LY333531 attenuates contraction of tumor necrosis factor-α-sensitized human airway smooth muscle cells

OBJECTIVE

Protein kinase C (PKC) has been implicated in the increased contraction of human airway smooth muscle cells (HASMCs) in asthma. Using the three-dimensional collagen gel contraction system, the study aimed to determine the effects of LY333531, a specific inhibitor of the PKC-β isoform, on the contraction of tumor necrosis factor (TNF)-α-sensitized HASMCs.

METHODS

Cultured HASMCs were divided into five groups: the control group received no treatment, and the cells in the TNF-α group were sensitized with 10 ng/mL TNF-α for 48 h, while TNF-α was administered to sensitize HASMCs in the presence of 0.1, 0.2, and 0.5 μM LY333531 for 48 h in the 0.1LY, 0.2LY, and 0.5LY groups, respectively. Following this, HASMCs contraction was stimulated with 1 mM acetylcholine (ACh) for up to 24 h in each group and assessed using a three-dimensional collagen gel contraction assay. Furthermore, western blot and immunofluorescence analysis were performed.

RESULTS

The collagen gel contraction assay revealed that TNF-α increased the protein expression of phosphorylated PKC-β2, CPI-17, and MLC while exacerbating ACh-induced HASMCs contraction. LY333531 significantly attenuated HASMCs contraction and downregulated the protein expression of both p-CPI-17 and p-MLC.

CONCLUSIONS

At least in part by regulating CPI-17 and MLC phosphorylation, LY333531 attenuates augmented contraction of TNF-α-sensitized HASMCs in a collagen gel contraction system.

Phorbol 12,13-dibutyrate-induced protein kinase C activation triggers sustained contracture in human myometrium in vitro

BACKGROUND

Although physiologic transition from rhythmic contractions to uterine retraction postpartum remains a poorly understood process, it has been shown that the latter is essential in the prevention of hemorrhage and its negative consequences.

OBJECTIVE

To investigate the transition from oscillatory contractions to tonic contracture in human myometrium after delivery, a mechanism purported to facilitate postpartum hemostasis. Protein kinase C (PKC) plays a key regulatory role in human uterine contractions because it can prevent dephosphorylation of regulatory proteins and sensitize the contractile machinery to low Ca²⁺. Thus, activation of PKC by phorbol 12,13-dibutyrate (PDBu) may act as a strong uterotonic agent.

STUDY DESIGN

Uterine biopsies were obtained from consenting women undergoing elective caesarian delivery at term without labor (N = 19). Isometric tension measurements were performed on uterine strips (n = 114). The amplitudes and area under the curve of phasic contractions and tonic responses were measured and compared. A total of 1 μM PDBu was added to the isolated organ baths, and maximal tension of the uterine contracture was determined in the absence and presence of either 1 μM of staurosporine, 100 nM nifedipine, or 10 μM cyclopiazonic acid to assess the role of PKC and calcium sensitivity on uterine contractility.

RESULTS

On the addition of PDBu on either basal or oxytocin-induced activity, consistent contractures were obtained concomitant with complete inhibition of phasic contractions. After a 30-minute incubation period, the mean amplitude of the PDBu-induced tone represented 65.3% of the amplitude of spontaneous contraction. Staurosporine, a protein kinase inhibitor, induced a 91.9% inhibition of PDBu contractures, a process not affected by nifedipine or cyclopiazonic acid, thus indicating that this mechanism is largely Ca²⁺ independent.

CONCLUSION

Pharmacologic activation of PKC leads to a significant contracture of the myometrium. Together, these data suggest that the up-regulation of PKC plays a physiologic role in the modulation of uterine contracture after delivery. A switch from phasic to strong tonic contractions potentially may facilitate postpartum hemostasis.

PKC-dependent regulation of Kv7.5 channels by the bronchoconstrictor histamine in human airway smooth muscle cells

Kv7 potassium channels have recently been found to be expressed and functionally important for relaxation of airway smooth muscle. Previous research suggests that native Kv7 currents are inhibited following treatment of freshly isolated airway smooth muscle cells with bronchoconstrictor agonists, and in intact airways inhibition of Kv7 channels is sufficient to induce bronchiolar constriction. However, the mechanism by which Kv7 currents are inhibited by bronchoconstrictor agonists has yet to be elucidated. In the present study, native Kv7 currents in cultured human trachealis smooth muscle cells (HTSMCs) were observed to be inhibited upon treatment with histamine; inhibition of Kv7 currents was associated with membrane depolarization and an increase in cytosolic Ca²⁺ ([Ca²⁺]_cyt). The latter response was inhibited by verapamil, a blocker of L-type voltage-sensitive Ca²⁺ channels (VSCCs). Protein kinase C (PKC) has been implicated as a mediator of bronchoconstrictor actions, although the targets of PKC are not clearly established. We found that histamine treatment significantly and dose-dependently suppressed currents through overexpressed wild-type human Kv7.5 (hKv7.5) channels in cultured HTSMCs, and this effect was inhibited by the PKC inhibitor Ro-31-8220 (3 µM). The PKC-dependent suppression of hKv7.5 currents corresponded with a PKC-dependent increase in hKv7.5 channel phosphorylation. Knocking down or inhibiting PKCα, or mutating hKv7.5 serine 441 to alanine, abolished the inhibitory effects of histamine on hKv7.5 currents. These findings provide the first evidence linking PKC activation to suppression of Kv7 currents, membrane depolarization, and Ca²⁺ influx via L-type VSCCs as a mechanism for histamine-induced bronchoconstriction.

Ca2+ oscillations, Ca2+ sensitization, and contraction activated by protein kinase C in small airway smooth muscle

Protein kinase C (PKC) has been implicated in the regulation of smooth muscle cell (SMC) contraction and may contribute to airway hyperresponsiveness. Here, we combined optical and biochemical analyses of mouse lung slices to determine the effects of PKC activation on Ca²⁺ signaling, Ca²⁺ sensitivity, protein phosphorylation, and contraction in SMCs of small intrapulmonary airways. We found that 10 µM phorbol-12-myristate-13-acetate or 1 µM phorbol 12,13-dibutyrate induced repetitive, unsynchronized, and transient contractions of the SMCs lining the airway lumen. These contractions were associated with low frequency Ca²⁺ oscillations in airway SMCs that resulted from Ca²⁺ influx through L-type voltage-gated Ca²⁺ channels and the subsequent release of Ca²⁺ from intracellular stores through ryanodine receptors. Phorbol ester stimulation of lung slices in which SMC intracellular Ca²⁺ concentration ([Ca²⁺]_i) was “clamped” at a high concentration induced strong airway contraction, indicating that PKC mediated sensitization of the contractile response to [Ca²⁺]_i. This Ca²⁺ sensitization was accompanied by phosphorylation of both the PKC-potentiated PP1 inhibitory protein of 17 kD (CPI-17) and the regulatory myosin light chain. Thrombin, like the phorbol esters, induced a strong Ca²⁺ sensitization that was inhibited by the PKC inhibitor GF-109203X and also potentiated airway contraction to membrane depolarization with KCl. In conclusion, we suggest that PKC activation in small airways leads to both the generation of Ca²⁺ oscillations and strong Ca²⁺ sensitization; agents associated with airway inflammation, such as thrombin, may activate this pathway to sensitize airway smooth muscle to agonists that cause membrane depolarization and Ca²⁺ entry and induce airway hyperresponsiveness.

Regulation of the alternative splicing of sarcoplasmic reticulum Ca²⁺-ATPase1 (SERCA1) by phorbol 12-myristate 13-acetate (PMA) via a PKC pathway

Myotonic dystrophy type 1 (DM1) is a multi-systemic disease with no established treatment to date. Small, cell-permeable molecules hold the potential to treat DM1. In this study, we investigated the association between protein kinase C (PKC) signaling and splicing of sarcoplasmic reticulum Ca(2+)-ATPase1 (SERCA1). Our aim was to clarify the mechanisms underlying the regulation of alternative splicing, in order to explore new therapeutic strategies for DM1. By assessing the splicing pattern of the endogenous SERCA1 gene in HEK293 cells, we found that treatment with phorbol 12-myristate 13-acetate (PMA) regulated SERCA1 splicing. Interestingly, treatment with PMA for 48 h normalized SERCA1 splicing, while treatment for 1.5h promoted aberrant splicing. These two responses showed dose dependency and were completely abolished by the PKC inhibitor Ro 31-8220. Furthermore, repression of PKCβII and PKCθ by RNAi mimicked prolonged PMA treatment. These results indicate that PKC signaling is involved in the splicing of SERCA1 and provide new evidence for a link between alternative splicing and PKC signaling.

Bronchial inflammation induced PKCζ over-expression: involvement in mechanical properties of airway smooth muscle

Protein kinase C variants (PKCs) have been involved in the control of airway smooth muscle (ASM) tone, and abnormalities in PKC-dependent signaling have been associated with respiratory diseases such as asthma. In this study, the role of atypical PKCζ in airway hyperresponsiveness was investigated, using an in-vitro model of TNFα-treated human bronchi and an in vivo guinea pig model of chronic asthma. Our results demonstrated that PKCζ-specific inhibition produced a significant increase in isoproterenol sensitivity in TNFα-treated bronchi and ovalbumin (OVA)-sensitized guinea pig bronchi. The role of epoxy-eicosanoids, known to exert anti-inflammatory effects in lung, on PKCζ expression and activity in these models was evaluated. An enhanced PKCζ protein expression was delineated in TNFα-treated bronchi when compared with control (untreated) and epoxy-eicosanoid-treated bronchi. Measurements of Ca(2+) sensitivity, performed in TNFα-treated bronchi, demonstrated that treatment with myristoylated (Myr) PKCζ peptide inhibitor resulted in significant reductions of pCa-induced tension. Epoxy-eicosanoid treatments had similar effects on Ca(2+) sensitivity in TNFα-treated bronchi. In control and epoxy-eicosanoid-treated bronchi, the phosphorylated forms of p38MAPK and CPI-17 were significantly decreased compared with the TNFα-treated bronchi. An enhanced expression of PKCζ was ascertained in our in-vivo model of allergic asthma. Hence an increased Ca(2+) sensitivity could be explained by the phosphorylation of p38-MAPK, which in turn leads to phosphorylation and activation of the CPI-17 regulatory protein. This process was reversed upon treatment with the Myr-PKCζ-peptide inhibitor. The present data provide relevant evidence regarding the role of PKCζ in human and rodent models of airways inflammation.

The contribution of protein kinase C and CPI-17 signaling pathways to hypercontractility in murine experimental colitis

BACKGROUND

Colonic smooth muscle contractility is altered in colitis, and several protein kinase pathways can mediate colonic smooth muscle contraction. In the present study, we investigated whether protein kinase C (PKC) pathways also play a role in colonic hypercontractility observed during T(H) 2 colitis in BALB/c mice.

METHODS

Colitis was induced in BALB/c mice by provision of 5% dextran sodium sulfate (DSS) for 7 days. Changes in smooth muscle contractility were examined using dissected circular smooth muscle preparations from the distal colon. The contribution of conventional and novel PKC isozymes to the hypercontractile response was examined with pharmacological PKC inhibitors. Western blot analyses were used to examine protein expression and phosphorylation changes.

KEY RESULTS

Colonic smooth muscle was associated with inflammation-induced hypercontractility and altered PKC expression. Carbachol-induced peak (phasic) and sustained (tonic) contractions were increased. Chelerythrine was the most effective PKC inhibitor of both phasic and tonic contractions. There was no general difference in the percent contribution of conventional and novel PKC isozymes toward the DSS-induced hypercontractility, but inhibition of sustained force with GF109203x was higher for inflamed muscle. The CPI-17 phosphorylation was equally suppressed in both normal and DSS conditions by Gö6976 and chelerythrine, but only for the phasic component of contraction.

CONCLUSIONS & INFERENCES

The outcomes suggest that both conventional and novel PKC isozymes contribute to the phasic and tonic contractile components of BALB/c colonic circular smooth muscle under normal conditions, with novel PKC isozymes having a greater contribution to the tonic contraction. However, no effect of inflammation was observed on the relative contribution of PKC and CPI-17 toward the observed hypercontractility.

The anti-inflammatory role of heme oxygenase-1 in lipopolysaccharide and cytokine-stimulated inducible nitric oxide synthase and nitric oxide production in human periodontal ligament cells

BACKGROUND

Although heme oxygenase-1 (HO-1) is involved in anti-inflammation, the mechanisms of its activity in regulating periodontal inflammation are largely unclear. Therefore, the aim of this study is to investigate the anti-inflammatory properties of HO-1 in lipopolysaccharide (LPS)- and proinflammatory cytokine-stimulated inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production in human periodontal ligament (PDL) cells.

METHODS

PDL cells were treated with LPS plus a combination of tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta in serum-free media for 1 day. The production of NO was evaluated using a Griess reagent kit. The expression of iNOS and HO-1 proteins and mRNAs was evaluated using Western blotting and reverse transcriptase-polymerase chain reaction, respectively.

RESULTS

Proinflammatory cytokines and LPS triggered iNOS and HO-1 expression and NO production in PDL cells. HO-1 inhibitor and HO-1 small interfering RNA (siRNA) attenuated the LPS- and cytokine-stimulated NO release and iNOS and HO-1 expression. Specific inhibitors of p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinases phosphatidylinositol 3-kinase (PI3K), nuclear factor-kappa B (NF-kappaB), and protein kinase C delta (PKC-delta) greatly reduced the levels of iNOS and HO-1 expression induced by LPS plus cytokines.

CONCLUSIONS

Collectively, these data suggested that HO-1 inhibition blocked LPS- and proinflammatory cytokine-stimulated iNOS expression and NO production in PDL cells via a mechanism that involves p38, ERK, PI3K, NF-kappaB, and PKC-delta. Thus, the regulation of HO-1 activity may be a therapeutic strategy for periodontal disease.

Induction of ANGPTL4 expression in human airway smooth muscle cells by PMA through activation of PKC and MAPK pathways

In this study, we demonstrate that protein kinase C (PKC) activators, including phorbol-12-myristate-13-acetate (PMA), 1,2-dioctanoyl-sn-glycerol (DOG), and platelet-derived growth factor alpha are potent inducers of angiopoietin-like protein 4 (ANGPTL4) expression in several normal lung cell types and carcinoma cell lines. In human airway smooth muscle (HASM) cells induction of ANGPTL4 expression is observed as early as 2 h after the addition of PMA. PMA also increases the level of ANGPTL4 protein released in the medium. PKC inhibitors Ro31-8820 and Gö6983 greatly inhibit the induction of ANGPTL4 mRNA by PMA suggesting that this up-regulation involves activation of PKC. Knockdown of several PKCs by corresponding siRNAs suggest a role for PKCalpha. PMA does not activate MAPK p38 and p38 inhibitors have little effect on the induction of ANGPTL4 indicating that p38 is not involved in the regulation of ANGPTL4 by PMA. In contrast, treatment of HASM by PMA induces phosphorylation and activation of Ra, MEK1/2, ERK1/2, JNK, Elk-1, and c-Jun. The Ras inhibitor manumycin A, the MEK1/2 inhibitor U0126, and the JNK inhibitor SP600125, greatly reduce the increase in ANGPTL4 expression by PMA. Knockdown of MEK1/2 and JNK1/2 expression by corresponding siRNAs inhibits the induction of ANGPTL4. Our observations suggest that the induction of ANGPTL4 by PMA in HASM involves the activation of PKC, ERK, and JNK pathways. This induction may play a role in tissue remodeling during lung injury and be implicated in several lung pathologies.