Health Research

Quantitative changes in focal adhesion kinase and its inhibitor, FRNK, drive load-dependent expression of costamere components

Costameres are mechanosensory sites of focal adhesion in the sarcolemma that reinforce the muscle-fiber composite and provide an anchor for myofibrillogenesis. We hypothesized that elevated content of the integrin-associated regulator of costamere turnover in culture, focal adhesion kinase (FAK), drives changes in costamere component content in antigravity muscle in a load-dependent way in correspondence with altered muscle weight. The content of FAK in soleus muscle being phosphorylated at autoregulatory tyrosine 397 (FAK-pY397) was increased after 20 s of stretch. FAK-pY397 content remained elevated after 24 h of stretch-overload due to upregulated FAK content. Overexpression of FAK in soleus muscle fibers by means of gene electrotransfer increased the β1-integrin (+56%) and meta-vinculin (+88%) content. α7-Integrin (P = 0.46) and γ-vinculin (P = 0.18) content was not altered after FAK overexpression. Co-overexpression of the FAK inhibitor FAK-related nonkinase (FRNK) reduced FAK-pY397 content by 33% and increased the percentage of fast-type fibers that arose in connection with hybrid fibers with gene transfer. Transplantation experiments confirmed the association of FRNK expression with slow-to-fast fiber transformation. Seven days of unloading blunted the elevation of FAK-pY397, β1-integrin, and meta-vinculin content with FAK overexpression, and this was reversed by 1 day of reloading. The results highlight that the expression of components for costameric attachment sites of myofibrils is under load- and fiber type-related control via FAK and its inhibitor FRNK.

Role of CXCR4-FAK signaling pathway in migration and adhesion of hypoxia-preconditioned bone marrow mesenchymal stem cells towards damaged tissues resulting from spinal cord ischemia-reperfusion injury in rats

Objective To investigate the role of CXC chemokine receptor 4-focal adhesion kinase (CXCR4-FAK) signaling pathway in migration and adhesion of hypoxia-preconditioned bone marrow mesenchymal stem cells (BMSCs) towards damaged tissues resulting from spinal cord ischemia-reperfusion (I/R) injury in rats.Methods Part I Rat BMSCs transfected with recombinant adenovirus-mediated green fluorescent protein gene 3 were seeded in 24-well plates and randomly divided into 5 groups (n =18 wells each):control group (group C),normoxia-incubated group (group N),HP group (group H),HP + CXCR4 antagonist AMD3100 group (group HA) and HP + FAK inhibitor FAK-related nonkinase group (group HF).In group C,BMSCs were incubated in DMEM culture medium.In group N,BMSCs were exposed to 21％ O2-74％ N2-5％ CO2 for 36 h.In group H,BMSCs were exposed to 0.5％O2-94.5％ N2-5.0％CO2 for 24 h followed by 12 h exposure to normoxia.In groups HA and HF,5 μg/ml AMD3100 and 10 μg/ml FAK-related nonkinase were added to the culture medium before HP,respectively.The expression of stromal derived factor-1α (SDF-1α),CXCR4 and phosphorylated FAK (p-FAK) in BMSCs was determined by Western blot.The migratory capability and adhesive ability of BMSCs were measured by Transwell invasive assay and fibronectin adhesive assay,respectively.Part Ⅱ Two hundred and sixteen male Sprague-Dawley rats weighing 300-350 g were used and 210 out of the 216 rats underwent spinal cord ischemia by occlusion of the thoracic aorta combined with controlled hypotension.Thirty-six rats were chosen and sacrificed before spinal cord I/R and at 12 h and 1,3,5 and 7 days of reperfusion (T0-5) and the lumbar segment of spinal cord was removed for detection of the content of SDF-1α.The left 180 rats with spinal cord I/R were randomly divided into 5 groups (n =36 each).IT DMEM medium 300 μl was injected in group C and BMSC suspension 300 μl (1 × 106/ml) was injected in groups N,H,HA and HF immediately after onset of reperfusion.Neurological function was scored at T0-5.The animals were then sacrificed and the lumbar segment of spinal cord was removed for detection of the degree of BMSC aggregation.Results There was no significant difference in the expression of SDF-1α,CXCR4 and p-FAK,migratory capability and adhesive ability of BMSCs,neurological function scores and degree of BMSC aggregation between groups C and N (P ＞ 0.05).Compared with group N,the expression of SDF-1α,CXCR4 and p-FAK was significantly up-regulated,and migratory capability and adhesive ability of BMSCs,neurological function scores and the degree of BMSC aggregation were increased in group H,while no significant change was found in the expression of p-FAK,migratory capability and adhesive ability of BMSCs,neurological function scores and degree of BMSC aggregation in HA and HF groups (P ＞ 0.05).Compared with group H,the expression of p-FAK was down-regulated and the migratory capability and adhesive ability of BMSCs,neurological function scores and degree of BMSC aggregation were decreased in groups HA and HF (P ＜0.05).The content of SDF-1α was significantly higher at T2,3 than at T0.Conclusion HP can promote migration and adhesion of BMSCs towards damaged tissues resulting from spinal cord I/R injury through CXCR4-FAK signaling pathway in rats; thus CXCR4-FAK signal pathway provides the protective effect on spinal cord. Key words: Receptors, CXCR4; Focal adhesion protein-tyrosine kinases; Mesenchymal stem cell transplantation ; Cell Hypoxia ; Ischemic preconditioning ; Cell movement; Cell adhesion; Spinal cord ; Reperfusion injury

Focal Adhesion Kinase Regulates Collagen I–Induced Airway Smooth Muscle Phenotype Switching

Increased extracellular matrix (ECM) deposition and airway smooth muscle (ASM) mass are major contributors to airway remodeling in asthma. Recently, we demonstrated that the ECM protein collagen I, which is increased surrounding asthmatic ASM, induces a proliferative, hypocontractile ASM phenotype. Little is known, however, about the signaling pathways involved. Using bovine tracheal smooth muscle, we investigated the role of focal adhesion kinase (FAK) and downstream signaling pathways in collagen I-induced ASM phenotype modulation. Phosphorylation of FAK was increased during adhesion to both uncoated and collagen I-coated culture dishes, without differences between these matrices. Nor were any differences found in cellular adhesion. Inhibition of FAK activity by overexpression of the FAK deletion mutants FAT (focal adhesion targeting domain) and FRNK (FAK-related nonkinase) attenuated adhesion. After attachment, FAK phosphorylation increased in a time-dependent manner in cells cultured on collagen I, whereas no activation was found on an uncoated plastic matrix. In addition, collagen I increased in a time- and concentration-dependent manner the cell proliferation, which was fully inhibited by FAT and FRNK. Similarly, the specific pharmacologic FAK inhibitor PF-573228 [6-((4-((3-(methanesulfonyl)benzyl)amino)-5-trifluoromethylpyrimidin-2-yl) amino)-3,4-dihydro-1H-quinolin-2-one] as well as specific inhibitors of p38 mitogen-activated protein kinase (MAPK) and Src also fully inhibited collagen I-induced proliferation, whereas partial inhibition was observed by inhibition of phosphatidylinositol-3-kinase (PI3-kinase) and mitogen-activated protein kinase kinase (MEK). The inhibition of cell proliferation by these inhibitors was associated with attenuation of the collagen I-induced hypocontractility. Collectively, the results indicate that induction of a proliferative, hypocontractile ASM phenotype by collagen I is mediated by FAK and downstream signaling pathways.

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.