Modulation of Na-K-2Cl cotransport by intracellular Cl(-) and protein kinase C-delta in Calu-3 cells

Aldosterone rapidly activates p-PKC delta and GPR30 but suppresses p-PKC epsilon protein levels in rat kidney

OBJECTIVES

Aldosterone rapidly enhances protein kinase C (PKC) alpha and beta1 proteins in the rat kidney. The G protein-coupled receptor 30 (GPR30)-mediated PKC pathway is involved in the inhibition of the potassium channel in HEK-239 cells. GPR30 mediates rapid actions of aldosterone in vitro. There are no reports available regarding the aldosterone action on other PKC isoforms and GPR30 proteins in vivo. The aim of the present study was to examine rapid actions of aldosterone on protein levels of phosphorylated PKC (p-PKC) delta, p-PKC epsilon, and GPR30 simultaneously in the rat kidney.

METHODS

Male Wistar rats were intraperitoneally injected with normal saline solution or aldosterone (150 µg/kg body weight). After 30 minutes, abundance and immunoreactivity of p-PKC delta, p-PKC epsilon, and GPR30 were determined by Western blot analysis and immunohisto-chemistry, respectively.

RESULTS

Aldosterone administration significantly increased the renal protein abundance of p-PKC delta by 80% (p<0.01) and decreased p-PKC epsilon protein by 50% (p<0.05). Aldosterone injection enhanced protein immunoreactivity of p-PKC delta but suppressed p-PKC epsilon protein intensity in both kidney cortex and medulla. Protein abundance of GPR30 was elevated by aldosterone treatment (p<0.05), whereas the immunoreactivity was obviously changed in the kidney cortex and inner medulla. Aldosterone translocated p-PKC delta and GPR30 proteins to the brush border membrane of proximal convoluted tubules.

CONCLUSIONS

This is the first in vivo study simultaneously demonstrating that aldosterone administration rapidly elevates protein abundance of p-PKC delta and GPR30, while p-PKC epsilon protein is suppressed in rat kidney. The stimulation of p-PKC delta protein levels by aldosterone may be involved in the activation of GPR30.

Nongenomic effects of fluticasone propionate and budesonide on human airway anion secretion

This study investigated the physiological effects of inhaled corticosteroids, which are used widely to treat asthma. The application of fluticasone propionate (FP, 100 μM) induced sustained increases in the short-circuit current (I(SC)) in human airway Calu-3 epithelial cells. The FP-induced I(SC) was prevented by the presence of H89 (10 μM, a protein kinase A inhibitor) and SQ22536 (100 μM, an adenylate cyclase inhibitor). The FP-induced responses involved bumetanide (a Na(+)-K(+)-2Cl(-) cotransporter inhibitor)-sensitive and 4,4'-dinitrostilbene-2,2'-disulfonic acid (an inhibitor of HCO(3)(-)-dependent anion transporters)-sensitive components, both of which reflect basolateral anion transport. Further, FP augmented apical membrane Cl(-) current (I(Cl)), reflecting cystic fibrosis transmembrane conductance regulator (CFTR)-mediated conductance, in the nystatin-permeabilized monolayer. In I(SC) and I(Cl) responses, FP failed to enhance the responses to forskolin (10 μM, an adenylate cyclase activator). Nevertheless, we found that FP synergistically increased cytosolic cAMP concentrations in combination with forskolin. All these effects of FP were reproduced with the use of budesonide. Collectively, inhaled corticosteroids such as FP and budesonide stimulate CFTR-mediated anion transport through adenylate cyclase-mediated mechanisms in a nongenomic fashion, thus sharing elements of a common pathway with forskolin. However, the corticosteroids cooperate with forskolin for synergistic cAMP production, suggesting that the corticosteroids and forskolin do not compete with each other to exert their effects on adenylate cyclase. Considering that such synergism was also observed in the FP/salmeterol combination, these nongenomic aspects may play therapeutic roles in mucus congestive airway diseases, in addition to genomic aspects that are generally recognized.

Effects of furosemide on allergic asthmatic responses in mice

BACKGROUND

The syndrome of allergic asthma features reversible bronchoconstriction, airway inflammation and hyperresponsiveness as well as airway remodelling, including goblet cell hyperplasia. Managing severe asthma is still a clinical challenge. Numerous studies report that furosemide, an inhibitor of Na(+)-K(+)-Cl(-) cotransporter (NKCC) reduces airway hyperresponsiveness (AHR) in asthmatic patients. However, the mechanism by which furosemide exerts anti-asthmatic action remains unclear.

OBJECTIVE

This study sought to investigate the cellular profile of NKCC1 expression in the lung and examine the effects of furosemide on several outcome measurements in a mouse model of allergic asthma.

METHODS

Mice were sensitized and challenged with ovalbumin (OVA). Before challenge, the OVA-sensitized mice were treated with furosemide (4.0 mg/kg/day, via daily intraperitoneal injection for 5 days). Outcome measurements in naïve, OVA-exposure, furosemide-treated naïve and furosemide-treated OVA-exposed mice included the slope of the relationship between inhaled methacholine (MCh) concentration and respiratory system resistance (Slope·R(RS)), bronchoalveolar lavage (BAL) cell counts and immunohistochemical and immunoblotting assays of lung tissues.

RESULTS

NKCC1 immunoreactivity was observed in airway epithelial cells (AECs) and alveolar type II (ATII) cells of the control mice. OVA exposure enhanced the expression of NKCC1 in AECs and ATII cells, and increased the infiltration of NKCC1-expressing T lymphocytes in the lung. NKCC1 immunoreactivity was not detected in the airway smooth muscle (ASM) cells. Furosemide treatment reduced the Slope·R(RS) in both naïve and OVA-exposed mice by about 50%. Furosemide treatment also increased T lymphocyte infiltration to the lung in OVA-exposed mice by approximately 53%, but had no effect on pulmonary goblet cell hyperplasia.

CONCLUSIONS AND CLINICAL RELEVANCE

Furosemide decreases basal airway responsiveness, thereby reducing the extent of allergen-induced AHR. However, the same treatment also increases T lymphocytes infiltration in the course of allergic asthma. Further studies are necessary to address the usefulness of furosemide in the clinical treatment of asthma.

Capsaicinoids regulate airway anion transporters through Rho kinase- and cyclic AMP-dependent mechanisms

To investigate the effects of capsaicinoids on airway anion transporters, we recorded and analyzed transepithelial currents in human airway epithelial Calu-3 cells. Application of capsaicin (100 μM) attenuated vectorial anion transport, estimated as short-circuit currents (I(SC)), before and after stimulation by forskolin (10 μM) with concomitant reduction of cytosolic cyclic AMP (cAMP) levels. The capsaicin-induced inhibition of I(SC) was also observed in the response to 8-bromo-cAMP (1 mM, a cell-permeable cAMP analog) and 3-isobutyl-1-methylxanthine (1 mM, an inhibitor of phosphodiesterases). The capsaicin-induced inhibition of I(SC) was attributed to suppression of bumetanide (an inhibitor of the basolateral Na(+)-K(+)-2 Cl(-) cotransporter 1)- and 4,4'-dinitrostilbene-2,2'-disulfonic acid (an inhibitor of basolateral HCO(3)(-)-dependent anion transporters)-sensitive components, which reflect anion uptake via basolateral cAMP-dependent anion transporters. In contrast, capsaicin potentiated apical Cl(-) conductance, which reflects conductivity through the cystic fibrosis transmembrane conductance regulator, a cAMP-regulated Cl(-) channel. All these paradoxical effects of capsaicin were mimicked by capsazepine. Forskolin application also increased phosphorylated myosin phosphatase target subunit 1, and the phosphorylation was prevented by capsaicin and capsazepine, suggesting that these capsaicinoids assume aspects of Rho kinase inhibitors. We also found that the increments in apical Cl(-) conductance were caused by conventional Rho kinase inhibitors, Y-27632 (20 μM) and HA-1077 (20 μM), with selective inhibition of basolateral Na(+)-K(+)-2 Cl(-) cotransporter 1. Collectively, capsaicinoids inhibit cAMP-mediated anion transport through down-regulation of basolateral anion uptake, paradoxically accompanied by up-regulation of apical cystic fibrosis transmembrane conductance regulator-mediated anion conductance. The latter is mediated by inhibition of Rho-kinase, which is believed to interact with actin cytoskeleton.

Activated PKC{delta} and PKC{epsilon} inhibit epithelial chloride secretion response to cAMP via inducing internalization of the Na+-K+-2Cl- cotransporter NKCC1

The basolateral Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) is a key determinant of transepithelial chloride secretion and dysregulation of chloride secretion is a common feature of many diseases including secretory diarrhea. We have previously shown that activation of protein kinase C (PKC) markedly reduces transepithelial chloride secretion in human colonic T84 cells, which correlates with both functional inhibition and loss of the NKCC1 surface expression. In the present study, we defined the specific roles of PKC isoforms in regulating epithelial NKCC1 and chloride secretion utilizing adenoviral vectors that express shRNAs targeting human PKC isoforms (α, δ, ε) (shPKCs) or LacZ (shLacZ, non-targeting control). After 72 h of adenoviral transduction, protein levels of the PKC isoforms in shPKCs-T84 cells were decreased by ∼90% compared with the shLacZ-control. Activation of PKCs by phorbol 12-myristate 13-acetate (PMA) caused a redistribution of NKCC1 immunostaining from the basolateral membrane to intracellular vesicles in both shLacZ- and shPKCα-T84 cells, whereas the effect of PMA was not observed in shPKCδ- and shPKCε- cells. These results were further confirmed by basolateral surface biotinylation. Furthermore, activation of PKCs by PMA inhibited cAMP-stimulated chloride secretion in the uninfected, shLacZ- and shPKCα-T84 monolayers, but the inhibitory effect was significantly attenuated in shPKCδ- and shPKCε-T84 monolayers. In conclusion, the activated novel isoforms PKCδ or PKCε, but not the conventional isoform PKCα, inhibits transepithelial chloride secretion through inducing internalization of the basolateral surface NKCC1. Our study reveals that the novel PKC isoform-regulated NKCC1 surface expression plays an important role in the regulation of chloride secretion.

Heterologous regulation of anion transporters by menthol in human airway epithelial cells

The present study concerns previously unreported effects of menthol, a cyclic terpene alcohol produced by the peppermint herb, on anion transporters in polarized human airway Calu-3 epithelia. Application of menthol (0.01-1mM) attenuated transepithelial anion transport, estimated as short-circuit currents (I(SC)), after stimulation by forskolin (10microM) but not before. In contrast, menthol potentiated forskolin-stimulated and -unstimulated apical Cl(-) conductance, which reflected the cystic fibrosis transmembrane conductance regulator (CFTR: the cAMP-regulated Cl(-) channel)-mediated conductance, without correlation to changes in cytosolic cAMP levels. These results indicate that menthol-induced attenuation of forskolin-induced I(SC) despite CFTR up-regulation was due to cAMP-independent inhibition of basolateral anion uptake, which is the rate-limiting step for transepithelial anion transport. Analyses of the responsible basolateral anion transporters revealed that forskolin increased both bumetanide (an inhibitor of the basolateral Na(+)-K(+)-2Cl(-) cotransporter [NKCC1])- and DNDS (an inhibitor of basolateral HCO(3)(-)-dependent anion transporters [NBC1/AE2])-sensitive I(SC) in the control whereas only the former was prevented by the application of menthol. Neither the bumetanide- nor DNDS-sensitive component was, however, reduced by menthol without forskolin. These heterologous effects of menthol were reproduced by latrunculin B, an inhibitor of actin polymerization. F-actin staining showed that menthol prevented forskolin-stimulated rearrangements of actin microfilaments without affecting the distribution of forskolin-unstimulated microfilaments. Collectively, menthol functions as an activator of CFTR and prevents activation of NKCC1 without affecting NBC1/AE although all of these transporters are commonly cAMP-dependent. The heterologous effects may be mediated by the actin cytoskeleton, which interacts with CFTR and NKCC1.

Protease-activated receptor-2 stimulates intestinal epithelial chloride transport through activation of PLC and selective PKC isoforms

Serine proteases play important physiological roles through their activity at G protein-coupled protease-activated receptors (PARs). We examined the roles that specific phospholipase (PL) C and protein kinase (PK) C (PKC) isoforms play in the regulation of PAR(2)-stimulated chloride secretion in intestinal epithelial cells. Confluent SCBN epithelial monolayers were grown on Snapwell supports and mounted in modified Ussing chambers. Short-circuit current (I(sc)) responses to basolateral application of the selective PAR(2) activating peptide, SLIGRL-NH(2), were monitored as a measure of net electrogenic ion transport caused by PAR(2) activation. SLIGRL-NH(2) induced a transient I(sc) response that was significantly reduced by inhibitors of PLC (U73122), phosphoinositol-PLC (ET-18), phosphatidylcholine-PLC (D609), and phosphatidylinositol 3-kinase (PI3K; LY294002). Immunoblot analysis revealed the phosphorylation of both PLCbeta and PLCgamma following PAR(2) activation. Pretreatment of the cells with inhibitors of PKC (GF 109203X), PKCalpha/betaI (Gö6976), and PKCdelta (rottlerin), but not PKCzeta (selective pseudosubstrate inhibitor), also attenuated this response. Cellular fractionation and immunoblot analysis, as well as confocal immunocytochemistry, revealed increases of PKCbetaI, PKCdelta, and PKCepsilon, but not PKCalpha or PKCzeta, in membrane fractions following PAR(2) activation. Pretreatment of the cells with U73122, ET-18, or D609 inhibited PKC activation. Inhibition of PI3K activity only prevented PKCdelta translocation. Immunoblots revealed that PAR(2) activation induced phosphorylation of both cRaf and ERK1/2 via PKCdelta. Inhibition of PKCbetaI and PI3K had only a partial effect on this response. We conclude that basolateral PAR(2)-induced chloride secretion involves activation of PKCbetaI and PKCdelta via a PLC-dependent mechanism resulting in the stimulation of cRaf and ERK1/2 signaling.

Dual pathway activated by tert-butyl hydroperoxide in human airway anion secretion

We analyzed the mechanisms underlying the ion transport induced by tert-butyl hydroperoxide (t-BOOH), a membrane-permeant oxidant that has been widely used as a model of oxidative stress, in human airway epithelial cells (Calu-3). We found that t-BOOH induced a short-circuit current that was composed of two distinct components, a peaked component (PC) and a sustained component (SC). Both components were reduced by the presence of H-89 (N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline) [10 microM, a protein kinase A (PKA) inhibitor] and clofilium (100 microM, a cAMP-dependent K+ channel inhibitor) but not by charybdotoxin (50 nM, a human intermediate conductance Ca2+-activated K+ channel inhibitor), suggesting that both PC and SC were generated through a common PKA-dependent/Ca2+-independent pathway. Notwithstanding, analyses of the physiological properties revealed that PC and SC were attributable to different pathways. PC, but not SC, was correlated with apical membrane Cl- conductance and was inhibited by the cyclooxygenase (COX)-2 inhibitor NS-398 (N-[2-(cyclohexyloxyl)-4-nitrophenyl]-methane sulfonamide; 10 microM). In contrast, SC, but not PC, was composed of a component sensitive to bumetanide (50 microM), an inhibitor of the basolateral Na+-K+-2Cl- cotransporter (NKCC1), and was abolished by the cytoskeleton dysfunction induced by cytochalasin D (10 microM) and (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexane carboxamide (Y-27632; 20 microM). Collectively, t-BOOH induces PKA-related anion secretion through two independent pathways: rapid activation of apical anion efflux through a COX-2-dependent/cytoskeleton-independent pathway and relatively delayed activation of NKCC1 for basolateral anion uptake through a COX-2-independent/cytoskeleton-dependent pathway.

SPAK and OSR1, key kinases involved in the regulation of chloride transport

Reversible phosphorylation by protein kinases is probably one of the most important examples of post-translational modification of ion transport proteins. Ste20-related proline alanine-rich kinase (SPAK) and oxidative stress response kinase (OSR1) are two serine/threonine kinases belonging to the germinal centre-like kinase subfamily VI. Genetic analysis suggests that OSR1 evolved first, with SPAK arising following a gene duplication in vertebrate evolution. SPAK and OSR1 are two recently discovered kinases which have been linked to several key cellular processes, including cell differentiation, cell transformation and proliferation, cytoskeleton rearrangement, and most recently, regulation of ion transporters. Na-K-2Cl cotransporter activity is regulated by phosphorylation. Pharmacological evidence has identified several kinases and phosphatases which alter cotransporter function, however, no direct linkage between these enzymes and the cotransporter has been demonstrated. This article will review some of the physical and physiological properties of SPAK and OSR1, and present new evidence of a direct interaction between the Na-K-Cl cotransporter and the stress kinases.

Dynamic regulation of Na(+)-K(+)-2Cl(-) cotransporter surface expression by PKC-{epsilon} in Cl(-)--secretory epithelia

In secretory epithelia, activation of PKC by phorbol ester and carbachol negatively regulates Cl(-) secretion, the transport event of secretory diarrhea. Previous studies have implicated the basolateral Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) as a target of PKC-dependent inhibition of Cl(-) secretion. In the present study, we examined the regulation of surface expression of NKCC1 in response to the activation of PKC. Treatment of confluent T84 intestinal epithelial cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (PMA) reduced the amount of NKCC1 accessible to basolateral surface biotinylation. Loss of cell surface NKCC1 was due to internalization as shown by 1) the resistance of biotinylated NKCC1 to surface biotin stripping after incubation with PMA and 2) indirect immunofluorescent labeling. PMA-induced internalization of NKCC1 is dependent on the epsilon-isoform of PKC as determined on the basis of sensitivity to a panel of PKC inhibitors. The effect of PMA on surface expression of NKCC1 was specific because PMA did not significantly alter the amount of Na(+)-K(+)-ATPase or E-cadherin available for surface biotinylation. After extended PMA exposure (>2 h), NKCC1 became degraded in a proteasome-dependent fashion. Like PMA, carbachol reduced the amount of NKCC1 accessible to basolateral surface biotinylation in a PKC-epsilon-dependent manner. However, long-term exposure to carbachol did not result in degradation of NKCC1; rather, NKCC1 that was internalized after exposure to carbachol was recycled back to the cell membrane. PKC-epsilon-dependent alteration of NKCC1 surface expression represents a novel mechanism for regulating Cl(-) secretion.

Fluid secretion and the Na+-K+-2Cl- cotransporter in mouse exorbital lacrimal gland

We have previously suggested that fluid flow in the mouse exorbital lacrimal gland is driven by the opening of apical Cl- and K+ channels. These ions move into the lumen of the gland and water follows by osmosis. In many tissues, the Na+-K+-2Cl- cotransporter (NKCC1) replaces the Cl- and K+ ions that move into the lumen. We hypothesize that mouse exorbital lacrimal glands would have NKCC1 co-transporters and that they would be important in fluid transport by this gland. We used immunocytochemistry to localize NKCC1-like immunoreactivity to the membranes of the acinar cells as well as to the basolateral membranes of the duct cells. We developed a method to measure tear flow and its composition from mouse glands in situ. Stimulation with the acetylcholine agonist carbachol produced a peak flow followed by a plateau. Ion concentration measurements of this stimulated fluid showed it was high in K+ and Cl-. Treatment of the gland with furosemide, a blocker of the NKCC1 cotransporter, reduced the plateau phase of fluid flow by approximately 30%. Isolated cells exposed to a hypertonic shock shrank by approximately 20% and then showed a regulatory volume increase (RVI). Both the RVI and swelling were blocked by treatment with furosemide. Cells isolated from these glands shrink by approximately 10% in the presence of carbachol. Blocking NKCC1 with furosemide reduced the amount of shrinkage by approximately 50%. These data suggest that NKCC1 plays an important role in fluid secretion by the exorbital gland of mice.

Involvement of NH2 terminus of PKC-delta in binding to F-actin during activation of Calu-3 airway epithelial NKCC1

Direct binding of nonmuscle F-actin and the C2-like domain of PKC-delta (deltaC2-like domain) is involved in hormone-mediated activation of epithelial Na-K-2Cl cotransporter isoform 1 (NKCC1) in a Calu-3 airway epithelial cell line. The goal of this study was to determine the site of actin binding on the 123-amino acid deltaC2-like domain. Truncations of the deltaC2-like domain were made by restriction digestion and confirmed by nucleotide sequencing. His6-tagged peptides were expressed in bacteria, purified, and analyzed with a Coomassie blue stain for predicted size and either a 6xHis protein tag stain or an INDIA His6 probe for expression of the His6 tag. Truncated peptides were tested for competitive inhibition of binding of activated, recombinant PKC-delta with nonmuscle F-actin. Peptides from the NH2-terminal region, but not the COOH-terminal region, of the deltaC2-like domain blocked binding of activated PKC-delta to F-actin. The deltaC2-like domain and three NH2-terminal truncated peptides of 17, 83, or 108 amino acids blocked binding, with IC50 values ranging from 1.2 to 2.2 nmol (6-11 microM). NH2-terminal deltaC2-like peptides also prevented methoxamine-stimulated NKCC1 activation and pulled down endogenous actin from Calu-3 cells. The proximal NH2 terminus of the deltaC2-like domain encodes a beta1-sheet region. The amino acid sequence of the actin-binding domain is distinct from actin-binding domains in other PKC isotypes and actin-binding proteins. Our results indicate that F-actin likely binds to the beta1-sheet region of the deltaC2-like domain in airway epithelial cells.

Mucin secretion and PKC isoforms in SPOC1 goblet cells: differential activation by purinergic agonist and PMA

SPOC1 cells, which are a mucin-secreting model of rat airway goblet cells, possess a luminal P2Y2 purinoceptor through which UTP, ATP, and ATPgammaS stimulate secretion with EC50 values of approximately 3 microM. PMA elicits mucin secretion with high EC50 (75 nM) and saturation (300 nM) values. For the first time in airway mucin-secreting cells, the PKC isoforms expressed and activated by a secretagogue were determined using RT-PCR/restriction-enzyme mapping and Western blotting. Five isoforms were expressed: cPKCalpha, nPKCdelta and -eta, and aPKCzeta and -iota/lambda. PMA caused cPKCalpha and nPKCdelta to translocate to the membrane fraction of SPOC1 cells; only nPKCdelta so responded to ATPgammaS. Membrane-associated nPKCdelta and mucin secretion increased in parallel with ATPgammaS concentration and yielded EC50 values of 2-3 microM and maximum values of 100 microM. Effects of PMA to increase membrane-associated cPKCalpha and nPKCdelta saturated at 30 nM, whereas mucin secretion saturated at 300 nM, which suggests a significant PKC-independent effect of PMA on mucin secretion. A prime alternate phorbol ester-receptor candidate is the C1-domain protein MUNC13. RT-PCR revealed the expression of ubiquitous (ub)MUNC13-2 and its binding partner, DOC2-gamma. Hence, P2Y2 agonists activate nPKCdelta in SPOC1 cells. PMA activates cPKCalpha and nPKCdelta at high affinity and stimulates a lower affinity PKC-independent pathway that leads to mucin secretion.

Stability of actin cytoskeleton and PKC-delta binding to actin regulate NKCC1 function in airway epithelial cells

Activation of airway epithelial Na-K-2Cl cotransporter (NKCC)1 requires increased activity of protein kinase C (PKC)-delta, which localizes predominantly to the actin cytoskeleton. Prompted by reports of a role for actin in NKCC1 function, we studied a signaling mechanism linking NKCC1 and PKC. Stabilization of actin polymerization with jasplakinolide increased activity of NKCC1, whereas inhibition of actin polymerization with latrunculin B prevented hormonal activation of NKCC1. Protein-protein interactions among NKCC1, actin, and PKC-delta were verified by Western blot analysis of immunoprecipitated proteins. PKC-delta was detected in immunoprecipitates of NKCC1 and vice versa. Actin was also detected in immunoprecipitates of NKCC1 and PKC-delta. Pulldown of endogenous actin revealed the presence of NKCC1 and PKC-delta. Binding of recombinant PKC-delta to NKCC1 was not detected in overlay assays. Rather, activated PKC-delta bound to actin, and this interaction was prevented by a peptide encoding deltaC2, a C2-like domain based on the amino acid sequence of PKC-delta. deltaC2 also blocked stimulation of NKCC1 function by methoxamine. Immunofluorescence and confocal microscopy revealed PKC-delta in the cytosol and cell periphery. Merged images of cells stained for actin and PKC-delta indicated colocalization of PKC-delta and actin at the cell periphery. The results indicate that actin is critical for the activation of NKCC1 through a direct interaction with PKC-delta.