A role for the tyrosine kinase Pyk2 in depolarization-induced contraction of vascular smooth muscle

p90RSK2, a new MLCK mediates contractility in myosin light chain kinase null smooth muscle

Introduction: Phosphorylation of smooth muscle (SM) myosin regulatory light chain (RLC20) is a critical switch leading to SM contraction. The canonical view held that only the short isoform of myosin light chain kinase (MLCK1) catalyzed this reaction. It is now accepted that auxiliary kinases may contribute to vascular SM tone and contractility. We have previously reported that p90 ribosomal S6 kinase (RSK2) functions as such a kinase, in parallel with MLCK1, contributing ∼25% of the maximal myogenic force in resistance arteries. Thus, RSK2 may be instrumental in the regulation of basal vascular tone and blood pressure. Here, we take advantage of a MLCK1 null mouse (mylk1 -/-) to further test our hypothesis that RSK2 can function as an MLCK, playing a significant physiological role in SM contractility. Methods: Using fetal (E14.5-18.5) SM tissues, as embryos die at birth, we investigated the necessity of MLCK for contractility and fetal development and determined the ability of RSK2 kinase to compensate for the lack of MLCK and characterized its signaling pathway in SM. Results and Discussion: Agonists induced contraction and RLC20 phosphorylation in mylk1 -/- SM was attenuated by RSK2 inhibition. The pCa-tension relationships in permeabilized strips of bladder showed no difference in Ca2+ sensitivity in WT vs mylk1 -/- muscles, although the magnitude of force responses was considerably smaller in the absence of MLCK. The magnitude of contractile responses was similar upon addition of GTPγS to activate the RhoA/ROCK pathway or calyculinA to inhibit the myosin phosphatase. The Ca2+-dependent tyrosine kinase, Pyk2, contributed to RSK2-mediated contractility and RLC20 phosphorylation. Proximity-ligation and immunoprecipitation assays demonstrated an association of RSK2, PDK1 and ERK1/2 with MLCK and actin. RSK2, PDK1, ERK1/2 and MLCK formed a signaling complex on the actin filament, positioning them for interaction with adjacent myosin heads. The Ca2+-dependent component reflected the agonist mediated increases in Ca2+, which activated the Pyk2/PDK1/RSK2 signaling cascade. The Ca2+-independent component was through activation of Erk1/2/PDK1/RSK2 leading to direct phosphorylation of RLC20, to increase contraction. Overall, RSK2 signaling constitutes a new third signaling pathway, in addition to the established Ca2+/CaM/MLCK and RhoA/ROCK pathways to regulate SM contractility.

PF-431396 hydrate inhibition of kinase phosphorylation during adherent-invasive Escherichia coli infection inhibits intra-macrophage replication and inflammatory cytokine release

Adherent-invasive Escherichia coli (AIEC) have been implicated in the aetiology of Crohn's disease (CD). They are characterized by an ability to adhere to and invade intestinal epithelial cells, and to replicate intracellularly in macrophages resulting in inflammation. Proline-rich tyrosine kinase 2 (PYK2) has previously been identified as a risk locus for inflammatory bowel disease and a regulator of intestinal inflammation. It is overexpressed in patients with colorectal cancer, a major long-term complication of CD. Here we show that Pyk2 levels are significantly increased during AIEC infection of murine macrophages while the inhibitor PF-431396 hydrate, which blocks Pyk2 activation, significantly decreased intramacrophage AIEC numbers. Imaging flow cytometry indicated that Pyk2 inhibition blocked intramacrophage replication of AIEC with no change in the overall number of infected cells, but a significant reduction in bacterial burden per cell. This reduction in intracellular bacteria resulted in a 20-fold decrease in tumour necrosis factor α secretion by cells post-AIEC infection. These data demonstrate a key role for Pyk2 in modulating AIEC intracellular replication and associated inflammation and may provide a new avenue for future therapeutic intervention in CD.

p90RSK2, a new MLCK, rescues contractility in myosin light chain kinase null smooth muscle

Background

Phosphorylation of smooth muscle (SM) myosin regulatory light chain (RLC 20 ) is a critical switch leading to contraction or cell migration. The canonical view held that the only kinase catalyzing this reaction is the short isoform of myosin light chain kinase (MLCK1). Auxiliary kinases may be involved and play a vital role in blood pressure homeostasis. We have previously reported that p90 ribosomal S6 kinase (RSK2) functions as such a kinase, in parallel with the classical MLCK1, contributing ∼25% of the maximal myogenic force in resistance arteries and regulating blood pressure. Here, we take advantage of a MLCK1 null mouse to further test our hypothesis that RSK2 can function as an MLCK, playing a significant physiological role in SM contractility.

Methods

Fetal (E14.5-18.5) SM tissues were used as embryos die at birth. We investigated the necessity of MLCK for contractility, cell migration and fetal development and determined the ability of RSK2 kinase to compensate for the lack of MLCK and characterized it's signaling pathway in SM.

Results

Agonists induced contraction and RLC 20 phosphorylation in mylk1 -/- SM, that was inhibited by RSK2 inhibitors. Embryos developed and cells migrated in the absence of MLCK. The pCa-tension relationships in WT vs mylk1 -/- muscles demonstrated a Ca 2+ -dependency due to the Ca 2+ -dependent tyrosine kinase Pyk2, known to activate PDK1 that phosphorylates and fully activates RSK2. The magnitude of contractile responses was similar upon addition of GTPγS to activate the RhoA/ROCK pathway. The Ca 2+ -independent component was through activation of Erk1/2/PDK1/RSK2 leading to direct phosphorylation of RLC 20 , to increase contraction. RSK2, PDK1, Erk1/2 and MLCK formed a signaling complex on the actin filament, optimally positioning them for interaction with adjacent myosin heads.

Conclusions

RSK2 signaling constitutes a new third signaling pathway, in addition to the established Ca 2+ /CAM/MLCK and RhoA/ROCK pathways to regulate SM contractility and cell migration.

Dual thick and thin filament linked regulation of stretch- and L-NAME-induced tone in young and senescent murine basilar artery

Stretch-induced vascular tone is an important element of autoregulatory adaptation of cerebral vasculature to maintain cerebral flow constant despite changes in perfusion pressure. Little is known as to the regulation of tone in senescent basilar arteries. We tested the hypothesis, that thin filament mechanisms in addition to smooth muscle myosin-II regulatory-light-chain-(MLC20)-phosphorylation and non-muscle-myosin-II, contribute to regulation of stretch-induced tone. In young BAs (y-BAs) mechanical stretch does not lead to spontaneous tone generation. Stretch-induced tone in y-BAs appeared only after inhibition of NO-release by L-NAME and was fully prevented by treatment with 3 μmol/L RhoA-kinase (ROK) inhibitor Y27632. L-NAME-induced tone was reduced in y-BAs from heterozygous mice carrying a point mutation of the targeting-subunit of the myosin phosphatase, MYPT1 at threonine696 (MYPT1-T696A/+). In y-BAs, MYPT1-T696A-mutation also blunted the ability of L-NAME to increase MLC20-phosphorylation. In contrast, senescent BAs (s-BAs; >24 months) developed stable spontaneous stretch-induced tone and pharmacological inhibition of NO-release by L-NAME led to an additive effect. In s-BAs the MYPT1-T696A mutation also blunted MLC20-phosphorylation, but did not prevent development of stretch-induced tone. In s-BAs from both lines, Y27632 completely abolished stretch- and L-NAME-induced tone. In s-BAs phosphorylation of non-muscle-myosin-S1943 and PAK1-T423, shown to be down-stream effectors of ROK was also reduced by Y27632 treatment. Stretch- and L-NAME tone were inhibited by inhibition of non-muscle myosin (NM-myosin) by blebbistatin. We also tested whether the substrate of PAK1 the thin-filament associated protein, caldesmon is involved in the regulation of stretch-induced tone in advanced age. BAs obtained from heterozygotes Cald1+/− mice generated stretch-induced tone already at an age of 20–21 months old BAs (o-BA). The magnitude of stretch-induced tone in Cald1+/− o-BAs was similar to that in s-BA. In addition, truncation of caldesmon myosin binding Exon2 (CaD-▵Ex2−/−) did not accelerate stretch-induced tone. Our study indicates that in senescent cerebral vessels, mechanisms distinct from MLC20 phosphorylation contribute to regulation of tone in the absence of a contractile agonist. While in y-and o-BA the canonical pathways, i.e., inhibition of MLCP by ROK and increase in pMLC20, predominate, tone regulation in senescence involves ROK regulated mechanisms, involving non-muscle-myosin and thin filament linked mechanisms involving caldesmon.

Mfge8 attenuates human gastric antrum smooth muscle contractions

Coordinated gastric smooth muscle contraction is critical for proper digestion and is adversely affected by a number of gastric motility disorders. In this study we report that the secreted protein Mfge8 (milk fat globule-EGF factor 8) inhibits the contractile responses of human gastric antrum muscles to cholinergic stimuli by reducing the inhibitory phosphorylation of the MYPT1 (myosin phosphatase-targeting subunit (1) subunit of MLCP (myosin light chain phosphatase), resulting in reduced LC20 (smooth muscle myosin regulatory light chain (2) phosphorylation. Mfge8 reduced the agonist-induced increase in the F-actin/G-actin ratios of β-actin and γ-actin1. We show that endogenous Mfge8 is bound to its receptor, α8β1 integrin, in human gastric antrum muscles, suggesting that human gastric antrum muscle mechanical responses are regulated by Mfge8. The regulation of gastric antrum smooth muscles by Mfge8 and α8 integrin functions as a brake on gastric antrum mechanical activities. Further studies of the role of Mfge8 and α8 integrin in regulating gastric antrum function will likely reveal additional novel aspects of gastric smooth muscle motility mechanisms.

Sperm-oocyte signaling: the role of IZUMO1R and CD9 in PTK2B activation and actin remodeling at the sperm binding site†

Sperm-oocyte binding initiates an outside-in signaling event in the mouse oocyte that triggers recruitment and activation of the cytosolic protein kinase PTK2B in the cortex underlying the bound sperm. While not involved in gamete fusion, PTK2B activity promotes actin remodeling events important during sperm incorporation. However, the mechanism by which sperm-oocyte binding activates PTK2B is unknown, and the present study examined the possibility that sperm interaction with specific oocyte surface proteins plays an important role in PTK2B activation. Imaging studies revealed that as IZUMO1R and CD9 became concentrated at the sperm binding site, activated (phosphorylated) PTK2B accumulated in the cortex underlying the sperm head and in microvilli partially encircling the sperm head. In order to determine whether IZUMO1R and/or CD9 played a significant role in PTK2B recruitment and activation at the sperm binding site, the ability of oocytes null for Izumo1r or Cd9, to initiate an increase in PTK2B content and activation was tested. The results revealed that IZUMO1R played a minor role in PTK2B activation and had no effect on actin remodeling; however, CD9 played a very significant role in PTK2B activation and subsequent actin remodeling at the sperm binding site. These findings suggest the possibility that interaction of sperm surface proteins with CD9 or CD9-associated oocyte proteins triggers PTK2B activation at the sperm binding site.

Acute stress induces visceral hypersensitivity via glucocorticoid receptor-mediated membrane insertion of TRPM8: Involvement of a non-receptor tyrosine kinase Pyk2

BACKGROUND

Psychological stress is an important factor for the development and recurrence of irritable bowel syndrome (IBS). The mechanisms underlying stress-induced visceral hypersensitivity (VH), a key pathophysiological component in IBS, are still incompletely understood. We aimed to test whether transient receptor potential melastatin 8 (TRPM8) participates in acute stress-induced VH.

METHODS

Rats were subjected to 1-hour water avoidance stress (WAS). Visceral sensitivity was measured with visceromotor response to colorectal distension. Western blot and immunofluorescence were applied to evaluate the expression of GR and TRPM8 and activation of PKA, Akt, and PKC pathways.

RESULTS

WAS-caused VH depended on glucocorticoid receptors (GRs) and TRPM8 channels. In a dorsal root ganglion (DRG)-derived cell line, corticosterone rapidly (within 30 minutes) induced membrane expression of TRPM8. This effect was inhibited by GR antagonism and was mimicked by membrane-impermeable corticosterone. PKA, PI3K/Akt, and PKC pathways, which lied downstream of GR and acted in parallel to promote membrane expression of TRPM8, contributed to WAS-induced VH. The non-receptor tyrosine kinase Pyk2, which may serve as a convergence point for PKA, PI3K/Akt, and PKC pathways, facilitated membrane insertion of TRPM8 via tyrosine-phosphorylating TRPM8 in L6-S2 DRGs and participated in WAS-induced VH.

CONCLUSIONS

Collectively, acute stress-induced VH could involve membrane-bound GR-dependent enhancement of TRPM8 function in nociceptive DRG neurons. Mechanistically, Pyk2 could act as a key mediator that coordinates multiple protein kinase signaling and triggers phosphorylation and membrane insertion of TRPM8.

A Fyn biosensor reveals pulsatile, spatially localized kinase activity and signaling crosstalk in live mammalian cells

Cell behavior is controlled through spatio-temporally localized protein activity. Despite unique and often contradictory roles played by Src-family-kinases (SFKs) in regulating cell physiology, activity patterns of individual SFKs have remained elusive. Here, we report a biosensor for specifically visualizing active conformation of SFK-Fyn in live cells. We deployed combinatorial library screening to isolate a binding-protein (F29) targeting activated Fyn. Nuclear-magnetic-resonance (NMR) analysis provides the structural basis of F29 specificity for Fyn over homologous SFKs. Using F29, we engineered a sensitive, minimally-perturbing fluorescence-resonance-energy-transfer (FRET) biosensor (FynSensor) that reveals cellular Fyn activity to be spatially localized, pulsatile and sensitive to adhesion/integrin signaling. Strikingly, growth factor stimulation further enhanced Fyn activity in pre-activated intracellular zones. However, inhibition of focal-adhesion-kinase activity not only attenuates Fyn activity, but abolishes growth-factor modulation. FynSensor imaging uncovers spatially organized, sensitized signaling clusters, direct crosstalk between integrin and growth-factor-signaling, and clarifies how compartmentalized Src-kinase activity may drive cell fate.

Pu-Erh Tea Relaxes the Thoracic Aorta of Rats by Reducing Intracellular Calcium

Previous studies suggested that pu-erh tea aqueous extract could lower blood pressure and ameliorate hypertension symptoms. However, the antihypertension mechanisms of pu-erh tea remain unclear. In this work, the direct effects of pu-erh tea on vessels and cells were investigated by detecting isometric tension and intracellular calcium ([Ca²⁺]_i), respectively. Additionally, to identify the main active components, the aqueous extract of pu-erh was separated by organic solvents to obtain various fractions, and the effects of these fractions on arteries were assessed. The results showed that pu-erh aqueous extract vasodilated rat thoracic aortas preconstricted by phenylephrine or KCl. These vasodilation effects were not significantly affected by the removal of the endothelium or by preincubation with potassium channel blockers (tetraethylammonium, glibenclamide, aminopyridine, or barium chloride). Moreover, pu-erh aqueous extract could reduce the vessel contractibility induced by CaCl₂ and phenylephrine under KCl-depolarizing or Ca²⁺-free buffer conditions, respectively. Furthermore, pu-erh aqueous extract attenuated the KCl-induced increase in [Ca²⁺]_i in cultured rat aortic smooth muscle A7r5 cells. In addition, the chloroform precipitate of pu-erh aqueous extract produced the most potent vasodilation. Theabrownins (the characteristic components of pu-erh tea) accounted for 41.91 ± 1.09 % of the chloroform precipitate and vasodilated arteries in an endothelium-independent manner. In addition, the vasodilation effect of caffeine was verified. In conclusion, theabrownins and caffeine should be the two main active components in pu-erh tea. Pu-erh aqueous extract vasodilated arteries in an endothelium-independent manner, which might partly be attributed to the decrease in extracellular Ca²⁺ influx. Moreover, our study provided data on the potential mechanism of the hypotensive actions of pu-erh tea, which might improve our understanding of the effect of pu-erh tea on the prevention and treatment of hypertension.

Pyk2-dependent phosphorylation of LSR enhances localization of LSR and tricellulin at tricellular tight junctions

Tight junctions (TJs) are cellular junctions within the mammalian epithelial cell sheet that function as a physical barrier to molecular transport within the intercellular space. Dysregulation of TJs leads to various diseases. Tricellular TJs (tTJs), specialized structural variants of TJs, are formed by multiple transmembrane proteins (e.g., lipolysis-stimulated lipoprotein receptor [LSR] and tricellulin) within tricellular contacts in the mammalian epithelial cell sheet. However, the mechanism for recruiting LSR and tricellulin to tTJs is largely unknown. Previous studies have identified that tyrphostin 9, the dual inhibitor of Pyk2 (a nonreceptor tyrosine kinase) and receptor tyrosine kinase platelet-derived growth factor receptor (PDGFR), suppresses LSR and tricellulin recruitment to tTJs in EpH4 (a mouse mammary epithelial cell line) cells. In this study, we investigated the effect of Pyk2 inhibition on LSR and tricellulin localization to tTJs. Pyk2 inactivation by its specific inhibitor or repression by RNAi inhibited the localization of LSR and downstream tricellulin to tTJs without changing their expression level in EpH4 cells. Pyk2-dependent changes in subcellular LSR and tricellulin localization were independent of c-Jun N-terminal kinase (JNK) activation and expression. Additionally, Pyk2-dependent LSR phosphorylation at Tyr-237 was required for LSR and tricellulin localization to tTJs and decreased epithelial barrier function. Our findings indicated a novel mechanism by which Pyk2 regulates tTJ assembly and epithelial barrier function in the mammalian epithelial cell sheet.

Carbon Monoxide Releasing Molecule-2-Upregulated ROS-Dependent Heme Oxygenase-1 Axis Suppresses Lipopolysaccharide-Induced Airway Inflammation

The up-regulation of heme oxygenase-1 (HO-1) is mediated through nicotinamaide adenine dinucleotide phosphate (NADPH) oxidases (Nox) and reactive oxygen species (ROS) generation, which could provide cytoprotection against inflammation. However, the molecular mechanisms of carbon monoxide-releasing molecule (CORM)-2-induced HO-1 expression in human tracheal smooth muscle cells (HTSMCs) remain unknown. Here, we found that pretreatment with CORM-2 attenuated the lipopolysaccharide (LPS)-induced intercellular adhesion molecule (ICAM-1) expression and leukocyte count through the up-regulation of HO-1 in mice, which was revealed by immunohistochemistrical staining, Western blot, real-time PCR, and cell count. The inhibitory effects of HO-1 by CORM-2 were reversed by transfection with HO-1 siRNA. Next, Western blot, real-time PCR, and promoter activity assay were performed to examine the HO-1 induction in HTSMCs. We found that CORM-2 induced HO-1 expression via the activation of protein kinase C (PKC)α and proline-rich tyrosine kinase (Pyk2), which was mediated through Nox-derived ROS generation using pharmacological inhibitors or small interfering ribonucleic acids (siRNAs). CORM-2-induced HO-1 expression was mediated through Nox-(1, 2, 4) or p47^phox, which was confirmed by transfection with their own siRNAs. The Nox-derived ROS signals promoted the activities of extracellular signal-regulated kinase 1/2 (ERK1/2). Subsequently, c-Fos and c-Jun-activator protein-1 (AP-1) subunits-were up-regulated by activated ERK1/2, which turned on transcription of the HO-1 gene by regulating the HO-1 promoter. These results suggested that in HTSMCs, CORM-2 activates PKCα/Pyk2-dependent Nox/ROS/ERK1/2/AP-1, leading to HO-1 up-regulation, which suppresses the lipopolysaccharide (LPS)-induced airway inflammation.

Quantitative in situ proximity ligation assays examining protein interactions and phosphorylation during smooth muscle contractions

Antibody-based in situ proximity ligation assays (isPLA) have the potential to study protein phosphorylation and protein interactions with spatial resolution in intact tissues. However, the application of isPLA at the tissue level is limited by a lack of appropriate positive and negative controls and the difficulty in accounting for changes in tissue shape. Here we demonstrate a set of experimental and computational approaches using gastric fundus smooth muscles to improve the validity of quantitative isPLA. Appropriate positive and negative biological controls and PLA technical controls were selected to ensure experimental rigor. To account for changes in morphology between relaxed and contracted smooth muscles, target PLA spots were normalized to smooth muscle myosin light chain 20 PLA spots or the cellular cross-sectional areas. We describe the computational steps necessary to filter out false-positive improperly sized spots and set the thresholds for counting true positive PLA spots to quantify the PLA signals. We tested our approach by examining protein phosphorylation and protein interactions in smooth muscle myofilament Ca²⁺ sensitization pathways from resting and contracted gastric fundus smooth muscles. In conclusion, our tissue-level isPLA method enables unbiased quantitation of protein phosphorylation and protein-protein interactions in intact smooth muscle tissues, suggesting the potential for quantitative isPLA applications in other types of intact tissues.

Regulation of gastric smooth muscle contraction via Ca2+-dependent and Ca2+-independent actin polymerization

In gastrointestinal smooth muscle, acetylcholine induced muscle contraction is biphasic, initial peak followed by sustained contraction. Contraction is regulated by phosphorylation of 20 kDa myosin light chain (MLC) at Ser¹⁹, interaction of actin and myosin, and actin polymerization. The present study characterized the signaling mechanisms involved in actin polymerization during initial and sustained muscle contraction in response to muscarinic M3 receptor activation in gastric smooth muscle cells by targeting the effectors of initial (phospholipase C (PLC)-β/Ca²⁺ pathway) and sustained (RhoA/focal adhesion kinase (FAK)/Rho kinase pathway) contraction. The initial Ca²⁺ dependent contraction and actin polymerization is mediated by sequential activation of PLC-β1 via Gα_q, IP₃ formation, Ca²⁺ release and Ca²⁺ dependent phosphorylation of proline-rich-tyrosine kinase 2 (Pyk2) at Tyr⁴⁰². The sustained Ca²⁺ independent contraction and actin polymerization is mediated by activation of RhoA, and phosphorylation of FAK at Tyr³⁹⁷. Both phosphorylation of Pyk2 and FAK leads to phosphorylation of paxillin at Tyr¹¹⁸ and association of phosphorylated paxillin with the GEF proteins p21-activated kinase (PAK) interacting exchange factor α, β (α and β PIX) and DOCK 180. These GEF proteins stimulate Cdc42 leading to the activation of nucleation promoting factor N-WASP (neuronal Wiskott-Aldrich syndrome protein), which interacts with actin related protein complex 2/3 (Arp2/3) to induce actin polymerization and muscle contraction. Acetylcholine induced muscle contraction is inhibited by actin polymerization inhibitors. Thus, our results suggest that a novel mechanism for the regulation of smooth muscle contraction is mediated by actin polymerization in gastrointestinal smooth muscle which is independent of MLC₂₀ phosphorylation.

Tyrosine Kinase Pyk2 is Involved in Colonic Smooth Muscle Contraction via the RhoA/ROCK Pathway

The contraction of gastrointestinal (GI) smooth muscles is regulated by both Ca(2+)-dependent and Ca(2+) sensitization mechanisms. Proline-rich tyrosine kinase 2 (Pyk2) is involved in the depolarization-induced contraction of vascular smooth muscle via a Ca(2+) sensitization pathway. However, the role of Pyk2 in GI smooth muscle contraction is unclear. The spontaneous contraction of colonic smooth muscle was measured by using isometric force transducers. Protein and phosphorylation levels were determined by using western blotting. Pyk2 protein was expressed in colonic tissue, and spontaneous colonic contractions were inhibited by PF-431396, a Pyk2 inhibitor, in the presence of tetrodotoxin (TTX). In cultured colonic smooth muscle cells (CSMCs), PF-431396 decreased the levels of myosin light chain (MLC20) phosphorylated at Ser19 and ROCK2 protein expression, but myosin light chain kinase (MLCK) expression was not altered. However, Y-27632, a Rho kinase inhibitor, increased phosphorylation of Pyk2 at Tyr402 and concomitantly decreased ROCK2 levels; the expression of MLCK in CSMCs did not change. The expression of P(Tyr402)-Pyk2 and ROCK2 was increased when CSMCs were treated with Ach. Pyk2 is involved in the process of colonic smooth muscle contraction through the RhoA/ROCK pathway. These pathways may provide very important targets for investigating GI motility disorders.

JAM-A knockdown accelerates the proliferation and migration of human keratinocytes, and improves wound healing in rats via FAK/Erk signaling

Junctional adhesion molecule-A (JAM-A) belongs to the immunoglobulin superfamily, it predominantly exists at the tight junctions of epithelial and endothelial cells. JAM-A is known to regulate leukocyte trans-endothelial migration, however, how it affects the proliferation and migration of keratinocytes, the two essential steps during wound healing, has less been explored. In this study, we showed that JAM-A was significantly expressed in normal skin epidermis. RNAi-mediated JAM-A knockdown remarkably promoted the proliferation and migration of keratinocytes. We also found that loss of JAM-A increased the protein levels of p-FAK, p-Erk1/2, and p-JNK; however, FAK inhibitor PF-562271 restrained the expression of p-FAK and p-Erk1/2 elevated by JAM-A RNAi, but not p-JNK, and also slowed down keratinocyte proliferation and migration. Finally, in a rat wound model we showed that absence of JAM-A significantly promoted the wound healing process, while the use of PF-562271 or Erk1/2 inhibitor PD98059 repressed those effects. These data collectively demonstrate that suppressing JAM-A expression could promote the proliferation and migration of keratinocytes and accelerate the healing process of rat skin wounds, potentially via FAK/Erk pathway, indicating that JAM-A might serve as a potential therapeutic target for the treatment of chronic refractory wounds.

A role for focal adhesion kinase in facilitating the contractile responses of murine gastric fundus smooth muscles

KEY POINTS

Activation of focal adhesion kinase (FAK) by integrin signalling facilitates smooth muscle contraction by transmitting the force generated by myofilament activation to the extracellular matrix and throughout the smooth muscle tissue. Here we report that electrical field stimulation (EFS) of cholinergic motor neurons activates FAK in gastric fundus smooth muscles, and that FAK activation by EFS is atropine-sensitive but nicardipine-insensitive. PDBu and calyculin A contracted gastric fundus muscles Ca²⁺ -independently and also activated FAK. Inhibition of FAK activation inhibits the contractile responses evoked by EFS, and inhibits CPI-17 phosphorylation at T38. This study indicates that mechanical force or tension is sufficient to activate FAK, and that FAK appears to be involved in the activation of the protein kinase C-CPI-17 Ca²⁺ sensitization pathway in gastric fundus smooth muscles. These results reveal a novel role for FAK in gastric fundus smooth muscle contraction by facilitating CPI-17 phosphorylation.

ABSTRACT

Smooth muscle contraction involves regulating myosin light chain phosphorylation and dephosphorylation by myosin light chain kinase and myosin light chain phosphatase. C-kinase potentiated protein phosphatase-1 inhibitor of 17 kDa (CPI-17) and myosin phosphatase targeting subunit of myosin light-chain phosphatase (MYPT1) are crucial for regulating gastrointestinal smooth muscle contraction by inhibiting myosin light chain phosphatase. Integrin signalling involves the dynamic recruitment of several proteins, including focal adhesion kinase (FAK), to focal adhesions. FAK tyrosine kinase activation is involved in cell adhesion to the extracellular matrix via integrin signalling. FAK participates in linking the force generated by myofilament activation to the extracellular matrix and throughout the smooth muscle tissue. Here, we show that cholinergic stimulation activates FAK in gastric fundus smooth muscles. Electrical field stimulation in the presence of N^ω -nitro-l-arginine methyl ester and MRS2500 contracted gastric fundus smooth muscle strips and increased FAK Y397 phosphorylation (pY397). Atropine blocked the contractions and prevented the increase in pY397. The FAK inhibitor PF-431396 inhibited the contractions and the increase in pY397. PF-431396 also inhibited the electrical field stimulation-induced increase in CPI-17 T38 phosphorylation, and reduced MYPT1 T696 and T853, and myosin light chain S19 phosphorylation. Ca²⁺ influx was unaffected by PF-431396. Nicardipine inhibited the contractions but had no effect on the increase in pY397. Phorbol 12,13-dibutyrate or calyculin A contracted gastric fundus smooth muscle strips Ca²⁺ independently and increased pY397. Our findings suggest that FAK is activated by mechanical forces during contraction and reveal a novel role of FAK in the regulation of CPI-17 phosphorylation.

Focal adhesion kinase a potential therapeutic target for pancreatic cancer and malignant pleural mesothelioma

The non-receptor cytoplasmic tyrosine kinase, Focal Adhesion Kinase (FAK) is known to play a key role in a variety of normal and cancer cellular functions such as survival, proliferation, migration and invasion. It is highly active and overexpressed in various cancers including Pancreatic Ductal Adenocarcinoma (PDAC) and Malignant Pleural Mesothelioma (MPM). Here, initially, we demonstrate that FAK is overexpressed in both PDAC and MPM cell lines. Then we analyze effects of two small molecule inhibitors PF-573228, and PF-431396, which are dual specificity inhibitors of FAK and proline rich tyrosine kinase 2 (PYK2), as well as VS-6063, another small molecule inhibitor that specifically inhibits FAK but not PYK2 for cell growth, motility and invasion of PDAC and MPM cell lines. Treatment with PF-573228, PF-431396 and VS-6063 cells resulted in a dose-dependent inhibition of growth and anchorage-independent colony formation in both cancer cell lines. Furthermore, these compounds suppressed the phosphorylation of FAK at its active site, Y397, and functionally induced significant apoptosis and cell cycle arrest in both cell lines. Using the ECIS (Electric cell-substrate impedance sensing) system, we found that treatment of both PF compounds suppressed adherence and migration of PDAC cells on fibronectin. Interestingly, 3D-tumor organoids derived from autochthonous KC (Kras;PdxCre) mice treated with PF-573228 revealed a significant decrease in tumor organoid size and increase in organoid cell death. Taken together, our results show that FAK is an important target for mesothelioma and pancreatic cancer therapy that merit further translational studies.

CF airway smooth muscle transcriptome reveals a role for PYK2

Abnormal airway smooth muscle function can contribute to cystic fibrosis (CF) airway disease. We previously found that airway smooth muscle from newborn CF pigs had increased basal tone, an increased bronchodilator response, and abnormal calcium handling. Since CF pigs lack airway infection and inflammation at birth, these findings suggest intrinsic airway smooth muscle dysfunction in CF. In this study, we tested the hypothesis that CFTR loss in airway smooth muscle would produce a distinct set of changes in the airway smooth muscle transcriptome that we could use to develop novel therapeutic targets. Total RNA sequencing of newborn wild-type and CF airway smooth muscle revealed changes in muscle contraction-related genes, ontologies, and pathways. Using connectivity mapping, we identified several small molecules that elicit transcriptional signatures opposite of CF airway smooth muscle, including NVP-TAE684, an inhibitor of proline-rich tyrosine kinase 2 (PYK2). In CF airway smooth muscle tissue, PYK2 phosphorylation was increased and PYK2 inhibition decreased smooth muscle contraction. In vivo NVP-TAE684 treatment of wild-type mice reduced methacholine-induced airway smooth muscle contraction. These findings suggest that studies in the newborn CF pig may provide an important approach to enhance our understanding of airway smooth muscle biology and for discovery of novel airway smooth muscle therapeutics for CF and other diseases of airway hyperreactivity.

Pyk2 inhibition promotes contractile differentiation in arterial smooth muscle

Modulation from contractile to synthetic phenotype of vascular smooth muscle cells is a central process in disorders involving compromised integrity of the vascular wall. Phenotype modulation has been shown to include transition from voltage-dependent toward voltage-independent regulation of the intracellular calcium level, and inhibition of non-voltage dependent calcium influx contributes to maintenance of the contractile phenotype. One possible mediator of calcium-dependent signaling is the FAK-family non-receptor protein kinase Pyk2, which is activated by a number of stimuli in a calcium-dependent manner. We used the Pyk2 inhibitor PF-4594755 and Pyk2 siRNA to investigate the role of Pyk2 in phenotype modulation in rat carotid artery smooth muscle cells and in cultured intact arteries. Pyk2 inhibition promoted the expression of smooth muscle markers at the mRNA and protein levels under stimulation by FBS or PDGF-BB and counteracted phenotype shift in cultured intact carotid arteries and balloon injury ex vivo. During long-term (24-96 hr) treatment with PF-4594755, smooth muscle markers increased before cell proliferation was inhibited, correlating with decreased KLF4 expression and differing from effects of MEK inhibition. The Pyk2 inhibitor reduced Orai1 and preserved SERCA2a expression in carotid artery segments in organ culture, and eliminated the inhibitory effect of PDGF stimulation on L-type calcium channel and large-conductance calcium-activated potassium channel expression in carotid cells. Basal intracellular calcium level, calcium wave activity, and store-operated calcium influx were reduced after Pyk2 inhibition of growth-stimulated cells. Pyk2 inhibition may provide an interesting approach for preserving vascular smooth muscle differentiation under pathophysiological conditions.

Flucrypyrim, a novel uterine relaxant, has antinociceptive and anti-inflammatory effects in vivo

Consequences of primary dsysmenorrhea (PD) can be severe. Increased prostaglandin production leads to uterine contraction and insufficient blood flow to the endometrium causing ischemia and pain symptoms. Protein tyrosine kinase/phosphatase activities contribute to the modulation of uterine contraction. In our previous study, we found the synthetic β-methoxyacrylates compound Fluacrypyrim (FAPM), significantly increased protein tyrosine phosphatases (PTPs) activity, resulting in dephosphorylation of tyrosine kinases. In the present study, we found that FAPM near completely inhibited prostaglandin F2α (PGF_2α)-, oxytocin-, acetylcholine-, and high K⁺-induced uterine contractions in rats in vitro, and decreased rat myometrial myosin light chain (MLC₂₀) phosphorylation induced by PGF_2α. A structure–activity relationship assay indicated that the β-methoxyacrylates structure of FAPM is crucial for the inhibition of PGF_2α-induced uterine contractions. FAPM caused a concentration-dependent parallel rightward shift of the concentration–response curve induced by oxytocin, dose-dependently reduced the number of abdominal constrictions and increased the latency time in PGF_2α- and acetic acid-induced writhing test in mice in vivo. Furthermore, FAPM considerably inhibited the development of Carr-induced rat paw edemas and thexylene-induced mouse ear edemas. Taken together, our results indicate that FAPM exerts antinociceptive and anti-inflammatory effects in vivo with considerable potential as a novel uterine relaxant.

MicroRNA-203 mimics age-related aortic smooth muscle dysfunction of cytoskeletal pathways

Increased aortic stiffness is a biomarker for subsequent adverse cardiovascular events. We have previously reported that vascular smooth muscle Src-dependent cytoskeletal remodelling, which contributes to aortic plasticity, is impaired with ageing. Here, we use a multi-scale approach to determine the molecular mechanisms behind defective Src-dependent signalling in an aged C57BL/6 male mouse model. Increased aortic stiffness, as measured in vivo by pulse wave velocity, was found to have a comparable time course to that in humans. Bioinformatic analyses predicted several miRs to regulate Src-dependent cytoskeletal remodelling. qRT-PCR was used to determine the relative levels of predicted miRs in aortas and, notably, the expression of miR-203 increased almost twofold in aged aorta. Increased miR-203 expression was associated with a decrease in both mRNA and protein expression of Src, caveolin-1 and paxillin in aged aorta. Probing with phospho-specific antibodies confirmed that overexpression of miR-203 significantly attenuated Src and extracellular signal regulated kinase (ERK) signalling, which we have previously found to regulate vascular smooth muscle stiffness. In addition, transfection of miR-203 into aortic tissue from young mice increased phenylephrine-induced aortic stiffness ex vivo, mimicking the aged phenotype. Upstream of miR-203, we found that DNA methyltransferases (DNMT) 1, 3a, and 3b are also significantly decreased in the aged mouse aorta and that DNMT inhibition significantly increases miR-203 expression. Thus, the age-induced increase in miR-203 may be caused by epigenetic promoter hypomethylation in the aorta. These findings indicate that miR-203 promotes a re-programming of Src/ERK signalling pathways in vascular smooth muscle, impairing the regulation of stiffness in aged aorta.

Regulation of arterial reactivity by concurrent signaling through the E-prostanoid receptor 3 and angiotensin receptor 1

Prostaglandin E2 (PGE2), a cyclooxygenase metabolite that generally acts as a systemic vasodepressor, has been shown to have vasopressor effects under certain physiologic conditions. Previous studies have demonstrated that PGE2 receptor signaling modulates angiotensin II (Ang II)-induced hypertension, but the interaction of these two systems in the regulation of vascular reactivity is incompletely characterized. We hypothesized that Ang II, a principal effector of the renin-angiotensin-aldosterone system, potentiates PGE2-mediated vasoconstriction. Here we demonstrate that pre-treatment of arterial rings with 1nM Ang II potentiated PGE2-evoked constriction in a concentration dependent manner (AUC-Ang II 2.778±2.091, AUC+Ang II 22.830±8.560, ***P<0.001). Using genetic deletion models and pharmacological antagonists, we demonstrate that this potentiation effect is mediated via concurrent signaling between the angiotensin II receptor 1 (AT1) and the PGE2 E-prostanoid receptor 3 (EP3) in the mouse femoral artery. EP3 receptor-mediated vasoconstriction is shown to be dependent on extracellular calcium in combination with proline-rich tyrosine kinase 2 (Pyk2) and Rho-kinase. Thus, our findings reveal a novel mechanism through which Ang II and PGE2 regulate peripheral vascular reactivity.

Caveolin-1 regulates corneal wound healing by modulating Kir4.1 activity

The expression of caveolin-1 (Cav1) in corneal epithelium is associated with regeneration potency. We used Cav1(-/-) mice to study the role of Cav1 in modulating corneal wound healing. Western blot and whole cell patch clamp were employed to study the effect of Cav1 deletion on Kir4.1 current density in corneas. We found that Ba(2+)-sensitive K(+) currents in primary cultured murine corneal epithelial cells (pMCE) from Cav1(-/-) were dramatically reduced (602 pA) compared with those from wild type (WT; 1,300 pA). As a consequence, membrane potential was elevated in pMCE from Cav1(-/-) compared with that from WT (-43 ± 7.5 vs. -58 ± 4.0 mV, respectively). Western blot showed that either inhibition of Cav1 expression or Ba(2+) incubation stimulated phosphorylation of the EGFR. The transwell migration assay showed that Cav1 genetic inactivation accelerated cell migration. The regrowth efficiency of human corneal epithelial cells (HCE) transfected with siRNA-Cav1 or negative control was evaluated by scrape injury assay. With the presence of mitomycin C (10 μg/ml) to avoid the influence of cell proliferation, Cav1 inhibition with siRNA significantly increased migration compared with control siRNA in HCE. This promoting effect by siRNA-Cav1 could not be further enhanced by cotransfection with siRNA-Kcnj10. By using corneal debridement, we found that wound healing was significantly accelerated in Cav1(-/-) compared with WT mice (70 ± 10 vs. 36 ± 3%, P < 0.01). Our findings imply that the mechanism by which Cav-1 knockout promotes corneal regrowth is, at least partially, due to the inhibition of Kir4.1 which stimulates EGFR signaling.

Mechanisms of Vascular Smooth Muscle Contraction and the Basis for Pharmacologic Treatment of Smooth Muscle Disorders

The smooth muscle cell directly drives the contraction of the vascular wall and hence regulates the size of the blood vessel lumen. We review here the current understanding of the molecular mechanisms by which agonists, therapeutics, and diseases regulate contractility of the vascular smooth muscle cell and we place this within the context of whole body function. We also discuss the implications for personalized medicine and highlight specific potential target molecules that may provide opportunities for the future development of new therapeutics to regulate vascular function.

Analysis of phosphorylation of the myosin-targeting subunit of myosin light chain phosphatase by Phos-tag SDS-PAGE

Phosphorylation of the myosin-targeting subunit 1 of myosin light chain phosphatase (MYPT1) plays an important role in the regulation of smooth muscle contraction, and several sites of phosphorylation by different protein Ser/Thr kinases have been identified. Furthermore, in some instances, phosphorylation at specific sites affects phosphorylation at neighboring sites, with functional consequences. Characterization of the complex phosphorylation of MYPT1 in tissue samples at rest and in response to contractile and relaxant stimuli is, therefore, challenging. We have exploited Phos-tag SDS-PAGE in combination with Western blotting using antibodies to MYPT1, including phosphospecific antibodies, to separate multiple phosphorylated MYPT1 species and quantify MYPT1 phosphorylation stoichiometry using purified, full-length recombinant MYPT1 phosphorylated by Rho-associated coiled-coil kinase (ROCK) and cAMP-dependent protein kinase (PKA). This approach confirmed that phosphorylation of MYPT1 by ROCK occurs at Thr(697)and Thr(855), PKA phosphorylates these two sites and the neighboring Ser(696)and Ser(854), and prior phosphorylation at Thr(697)and Thr(855)by ROCK precludes phosphorylation at Ser(696)and Ser(854)by PKA. Furthermore, phosphorylation at Thr(697)and Thr(855)by ROCK exposes two other sites of phosphorylation by PKA. Treatment of Triton-skinned rat caudal arterial smooth muscle strips with the membrane-impermeant phosphatase inhibitor microcystin or treatment of intact tissue with the membrane-permeant phosphatase inhibitor calyculin A induced slow, sustained contractions that correlated with phosphorylation of MYPT1 at 7 to ≥10 sites. Phos-tag SDS-PAGE thus provides a suitable and convenient method for analysis of the complex, multisite MYPT1 phosphorylation events involved in the regulation of myosin light chain phosphatase activity and smooth muscle contraction.

α5-Integrin-mediated cellular signaling contributes to the myogenic response of cerebral resistance arteries

The myogenic response of resistance arterioles and small arteries involving constriction in response to intraluminal pressure elevation and dilation on pressure reduction is fundamental to local blood flow regulation in the microcirculation. Integrins have garnered considerable attention in the context of initiating the myogenic response, but evidence indicative of mechanotransduction by integrin adhesions, for example established changes in tyrosine phosphorylation of key adhesion proteins, has not been obtained to substantiate this interpretation. Here, we evaluated the role of integrin adhesions and associated cellular signaling in the rat cerebral arterial myogenic response using function-blocking antibodies against α5β1-integrins, pharmacological inhibitors of focal adhesion kinase (FAK) and Src family kinase (SFK), an ultra-high-sensitivity western blotting technique, site-specific phosphoprotein antibodies to quantify adhesion and contractile filament protein phosphorylation, and differential centrifugation to determine G-actin levels in rat cerebral arteries at varied intraluminal pressures. Pressure-dependent increases in the levels of phosphorylation of FAK (FAK-Y397, Y576/Y577), SFK (SFK-Y416; Y527 phosphorylation was reduced), vinculin-Y1065, paxillin-Y118 and phosphoinositide-specific phospholipase C-γ1 (PLCγ1)-Y783 were detected. Treatment with α5-integrin function-blocking antibodies, FAK inhibitor FI-14 or SFK inhibitor SU6656 suppressed the changes in adhesion protein phosphorylation, and prevented pressure-dependent phosphorylation of the myosin targeting subunit of myosin light chain phosphatase (MYPT1) at T855 and 20kDa myosin regulatory light chains (LC20) at S19, as well as actin polymerization that are necessary for myogenic constriction. We conclude that mechanotransduction by integrin adhesions and subsequent cellular signaling play a fundamental role in the cerebral arterial myogenic response.