Activation of pyk2/related focal adhesion tyrosine kinase and focal adhesion kinase in cardiac remodeling

Inhibition of Pyk2 Improves Cx43 Intercalated Disc Localization, Infarct Size, and Cardiac Function in Rats With Heart Failure

BACKGROUND

Heart failure causes changes in Cx43 (Connexin43) regulation that are associated with arrhythmic heart disease. Pyk2 (proline-rich tyrosine kinase 2) is activated in cardiomyopathies and phosphorylates Cx43 to decrease intercellular communication. This study was designed to determine if Pyk2 inhibition improves cardiac function in a myocardial infarction (MI)-induced heart failure model in rats.

METHODS

MI (ligation of left anterior descending artery) rats were treated with the Pyk2 inhibitor PF4618433. Hemodynamic and structural parameters were monitored in Sham (n=5), MI-vehicle (n=5), and MI-PF4618433 (n=8) groups. Heart tissues were collected after 6 weeks to assess Pyk2 and Cx43 protein level and localization.

RESULTS

PF4618433 produced no observed adverse effects and inhibited ventricular Pyk2. PF4618433 reduced the MI infarct size from 34% to 17% (P=0.007). PF4618433 improved stroke volume (P=0.031) and cardiac output (P=0.009) in comparison to MI-vehicle with values similar to the Sham group. PF4618433 also led to an increase in the ejection fraction (P=0.002) and fractional shortening (P=0.006) when compared with the MI-vehicle (32% and 35% improvement, respectively) yet were lower in comparison with the Sham group. Pyk2 inhibition decreased Cx43 tyrosine phosphorylation (P=0.043) and maintained Cx43 at the intercalated disc in the distal ventricle 6 weeks post-MI.

CONCLUSIONS

Unlike other attempts to decrease Cx43 remodeling after MI-induced heart failure, inhibition of Pyk2 activity maintained Cx43 at the intercalated disc. This may have aided in the reduced infarct size (acute time frame) and improved cardiac function (chronic time frame). Additionally, we provide evidence that Pyk2 is activated following MI in human left ventricle, implicating a novel potential target for therapy in patients with heart failure.

Acidic environments trigger intracellular H+-sensing FAK proteins to re-balance sarcolemmal acid-base transporters and auto-regulate cardiomyocyte pH

AIMS

In cardiomyocytes, acute disturbances to intracellular pH (pHi) are promptly corrected by a system of finely tuned sarcolemmal acid-base transporters. However, these fluxes become thermodynamically re-balanced in acidic environments, which inadvertently causes their set-point pHi to fall outside the physiological range. It is unclear whether an adaptive mechanism exists to correct this thermodynamic challenge, and return pHi to normal.

METHODS AND RESULTS

Following left ventricle cryo-damage, a diffuse pattern of low extracellular pH (pHe) was detected by acid-sensing pHLIP. Despite this, pHi measured in the beating heart (13C NMR) was normal. Myocytes had adapted to their acidic environment by reducing Cl-/HCO3- exchange (CBE)-dependent acid-loading and increasing Na+/H+ exchange (NHE1)-dependent acid-extrusion, as measured by fluorescence (cSNARF1). The outcome of this adaptation on pHi is revealed as a cytoplasmic alkalinization when cells are superfused at physiological pHe. Conversely, mice given oral bicarbonate (to improve systemic buffering) had reduced myocardial NHE1 expression, consistent with a needs-dependent expression of pHi-regulatory transporters. The response to sustained acidity could be replicated in vitro using neonatal ventricular myocytes incubated at low pHe for 48 h. The adaptive increase in NHE1 and decrease in CBE activities was linked to Slc9a1 (NHE1) up-regulation and Slc4a2 (AE2) down-regulation. This response was triggered by intracellular H+ ions because it persisted in the absence of CO2/HCO3- and became ablated when acidic incubation media had lower chloride, a solution manoeuvre that reduces the extent of pHi-decrease. Pharmacological inhibition of FAK-family non-receptor kinases, previously characterized as pH-sensors, ablated this pHi autoregulation. In support of a pHi-sensing role, FAK protein Pyk2 (auto)phosphorylation was reduced within minutes of exposure to acidity, ahead of adaptive changes to pHi control.

CONCLUSIONS

Cardiomyocytes fine-tune the expression of pHi-regulators so that pHi is at least 7.0. This autoregulatory feedback mechanism defines physiological pHi and protects it during pHe vulnerabilities.

Aging-related modifications to G protein-coupled receptor signaling diversity

Aging is a highly complex molecular process, affecting nearly all tissue systems in humans and is the highest risk factor in developing neurodegenerative disorders such as Alzheimer's and Parkinson's disease, cardiovascular disease and Type 2 diabetes mellitus. The intense complexity of the aging process creates an incentive to develop more specific drugs that attenuate or even reverse some of the features of premature aging. As our current pharmacopeia is dominated by therapeutics that target members of the G protein-coupled receptor (GPCR) superfamily it may be prudent to search for effective anti-aging therapeutics in this fertile domain. Since the first demonstration of GPCR-based β-arrestin signaling, it has become clear that an enhanced appreciation of GPCR signaling diversity may facilitate the creation of therapeutics with selective signaling activities. Such 'biased' ligand signaling profiles can be effectively investigated using both standard molecular biological techniques as well as high-dimensionality data analyses. Through a more nuanced appreciation of the quantitative nature across the multiple dimensions of signaling bias that drugs possess, researchers may be able to further refine the efficacy of GPCR modulators to impact the complex aberrations that constitute the aging process. Identifying novel effector profiles could expand the effective pharmacopeia and assist in the design of precision medicines. This review discusses potential non-G protein effectors, and specifically their potential therapeutic suitability in aging and age-related disorders.

Inhibition of Pyk2 and Src activity improves Cx43 gap junction intercellular communication

Identification of proteins that interact with Cx43 has been instrumental in the understanding of gap junction (GJ) regulation. An in vitro phosphorylation screen identified that Protein tyrosine kinase 2 beta (Pyk2) phosphorylated purified Cx43CT and this led us to characterize the impact of this phosphorylation on Cx43 function. Mass spectrometry identified Pyk2 phosphorylates Cx43 residues Y247, Y265, Y267, and Y313. Western blot and immunofluorescence staining using HeLa^Cx43 cells, HEK 293 T cells, and neonatal rat ventricular myocytes (NRVMs) revealed Pyk2 can be activated by Src and active Pyk2 interacts with Cx43 at the plasma membrane. Overexpression of Pyk2 increases Cx43 phosphorylation and knock-down of Pyk2 decreases Cx43 phosphorylation, without affecting the level of active Src. In HeLa^Cx43 cells treated with PMA to activate Pyk2, a decrease in Cx43 GJ intercellular communication (GJIC) was observed when assayed by dye transfer. Moreover, PMA activation of Pyk2 could be inhibited by the small molecule PF4618433. This partially restored GJIC, and when paired with a Src inhibitor, returned GJIC to the no PMA control-level. The ability of Pyk2 and Src inhibitors to restore Cx43 function in the presence of PMA was also observed in NRVMs. Additionally, an animal model of myocardial infarction induced heart failure showed a higher level of active Pyk2 activity and increased interaction with Cx43 in ventricular myocytes. Src inhibitors have been used to reverse Cx43 remodeling and improve heart function after myocardial infarction; however, they alone could not fully restore proper Cx43 function. Our data suggest that Pyk2 may need to be inhibited, in addition to Src, to further (if not completely) reverse Cx43 remodeling and improve intercellular communication.

Valsartan inhibits RhoA-ROCK2-MYL pathway in rat model of alcoholic cardiomyopathy

The present study aimed to investigate variations in the Ras homolog gene family, member A (RhoA)-Rho-associated protein kinase 2 (ROCK2)-myosin light chain (MYL) pathway in a rat model of alcoholic cardiomyopathy (ACM) and the role of angiotensin-converting enzyme inhibitor drugs. Rat models of ACM were established via alcoholic gavage + free access to alcohol. The structural and functional changes of the heart were analyzed by hematoxylin-eosin staining, Masson's trichrome staining, immunohistochemistry staining, western blotting and fluorescence quantitative polymerase chain reaction. A total of 16 weeks later, a decreased ejection fraction and left ventricular fractional shortening in the alcohol group compared with the control group were demonstrated resulting in an increased left ventricular end diastolic diameter. These adverse effects were ameliorated following treatment with valsartan. In addition, the alcohol group revealed a disorganized arrangement of myocardial filaments, which was improved upon treatment with valsartan. RhoA and ROCK2 protein expression significantly increased in myocardial cells in the alcohol compared with the control group. Following drug intervention with valsartan, expression of RhoA and ROCK2 proteins were inhibited in the alcohol group. Furthermore, significantly elevated RhoA and ROCK2 and decreased MYL protein and mRNA expression in the alcohol group was demonstrated compared with the control group. Administration of valsartan reversed the expression profile of RhoA, ROCK and MYL in ACM. Expression of RhoA and ROCK were elevated with downregulation of MYL resulting in heart failure. However, the angiotensin receptor antagonist diminished the expression of RhoA and ROCK and enhanced the expression of MYL. The results of the present study suggest a curative effect of valsartan in ACM.

Tyrosine phosphorylation of eNOS regulates myocardial survival after an ischaemic insult: role of PYK2

Aims

Endothelial nitric oxide (NO) synthase (eNOS) is known to play a cardioprotective protective. However, the molecular mechanisms regulating eNOS activity during ischaemia/reperfusion (I/R) injury are incompletely understood. eNOS is a substrate for several kinases that positively or negatively affect its enzymatic activity. Herein, we sought to correlate eNOS phosphorylation status with cardiomyocyte survival and we investigated the contribution of the proline-rich tyrosine kinase 2 (PYK2)/eNOS axis to the regulation of myocardial infarct size in vivo.

Methods and results

Exposure of H9c2 cardiomyocytes to H2O2 lead to PYK2 phosphorylation on its activator site (Y402) and eNOS phosphorylation on the inhibitor site Y656 and the activator site S1176. Both H2O2-induced eNOS phosphorylation events were abolished by PYK2 pharmacological inhibition or gene knockdown. Activity assays demonstrated that phosphorylation of the tyrosine inhibitory site exerts a dominant effect over S1176. In cardiomyocytes subjected to oxidative stress or oxygen-glucose deprivation, inhibition of PYK2 limited cell injury; this effect was prevented by inhibition of NO production. In vivo, ischaemia-reperfusion induced an early activation of PYK2, leading to eNOS phosphorylation on Y656, which, in turn, reduced NO output, as judged by the low tissue levels of its downstream effector cGMP. Moreover, pharmacological blockade of PYK2 alleviated eNOS inhibition and prevented cardiac damage following I/R injury in wild-type, but not in eNOS KO mice.

Conclusion

The current studies demonstrate that PYK2 is a pivotal regulator of eNOS function in myocardial infarction and identify PYK2 as a novel therapeutic target for cardioprotection.

Cardiomyocyte-specific expression of CRNK, the C-terminal domain of PYK2, maintains ventricular function and slows ventricular remodeling in a mouse model of dilated cardiomyopathy

Up-regulation and activation of PYK2, a member of the FAK family of protein tyrosine kinases, is involved in the pathogenesis of left ventricular (LV) remodeling and heart failure (HF). PYK2 activation can be prevented by CRNK, the C-terminal domain of PYK2. We previously demonstrated that adenoviral-mediated CRNK gene transfer improved survival and LV function, and slowed LV remodeling in a rat model of coronary artery ligation-induced HF. We now interrogate whether cardiomyocyte-specific, transgenic CRNK expression prevents LV remodeling and HF in a mouse model of dilated cardiomyopathy (DCM) caused by constitutively active Protein Kinase Cε (caPKCε). Transgenic (TG; FVB/N background) mice were engineered to express rat CRNK under control of the α-myosin heavy chain promoter, and crossed with FVB/N mice with cardiomyocyte-specific expression of caPKCε to create double TG mice. LV structure, function, and gene expression were evaluated in all 4 groups (nonTG FVB/N; caPKCε(+/-); CRNK(+/-); and caPKCε×CRNK (PXC) double TG mice) at 1, 3, 6, 9 and 12mo of age. CRNK expression followed a Mendelian distribution, and CRNK mice developed and survived normally through 12mo. Cardiac structure, function and selected gene expression of CRNK mice were similar to nonTG littermates. CRNK had no effect on caPKCε expression and vice versa. PYK2 was up-regulated ~6-fold in caPKCε mice, who developed a non-hypertrophic, progressive DCM with reduced systolic (Contractility Index=151±5 vs. 90±4s(-1)) and diastolic (Tau=7.5±0.5 vs. 14.7±1.3ms) function, and LV dilatation (LV Remodeling Index (LVRI)=4.2±0.1 vs. 6.0±0.3 for FVB/N vs. caPKCε mice, respectively; P<0.05 for each at 12mo). In double TG PXC mice, CRNK expression significantly prolonged survival, improved contractile function (Contractile Index=115±8s(-1); Tau=9.5±1.0ms), and reduced LV remodeling (LVRI=4.9±0.1). Cardiomyocyte-specific expression of CRNK improves contractile function and slows LV remodeling in a mouse model of DCM.

Focal adhesion signaling in heart failure

In this brief review, recent evidence is presented to indicate a role for specific components of the cardiomyocyte costamere (and its related structure the focal adhesion complex of cultured cardiomyocytes) in initiating and sustaining the aberrant signal transduction that contributes to myocardial remodeling and the progression to heart failure (HF). Special attention is devoted to the focal adhesion kinase family of nonreceptor protein tyrosine kinases in bidirectional signal transduction during cardiac remodeling and HF progression. Finally, some speculations and directions for future study are provided for this rapidly developing field of research.

Prioritising risk pathways of complex human diseases based on functional profiling

Analysis of the biological pathways involved in complex human diseases is an important step in elucidating the pathogenesis and mechanism of diseases. Most pathway analysis approaches identify disease-related biological pathways using overlapping genes between pathways and diseases. However, these approaches ignore the functional biological association between pathways and diseases. In this paper, we designed a novel computational framework for prioritising disease-risk pathways based on functional profiling. The disease gene set and biological pathways were translated into functional profiles in the context of GO annotations. We then implemented a semantic similarity measurement for calculating the concordance score between a functional profile of disease genes and a functional profile of pathways (FPP); the concordance score was then used to prioritise and infer disease-risk pathways. A freely accessible web toolkit, 'Functional Profiling-based Pathway Prioritisation' (FPPP), was developed (http://bioinfo.hrbmu.edu.cn/FPPP). During validation, our method successfully identified known disease-pathway pairs with area under the ROC curve (AUC) values of 96.73 and 95.02% in tests using both pathway randomisation and disease randomisation. A robustness analysis showed that FPPP is reliable even when using data containing noise. A case study based on a dilated cardiomyopathy data set indicated that the high-ranking pathways from FPPP are well known to be linked with this disease. Furthermore, we predicted the risk pathways of 413 diseases by using FPPP to build a disease similarity landscape that systematically reveals the global modular organisation of disease associations.

Beta1-adrenergic receptors promote focal adhesion signaling downregulation and myocyte apoptosis in acute volume overload

Numerous studies demonstrated increased expression of extracellular matrix (ECM) proteins and activation of focal adhesion (FA) signaling pathways in models of pressure overload-induced cardiac hypertrophy. However, little is known about FA signaling in response to volume overload where cardiac hypertrophy is associated with ECM loss. This study examines the role of beta1-adrenergic receptors (β(1)-ARs) in FA signaling changes and myocyte apoptosis induced during acute hemodynamic stress of volume overload. Rats with eccentric cardiac hypertrophy induced after aorto-caval fistula (ACF) develop reduced interstitial collagen content and decreased tyrosine phosphorylation of key FA signaling molecules FAK, Pyk(2) and paxillin along with an increase in cardiac myocyte apoptosis. ACF also increased activation of PTEN, a dual lipid and protein phosphatase, and its interaction with FA proteins. β(1)-AR blockade (extended-release of metoprolol succinate, 100mg QD) markedly attenuated PTEN activation, restored FA signaling and reduced myocyte apoptosis induced by ACF at 2days, but failed to reduce interstitial collagen loss and left ventricular dilatation. Treating cultured myocytes with β(1)-AR agonists or adenoviral expression of β(1)-ARs caused PTEN activation and interaction with FA proteins, thus leading to FA signaling downregulation and myocyte apoptosis. Adenoviral-mediated expression of a catalytically inactive PTEN mutant or wild-type FAK restored FA signaling downregulation and attenuated myocyte apoptosis induced by β(1)-ARs. Collectively, these data show that β(1)-AR stimulation in response to ACF induces FA signaling downregulation through an ECM-independent mechanism. This effect involves PTEN activation and may contribute to adverse cardiac remodeling and function in the course of volume overload.

Role of Pyk2 in cardiac arrhythmogenesis

Proline-rich tyrosine kinase 2 (Pyk2) is a nonreceptor protein kinase regulated by intracellular Ca2+, CaMK, and PKC and can be activated by different stress signals involved in heart failure. However, Pyk2 has not been investigated in the human heart, and the functional role of Pyk2 signaling at the whole heart level has not been elucidated. We hypothesize that Ca2+-dependent activation of Pyk2 is involved in cardiac electrophysiology. We examined the expression of Pyk2 in nonfailing versus ischemic and nonischemic failing human hearts ( n = 6 hearts/group). To investigate Pyk2 function, we optically mapped perfused hearts from wild-type (WT; n = 7) and knockout (Pyk2−/−; n = 8) mice during autonomic stimulation. Experiments were done in control mice and after 1 wk of transverse aortic constriction. We used the Illumina beadarray approach for transcriptional profiling of WT and Pyk2−/− mouse ventricles. Western blot analysis revealed a doubling of Pyk2 activation in nonischemic failing versus nonfailing human hearts. In mouse hearts, we observed a much higher probability of ventricular tachyarrhythmia during ACh perfusion in Pyk2−/− versus WT mice. Parasympathetic stimulation resulted in a dose-dependent decrease of atrial action potential duration (APD) in both WT and Pyk2−/− mice, whereas in ventricles it induced APD shortening in Pyk2−/− mice but not in WT mice. Deficiency of Pyk2 abolished ACh-induced prolongation of atrioventricular delay in Pyk2−/− mouse hearts but did not affect heart rate. Lower mRNA and protein levels of sarco(endo)plasmic reticulum Ca2+-ATPase 2 and higher mRNA levels of Na+/Ca2+ exchanger 1 were detected in Pyk2−/− hearts compared with WT hearts. The transverse aortic constriction protocol did not change the phenotype. In conclusion, our results indicate a protective role of Pyk2 with respect to ventricular tachyarrhythmia during parasympathetic stimulation by regulation of gene expression related to Ca2+ handling. We hypothesize that activation of Pyk2 in the human heart during heart failure may contribute to protection against arrhythmia.

Hic-5 is required for fetal gene expression and cytoskeletal organization of neonatal cardiac myocytes

Cardiac costameres link the extracellular matrix to the sarcomere at the z-disc and contain proteins such as integrins and other signaling molecules implicated in the regulation of pathological hypertrophy. Paxillin family members, hic-5 and paxillin, are scaffolding proteins associated with the integrin complex that have been shown to mediate numerous protein interactions in other cell types. While paxillin has been described in postnatal heart, hic-5 has not been identified. Our results provide evidence of hic-5 in neonatal cardiac myocytes co-localized with paxillin and alpha-actinin at the z-discs and the ends of actin filaments. Treatment with the hypertrophic agonist phenylephrine resulted in increased hic-5 expression while having no effect on paxillin levels. To see if increased hic-5 expression was sufficient to induce changes in cytoskeletal organization, hic-5 was overexpressed in myocytes by adenoviral infection. Hic-5 overexpression significantly increased the number of cells with organized cytoskeleton. Using siRNA mediated knockdown, we examined the requirement of hic-5 and paxillin in regulation of phenylephrine induced gene expression and cytoskeletal organization. Our results indicate that hic-5, not paxillin is required for upregulation of ANF and alpha-skeletal actin genes as well as in cytoskeletal reorganization. Finally, we demonstrated that hic-5 upregulation occurs downstream of MEK1/2-ERK1/2 signaling as inhibition of MEK1/2 using U0126 inhibitor completely inhibited hic-5 upregulation by PE. In a complimentary study, we showed that hic-5 knockdown had no effect on PE induced ERK1/2 phosphorylation. These findings demonstrate a novel role for hic-5 in the regulation of actin cytoskeleton and fetal gene expression.

Differential effects of Pyk2 and FAK on the hypertrophic response of cardiac myocytes

The related cytoplasmic non-receptor tyrosine kinases Pyk2 (proline-rich tyrosine kinase 2) and FAK (focal adhesion kinase) have been implicated in phenylephrine-induced G-protein-coupled receptor-mediated signaling mechanisms leading to cardiomyocyte hypertrophy. We report that, in phenylephrine-stimulated neonatal rat ventricular myocytes (NRVM), Pyk2 augments expression of the hypertrophic marker atrial natriuretic factor (ANF) but reduces cytoskeletal organization and cell spreading. In contrast, FAK attenuates ANF production but does not alter cytoskeletal organization and cell spreading. Pyk2 and FAK exhibit differential localization in both unstimulated and phenylephrine-stimulated myocytes. Pyk2 catalytic activity is required for Pyk2 to augment ANF secretion but is not necessary to reduce cell spreading. Pyk2 autophosphorylation is required but not sufficient for Pyk2 to augment ANF secretion. Expression of the Pyk2 FERM domain as an autonomous fragment inhibits phenylephrine-mediated ANF secretion and reduces cell spreading. In addition, expression of the Pyk2 FERM domain inhibits the ability of Pyk2 to augment ANF secretion; this is correlated with reduced Pyk2 autophosphorylation. These data indicate that Pyk2 and FAK have different roles and occupy different positions in signaling pathways leading to the development of cardiomyocyte hypertrophy.

Sympathetic activation causes focal adhesion signaling alteration in early compensated volume overload attributable to isolated mitral regurgitation in the dog

We reported that left ventricular (LV) dilatation after 4 weeks of isolated mitral regurgitation (MR) in the dogs is marked by extracellular matrix loss and an increase in adrenergic drive. Given that extracellular matrix proteins and their receptor integrins influence beta-adrenergic receptor (beta-AR) responses in vitro, we tested whether beta1-AR activation modulates focal adhesion (FA) signaling and LV remodeling in these same dogs with isolated MR. Normal dogs were compared with dogs with MR of a 4-week duration and with MR dogs treated with beta(1)-AR blockade (beta(1)-RB) (extended-release metoprolol succinate, 100 mg QD) that was started 24 hours after MR induction. In MR LVs, a decrease in collagen accumulation compared with normal dogs was associated with a decrease in FA kinase tyrosine phosphorylation, along with FA kinase interaction with adapter and cytoskeletal proteins, p130(Cas) and paxillin, respectively, as determined by immunoprecipitation assays. There was increased phosphorylation of stress related molecules p38 mitogen-activated protein kinase (MAPK) and Hsp27 and survival signaling kinases extracellular signal-regulated kinase 1/2 and AKT, with no evidence of cardiomyocyte apoptosis. beta(1)-RB attenuated FA signaling loss and prevented p38 MAPK, Hsp27, and AKT phosphorylation induced by MR and significantly increased LV epicardial collagen content. However, beta(1)-RB did not improve LV endocardial collagen loss or LV dilatation induced by MR. Isolated myocytes from normal and MR dog hearts treated with beta(1)- or beta(2)-AR agonists demonstrated no difference in FA kinase, p38 MAPK, Hsp27, or AKT phosphorylation. These results showed that chronic stimulation of beta(1)-AR during early compensated MR impairs FA signaling that may affect myocyte/fibroblast-extracellular matrix scaffolding necessary for LV remodeling.

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.

Application of proteomics technology for analyzing the interactions between host cells and intracellular infectious agents

Host–pathogen interactions involve protein expression changes within both the host and the pathogen. An understanding of the nature of these interactions provides insight into metabolic processes and critical regulatory events of the host cell as well as into the mechanisms of pathogenesis by infectious microorganisms. Pathogen exposure induces changes in host proteins at many functional levels including cell signaling pathways, protein degradation, cytokines and growth factor production, phagocytosis, apoptosis, and cytoskeletal rearrangement. Since proteins are responsible for the cell biological functions, pathogens have evolved to manipulate the host cell proteome to achieve optimal replication. Intracellular pathogens can also change their proteome to adapt to the host cell and escape from immune surveillance, or can incorporate cellular proteins to invade other cells. Given that the interactions of intracellular infectious agents with host cells are mainly at the protein level, proteomics is the most suitable tool for investigating these interactions. Proteomics is the systematic analysis of proteins, particularly their interactions, modifications, localization and functions, that permits the study of the association between pathogens with their host cells as well as complex interactions such as the host–vector–pathogen interplay. A review on the most relevant proteomic applications used in the study of host–pathogen interactions is presented.

Western array analysis of cell cycle protein changes during the hyperplastic to hypertrophic transition in heart development

Cardiac myocytes proliferate most rapidly during the hyperplastic phase of heart development; however, the level of cell cycle activity is drastically down regulated after birth. Further growth of the heart is achieved by hypertrophic growth of cardiac myocytes. The mechanism that controls the switch from hyperplastic proliferation to hypertrophic growth in cardiac myocytes is unknown. Understanding this fundamental mechanism of cardiac myocyte biology would be most beneficial for studies directed towards myocardial regeneration. In this study, we identified changes in the expression of proteins involved in cell cycle regulation during the hyperplastic to hypertrophic transition of cardiac myocytes. Using a high-throughput immunoblotting technique, we examined 200+ proteins in primary cultures of cardiac myocytes at different developmental time points to determine the important regulators of this transition. In addition, we also analyzed samples from an immortalized cardiac myocyte cell line to compare expression levels of cell cycle regulatory proteins to our primary cultures. Our findings by this uncovered proteomic screen identified several potential key regulatory proteins and provide insight into the important components of cardiac myocyte cell cycle regulation.

Myocyte-restricted focal adhesion kinase deletion attenuates pressure overload-induced hypertrophy

Focal adhesion kinase (FAK) is a ubiquitously expressed cytoplasmic tyrosine kinase strongly activated by integrins and neurohumoral factors. Previous studies have shown that cardiac FAK activity is enhanced by hypertrophic stimuli before the onset of overt hypertrophy. Herein, we report that conditional deletion of FAK from the myocardium of adult mice did not affect basal cardiac performance, myocyte viability, or myofibrillar architecture. However, deletion of FAK abolished the increase in left ventricular posterior wall thickness, myocyte cross-sectional area, and hypertrophy-associated atrial natriuretic factor induction following pressure overload. Myocyte-restricted deletion of FAK attenuated the initial wave of extracellular signal-regulated kinase activation and cFos expression induced by adrenergic agonists and biomechanical stress. In addition, we found that persistent challenge of mice with myocyte-restricted FAK inactivation leads to enhanced cardiac fibrosis and cardiac dysfunction in comparison to challenged genetic controls. These studies show that loss of FAK impairs normal compensatory hypertrophic remodeling without a concomitant increase in apoptosis in response to cardiac pressure overload and highlight the possibility that FAK activation may be a common requirement for the initiation of this compensatory response.

Focal adhesion kinase controls cellular levels of p27/Kip1 and p21/Cip1 through Skp2-dependent and -independent mechanisms

Endothelial cell proliferation is a critical step in angiogenesis and requires a coordinated response to soluble growth factors and the extracellular matrix. As focal adhesion kinase (FAK) integrates signals from both adhesion events and growth factor stimulation, we investigated its role in endothelial cell proliferation. Expression of a dominant-negative FAK protein, FAK-related nonkinase (FRNK), impaired phosphorylation of FAK and blocked DNA synthesis in response to multiple angiogenic stimuli. These results coincided with elevated cyclin-dependent kinase inhibitors (CDKIs) p21/Cip and p27/Kip, as a consequence of impaired degradation. FRNK inhibited the expression of Skp2, an F-box protein that targets CDKIs, by inhibiting mitogen-induced mRNA. The FAK-regulated degradation of p27/Kip was Skp2 dependent, while levels of p21/Cip were regulated independent of Skp2. Skp2 is required for endothelial cell proliferation as a consequence of degrading p27. Finally, knockdown of both p21 and p27 in FRNK-expressing cells completely restored mitogen-induced endothelial cell proliferation. These data demonstrate a critical role for FAK in the regulation of CDKIs through two independent mechanisms: Skp2 dependent and Skp2 independent. They also provide important insights into the requirement of focal adhesion kinase for normal vascular development and reveal novel regulatory control points for angiogenesis.

Gene expression and protein profiling of AGS gastric epithelial cells upon infection with Helicobacter pylori

Helicobacter pylori, one of the most common bacterial pathogens, colonizes the human stomach and causes a variety of gastric diseases. This pathogen elicits a range of phenotypic responses in infected cultured AGS gastric epithelial cells, including expression of proinflammatory genes and changes in the actin cytoskeleton. Some of these responses are mediated by the type IV secretion system (T4SS) encoded by the cag pathogenicity island. We have used two global approaches, namely 2-DE combined with PMF and cDNA expression array analyses, to study in both a comprehensive and quantitative manner the protein profile and the temporal patterns of mRNA accumulation in AGS cells upon infection with H. pylori and isogenic T4SS mutants. We identified 140 transcripts and detected 190 protein species that were differentially regulated upon infection. Infection with wild-type H. pylori induced expression of a variety of host genes and changes in protein pattern involved in transcriptional responses, cell shape regulation and signal transduction. Among them, some were differentially regulated in a cag PAI-dependent manner, as shown by both the proteomic and cDNA expression array approaches. While 2-DE and PMF allowed us to examine the protein profiles in the infected host, array analysis enabled us to demonstrate dynamic temporal changes in host gene expression profile. In conclusion, our combined application of the two global approaches provides further molecular details on how the host cell responds to infection by H. pylori and its isogenic T4SS mutants on both transcriptional and protein levels. The findings pinpoint host proteins such as serine/threonine and tyrosine kinases, transcription factors, cell cycle related components and actin cytoskeletal signaling molecules as potential targets of individual H. pylori virulence determinants. This study serves as a basis for future work on transcription and proteome analyses of the H. pylori infection model.

Costameres, focal adhesions, and cardiomyocyte mechanotransduction

Mechanotransduction refers to the cellular mechanisms by which load-bearing cells sense physical forces, transduce the forces into biochemical signals, and generate appropriate responses leading to alterations in cellular structure and function. This process affects the beat-to-beat regulation of cardiac performance but also affects the proliferation, differentiation, growth, and survival of the cellular components that comprise the human myocardium. This review focuses on the experimental evidence indicating that the costamere and its structurally related structure the focal adhesion complex are critical cytoskeletal elements involved in cardiomyocyte mechanotransduction. Biochemical signals originating from the extracellular matrix-integrin-costameric protein complex share many common features with those signals generated by growth factor receptors. The roles of key regulatory kinases and other muscle-specific proteins involved in mechanotransduction and growth factor signaling are discussed, and issues requiring further study in this field are outlined.

Atrial natriuretic peptide promotes cardiomyocyte survival by cGMP-dependent nuclear accumulation of zyxin and Akt

This study delineates a mechanism for antiapoptotic signaling initiated by atrial natriuretic peptide (ANP) stimulation leading to elevation of cGMP levels and subsequent nuclear accumulation of Akt kinase associated with zyxin, a cytoskeletal LIM-domain protein. Nuclear targeting of zyxin induces resistance to cell death coincident with nuclear accumulation of activated Akt. Nuclear translocation of zyxin triggered by cGMP also promotes nuclear Akt accumulation. Additional supportive evidence for nuclear accumulation of zyxin-enhancing cardiomyocyte survival includes the following: (a) promotion of zyxin nuclear localization by cardioprotective stimuli; (b) zyxin association with phospho-Akt473 induced by cardioprotective stimuli; and (c) recruitment of zyxin to the nucleus by activated nuclear-targeted Akt as well as recruitment of Akt by nuclear-targeted zyxin. Nuclear accumulation of zyxin requires both Akt activation and nuclear localization. Potentiation of cell survival is sensitive to stimulation intensity with high-level induction by ANP or cGMP signaling leading to apoptotic cell death rather than enhancing resistance to apoptotic stimuli. Myocardial nuclear accumulation of zyxin and Akt responds similarly in vivo following treatment of mice with ANP or cGMP. Thus, zyxin and activated Akt participate in a cGMP-dependent signaling cascade leading from ANP receptors to nuclear accumulation of both molecules. Nuclear accumulation of zyxin and activated Akt may represent a fundamental mechanism that facilitates nuclear-signal transduction and potentiates cell survival.

Suppression of RhoA activity by focal adhesion kinase-induced activation of p190RhoGAP: role in regulation of endothelial permeability

The interaction of endothelial cells with extracellular matrix proteins at focal adhesions sites contributes to the integrity of vascular endothelial barrier. Although focal adhesion kinase (FAK) activation is required for the recovery of the barrier function after increased endothelial junctional permeability, the basis for the recovery remains unclear. We tested the hypothesis that FAK activates p190RhoGAP and, thus, negatively regulates RhoA activity and promotes endothelial barrier restoration in response to the permeability-increasing mediator thrombin. We observed that thrombin caused a transient activation of RhoA but a more prolonged FAK activation temporally coupled to the recovery of barrier function. Thrombin also induced tyrosine phosphorylation of p190RhoGAP, which coincided with decrease in RhoA activity. We further showed that FAK was associated with p190RhoGAP, and importantly, recombinant FAK phosphorylated p190RhoGAP in vitro. Inhibition of FAK by adenoviral expression of FRNK (a dominant negative FAK construct) in monolayers prevented p190RhoGAP phosphorylation, increased RhoA activity, induced actin stress fiber formation, and produced an irreversible increase in endothelial permeability in response to thrombin. We also observed that p190RhoGAP was unable to attenuate RhoA activation in the absence of FAK activation induced by FRNK. The inhibition of RhoA by the C3 toxin (Clostridium botulinum toxin) restored endothelial barrier function in the FRNK-expressing cells. These findings in endothelial cells were recapitulated in the lung microcirculation in which FRNK expression in microvessel endothelia increased vascular permeability. Our studies demonstrate that FAK-induced down-modulation of RhoA activity via p190RhoGAP is a crucial step in signaling endothelial barrier restoration after increased endothelial permeability.

Involvement of palladin and alpha-actinin in targeting of the Abl/Arg kinase adaptor ArgBP2 to the actin cytoskeleton

Palladin and alpha-actinin are major components of stress fiber dense bodies, cardiomyocyte Z-discs and neuronal synapses. They function as structural molecules and cytoskeletal regulators but also as docking sites to other proteins. Both antisense and transient overexpression experiments have shown that palladin plays an important role in the regulation of actin cytoskeleton. ArgBP2 is a multi-domain scaffolding protein which shares both the tissue distribution and subcellular localization with palladin. ArgBP2 is directly linked to intracellular signaling cascades by its interaction with Abl family kinases, Pyk2 and the ubiquitin ligase Cbl. It has several actin associated binding partners and has been shown to regulate cytoskeletal dynamics. Here, we show by in vivo and in vitro methods that palladin's amino-terminal poly-proline sequences directly interact with the first carboxy-terminal SH3 domain of ArgBP2. We further demonstrate a direct interaction between alpha-actinin and the amino-terminal segment of ArgBP2. Immunoprecipitation and targeting assays suggest that a three-way complex of the proteins occurs in vivo. The interactions provide an explanation to the previously observed Z-disc-specific localization of ArgBP2 and indicate interplay between signaling adaptors and structural proteins of the Z-disc.

PYK2 regulates SERCA2 gene expression in neonatal rat ventricular myocytes

The nonreceptor protein tyrosine kinase (PTK) proline-rich tyrosine kinase 2 (PYK2) has been implicated in cell signaling pathways involved in left ventricular hypertrophy and heart failure, but its exact role has not been elucidated. In this study, replication-defective adenoviruses (Adv) encoding green fluorescent protein (GFP)-tagged, wild-type (WT), and mutant forms of PYK2 were used to determine whether PYK2 overexpression activates MAPKs, and downregulates SERCA2 mRNA levels in neonatal rat ventricular myocytes (NRVM). PYK2 overexpression significantly decreased SERCA2 mRNA (as determined by Northern blot analysis and real-time RT-PCR) to 54 ± 4% of Adv-GFP-infected cells 48 h after Adv infection. Adv-encoding kinase-deficient (KD) and Y402F phosphorylation-deficient mutants of PYK2 also significantly reduced SERCA2 mRNA (WT>KD>Y402F). Conversely, the PTK inhibitor PP2 (which blocks PYK2 phosphorylation by Src-family PTKs) significantly increased SERCA2 mRNA levels. PYK2 overexpression had no effect on ERK1/2, but increased JNK1/2 and p38MAPKphosphorylation from fourfold to eightfold compared with GFP overexpression. Activation of both “stress-activated” protein kinase cascades appeared necessary to reduce SERCA2 mRNA levels. Adv-mediated overexpression of constitutively active (ca)MKK6 or caMKK7, which activated only p38MAPKor JNKs, respectively, was not sufficient, whereas combined infection with both Adv reduced SERCA2 mRNA levels to 45 ± 12% of control. WTPYK2 overexpression also significantly reduced SERCA2 promoter activity, as determined by transient transfection of a 3.8-kb SERCA2 promoter-luciferase construct. Thus a PYK2-dependent signaling cascade may have a role in abnormal cardiac Ca2+handling in left ventricular hypertrophy and heart failure via downregulation of SERCA2 gene transcription.

Ca(2+)-sensitive tyrosine kinase Pyk2/CAK beta-dependent signaling is essential for G-protein-coupled receptor agonist-induced hypertrophy

G-protein-coupled receptor agonists including endothelin-1 (ET-1) and phenylephrine (PE) induce hypertrophy in neonatal ventricular cardiomyocytes. Others and we previously reported that Rac1 signaling pathway plays an important role in this agonist-induced cardiomyocyte hypertrophy. In this study reported here, we found that a Ca(2+)-sensitive non-receptor tyrosine kinase, proline-rich tyrosine kinase 2 (Pyk2)/cell adhesion kinase beta (CAKbeta), is involved in ET-1- and PE-induced cardiomyocyte hypertrophy medicated through Rac1 activation. ET-1, PE or the Ca(2+) inophore, ionomycin, stimulated a rapid increase in tyrosine phosphorylation of Pyk2. The tyrosine phosphorylation of Pyk2 was suppressed by the Ca(2+) chelator, BAPTA. ET-1- or PE-induced increases in [(3)H]-leucine incorporation and expression of atrial natriuretic factor and the enhancement of sarcomere organization. Infection of cardiomyocytes with an adenovirus expressing a mutant Pyk2 which lacked its kinase domain or its ability to bind to c-Src, eliminated ET-1- and PE-induced hypertrophic responses. Inhibition of Pyk2 activation also suppressed Rac1 activation and reactive oxygen species (ROS) production. These findings suggest that the signal transduction pathway leading to hypertrophy involves Ca(2+)-induced Pyk2 activation followed by Rac1-dependent ROS production.

Cardiomyocyte apoptosis triggered by RAFTK/pyk2 via Src kinase is antagonized by paxillin

Altered cellular adhesion and apoptotic signaling in cardiac remodeling requires coordinated regulation of multiple constituent proteins that comprise cytoskeletal focal adhesions. One such protein activated by cardiac remodeling is related adhesion focal tyrosine kinase (RAFTK, also known as pyk2). Adenoviral-mediated expression of RAFTK in neonatal rat cardiomyocytes involves concurrent increases in phosphorylation of Src, c-Jun N-terminal kinase, and p38 leading to characteristic apoptotic changes including cleavage of poly(ADP-ribose) polymerase, caspase-3 activation, and increased DNA laddering. DNA laddering was decreased by mutation of the Tyr(402) Src-binding site in RAFTK, suggesting a central role for Src activity in apoptotic cell death that was confirmed by adenoviral-mediated Src expression. Multiple apoptotic signaling cascades are recruited by RAFTK as demonstrated by prevention of apoptosis using caspase-3 inhibitor IV (caspase-3 specific inhibitor), PP2 (Src-specific kinase inhibitor), or Csk (cellular negative regulator for Src), as well as dominant negative constructs for p38beta or MKP-1. These RAFTK-mediated phenotypic characteristics are prevented by concurrent expression of wild-type or a phosphorylation-deficient paxillin mutated at Tyr(31) and Tyr(118). Wild-type or mutant paxillin protein accumulation in the cytoplasm has no overt effect upon cell structure, but paxillin accumulation prevents losses of myofibril organization as well as focal adhesion kinase, vinculin, and paxillin protein levels mediated by RAFTK. Apoptotic signaling cascade inhibition by paxillin indicates interruption of signaling proximal to but downstream of RAFTK activity. Chronic RAFTK activation in cardiac remodeling may represent a maladaptive reactive response that can be modulated by paxillin, opening up novel possibilities for inhibition of cardiomyocyte apoptosis and structural degeneration in heart failure.

RAFTK/Pyk2 activation is mediated by trans-acting autophosphorylation in a Src-independent manner

The related adhesion focal tyrosine kinase (RAFTK), also known as Pyk2, undergoes autophosphorylation upon its stimulation. This leads to cascades of intracellular signaling that result in the regulation of various cellular activities. However, the molecular mechanism of RAFTK autophosphorylation is not yet known. Using various RAFTK constructs fused with two different tags, we found that the autophosphorylation of RAFTK was mediated by a trans-acting mechanism, not a cis-acting mechanism. In addition, overexpression of kinase-mutated RAFTK inhibited wild type RAFTK autophosphorylation in a dose-dependent manner by a trans-acting interaction. Trans-acting autophosphorylation was also observed between endogenous and exogenous RAFTK upon potassium depolarization of neuroendocrine PC12 cells. Using immunoprecipitation and affinity chromatography, we detected RAFTK self-association that was not affected by deletion of a single region or domain of RAFTK. Furthermore, RAFTK autophosphorylation occurred only at site Tyr402 in a Src kinase activity-independent manner. However, Src significantly enhanced RAFTK-mediated paxillin phosphorylation, suggesting a key role for Src in RAFTK activation and phosphorylation of downstream substrates. Our results indicate that the activation of RAFTK occurs in several steps. First, upon stimulus, RAFTK trans-autophosphorylates Tyr402. Second, phosphorylated Tyr402 recruits and activates Src kinase that in turn phosphorylates RAFTK and enhances its kinase activity. Lastly, the enhanced RAFTK activity induces the activation of downstream signaling molecules. Taken together, these studies provide insights into the molecular mechanism of RAFTK autophosphorylation and the specific role of Src in the regulation of RAFTK activation.

Restoration of resting sarcomere length after uniaxial static strain is regulated by protein kinase Cepsilon and focal adhesion kinase

Physiological or pathological stresses and strains produce longer or wider muscle cells, but resting sarcomere length remains constant. Our goal was to investigate the cellular mechanisms for controlling this optimal, resting sarcomere length. To do so, we cultured neonatal rat cardiomyocytes on microfabricated peg-and-groove, laminin-coated silicone surfaces and applied a uniaxial static strain of 10%. Sarcomere length was accurately measured by fast Fourier transform analysis of images before, within 5 minutes of, and 4 to 6 hours after imposition of the strain. Sarcomere length of aligned cardiomyocytes (1.94+/-0.07 microm) was lengthened acutely (2.06+/-0.06 microm), and recovered (1.95+/-0.07 microm) by 4 hours. Puromycin, an mRNA translational inhibitor, prevented recovery of resting sarcomere length by 4 hours, thus indicating a requirement for new protein synthesis in the recovery process. Furthermore, activation of protein kinase Cepsilon (PKCepsilon) was necessary for length recovery, as nonselective PKC inhibitors [staurosporine (5 micromol/L) and chelerythrine chloride (10 micromol/L)], and a replication-defective adenovirus (Adv) encoding a dominant-negative mutant of PKCepsilon prevented the restoration of sarcomere length. To assess the importance of focal adhesion complexes, cardiomyocytes were infected with an Adv encoding a dominant-negative inhibitor of focal adhesion kinase (FAK) (Adv-GFP-FRNK). Adv-GFP-FRNK also prevented resting sarcomere length recovery, whereas a control Adv encoding only GFP did not. In conclusion, using our novel culture system, we provide evidence indicating that the length remodeling process requires new protein synthesis, PKCepsilon and FAK.

Vascular endothelial growth factor regulates focal adhesion assembly in human brain microvascular endothelial cells through activation of the focal adhesion kinase and related adhesion focal tyrosine kinase

Vascular endothelial growth factor (VEGF) plays a significant role in blood-brain barrier breakdown and angiogenesis after brain injury. VEGF-induced endothelial cell migration is a key step in the angiogenic response and is mediated by an accelerated rate of focal adhesion complex assembly and disassembly. In this study, we identified the signaling mechanisms by which VEGF regulates human brain microvascular endothelial cell (HBMEC) integrity and assembly of focal adhesions, complexes comprised of scaffolding and signaling proteins organized by adhesion to the extracellular matrix. We found that VEGF treatment of HBMECs plated on laminin or fibronectin stimulated cytoskeletal organization and increased focal adhesion sites. Pretreating cells with VEGF antibodies or with the specific inhibitor SU-1498, which inhibits Flk-1/KDR receptor phosphorylation, blocked the ability of VEGF to stimulate focal adhesion assembly. VEGF induced the coupling of focal adhesion kinase (FAK) to integrin alphavbeta5 and tyrosine phosphorylation of the cytoskeletal components paxillin and p130cas. Additionally, FAK and related adhesion focal tyrosine kinase (RAFTK)/Pyk2 kinases were tyrosine-phosphorylated by VEGF and found to be important for focal adhesion sites. Overexpression of wild type RAFTK/Pyk2 increased cell spreading and the migration of HBMECs, whereas overexpression of catalytically inactive mutant RAFTK/Pyk2 markedly suppressed HBMEC spreading ( approximately 70%), adhesion ( approximately 82%), and migration ( approximately 65%). Furthermore, blocking of FAK by the dominant-interfering mutant FRNK (FAK-related non-kinase) significantly inhibited HBMEC spreading and migration and also disrupted focal adhesions. Thus, these studies define a mechanism for the regulatory role of VEGF in focal adhesion complex assembly in HBMECs via activation of FAK and RAFTK/Pyk2.

Fibronectin fragment activation of proline-rich tyrosine kinase PYK2 mediates integrin signals regulating collagenase-3 expression by human chondrocytes through a protein kinase C-dependent pathway

Fibronectin fragments (FN-f), including the 110-kDa fragment that binds the alpha5beta1 integrin, stimulate collagenase-3 (MMP-13) production and cartilage destruction. In the present study, treatment of chondrocytes with the 110-kDa FN-f or an activating antibody to the alpha5beta1 integrin was found to increase tyrosine autophosphorylation (Tyr-402) of the proline-rich tyrosine kinase-2 (PYK2) without significant change in autophosphorylation (Tyr-397) of focal adhesion kinase (FAK). The tyrosine kinase inhibitor tyrphostin A9, shown previously to block a PYK2-dependent pathway, blocked the FN-f-stimulated increase in MMP-13, whereas tyrphostin A25 did not. FN-f-stimulated PYK2 phosphorylation and MMP-13 production was also blocked by reducing intracellular calcium levels. Adenovirally mediated overexpression of wild type but not mutant PYK2 resulted in increased MMP-13 production. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate stimulated PYK2 phosphorylation and MMP-13 production. MMP-13 expression stimulated by either phorbol 12-myristate 13-acetate or FN-f was blocked by PKC inhibitors including the PKCdelta inhibitor rottlerin. Furthermore, PKCdelta translocation from cytosol to membrane was noted within 5 min of stimulation with FN-f. Immortalized human chondrocytes, transiently transfected with MMP-13 promoter-luciferase reporter constructs, showed increased promoter activity after FN-f treatment that was inhibited by co-transfection with either of two dominant negative mutants of PYK2 (Y402F and K457A). No inhibition was seen after cotransfection with wild type PYK2, a dominant negative of FAK (FRNK) or empty vector plasmid. FN-f-stimulated MMP-13 promoter activity was also inhibited by chemical inhibitors of ERK, JNK, and p38 mitogen-activated protein (MAP) kinases or by co-transfection of dominant negative MAP kinase mutant constructs. These studies have identified a novel pathway for the MAP kinase regulation of MMP-13 production which involves FN-f stimulation of the alpha5beta1 integrin and activation of the nonreceptor tyrosine kinase PYK2 by PKC, most likely PKCdelta