Protein kinase C-alpha regulates proliferation but not apoptosis in rat coronary vascular smooth muscle cells

In a previous study (Am. J. Pathol. 1994, 145: 1265-1270) we found rat coronary vascular smooth muscle cell (SMC) proliferation and apoptosis to be regulated by protein kinase C (PKC). In the present study we analysed whether selective depletion of alpha isozyme of PKC would affect SMC proliferation and/or apoptosis. First, using Western blot technique, it was determined that the rat SMC express alpha, delta, epsilon and zeta isozymes of PKC. The selective depletion of PKC-alpha in SMC was achieved by exposing cells to antisense oligodeoxynucleotide to mRNA for PKC-alpha (AS-PKC-alpha). The effect of AS-PKC-alpha on SMC proliferation was analysed by measurement of 3H-thymidine incorporation. The results indicated that a single dose of AS-PKC-alpha at a concentration of 10-100microM caused long-lasting (for at least 4 days) inhibition (up to 55%) of 3H-thymidine incorporation by SMC. This observation indirectly demonstrates that PKC-alpha regulates SMC proliferation. However, it was not possible to induce a significant level of apoptosis in SMC exposed even to the highest dose of AS-PKC-alpha. These data, in conjunction with the previously shown induction of apoptosis in SMC by calphostin C, suggests that another isozyme of PKC is likely to be involved in regulation of SMC apoptosis. Finally, we observed that induction of apoptosis via PKC-dependent mechanism is prevented by supplementing the culture medium with serum. This shows striking similarity with the regulation of apoptosis by the c-myc-dependent pathway. In conclusion, PKC-alpha joins the group of proteins such as c-myc, proliferating-cell nuclear antigen and cdc2 kinase which may be therapeutical targets, for antisense oligodeoxynucleotides, in order to prevent SMC hyperplasia.

Angiopeptin, a somatostatin-14 analogue, decreases adhesiveness of rat leukocytes to unstimulated and IL-1 beta-activated rat heart endothelial cells

We have previously demonstrated that somatostatin-14 and its octapeptide analogue, angiopeptin, decrease the ability of rat heart endothelial cells to bind leukocytes [Leszczynski, et al., Reg. Pept. 43 (1993) 131-140]. Here, we examined whether exposure of leukocytes to angiopeptin modifies their adhesiveness to the unstimulated and to IL-1 beta-activated endothelium. Monolayers of unstimulated endothelial cells bind 274 +/- 12 leukocytes/mm2. Exposure of leukocytes for 1, 4 and 24 hours to angiopeptin (1 microM) reduced significantly (p < 0.05) adhesion of leukocytes from 274 +/- 12 to 188 +/- 10, 185 +/- 8 and 172 +/- 3 cells/mm2, respectively. Stimulation of endothelial cells with Il-1 beta (100 U/ml) for 24 hours increased endothelial adhesiveness from 274 +/- 12 to 381 +/- 17 adhering leukocytes/mm2. Exposure of leukocytes for 1, 4 and 24 hours to angiopeptin (1 microM) reduced significantly (p < 0.05) binding of leukocytes to IL-1 beta-activated endothelium from 381 +/- 17 to 237 +/- 8, 254 +/- 11 and 248 +/- 13 cells/mm2, respectively. Angiopeptin had no effect on the expression of lymphocyte function-associated molecule-1 (LFA-1; CD11a/CD18) by leukocytes, as assessed by flow cytometry. This suggests that angiopeptin modulates adhesive properties of leukocytes by (1) altering the expression of other than LFA-1 adhesion molecule(s) and/or (2) modulating the affinity of adhesion molecule(s) expressed by leukocytes. In conclusion, our results demonstrate that angiopeptin reduces leukocyte adhesiveness to unstimulated and to IL-1 beta-activated endothelium. It suggests that angiopeptin may suppress immune response via modulation of the leukocyte-endothelial interaction.

Long-wave ultraviolet radiation causes increase of membrane-bound fraction of protein kinase C in rat myeloid leukemia cells

We examined the effect of long-wave ultraviolet radiation (UVA) on protein kinase C (PKC) and on the proliferation of rat myeloid leukemia cell line (ChL). Exposure of cells to a single dose of UVA (8 J/cm2 at 372 +/- 10 nm) caused a rapid increase in the quantity of the membrane-bound PKC, as assessed by 3H-phorbol ester (3H-PMA) binding assay (performed at 4 degrees C). Within 2 h of UVA irradiation, three peaks of increased 3H-PMA binding to the ChL cells (by 70-100%) were observed at ca. 20, 60 and 95 min post-irradiation. The exposure of ChL to UVA caused also a rapid, but transient, decline in the cell proliferation rate (by 18% within 24 h). However, the statistically significant decrease in cell numbers was observed only 3 days later (down by 22%). The inhibition of ChL proliferation was not due to alteration of cell viability as determined by trypan blue exclusion assay, and neither was it caused by cell cycle arrest or apoptosis, as determined by flow cytometry analysis of propidium iodide-labelled cells and cell morphology in May-Grünvald-Giemsa-stained cell smears. Phorbol-ester-induced activation of PKC (performed at 37 degrees C) caused inhibition of ChL proliferation similar to that caused by UVA. This suggests that a UVA-induced increase of the membrane-bound fraction of PKC may be responsible for the UVA-induced inhibition of ChL proliferation.

Apoptosis of vascular smooth muscle cells. Protein kinase C and oncoprotein Bcl-2 are involved in regulation of apoptosis in non-transformed rat vascular smooth muscle cells

We examined the effect of several inhibitors/activators of various protein kinases on the proliferation and apoptosis of nontransformed rat coronary vascular smooth muscle cells (SMC). As expected, all the compounds (calphostin C, KT5720, KT5823, verapamil, W7, and dibutyryl-cAMP) inhibited SMC proliferation, as judged by [3H]thymidine incorporation. Three (calphostin C, verapamil and dibutyryl-cAMP) of the six compounds caused occurrence of the classical apoptotic morphology in SMC. The effect of calphostin C, an inhibitor of protein kinase C, was examined in more detail due to the known involvement of this kinase in regulation of apoptosis in a variety of cell types. In SMC cultures exposed for 1, 2, and 3 days to 0.1 mumol/L calphostin C, 7 +/- 1%, 32 +/- 3%, and 29 +/- 3% of cells underwent apoptosis, respectively, as assessed by cell morphology (control cultures had 1 to 3% of apoptotic cells). The effect of calphostin C was transient in that on day 6 following exposure to this compound the number of apoptotic cells declined to control values. Simultaneous with the induction of apoptotic morphology in SMC, a decline was seen (within 24 hours) in expression of the oncoprotein Bcl-2 in morphologically nonapoptotic SMC. An altered distribution of Bcl-2 was seen in the apoptotic cells. The calphostin C-induced generation of apoptotic cells in SMC cultures and the decline/alteration of Bcl-2 expression were not accompanied by degradation of DNA into nucleosomal fragments. In conclusion, normal, nontransformed rat coronary artery vascular SMC undergo apoptosis when exposed to an inhibitor of protein kinase C (calphostin C), to a calcium channel blocker (verapamil), and to a stimulator of cAMP-dependent protein kinase (dibutyryl-cAMP). The induction of apoptosis by the inhibitor of protein kinase C is accompanied by alterations in the Bcl-2 expression but not by DNA fragmentation.

IL-1 beta-stimulated leucocyte-endothelial adhesion is regulated, in part, by the cyclic-GMP-dependent signal transduction pathway

It is well known that the exposure of endothelial cells to IL-1 beta induces an increase in endothelial cell adhesiveness for leucocytes. Using rat heart endothelial cells we found that exposure of endothelial cells to IL-1 beta (100 U/ml) induces a 133-fold increase in the intracellular concentration of cyclic-GMP; from 11.5 +/- 0.2 fM to 1530 +/- 117.8 fM (per 10(6) cells). Therefore, we examined whether cyclic-GMP is involved in the regulation of endothelial adhesiveness for leucocytes. Cyclic-GMP analogue, dibutyryl cyclic-GMP Methylene blue, an inhibitor of guanylate cyclaese, and KT5823, a specific inhibitor of cyclic-GMP-dependent protein kinase, inhibited both basal as well as IL-1 beta-induced endothelial cell adhesiveness for leucocytes, and KT5823 abolished the dibutyryl-cyclic-GMP-induced increase in endothelial adhesiveness. The effect of cyclic-GMP, induced by IL-1 beta treatment, on the endothelial adhesiveness may be either direct or indirect because of the time-gap between the rise in cyclic-GMP level and the increase of endothelial adhesiveness. IL-1 beta (100 U/ml) and dibutyryl-cyclic-GMP (0.01 mM) both induced an increase in the expression of intercellular adhesion molecule-1 by endothelial cells. However, the fact that KT5823 failed to prevent this increase, suggests that, although the IL-1 beta-induced increase in adhesiveness is caused by the increase in intracellular levels of cyclic-GMP, it may not be mediated through intercellular adhesion molecule-1. In conclusion, the results obtained indicate that endothelial cell adhesiveness for leucocytes is, in part, regulated by the cyclic-GMP-dependent signal transduction pathway.

Angiopeptin, the octapeptide analogue of somatostatin, decreases rat heart endothelial cell adhesiveness for mononuclear cells

The effect of angiopeptin, a stable analogue of somatostatin, was studied on basal and interleukin-1-beta-induced endothelial cell adhesiveness for mononuclear cells, and compared to the effect of somatostatin. Angiopeptin and somatostatin decreased basal and interleukin-1-beta-induced endothelial cell adhesiveness for mononuclear cells. The decreased mononuclear cells adhesion to endothelial cells exposed to angiopeptin and somatostatin is not due to modulation of the expression of intrecellular adhesion molecule-1 because neither angiopeptin nor somatostatin decreased basal and interleukin-1-beta-induced expression of this adhesion molecule. The effect of angiopeptin in inhibiting endothelial cell adhesiveness for mononuclear cells was abolished by addition of dibutyryl-cyclic AMP. Angiopeptin induced a transient decrease in basal and interleukin-1-beta-induced cyclic AMP levels in endothelial cells. Exposure of unstimulated and interleukin-1-beta-activated endothelial cells to KT5720, a specific inhibitor of cyclic AMP-dependent protein kinase, decreased endothelial cell adhesiveness for mononuclear cells. Thus, angiopeptin most likely diminishes endothelial adhesiveness for mononuclear cells by affecting the cyclic AMP-dependent protein kinase signal transduction pathway. The findings suggest that angiopeptin and somatostatin may modify the development of the immune response by attenuating endothelial cell adhesiveness for mononuclear cells. Angiopeptin may have a potential clinical application as a modulator of some aspects of the immune response due to its long half-life and prolonged inhibitory effect on interleukin-1-beta induced endothelial adhesiveness for mononuclear cells.

Direct and endothelial cell-mediated effect of cyclosporin A on the proliferation of rat smooth muscle cells in vitro

Cyclosporin A (CsA) has been suggested to potentiate graft vascular disease by stimulation of smooth muscle cell (SMC) proliferation. Both the in vitro and in vivo data are discordant, showing both stimulatory and inhibitory effects of CsA on vascular SMC proliferation. The direct and endothelial cell-mediated effects of CsA on vascular SMC proliferation were examined in vitro using the incorporation of [3H]thymidine. All experiments were done in serum-free conditions. The exposure of SMC to CsA (0.0001 to 0.1 micrograms/ml) had no effect on proliferation. High doses of CsA (0.5 to 10.0 micrograms/ml) were toxic to the SMC and endothelial cells; 90% of SMC population died within 3 to 6 days of exposure to 10.0 micrograms/ml CsA. In the studies on the endothelial cell-mediated effect of CsA, the endothelial cell-conditioned medium (ECCM) significantly increased SMC proliferation. This stimulatory effect was significantly attenuated when the ECCM was obtained from endothelial cells exposed to CsA. Endothelin (ET) is suggested to be an endothelial-cell-derived growth factor for SMC, and implicated as a possible cause of the uncontrolled proliferation of SMC during development of graft vascular disease. Exposure of SMC to levels of recombinant ET similar to the levels found in the ECCM (0.19 + 0.01 pg/ml) significantly increased SMC proliferation. CsA increased fivefold ET concentration in the ECCM. However, despite this rise in ET levels, there was a 45% decrease in SMC proliferation. In conclusion, CsA does not exert a direct modulatory effect on SMC proliferation in vitro, but may inhibit SMC proliferation indirectly via endothelial cell-derived factors. These unidentified factor(s) inhibit SMC proliferation and abolish the mitogenic effect of ET on SMC.

Rat heart smooth muscle cells express high and low affinity receptors for somatostatin-14, which are involved in regulation of cell proliferation

We demonstrate that rat heart coronary artery smooth muscle cells express specific binding sites (receptors) for somatostatin-14. The sigmoidal shape kinetics of the somatostatin-14 binding by the cells suggests the presence of either an allosteric binding site or binding sites with different affinities towards the ligand. Scatchard analysis reveals presence of high affinity (Kd = 0.039 x 10(-9)M) and low affinity (Kd = 0.602 x 10(-9)M) binding sites. Somatostatin-14 and Angiopeptin can displace each other from the binding sites. The concentrations of Angiopeptin required to displace 28%-48% of bound somatostatin-14 (10(-9)M) are in the range of 10(-4)-10(-3)M. The concentrations of somatostatin-14 required to displace 8-27% of bound Angiopeptin (10(-6)M) are in the range of 10(-6)-10(-5)M. Thus, somatostatin-14 seems to possess much higher binding affinity than Angiopeptin. Binding of somatostatin-14 and Angiopeptin to rat smooth muscle cells triggers intracellular event(s) leading to inhibition of smooth muscle cell proliferation. Exposure of smooth muscle cells to somatostatin-14 and Angiopeptin decreases amount of phosphorylated tyrosine residues. The effect of somatostatin-14 and Angiopeptin on the expression of phosphotyrosine precedes and is most likely responsible, at least in part, for the inhibition of smooth muscle cell proliferation. This demonstrates that rat heart smooth muscle cells express physiologically active receptor(s) for somatostatin-14.

Properties of B cells and Thy-1-antigen-expressing cells infiltrating rat renal allografts

We have examined (1) the frequency of B cells secreting antibodies against donor major histocompatibility complex (MHC) antigens and (2) the properties of Thy-1-antigen-expressing leukocytes in rats rejecting renal allografts. Our results show that B cells secreting antibodies are present in the inflammatory cell population at the frequency of 1:850. Among them only 1 out of 2-150 is engaged in production of antibodies directed to the graft MHC antigens, depending on the method of assay. This suggests that despite the observed significant production of nonspecific immunoglobulin in situ, only a minority of the B-cell population is specifically committed to the graft MHC antigens. This finding is concordant with the described previously low frequencies of the T cells specifically directed toward the graft MHC antigen. The role of the "immunologically noncommitted" cells in graft rejection is unknown. We have found that a substantial part (up to 60%) of inflammatory cells invading a rat kidney allograft express the Thy-1 antigen. This suggests that they might be immature (progenitor?) cells and, therefore, unable to respond to the graft antigens. Progenitor-like properties of these cells have been confirmed by their ability to reconstitute lethally irradiated syngeneic rat. Finally, these immature cells are of lymphoid, not of myeloid, linkage, because they do not proliferate in the presence of GM-CSF.

The frequency of B cells secreting antibodies against donor MHC antigens in rats rejecting renal allografts

We have estimated the frequency of B cells secreting antibodies against donor MHC antigens in rats rejecting histoincompatible renal allografts. In a major plus minor antigen-incompatible DA-to-WF combination on day 4 post-transplantation, reverse protein A plaque assay demonstrated that in the graft the frequency of lymphoid cells secreting Ig was 1:850. A major locus-incompatible and minor locus-compatible, congeneic LBN-to-Lewis strain combination was then applied to estimate the specificity of the secreted antibody. The lymphoid inflammatory cells were fused with mouse myeloma cells, cultured under limiting dilution conditions, and assayed by ELISA to donor and irrelevant strain spleen cells. Among cells infiltrating the graft, the fusion frequency was 1:172 x 10(3) and the frequency of Ig-producing hybrids 1:400 x 10(3) (i.e., this assay was approximately three log orders less sensitive than the reverse pA assay). The frequency of hybridomas secreting specifics antibodies against donor MHC antigens was 1:720 x 10(3) (i.e., every second hybridoma deriving from inflammatory population produced specific Ig). In addition, there was at least one obviously polyspecific population of hybridomas, detectable only in the spleen and reactive with all rat strains tested with a frequency of 1:700 x 10(3). The inflammatory cells were also cultured directly under limiting dilution conditions, and the frequency of Ig-secreting cells was determined by ELISA. The frequency of inflammatory lymphocytes secreting detectable amounts of immunoglobulin in the supernatant was 1:14 x 10(3) in the graft (i.e., this assay was approximately one log order less sensitive than the reverse protein A plaque assay).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of granulocyte-macrophage colony stimulating factor on endothelial antigenicity

We have investigated if recombinant granulocyte-macrophage colony stimulating factor (GM-CSF), alone or in concert with recombinant gamma interferon, affects the endothelial cell expression of class I major histocompatibility complex antigen. Results obtained show that the GM-CSF increases class I expression on the endothelial cell in a time- and dose-dependent manner. The effect of interferon gamma on class I expression is diminished in the presence of GM-CSF, cAMP, or prostaglandin E2, but is increased in the presence of cGMP. N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA 1004), an inhibitor of cAMP- and cGMP-dependent protein kinases, abolished GM-CSF-induced class I expression, while indomethacin increased it. When added to the endothelial cell cultures together with interferon gamma GM-CSF, HA 1004 as well as indomethacin abolished the inhibitory effect of GM-CSF on interferon gamma-induced class I expression. The results suggest that GM-CSF diminishes effect of interferon gamma on class I major histocompatibility complex expression on the endothelial cell by inducing production of rostacyclin. This, in turn, induces cAMP as a second messenger, which then leads to the events inhibiting expression of class I major histocompatibility complex antigen.

Protein kinase C-regulated production of prostacyclin by rat endothelium is increased in the presence of lipoxin A4

Prostacyclin is generated by cultured rat endothelial cells. Compound blocking activity of protein kinase C and cyclic nucleotide-dependent protein kinases (H7) and compound blocking interaction between Ca2+ and calmodulin (W7) diminish generation of prostacyclin in rat endothelial cells. These compounds give a synergistic effect when they are introduced to the endothelial cell cultures simultaneously. Compound HA1004, an inhibitor of cAMP- and cGMP-dependent protein kinases has no effect on prostacyclin generation. Lipoxin A4, a potent direct stimulator of protein kinase C, rapidly induces prostacyclin generation in rat endothelium in a dose- and time-dependent fashion. Lipoxin A4-induced generation of prostacyclin can be inhibited by H7 and W7 but not by HA1004. Lipoxin B4 has no significant effect on prostacyclin generation in rat endothelium. In conclusion, our results demonstrate that generation of prostacyclin by rat endothelial cells is regulated via a pathway involving protein kinase C and Ca2+.

Interleukin-1 alpha inhibits the effects of gamma-interferon and tumor necrosis factor alpha on the expression of the major histocompatibility antigens by the rat endothelium

Modulation of the major histocompatibility (MHC) antigen expression on rat endothelial cells by a mixture of cytokines has been examined. Experiments were performed employing both enzyme-linked immunoassay (ELISA) and fluorescence-activated cell-sorting (FACS) techniques and recombinant cytokines: interleukin-1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF alpha), and gamma-interferon (tau IFN). The results obtained show that TNF alpha enhances the effect of tau IFN on the expression of class I and II MHC antigens. IL-1 alpha did not affect tau IFN-induced class I expression but did inhibit tau IFN-induced class II expression. Finally, TNF alpha-induced class I MHC expression was inhibited strongly by IL-1 alpha. Pretreatment of endothelium with tau IFN did not potentiate the effects of IL-1 alpha or TNF alpha on the endothelial MHC antigen expression. These results suggest a possible anti-inflammatory role of IL-1 alpha via down-regulation of MHC antigen expression by the endothelium.

Local events in graft rejection

It appears that allograft rejections can be considered as a series of cellular and molecular cascades of inflammation triggered by the immune response. In acute rejection, inflammatory changes with a prominent blast cell component dominate. The main result is toxic damage of several parenchymal components, particularly the microvascular endothelium, resulting in necrosis of the parenchyma and loss of the allograft within days after transplantation. In the chronic type of rejection, inflammation also exists, but the major manifestations are different. Adventitial inflammation and perivascular cuffing of leukocytes result in concentric intimal proliferation and atherosclerosis. Very little experimental data exist, at present, on the mechanisms of transplant atherosclerosis and chronic rejection.

Eicosanoids are regulatory molecules in gamma-interferon-induced endothelial antigenicity and adherence for leucocytes

When the endothelial cells (ECs) were stimulated with gamma-interferon (gIFN) in the presence of methylprednisolone (MP) or prostaglandin E2 (PGE2), MP enhanced gIFN-induced Ia antigen expression, whereas PGE2 inhibited it. On the other hand, while PGE2 had no effect on leucocyte binding to ECs, MP entirely inhibited it. By using selective inhibitors of the cyclo-oxygenase pathway (indomethacin, IM) and the 5-lipoxygenase pathway (L651.392), we found that addition of IM to gIFN-stimulated ECs enhanced Ia expression but had no effect on leucocyte adherence to ECs. Instead, addition of L651.392 to gIFN-stimulated ECs partially reduced leucocyte adherence to ECs but had no effect on Ia expression. Pretreatment of the ECs or leucocytes or both with monoclonal anti-class II antibody, had no effect on gIFN-induced leucocyte binding to ECs. These findings suggest that gIFN-induced endothelial cell antigenicity and leucocyte adherence are regulated independently of each other by different molecular pathways. Moreover, arachidonic acid metabolites appear to be the regulatory molecules in gIFN effects on the ECs.

Leukotriene B4 increases the lymphocyte binding to endothelial cells

Leukotrienes are potent mediators of local microvascular environment. Leukotriene B4 treatment of cultured endothelium increases the binding of lymphocytes to endothelial cell monolayers within minutes. This effect is dose-dependent and reversible upon removal of the leukotriene. Pretreatment of lymphocytes slightly decreases the binding and pretreatment of both lymphocytes and endothelium with leukotriene B4 prior to the adherence assay did not alter the binding. These results suggest that leukotriene B4 regulates exclusively the vascular side, but not the white cell side of this interaction.