Regulation of acetylcholine-induced phosphorylation of PLD1 in porcine tracheal smooth muscle

Direct association of RhoA with specific domains of PKC-α

Previous studies performed at our laboratory have shown that agonist-induced contraction of smooth muscle is associated with translocation of protein kinase C (PKC)-α and RhoA to the membrane and that this interaction is due to a direct protein-protein interaction. To determine the domains of PKC-α involved in direct interaction with RhoA, His-tagged PKC-α proteins of individual domains and different combinations of PKC-α domains were used to perform in vitro binding assays with the fusion protein glutathione- S-transferase (GST)-RhoA. Coimmunoprecipitation was also performed using smooth muscle cells transfected with truncated forms of PKC-α in this study. The data indicate that RhoA directly bound to full-length PKC-α, both in vitro (82.57 ± 15.26% above control) and in transfected cells. RhoA bound in vitro to the C1 domain of PKC-α [PKC-α (C1)] (70.48 ± 20.78% above control), PKC-α (C2) (72.26 ± 29.96% above control), and PKC-α (C4) (90.58 ± 26.79% above control), but not to PKC-α (C3) (0.64 ± 5.18% above control). RhoA bound in vitro and in transfected cells to truncated forms of PKC-α, PKC-α (C2, C3, and C4), and PKC-α (C3 and C4) (94.09 ± 12.13% and 85.10 ± 16.16% above control, respectively), but not to PKC-α (C1, C2, and C3) or to PKC-α (C2 and C3) (0.47 ± 1.26% and 7.45 ± 10.76% above control, respectively). RhoA bound to PKC-α (C1 and C2) (60.78 ± 13.78% above control) only in vitro, but not in transfected cells, and PKC-α (C2, C3, and C4) and PKC-α (C3 and C4) bound well to RhoA. These data suggest that RhoA bound to fragments that may mimic the active form of PKC-α. The studies using cells transfected with truncated forms of PKC-α indicate that PKC-α (C1 and C2), PKC-α (C1, C2, and C3), and PKC-α (C2 and C3) did not associate with RhoA. Only full-length PKC-α, PKC-α (C2, C3, and C4), and PKC-α (C3 and C4) associated with RhoA. The association increased upon stimulation with acetylcholine. These results suggest that the functional association of PKC-α with RhoA may require the C4 domain.

Prostanoids Secreted by Alveolar Macrophages Enhance Ionic Currents in Swine Tracheal Submucosal Gland Cells

We examined the effect of substances released by swine alveolar macrophages (AMs) on ionic currents in airway submucosal gland cells (SGCs). AMs obtained by lavage were activated by 24-h zymosan exposure (0.1 mg/ml). Supernatant was collected and used to stimulate short-circuit current changes (DeltaI(SC)) in SGC monolayers in Ussing chambers. Dexamethasone (1 microM) or indomethacin (5 muM) during zymosan exposure of AMs reduced or abolished the supernatant-induced DeltaI(SC). Zymosan exposure induced a 5-fold increase in cyclooxygenase (COX)-2 but not COX-1 protein levels in AMs. Prostaglandin E(2) (PGE(2)) concentration in the supernatant from zymosan-activated AMs was 550 +/- 10 nM (n = 3) compared with 28 +/- 3 nM for unstimulated AMs (n = 3). PGE(2), applied serosally, induced DeltaI(SC) with an EC(50) of 15.5 +/- 1.3 nM (n = 4) and 3.6 +/- 1.8 microM (n = 3) when applied apically. Four types of endoprostanoid receptors (EP(1-4)) were detected in SGCs using Western blot. PGE(2)-induced DeltaI(SC) were inhibited by AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) but not by SC19220 (8-chloro-dibenzo[b,f][1,4]oxazepine-10(11H)-carboxylic acid, 2-acetylhydrazide), suggesting that endoprostanoid (EP)(2) but not EP(1) receptors were activated by PGE(2). Pretreatment of SGCs with supernatant from zymosan-activated AMs, PGE(2), or forskolin enhanced the sensitivity to acetylcholine (ACh)-induced DeltaI(SC). PGE(2)-induced DeltaI(SC) were blocked by charybdotoxin (ChTX), chromanol 293B, or glibenclamide. ACh-induced DeltaI(SC) were only blocked by ChTX or glibenclamide. None of these blockers altered PGE(2) pretreatment-induced sensitization of ACh-induced DeltaI(SC). These results demonstrate that prostanoids released from activated AMs directly increase cystic fibrosis transmembrane conductance regulator and K(+) channel activity. ACh-induced DeltaI(SC) are also enhanced due to enhanced activation of Ca(2+)-activated K(+) channels (K(Ca)).