Transduction of the bradykinin response in human fibroblasts: prolonged elevation of diacylglycerol level and its correlation with protein kinase C activation

Bradykinin induces translocation of the protein kinase C isoforms alpha, epsilon, and zeta

Bradykinin exerts a broad spectrum of cellular effects on different tissues. It is believed that these effects are predominantly mediated by the recently cloned B2 receptor. The mechanism of post-receptor signal transduction is not known in detail. Involvement of protein kinase C (PKC) was suggested and activation of the classical PKC isoforms alpha and beta was recently demonstrated. The aim of the present study was to investigate whether the B2 receptor also activates new (delta, epsilon) and atypical (zeta) PKC isoforms. To investigate this, chinese hamster ovary (CHO) cells, stably transfected with human B2 receptor, were used. In these cells the PKC isoforms alpha, delta, epsilon and zeta were detected by immunoblotting with specific antibodies. To monitor hormone-induced PKC translocation plasma membranes were prepared. Stimulation of the cells with bradykinin resulted in a rapid (30-60 s) translocation of the PKC isoforms alpha, epsilon, and zeta. Translocation of PKC delta was not detected. The effect of bradykinin was reduced by simultaneous addition of the receptor antagonist HOE 140, a bradykinin-related decapeptide. The data show that the B2 receptor in this cell model is able to activate, in addition to the classical PKC isoform alpha, the new PKC isoform epsilon and the atypical PKC isoform zeta. To test whether these effects are as well observed in a non-transfected cell, the experiments were repeated in human foreskin fibroblasts which naturally express high levels of B2 receptors. In this cell system similar results on PKC alpha, epsilon, and zeta were observed, suggesting that all three PKC isoforms are involved in signal transduction of the B2 receptor.

Bradykinin and angiotensin II: activation of protein kinase C in arterial smooth muscle

The effects of bradykinin (BK) and angiotensin II (ANG II) were compared in cultured rat mesenteric arterial smooth muscle cells. BK and ANG II activated a phosphoinositide-specific phospholipase C, leading to the rapid release of [3H]inositol phosphates, an increase in intracellular calcium, and formation of sn-1,2-diacylglycerol (DAG). DAG formation was biphasic with a transient peak at 5 s followed by a sustained increase from 60 to 600 s. The BK-mediated increases in inositol triphosphate and DAG were dose dependent with half-maximal increases at concentrations of 5 and 2 nM, respectively. Both hormones were found to activate protein kinase C (PKC) as assessed by phosphorylation of the 68- to 72-kDa intracellular PKC substrate myristoylated alanine-rich C kinase substrate. However, despite similar phosphorylation of this substrate, only ANG II produced a significant increase in membrane-bound PKC activity. The mechanism accounting for the inability of BK to increase membrane-bound PKC activity is unclear. Our studies excluded differential translocation of PKC to the nuclear membrane, production of an inhibitor of membrane-bound PKC activity, and expression of BK and ANG II receptors on different cells as the mechanism. Vascular smooth muscle cells were found to express at least four different PKC isozymes: alpha, delta, zeta, and a faint band for epsilon. All of the isozymes except zeta-PKC were translocated by treatment with the phorbol ester 4 beta-phorbol 12-myristate 13-acetate. However, neither ANG II nor BK produced significant translocation of any measured isozyme; therefore, we could not exclude the possibility that ANG II and BK activate different isozymes of PKC. Both hormones were found to have a similar small and inconsistent effect in stimulating [3H]thymidine incorporation. These observations demonstrate that BK and ANG II have similar biochemical effects on vascular smooth muscle cells and imply that, in selected vessels, the vasodilatory effects of BK mediated by the endothelium may be partially counterbalanced by a vasoconstrictor effect on the underlying vascular smooth muscle cells.

Long-term action of lithium: a role for transcriptional and posttranscriptional factors regulated by protein kinase C

Lithium, a simple monovalent cation, represents one of psychiatry's most important treatments and is the most effective treatment for reducing both the frequency and severity of recurrent affective episodes. Despite extensive research, the underlying biologic basis for the therapeutic efficacy this drug remains unknown, and in recent years, research has focused on signal transduction pathways to explain lithium's efficacy in treating both poles of manic-depressive illness. Critical to attributions of therapeutic relevance to any observed biochemical effect, however, is the observation that the characteristic prophylactic action of lithium in stabilizing the profound mood cycling of bipolar disorder requires a lag period for onset and is not immediately reversed upon discontinuation of treatment. Biochemical changes requiring such prolonged administration of a drug suggest alterations at the genomic level but, until recently, little has been known about the transcriptional and posttranscriptional factors regulated by chronic drug treatment, although long-term changes in neuronal synaptic function are known to be dependent upon the selective regulation of gene expression. In this paper, we will present evidence to show that chronic lithium exerts significant transcriptional and posttranscriptional effects, and that these actions of lithium may be mediated via protein kinase C (PKC)-induced alterations in nuclear transcription regulatory factors responsible for modulating the expression of proteins involved in long-term neural plasticity and cellular response. Such target sites for chronic lithium may help unravel the processes by which a simple monovalent cation can produce a long-term stabilization of mood in individuals vulnerable to bipolar illness.

Diacylglycerol: formation and function in phospholipid-mediated signal transduction

1. Properties, distribution and multiplicity of phosphoinositidases (phospholipase C, PLC) are investigated. 2. Generation of diacylglycerol (DAG) by a variety of enzymes such as phosphoinositide and phosphatidylcholine specific PLC, by a combination of phospholipase D and phosphatidic hydrolase, and by triglyceride lipase is examined. 3. Ca2+ and phospholipid-dependent protein kinase C act as the target of DAG messenger action. 4. There are differences in the formation of DAG in normal and transformal cell.

Oxidant and angiotensin II-induced subcellular translocation of protein kinase C in pulmonary artery endothelial cells

We recently reported that nitrogen dioxide (NO2), an environmental oxidant, alters the dynamics of the plasma membrane lipid bilayer structure, resulting in increased phosphatidylserine content and angiotensin II (Ang II) receptor binding. Angiotensin II is known to elicit receptor-mediated stimulation of diacylglycerol (DAG) production in pulmonary artery endothelial cells. Because protein kinase C (PKC) is a phosphatidylserine-dependent enzyme and is activated by DAG, we examined whether NO2 resulted in activation and/or translocation of PKC from predominantly cytosolic to membrane fractions of these cells. We also evaluated whether NO2 exposure resulted in increased production of DAG in pulmonary artery endothelial cells. Exposure to 5 ppm NO2 for 1-24 hr resulted in significant increases in PKC activity in the cytosolic and membrane fractions (p less than 0.05 for both fractions) compared to activities in control fractions. Exposure to Ang II resulted in translocation of PKC activity from cytosol to membrane fractions of both control and NO2-exposed cells. This translocation of PKC from cytosolic to membrane fraction was prevented by the specific receptor antagonist [Sar1 Ile8] Ang II. Exposure of 5 ppm NO2 for 1-24 hr provoked rapid increases in [3H]glycerol labeling of DAG in pulmonary artery endothelial cells. These results demonstrate that exposure to NO2 increases the production of second messenger DAG and activates PKC in both the cytosolic and membrane fractions, whereas Ang II stimulates the redistribution of PKC from cytosolic to membrane fractions of pulmonary artery endothelial cells.