PYK2 selectively mediates signals for growth versus differentiation in response to stretch of spontaneously active vascular smooth muscle

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.

Novel pharmacological inhibitors demonstrate the role of the tyrosine kinase Pyk2 in adhesion and aggregation of human platelets

Pyk2 is a Ca2+-regulated kinase predominantly expressed in neuronal and in haematopoietic cells. Previous studies on Pyk2-null mice have demonstrated that Pyk2 plays a crucial role in platelet activation and thrombus formation, thus representing a possible target for antithrombotic therapy. Very limited information is available about the role of Pyk2 in human platelets, mainly because of the lack of specific pharmacological inhibitors. In this work, we have tested two novel Pyk2 inhibitors, PF-4594755 and PF-4520440, to validate their specificity and to investigate their ability to modulate platelet activation. Both molecules were able to efficiently block Pyk2 activity in human and mouse platelets stimulated with thrombin or with the Ca2+-ionophore. In wild-type murine platelets, PF-4594755 and PF-4520440 reduced thrombin-induced aggregation to the level observed in Pyk2 knockout platelets, but did not affect aggregation induced by GPVI stimulation. Importantly, neither compounds affected the residual thrombin-induced aggregation of Pyk2-null platelets, thus excluding possible off-target effects. In human platelets, PF-4594755 and PF-4520440 significantly reduced aggregation stimulated by thrombin, but not by the GPVI agonist convulxin. Both inhibitors reduced platelet adhesion on fibrinogen and prevented Akt phosphorylation in adherent cells, indicating that Pyk2 regulates PI3K and cell spreading downstream of integrins in human platelets. Finally, the Pyk2 inhibitors significantly inhibited thrombus formation upon blood perfusion on immobilized collagen under arterial flow rate. These results demonstrate that PF-4594755 and PF-4520440 are specific inhibitors of Pyk2 in intact platelets and allowed to reliably document that this kinase plays a relevant role in human platelet activation.

Supplementary Material to this article is available online at www.thrombosis-online.com.

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.

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

Depolarization of the vascular smooth muscle cell membrane evokes a rapid (phasic) contractile response followed by a sustained (tonic) contraction. We showed previously that the sustained contraction involves genistein-sensitive tyrosine phosphorylation upstream of the RhoA/Rho-associated kinase (ROK) pathway leading to phosphorylation of MYPT1 (the myosin-targeting subunit of myosin light chain phosphatase (MLCP)) and myosin regulatory light chains (LC20). In this study, we addressed the hypothesis that membrane depolarization elicits activation of the Ca(2+)-dependent tyrosine kinase Pyk2 (proline-rich tyrosine kinase 2). Pyk2 was identified as the major tyrosine-phosphorylated protein in response to membrane depolarization. The tonic phase of K(+)-induced contraction was inhibited by the Pyk2 inhibitor sodium salicylate, which abolished the sustained elevation of LC20 phosphorylation. Membrane depolarization induced autophosphorylation (activation) of Pyk2 with a time course that correlated with the sustained contractile response. The Pyk2/focal adhesion kinase (FAK) inhibitor PF-431396 inhibited both phasic and tonic components of the contractile response to K(+), Pyk2 autophosphorylation, and LC20 phosphorylation but had no effect on the calyculin A (MLCP inhibitor)-induced contraction. Ionomycin, in the presence of extracellular Ca(2+), elicited a slow, sustained contraction and Pyk2 autophosphorylation, which were blocked by pre-treatment with PF-431396. Furthermore, the Ca(2+) channel blocker nifedipine inhibited peak and sustained K(+)-induced force and Pyk2 autophosphorylation. Inhibition of Pyk2 abolished the K(+)-induced translocation of RhoA to the particulate fraction and the phosphorylation of MYPT1 at Thr-697 and Thr-855. We conclude that depolarization-induced entry of Ca(2+) activates Pyk2 upstream of the RhoA/ROK pathway, leading to MYPT1 phosphorylation and MLCP inhibition. The resulting sustained elevation of LC20 phosphorylation then accounts for the tonic contractile response to membrane depolarization.