Prolactin induces proliferation of vascular smooth muscle cells through a protein kinase C-dependent mechanism

The effects of prolactin (PRL) on A10 (aortic smooth muscle) cell proliferation were examined by measuring both [3H]thymidine incorporation and increases in cell number. PRL induced a significant proliferative response from 10(-11) to 10(-7) M, with optimal activity at 10(-10) M. PRL also enhanced platelet-derived growth factor (PDGF)-induced proliferation. The possibility that PRL induces proliferation through a protein kinase C (PKC)-mediated mechanism was also examined. PRL caused activation of PKC from 10(-12) to 10(-8) M. Antiserum to PRL, a monoclonal antibody directed against the PRL receptor and the immunosuppressive agent cyclosporine A, were able to inhibit PRL-induced proliferation and activation of PKC. The PKC inhibitors, staurosporine, sphingosine, and 1-(-5-iso-quinoline-sulfonyl)-2-methylpiperazine (H-7) also antagonized both proliferation and PKC activation. These data strongly suggest that PRL-induced A10 cell proliferation is mediated through the PKC pathway and that this may play a role in vascular smooth muscle cell hyperplasia, characteristic of the pathogenesis of cardiovascular diseases such as hypertension and atherosclerosis.     

Prolactin-dependent mitogenesis in Nb 2 node lymphoma cells: effects of immunosuppressive cyclopeptides

Prolactin (PRL)-stimulated ornithine decarboxylase (ODC) activity and subsequent proliferation are inhibited by the cyclopeptides cyclosporine (CsA) and didemnin B (DB) in Nb 2 node lymphoma cells. Similar concentrations of these agents also inhibit 125I-PRL binding, suggesting that their inhibitory effects on these PRL-dependent physiologic responses are mediated at least in part at the level of PRL receptor interactions. The phorbol ester TPA stimulated ODC activity and [3H]thymidine incorporation to 54% and 31% that of a near-optimal mitogenic concentration of PRL (10 ng/ml), suggesting that mitogenesis in these cells is coupled to some degree to the activation of protein kinase C (PKC). The calcium ionophore A23187 increased ODC activity only slightly and actually decreased [3H]thymidine incorporation to a value below the "cells only" controls. The addition of TPA plus A23187 did not further enhance the effects of TPA to elevate ODC activity and [3H]thymidine incorporation. However, A23187 significantly elevated PRL-stimulated ODC activity with a subsequent inhibition of [3H]thymidine incorporation, suggesting a block of entry into S phase. Both cyclopeptides decreased the elevation of ODC activity in G1 phase of cell cycle in response to PRL, suggestive of a site of action for these agents in early G1, a conclusion compatible with their ability to inhibit PRL binding to these cells. Addition of CsA or DB 2 hr after PRL had no effect on PRL-stimulated ODC activity detectable at 6 hr, but addition of either as late as 6 hr still affected the extent of mitogenesis. This is in line with the requirement for PRL to be present in the culture medium for a minimum of 3 to 6 hr to invoke a maximal effect on mitogenesis. Addition of either cyclopeptide after the cells were in S phase had no effect on the extent of [3H]thymidine incorporation. An inhibitor of the cyclooxygenase pathway (indomethacin) enhanced both PRL-stimulated ODC activity and proliferation, whereas inhibition of the lipoxygenase pathway by NDGA attenuated only proliferation, suggesting that in Nb 2 cells, products of the lipoxygenase pathway may contribute to the mechanism of PRL-stimulated mitogenesis. Because Nb 2 lymphoma cells were derived from estrogenized rats, estrogen was tested as a mitogen. By itself it was not mitogenic, but in conjunction with PRL, estradiol-17 beta elevated the ODC response and inhibited proliferation. Inhibitors of PKC known to have minimal effects on RNA synthesis, quercetin and gossypol, totally inhibited both the elevations of ODC activity and [3H]thymidine incorporation in response to PRL in Nb 2 lymphoma cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Signalling events mediating the activation of protein kinase C by interleukin-2 in cytotoxic T cells.

Interleukin-2 (IL-2) plays a vital role in the generation and regulation of the immune response, including important aspects of T cell survival. IL-2-mediated survival of T cells appears to be dependent on the activation of a pool of membrane-associated protein kinase C (PKC) that occurs in the absence of detectable translocation of the enzyme from the cytosol to membranes. In this report we investigate the mechanism(s) responsible for this PKC activation after IL-2 stimulation in the cytotoxic T cell line, CTLL-2. Tyrosine kinase activity, activated after IL-2 stimulation, was found not to be linked to the activation of PKC by the cytokine. On the other hand, a pertussis toxin (PTX)-sensitive G protein did appear coupled to PKC activation since PTX effectively blocked IL-2 stimulated PKC activity. Diacylglycerols (DAG), but not inositol 1,3,5-triphosphate (IP3) and intracellular Ca2+, increased after IL-2 stimulation suggesting that DAGs were generated via the phosphatidylcholine-phospholipase C (PC-PLC) or phosphatidylcholine-phospholipase D (PC-PLD) pathways. The increase in DAG by IL-2 was probably necessary for activation of membrane-resident PKC since exogenously applied DAG stimulated this PKC pool in both intact cells and in isolated membranes. IL-2 also increased arachidonic acid (AA) production in CTLL-2 cells, probably via phospholipase A2 (PLA2) since the PLA2 inhibitors oleoyloxyethyl phosphocholine and AACOCF3 (AACF) effectively blocked IL-2 stimulated PKC activation. Exogenous AA also increased PKC activity in intact cells and isolated membranes, suggesting that AA produced by IL-2 receptor stimulation was probably linked to PKC activation. These results suggest that the activation of membrane-resident PKC by IL-2 involves multiple second messengers, including G proteins, DAG and AA.     

Entamoeba invadens: Sphingolipids metabolic regulation is the main component of a PKC signaling pathway in controlling cell growth and proliferation

The sphingolipids biosynthesis pathway generates bioactive molecules crucial to the regulation of physiological processes. We have recently reported that DAG (diacylglycerol) generated during sphingomyelin synthesis, plays an important role in PKC (protein kinase C) activation, necessary for the transit through the cell cycle (G1 to S transition) and cell proliferation (Cerbon and Lopez-Sanchez, 2003. Diacylglycerol generated during sphingomyelin synthesis is involved in protein kinase C activation and cell proliferation in Madin-Darby canine kidney cells. Biochem. J. 373, 917-924). Since pathogenic Entamoeba invadens synthesize the sphingolipids inositol-phosphate ceramide (IPC) and ethanolamine-phosphate ceramide (EPC) as well as sphingomyelin (SM), we decided to investigate when during growth initiation, the synthesis of sphingolipids takes place, DAG is generated and PKC is activated. We found that during the first 6 h of incubation there was a significant increase in the synthesis of all three sphingolipids, accompanied by a progressive increment (up to 4-fold) in the level of DAG, and particulate PKC activity was increased 4-8 times. The enhanced DAG levels coincided with decrements in the levels of sphingoid bases, conditions adequate for the activation of PKC. Moreover, we found that inhibition of sphingolipid synthesis with myriocin, specific inhibitor of the synthesis of sphinganine, reduce DAG generation, PKC activation and cell proliferation. All these inhibitory processes were restored by metabolic complementation with exogenous d-erythrosphingosine, indicating that the DAG generated during sphingolipid synthesis was necessary for PKC activation and cell proliferation. Also, we show that PI (phosphatidylinositol), PE (phosphatidylethanolamine) and PC (phosphatidylcholine) are the precursors of their respective sphingolipids (IPC, EPC and SM), and therefore sources of DAG to activate PKC.     

Regulation of sn-1,2-diacylglycerol second-messenger formation in thrombin-stimulated human platelets. Potentiation by protein kinase C inhibitors.

Stimulation of platelets with thrombin leads to rapid degradation of inositol phospholipids, generation of diacylglycerol (DAG) and subsequent activation of protein kinase C (PKC). Previous studies indicated that prior activation of PKC with phorbol myristate acetate (PMA) desensitizes platelets to thrombin stimulation, as indicated by a decreased production of inositol phosphates and decreased Ca2+ mobilization. This suggests that PKC activation generates negative-feedback signals, which limit the phosphoinositide response. To test this hypothesis further, we examined the effects of PKC activators and inhibitors on thrombin-stimulated DAG mass formation in platelets. Pretreatment with PMA abolishes thrombin-stimulated DAG formation (50% inhibition at 60 nM). Pretreatment of platelets with the PKC inhibitors K252a or staurosporine potentiates DAG production in response to thrombin (3-4-fold) when using concentrations required to inhibit platelet PKC (1-10 microM). K252a does not inhibit phosphorylation of endogenous DAG or phosphorylation of a cell-permeant DAG in unstimulated platelets, indicating that DAG over-production is not due to inhibition of DAG kinase. Sphingosine, a PKC inhibitor with a different mechanism of action, also potentiates DAG formation in response to thrombin. Several lines of evidence indicate that DAG formation under the conditions employed occurs predominantly by phosphoinositide (and not phosphatidylcholine) hydrolysis: (1) PMA alone does not elicit DAG formation, but inhibits agonist-stimulated DAG formation; (2) thrombin-stimulated DAG formation is inhibited by neomycin (1-10 mM) but not by the phosphatidate phosphohydrolase inhibitor propranolol; and (3) no metabolism of radiolabelled phosphatidylcholine was observed upon stimulation by thrombin or PMA. These data provide strong support for a role of PKC in limiting the extent of platelet phosphoinositide hydrolysis.     

IFN-gamma induces a phospholipase D dependent triphasic activation of protein kinase C in endothelial cells.

The IFN-gamma linked PKC activation in endothelial cells was analysed. It was shown that IFN-gamma activates PKC in three transient and separate cycles within the first 60 minutes after IFN-gamma stimulation. Before each PKC activation there was an increase in DAG level. IP3, phosphocholine and choline productions were measured to determine the origin of DAG. Neither of the PLC products, IP3 or phosphocholine, were released after IFN-gamma stimulation. On the other hand the PLD products choline and PA were released before all the three activation cycles of PKC.     

PDGF initiates two distinct phases of protein kinase C activity that make unequal contributions to the G0 to S transition

BACKGROUND: Platelet-derived growth factor (PDGF) promotes cell-cycle progression by engaging signaling enzymes such as phospholipase Cgamma (PLCgamma). When activated, PLCgamma cleaves phosphatidylinositol-4,5-bisphosphate to produce inositol-1,4, 5-trisphosphate (IP(3)) and diacylglycerol (DAG). IP(3) stimulates the release of calcium from intracellular stores, which together with DAG activate some protein kinase C (PKC) family members. In this study we focused on putative downstream effectors of PLCgamma - PKC family members. We investigated whether, and when, DAG-responsive PKCs contribute to PDGF-dependent DNA synthesis. RESULTS: In HepG2 cells expressing wild-type PDGF beta receptors (betaPDGFRs), PDGF activated at least one PKC family member (PKCepsilon) at two distinct times - within 10 minutes after PDGF stimulation, and then for a longer duration between 5 and 9 hours. Blocking the early burst of PKC activity had no effect on PDGF-dependent DNA synthesis. In contrast, the DNA-synthesis response was reduced by 60-80% when the second phase of PKC activity was blocked. Similarly, DAG rescued PDGF-dependent DNA synthesis in the cells expressing a mitogenically incompetent mutant betaPDGFR, but only when DAG was added at times corresponding to the late phase of PKC activity. Our studies also indicate that the late phase of PKCepsilon activity can be induced by either phosphoinositide 3-kinase-dependent or DAG-dependent pathways in PDGF-stimulated HepG2 cells. CONCLUSIONS: We conclude that PDGF activates PKCs at two distinct times and that these two intervals of PKC activity make unequal contributions to the mitogenic response. The late phase of PKC activity is required for PDGF-dependent DNA synthesis, whereas the early phase of activity is dispensable.     

Ceramide does not inhibit protein kinase C beta-dependent phospholipase D activity stimulated by anti-Fas monoclonal antibody in A20 cells

We have investigated the roles of ceramide in Fas signalling leading to phospholipase D (PLD) activation in A20 cells. Upon stimulation of Fas signalling by anti-Fas monoclonal antibody, sphingomyelin hydrolysis and activation of PLD were induced. Also, the translocation of protein kinase C (PKC) betaI and betaII and the elevation of diacylglycerol (DAG) content were induced by Fas cross-linking. When phosphatidylcholine-specific phospholipase C (PC-PLC) was inhibited by D609, the Fas-induced changes in PLD activity, DAG content, and PKC translocation were inhibited. In contrast, D609 had no effect on Fas-induced alterations in sphingolipid metabolism, suggesting that changes in ceramide content do not account for Fas-induced PLD activation. Furthermore, C6-ceramide had no effect on Fas-induced PLD activation and PKC translocation. Taken together, these data might suggest that ceramide generated by Fas cross-linking does not affect PKC beta-dependent PLD activity stimulated by anti-Fas monoclonal antibody in A20 cells.     

New insights into the regulation of protein kinase C and novel phorbol ester receptors.

Protein kinase C (PKC), a family of related serine-threonine kinases, is a key player in the cellular responses mediated by the second messenger diacylglycerol (DAG) and the phorbol ester tumor promoters. The traditional view of PKCs as DAG/phospholipid-regulated proteins has expanded in the last few years by three seminal discoveries. First, PKC activity and maturation is controlled by autophosphorylation and transphosphorylation mechanisms, which includes phosphorylation of PKC isozymes by phosphoinositide-dependent protein kinases (PDKs) and tyrosine kinases. Second, PKC activity and localization are regulated by direct interaction with different types of interacting proteins. Protein-protein interactions are now recognized as important mechanisms that target individual PKCs to different intracellular compartments and confer selectivity by associating individual isozymes with specific substrates. Last, the discovery of novel phorbol ester receptors lacking kinase activity allows us to speculate that some of the biological responses elicited by phorbol esters or by activation of receptors coupled to elevation in DAG levels could be mediated by PKC-independent pathways.     

Mechanism of protein kinase C activation by phosphatidylinositol 4,5-bisphosphate.

The mechanism of protein kinase C (PKC) activation by phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-monophosphate (PIP), and phosphatidylinositol (PI) was investigated by using Triton X-100 mixed micellar methods. The activation of PKC by PIP2, for which maximal activity was 60% of that elicited by sn-1,2-diacyglycerol (DAG), was similar to activation by DAG in several respects: (1) activation by PIP2 and DAG required phosphatidylserine (PS) as a phospholipid cofactor, (2) PIP2 and DAG reduced the concentration of Ca2+ and PS required for activation, (3) the concentration dependences of activation by PIP2 and DAG depended on the concentration of PS, and (4) PIP2 and DAG complemented one another to achieve maximal activation. On the other hand, PIP2 activation of PKC differed from activation by DAG in several respects. With increasing concentrations of PIP2, (1) the optimal concentration of PS required was constant at 12 mol%, (2) the maximal activity at 12 mol% PS increased, and (3) the cooperativity for PS decreased. PIP2 did not inhibit [3H]phorbol 12,13-dibutyrate (PDBu) binding of PKC at saturating levels of PS; however, at subsaturating levels of PS, PIP2 enhanced [3H]PDBu binding by acting as a phospholipid cofactor. PIP did not function as an activator but served as a phospholipid cofactor in the presence of PS. While PIP2, PIP, and PI did not support DAG-dependent PKC activation as phospholipid cofactors, their presence reduced the amount of PS required for maximal activation to as low as 2 mol% from 8 mol%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endothelin-1 activates phospholipase D and thymidine incorporation in fibroblasts overexpressing protein kinase C beta 1.

Endothelins (ETs) are a family of extremely potent vasoconstrictor peptides. In addition, ET-1 acts as a potent mitogen and activates phospholipase C in smooth muscle cells and fibroblasts. We examined the effects of ET-1 on phosphatidylcholine (PC) metabolism and thymidine incorporation in control Rat-6 fibroblasts and in cells that overexpress protein kinase C beta 1 (PKC). PC pools were labeled with [3H]myristic acid, and formation of phosphatidylethanol (PEt), an unambiguous marker of phospholipase D (PLD) activation, was monitored. ET-1 stimulated much greater PEt formation in the PKC overexpressing cells. ET-1 action was dose-dependent with a half-maximal effect at 1.0 x 10(-9) M. With increasing ethanol concentrations, [3H]PEt formation increased at the expense of [3H]phosphatidic acid (PA). Propranolol, an inhibitor of PA phosphohydrolase, increased [3H]PA accumulation and decreased [3H]diacylglycerol (DAG) formation. These data are consistent with the formation of [3H]DAG from PC by the sequential action of PLD and PA phosphohydrolase. Phorbol esters are known to stimulate thymidine incorporation and PLD activity to a greater extent in PKC overexpressing cells than in control cells. ET-1 also stimulates thymidine incorporation to a greater extent in the PKC overexpressing cells. The effect of ET-1 on thymidine incorporation into DNA in the overexpressing cells was also dose-dependent with a half-maximal effect at 0.3 x 10(-9) M. Enhanced PLD activity induced by ET-1 in the overexpressing cells may contribute to the mitogenic response, especially in light of a possible role of the PLD product, PA, in regulation of cell growth.     

Role of diacylglycerol (DAG) in hormonal induction of S phase in hepatocytes: The DAG-dependent protein kinase C pathway is not activated by epidermal growth factor (EGF), but is involved in mediating the enhancement of responsiveness to EGF by vasopressin,angiotensin II,and norepinephrine

The role of diacylglycerol (DAG) in hormonal induction of S phase was investigated in primary cultures of rat hepatocytes. In this model, several agonists that bind to G protein-coupled receptors act as comitogens when added to the cells soon after plating (i.e., in G_o/early G_l phase), while the cells are most responsive to the mitogenic effect of epidermal growth factor (EGF) at 24–48 h of culturing (i.e., mid/late G_l). It was found that the cellular concentration of DAG rose markedly and progressively during the first 24 h of culturing. Exposure of the hepatocytes at 3 h to α_l-adrenergic stimulation (norepinephrine with timolol), vasopressin, or angiotensin II further increased this rise, producing a sustained increase in the DAG level. Norepinephrine, which was the most efficient comitogen, produced the most prolonged DAG elevation. In contrast, no significant increase of DAG was found in response to EGF, neither at 3 nor at 24 h, using concentrations that markedly stimulated the ERK subgroup of the mitogen-activated protein kinases (MAPK) and DNA synthesis. Addition of Bacillus cereus phosphatidylcholine-specific phospholipase C (PC-PLC) strongly elevated DAG, while Streptomyces phospholipase D (PLD) increased phosphatidic acid (PA) but not DAG. B. cereus PC-PLC and the protein kinase C (PKC) activator tetradecanoyl phorbol-acetate (TPA), like norepinephrine, vasopressin, and angiotensin II, stimulated MAPK and enhanced the stimulatory effect of EGF on DNA synthesis. The PKC inhibitor GF109203X did not diminish the effect of EGF on MAPK or DNA synthesis, but strongly inhibited the effects of norepinephrine, vasopressin, angiotensin II, TPA and B. cereus PC-PLC on MAPK and almost abolished the enhancement by these agents of EGF-stimulated DNA synthesis. These results suggest that although generation of DAG is not a direct downstream response mediating the effects of the EGF receptor in hepatocytes, a sustained elevation of DAG with activation of PKC markedly increases the responsiveness to EGF. Mechanisms involving DAG and PKC seem to play a role in the comitogenic effects of various agents that bind to G protein-coupled receptors and activate the cells early in G_l, such as norepinephrine, angiotensin II, and vasopressin. J. Cell. Physiol. 180:203–214, 1999. © 1999 Wiley-Liss, Inc.     

Roles of phospholipase D in phorbol myristate acetate‐stimulated neutrophil respiratory burst

The phorbol myristate acetate (PMA) stimulated nutrophil respiratory burst has been considered to simply involve the activation of protein kinase C (PKC). However, the PLD activity was also increased by 10‐fold in human neutrophils stimulated with 100 nM PMA. Unexpectedly, U73122, an inhibitor of phospholipase C, was found to significantly inhibit PMA‐stimulated respiratory burst in human neutrophils. U73122 at the concentrations, which were sufficient to inhibit the respiratory burst completely, caused partial inhibition of the PLD activity but no inhibition on PKC translocation and activation, suggesting that PLD activity is also required in PMA‐stimulated respiratory burst. Using 1‐butanol, a PLD substrate, to block phosphatidic acid (PA) generation, the PMA‐stimulated neutrophil respiratory burst was also partially inhibited, further indicating that PLD activation, possibly its hydrolytic product PA and diacylglycerol (DAG), is involved in PMA‐stimulated respiratory burst. Since GF109203X, an inhibitor of PKC that could completely inhibit the respiratory burst in PMA‐stimulated neutrophils, also caused certain suppression of PLD activation, it may suggest that PLD activation in PMA‐stimulated neutrophils might be, to some extent, PKC dependent. To further study whether PLD contributes to the PMA stimulated respiratory burst through itself or its hydrolytic product, 1,2‐dioctanoyl‐sn‐glycerol, an analogue of DAG , was used to prime cells at low concentration, and it reversed the inhibition of PMA‐stimulated respiratory burst by U73122. The results indicate that U73122 may act as an inhibitor of PLD, and PLD activation is required in PMA‐stimulated respiratory burst.     

Ceramide does not inhibit protein kinase C β-dependent phospholipase D activity stimulated by anti-Fas monoclonal antibody in A20 cells

We have investigated the roles of ceramide in Fas signalling leading to phospholipase D (PLD) activation in A20 cells. Upon stimulation of Fas signalling by anti-Fas monoclonal antibody, sphingomyelin hydrolysis and activation of PLD were induced. Also, the translocation of protein kinase C (PKC) βI and βII and the elevation of diacylglycerol (DAG) content were induced by Fas cross-linking. When phosphatidylcholine-specific phospholipase C (PC-PLC) was inhibited by D609, the Fas-induced changes in PLD activity, DAG content, and PKC translocation were inhibited. In contrast, D609 had no effect on Fas-induced alterations in sphingolipid metabolism, suggesting that changes in ceramide content do not account for Fas-induced PLD activation. Furthermore, C6-ceramide had no effect on Fas-induced PLD activation and PKC translocation. Taken together, these data might suggest that ceramide generated by Fas cross-linking does not affect PKC β-dependent PLD activity stimulated by anti-Fas monoclonal antibody in A20 cells.     

Dual effect of prolactin on protein kinase C activity in CHO cells expressing functional prolactin receptors

We investigated the effects of prolactin (PRL) on the protein kinase C (PKC) activity in Chinese hamster ovary (CHO-E32) cells stably transfected with rabbit mammary gland PRL receptor cDNA. These cells express a functional long form of PRL-R. A 10-min to 2-hour treatment with 5 nM PRL resulted in the translocation of PKC activity from the cytosol to the membrane. Longer treatment (10–24 h) with the same concentration of PRL decreased the PKC activity in both particulate and cytoplasmic fractions. The PRL effect was dose dependent: maximal action was obtained with 1–10 nM. The PRL-induced activation of PKC was blocked by 20 nM staurosporine, a PKC inhibitor. Two inhibitors of tyrosine kinase, herbimycin A (1.75 µM) and genistein (100 µM), had no effect on PRL-induced activation of PKC.     

Mechanism of membrane redistribution of protein kinase C by its ATP-competitive inhibitors

ATP-competitive inhibitors of PKC (protein kinase C) such as the bisindolylmaleimide GF 109203X, which interact with the ATP-binding site in the PKC molecule, have also been shown to affect several redistribution events of PKC. However, the reason why these inhibitors affect the redistribution is still controversial. In the present study, using immunoblot analysis and GFP (green fluorescent protein)-tagged PKC, we showed that, at commonly used concentrations, these ATP-competitive inhibitors alone induced redistribution of DAG (diacylglycerol)-sensitive PKCalpha, PKCbetaII, PKCdelta and PKCepsilon, but not atypical PKCzeta, to the endomembrane or the plasma membrane. Studies with deletion and point mutants showed that the DAG-sensitive C1 domain of PKC was required for membrane redistribution by these inhibitors. Furthermore, membrane redistribution was prevented by the aminosteroid PLC (phospholipase C) inhibitor U-73122, although an ATP-competitive inhibitor had no significant effect on acute DAG generation. Immunoblot analysis showed that an ATP-competitive inhibitor enhanced cell-permeable DAG analogue- or phorbol-ester-induced translocation of endogenous PKC. Furthermore, these inhibitors also enhanced [3H]phorbol 12,13-dibutyrate binding to the cytosolic fractions from PKCalpha-GFP-overexpressing cells. These results clearly demonstrate that ATP-competitive inhibitors cause redistribution of DAG-sensitive PKCs to membranes containing endogenous DAG by altering the DAG sensitivity of PKC and support the idea that the inhibitors destabilize the closed conformation of PKC and make the C1 domain accessible to DAG. Most importantly, our findings provide novel insights for the interpretation of studies using ATP-competitive inhibitors, and, especially, suggest caution about the interpretation of the relationship between the redistribution and kinase activity of PKC.     

5—HT和NA增强大鼠骶髓后连合核神经元甘氨酸门控Cl^—通道电流由蛋白激...

用制霉菌素穿孔膜片钳方法研究５－ＨＴ和ＮＡ对急性分离的大鼠骶髓后连合核神经元甘氨酸门控氯离子通道电流（ＩＧｌｙ）的调控作用及其胞内机制。发现：（１）５－ＨＴ激活与非胰岛激活蛋白（ＩＡＰ）敏感型Ｇ蛋白偶联的５－ＨＴ２受体亚型,激活磷脂酶Ｃ（ＰＬＣ）,增加甘油二酯（ＤＡＧ）的生成。ＤＡＧ增强不依赖Ｃａ＾２＋的新型ＰＫＣ（ｎＰＫＣ）的活性,从而增强ＩＧｌｙ;（２）ＮＡ激活与ＩＡＰ敏感型Ｇ蛋白偶联的α２受     

Insights into the behavior of unsaturated diacylglycerols in mixed lipid bilayers in relation to protein kinase C activation—A molecular dynamics simulation study

The lipid second messenger diacylglycerol (DAG) is known for its involvement in many types of cellular signaling, especially as an endogenous agonist for protein kinase C (PKC). Evidence has emerged that the degree of saturation of the DAG molecules can affect PKC activation. DAG molecules with different acyl chain saturation have not only been observed to induce varying extents of PKC activation, but also to express selectivity towards different PKC isozymes. Both qualities are important for precise therapeutic activation of PKC; understanding DAG behavior at the molecular level in different environments has much potential in the development of drugs to target PKC. We used molecular dynamics simulations to study the behavior of two different unsaturated DAG species in lipid environments with varying degrees of unsaturation. We focus on phosphatidylethanolamine (PE) instead of phosphatidylcholine (PC) to more accurately model the relevant biomembranes. The effect of cholesterol (CHOL) on these systems was also explored. We found that both high level of unsaturation in the acyl chains of the DAG species and presence of CHOL in the surrounding membrane increase DAG molecule availability at the lipid–water interface. This can partially explain the previously observed differences in PKC activation strength and specificity, the complete mechanism is, however, likely to be more complex. Our simulations coupled with the current understanding of lipids highlight the need for more simulations of biologically accurate lipid environments in order to determine the correct correlations between molecular mechanisms and biological behavior when studying PKC activation.