Tumor necrosis factor-alpha activates pulmonary artery endothelial protein kinase C

Fibroblasts from type 1 diabetics exhibit enhanced Ca(2+) mobilization after TNF or fat exposure

The effects of cytokine and fatty acid treatment on signal transduction in dermal fibroblasts from type 1 diabetics and matched controls were compared. Chronic exposure to TNF, accentuated Ca²⁺ mobilization in response to bradykinin (BK) in cells from both controls and diabetics; responses were three-fold greater in cells from diabetics than in controls. Similarly, with chronic exposure to IL-1β, BK-induced Ca²⁺ mobilization was accentuated in cells from type 1 diabetics compared to the controls. Pretreatment with the protein synthesis inhibitor cycloheximide or the protein kinase C inhibitor calphostin C prior to the addition of TNF completely abrogated the TNF-induced increment in peak bradykinin response. Ca²⁺ transients induced by depleting endoplasmic reticulum (ER) Ca²⁺ with thapsigargin were also greater in TNF treated fibroblasts than in untreated cells, with greater increases in cells from diabetics. Exposing fibroblasts for 48 hours to 2 mM oleate also increased both the peak bradykinin response and the TNF-induced increment in peak response, which were significantly greater in diabetics than controls. These data indicate that cells from diabetic patients acquire elevated ER Ca²⁺ stores in response to both cytokines and free fatty acids,and thus exhibit greater sensitivity to environmental inflammatory stimuli and elevated lipids.

Tumor necrosis factor-alpha in diabetic plasma increases the activity of core 2 GlcNAc-T and adherence of human leukocytes to retinal endothelial cells: significance of core 2 GlcNAc-T in diabetic retinopathy

A large body of evidence now implicates increased leukocyte-endothelial cell adhesion as a key early event in the development of diabetic retinopathy. We recently reported that raised activity of the glycosylating enzyme core 2 beta 1,6-N-acetylglucosaminyltransferase (GlcNAc-T) through protein kinase C (PKC)beta2-dependent phosphorylation plays a fundamental role in increased leukocyte-endothelial cell adhesion and capillary occlusion in retinopathy. In the present study, we demonstrate that following exposure to plasma from diabetic patients, the human promonocytic cell line U937 exhibits a significant elevation in core 2 GlcNAc-T activity and increased adherence to cultured retinal capillary endothelial cells. These effects of diabetic plasma on enzyme activity and cell adhesion, mediated by PKCbeta2-dependent phosphorylation of the core 2 GlcNAc-T protein, were found to be triggered by increased plasma levels of tumor necrosis factor (TNF)-alpha. Levels of enzyme activity in plasma-treated U937 cells were closely dependent on the severity of diabetic retinopathy, with the highest values observed upon treatment with plasma of patients affected by proliferative retinopathy. Furthermore, we noted much higher correlation, as compared with control subjects, between increased values of core 2 GlcNAc-T activity and cell adhesion properties. Based on the prominent role of TNF-alpha in the development of diabetic retinopathy, these observations further validate the significance of core 2 GlcNAc-T in the pathogenesis of capillary occlusion, thereby enhancing the therapeutic potential of specific enzyme inhibitors.

Protein kinase C modulates pulmonary endothelial permeability: a paradigm for acute lung injury

The intracellular serine/threonine kinase protein kinase C (PKC) has an important role in the genesis of pulmonary edema. This review discusses the PKC-mediated mechanisms that participate in the pulmonary endothelial response to agents involved in lung injury characteristic of the respiratory distress syndrome. Thus the paradigms of PKC-induced lung injury are discussed within the context of pulmonary transvascular fluid exchange. We focus on the signal transduction pathways that are modulated by PKC and their effect on lung endothelial permeability. Specifically, alpha-thrombin, tumor necrosis factor (TNF)-alpha, and reactive oxygen species are discussed because of their well-established roles in both human and experimental lung injury. We conclude that PKC, most likely PKC-alpha, is a primary supporter for lung endothelial injury in response to alpha-thrombin, TNF-alpha, and reactive oxygen species.

TNF-alpha enhances contraction and inhibits endothelial NO-cGMP relaxation in systemic vessels of pregnant rats

Tumor necrosis factor-alpha (TNF-alpha) is elevated in the plasma of preeclamptic women and may have a role in pregnancy-induced hypertension. However, whether the hemodynamic effects of TNF-alpha reflect the direct effects on vascular reactivity is unclear. We tested the hypothesis that TNF-alpha impairs endothelium-dependent relaxation and enhances vascular contraction in systemic vessels of pregnant rats. We measured isometric contraction in aortic strips isolated from virgin and pregnant Sprague-Dawley rats (nontreated vs. treated for 2 h with 10-1,000 pg/ml TNF-alpha). In endothelium-intact vascular strips, TNF-alpha caused greater enhancement of phenylephrine (Phe) contraction in pregnant than virgin rats. TNF-alpha caused significant inhibition of ACh- and bradykinin-induced vascular relaxation and nitrite/nitrate production that were more prominent in pregnant than virgin rats. N(G)-nitro-L-arginine methyl ester [L-NAME, 100 microM, an inhibitor of nitric oxide (NO) synthase] or 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 1 microM, an inhibitor of cGMP production in smooth muscle) inhibited ACh relaxation and enhanced Phe contraction in nontreated but to a lesser extent in TNF-alpha-treated vessels, particularly those of pregnant rats. Endothelium removal enhanced Phe contraction in nontreated but not TNF-alpha-treated vessels, especially those of pregnant rats. Relaxation of Phe contraction with the NO donor sodium nitroprusside was not different between nontreated and TNF-alpha-treated vessels. Thus TNF-alpha enhances vascular contraction and inhibits endothelium-dependent NO-cGMP-mediated vascular relaxation in systemic vessels, particularly those of pregnant rats. The results support a direct role for TNF-alpha as a possible mediator of increased vascular resistance associated with pregnancy-induced hypertension.

Down-modulation through protein kinase C-alpha of lipopolysaccharide-induced expression of membrane CD14 in mouse bone marrow granulocytes

We have previously shown that stimulation of mouse bone marrow granulocytes (BMC) by lipopolysaccharide (LPS) induces the expression of CD14. We found here that phorbol 12-myristate 13-acetate (PMA) blocks this LPS effect. The aim of this study was to investigate the mechanism by which PMA can block the LPS signaling pathway in BMC. The unmodified binding of a radiolabeled LPS in PMA-treated cells indicated that the PMA effect was not the consequence of a shedding or an internalization of the LPS receptor, but was rather due to a biochemical event that follows the interaction of LPS with its receptor. The observations that a selective activator of protein kinase C (PKC)-alpha (sapintoxin D) mimics the PMA effect, whereas a selective PKC-alpha inhibitor (Ro-320432) antagonizes this effect, suggest a regulatory role of PKC-alpha in the LPS signaling pathway in mouse BMC.

Protein kinase C-alpha mediates endothelial barrier dysfunction induced by TNF-alpha

We tested the hypothesis that protein kinase C-alpha (PKC-alpha) mediates tumor necrosis factor-alpha (TNF-alpha)-induced alterations in permeability of pulmonary microvessel endothelial monolayers (PEM). The permeability of PEM was assessed by the clearance rate of Evans blue-labeled albumin. PEM lysates were analyzed for PKC-alpha mRNA (Northern cDNA blot), protein (Western immunoblot), and activity (translocation and phosphorylation of myristoylated arginine-rich C kinase substrate). Incubation of PEM with TNF-alpha (1,000 U/ml) for 4 h resulted in increases in 1) PKC-alpha protein, 2) cytoskeletal-associated PKC-alpha, 3) PKC-alpha activity, and 4) permeability to albumin. The TNF-alpha-induced increase in PKC-alpha protein, PKC-alpha activity, and permeability was prevented by a 4-h pretreatment with PKC-alpha antisense oligonucleotide but not by the scrambled nonsense oligonucleotide. The TNF-alpha-induced increase in permeability to albumin was prevented by myristoylated protein kinase C inhibitor (an inhibitor of PKC-alpha/beta, 100 microM) and calphostin (an inhibitor of the classic and novel PKC isotypes, 200 nM). The treatment with calphostin from 0.5 to 3.0 h after TNF-alpha still prevented barrier dysfunction induced by 4 h of TNF-alpha treatment. The data indicate that prolonged activation of PKC-alpha, maintained by a translation-dependent pool of PKC-alpha protein, mediates TNF-alpha-induced increases in endothelial permeability in PEM.

The inflammatory cytokines tumor necrosis factor alpha and interleukin-1beta stimulate phosphatidylcholine secretion in primary cultures of rat type II pneumocytes

Tumor necrosis factor alpha and interleukin-1beta increase surfactant secretion in type II pneumocytes in a time- and dose-dependent manner. This stimulatory effect was additive to that of lipopolysaccharide, suggesting that cytokines and lipopolysaccharide may exert their actions through different signal transduction pathways. Tumor necrosis factor alpha and interleukin-1beta did not modify the increase on phosphatidylcholine secretion induced by the direct protein kinase C activator tetradecanoylphorbol 13-acetate, whereas this effect was inhibited by the protein kinase C inhibitors bisindolylmaleimide (2 x 10(-6) M) and 1-(5-isoquinolinylsulphonyl)-2-methyl piperazone (10(-4) M). In addition, the stimulatory effect of tumor necrosis factor alpha and interleukin-1beta was not suppressed by the intracellular Ca2+ chelator BAPTA (5 x 10(-6) M) or by KN-62 (3 x 10(-5) M), a specific inhibitor of Ca2+-calmodulin-dependent protein kinase. These results suggest that tumor necrosis factor alpha or interleukin-1beta stimulate phosphatidylcholine secretion via protein kinase C activation in a Ca2+-independent manner.