Protein kinase C regulates MHC-class II expression on endothelial cells

IFN-gamma-induced MHC class II expression: transactivation of class II transactivator promoter IV by IFN regulatory factor-1 is regulated by protein kinase C-alpha

Previous studies based on pharmacological evidence suggested a requirement for protein kinase C (PKC) activity in the regulation of IFN-gamma-induced MHC class II (MHC-II) expression. In the present study, we investigated the molecular mechanisms by which PKC-alpha modulates IFN-gamma-induced MHC-II expression in the mouse macrophage cell line RAW 264.7. Overexpression of a dominant-negative (DN) mutant of PKC-alpha inhibited the expression of IFN-gamma-induced MHC-II but had no effect on IFN-gamma-induced STAT1 nuclear translocation and DNA binding activity, as well as on the expression of inducible NO synthase, IFN consensus sequence binding protein, MHC class I, IFN regulatory factor (IRF)-1, and IFN-gamma-inducible protein-10. Further analysis showed that IFN-gamma-induced expression of the MHC class II transactivator (CIITA), a transcriptional coactivator essential for MHC-II expression, was inhibited in DN PKC-alpha-overexpressing cells. Studies with reporter constructs containing the promoter IV region of CIITA revealed that overexpression of a constitutively active mutant of PKC-alpha enhanced IRF-1, but not IRF-2, transcriptional activity. Furthermore, characterization of IRF-1 from both normal and DN PKC-alpha-overexpressing cells revealed differences in IRF-1 posttranslational modifications. Collectively, our data suggest a novel regulatory mechanism for IFN-gamma-induced MHC-II expression, whereby PKC regulates CIITA expression by selectively modulating the transcriptional activity of IRF-1.

The granzyme B inhibitor, PI-9, is present in endothelial and mesothelial cells, suggesting that it protects bystander cells during immune responses

Proteinase inhibitor 9 (PI-9) is a 42-kDa human intracellular serpin present in cytotoxic lymphocytes (CLs). PI-9 is an extremely efficient inhibitor of the pro-apoptotic CL granule proteinase granzyme B and is thought to function in the cytosol of CLs to protect against apoptosis induced by endogenously expressed or released granzyme B, particularly during target cell killing. Here we show by immunohistochemistry that PI-9 is also present in endothelial cells, in every tissue examined. Cultured endothelial cells express functional PI-9 (as assessed by binding to recombinant granzyme B) localized to the cytoplasm and nucleus. Immunohistochemistry also showed PI-9 in mesothelial cells, and this was confirmed by analysis of primary cells cultured from pleural and serous effusions. Granzyme B expression was not detected in either endothelial or mesothelial cells. In both cell types, PI-9 is up-regulated at the mRNA and protein level by exposure to the phorbol ester PMA, consistent with a response to inflammatory stimuli. We postulate that PI-9 is present in these lining cell types to protect against misdirected, free granzyme B released during a local immune response.

The effects of the broadband UVA radiation on myeloid leukemia cells: the possible role of protein kinase C in mediation of UVA-induced effects

We examined the effects of broadband UVA radiation (320-400 nm) on a rat myeloid leukemia cell line-chloroma (ChL). A Phillips face tanner model HB 171/A was used as a light source. Chloroma were irradiated through a 5 mm thick glass filter that cut off all of the UVB contamination. The irradiances were measured, from 250 to 400 nm, with a well-characterized and calibrated double-grating spectroradiometer Optronic 742. The overall uncertainty of dose evaluation was estimated to be +/-15% (2 sigma). The cells were irradiated with UVA doses of 4 and 8 J/cm2 and cultured thereafter for 24 h. After this period of time, a marked decline up to 50% was observed in cell proliferation in UVA-irradiated ChL cultures. The cell proliferation decline was found to be caused by simultaneously occurring G2/M phase cell cycle arrest and apoptosis in part of the UVA-irradiated ChL population. Concomitantly, with the decline in cell proliferation, an increase was observed in the expression of the major histocompatibility (MHC) class I and II antigens. Because protein kinase C (PKC) is known to regulate cell proliferation, apoptosis and expression of MHC antigens, and because UVA was shown to regulate PKC activity/expression, we therefore examined whether UVA irradiation has any effect on the expression of isozymes of PKC. Western blots revealed that ChL express alpha, beta I, delta, epsilon, eta, and zeta/iota isozymes of PKC and that expression of all isozymes declined 24 h after UVA irradiation (8 J/cm2). Finally, PKC activation in ChL by exposure to phorbol ester caused cell cycle arrest in G1 phase but did not induce apoptosis. This suggests that the previously shown UVA-induced PKC activation in ChL might be responsible for the induction of MHC antigens but the simultaneously observed ChL apoptosis is likely to be mediated by PKC down-regulation. All together, our results suggest that UVA, at irradiance levels that resemble the outdoor exposure, may have profound effects on the immune-related properties of leukocytes. Thus, we speculate that in vivo the immune functions of leukocytes passing through dermal capillaries might be altered by exposure to solar UVA radiation.

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.

Invariant chain (CD74) gene regulation: enhanced expression associated with activation of protein kinase C delta in a murine B lymphoma cell line

The invariant chain (Ii, CD74) is a transmembrane glycoprotein that is transiently associated with the MHC class II antigens in the endoplasmic reticulum and in endocytic vesicles. An activator of protein kinase C (PKC), 12-O-tetradecanoyl-1,2-phorbol 13-acetate (TPA), was found to enhance expression of Ii mRNA in the murine B lymphoma cell line, A20, 6-48 hr following treatment. In contrast, TPA did not induce the Ii in NIH 3T3 fibroblasts. TPA addition to either cell line activated PKC. Pretreatment of A20 cells with the PKC inhibitors, staurosporine or chelerythrine chloride, for 5 or 20 min prior to addition of TPA, decreased Ii mRNA levels when compared to cells treated with TPA alone. A 20 min preincubation with the highly specific PKC inhibitor, calphostin C, completely blocked the TPA enhanced expression of the Ii suggesting that activation of PKC was responsible for TPA increased Ii mRNA levels. IFN-gamma also blocked the TPA increased Ii mRNA levels. Constitutive expression of Ii mRNA was decreased by treatment with staurosporine but not chelerythrine chloride or calphostin C, suggesting that non-PKC protein kinases may also be important for maintaining high levels of Ii mRNA in these cells. Western blot analysis using PKC isotype specific antibodies showed that A20 cells express PKC delta abundantly whereas NIH 3T3 cells express primarily PKC alpha. These data suggest that a PKC delta mediated signal transduction pathway plays a crucial role in up-regulation of the Ii.

Influence of ion channel modulation on in vitro interferon-gamma induced MHC class I and II expression on macrophages

The in vitro effect of K+ channel blockers quinidine and verapamil, anion channel blocker SITS and K+ channel openers diazoxide, pinacidil, and BRL 38227 on interferon-gamma (IFN-gamma) induced MHC class I and II expression of Lewis rat peritoneal macrophages was investigated by cell ELISA assay. MHC class I expression was significantly enhanced by diazoxide at concentrations of 10(-5)M to 10(-6)M and by pinacidil and BRL 38227 at the concentration of 10(-6)M. MHC class II expression was enhanced by pinacidil and BRL 38227 at concentrations of 10(-5)M to 10(-6)M. The enhancing effect of pinacidil could be blocked by inhibitors of the protein kinases PKA and PKC suggesting that activation of both is required for optimum induction of MHC molecule expression. K+ and anion channel blockers were less active in modulation of MHC molecule expression. Verapamil had no influence, quinidine suppressed MHC class I expression at concentrations of 10(-4)M to 10(-5)M, and SITS suppressed MHC class I expression at the concentration of 10(-3)M. Since MHC class II expression is essential for efficient antigen presentation to T helper cells and MHC class I expression is required for target cell lysis by cytotoxic T cells, ion channel modulating drugs may be potential candidates for immunopharmacological intervention in inflammatory diseases.

Alpha E beta 7 and alpha 4 beta 7 integrins associated with intraepithelial and mucosal homing, are expressed on macrophages

The two beta 7 integrins alpha E beta 7 and alpha 4 beta 7 are the most recently described members of the integrins participating in intercellular binding. Their expression has been shown to be restricted to leukocytes and they have been suggested to be predominantly found in lymphocytes associating with the epithelium. Expression of beta 7 has mainly been studied on lymphocytes whereas macrophages have been reported not to express the beta 7 integrins. In this paper we have studied the expression of beta 7 integrins in monocytoid cells. The myelomonocytic cell lines HL-60 and THP-1 did not express beta 7 mRNA or protein, but differentiation of these cell lines to macrophages with phorbol 12-myristate 13-acetate (PMA) led to a strong induction of the beta 7 mRNA expression. A clear but less pronounced up-regulation of beta 7 mRNA-expression was also seen after treatment of HL-60 and THP-1 cells with interferon-gamma (IFN-gamma). However, its up-regulating effect on the surface expression of alpha 4 beta 7 and alpha E beta 7 complexes (detected by the monoclonal antibodies Act I and HML-1, respectively) exceeded that observed with PMA. To verify the in vitro cell line observations with normal cells, we also studied peripheral blood monocytes and tissue macrophages. Peripheral blood monocytes were Act I- and HML-1- in flow cytometry, but their expression was increased after a 72-h culture in the presence of PMA or IFN-gamma. Also, several Act I+ and HML-1+ macrophages were found in immunohistochemical stainings of both liver and edemic lung biopsies as well as in lymph node sinuses. We therefore conclude that while monocytes do not express beta 7 integrins the more differentiated cells of the monocyte-macrophage lineage do express both the alpha 4 beta 7 and alpha E beta 7 integrins, which might play a role in their intraepithelial homing.

Enhanced ICAM-1-dependent adhesion of myelomonocytic cells expressing increased levels of beta 2-integrins and CD43

Interaction of ICAM-1 and its ligands plays an important role in the leukocyte binding to endothelium. The best characterized ICAM-ligands belong to the family of beta 2-integrins (CD11/CD18), but recently it has been suggested that CD43, a molecule with no structural resemblance to integrins binds ICAM-1 also. On the leukocytes the main regulatory pathway for ICAM-mediated binding is believed to be a short-term regulation of the avidity of CD11/CD18. In this study the authors investigated whether a quantitative increase in the surface expression of ICAM-ligands also can lead to enhanced binding to purified ICAM-1. PMA-treatment differentiates myelomonocytic cell lines into macrophages with a concomitant increase in the surface expression and mRNA-levels of the beta 2-integrin alpha- and beta-chains as well as that of CD43, another ICAM-ligand. The binding of the PMA-treated THP-1 cells to ICAM-1 was increased simultaneously compared to non-treated cells. The binding was blocked completely with antibodies to CD18 and ICAM-1. It is concluded that in addition to the transient qualitative regulation, a long-term quantitative regulation of ICAM-1 ligands also plays a role in increasing the adhesiveness of myelomonocytic cells. This may be relevant in chronic inflammation episodes.

Expression of six protein kinase C isotypes in endothelial cells

Protein kinase C (PKC) family is an important regulatory element in signal transduction, cellular regulation and tumor promotion. The classical PKC isotypes (alpha, beta and gamma) are Ca(2+)-dependent and can be activated by diacylglycerol. The novel isotypes, PKC delta, PKC epsilon, PKC eta (L) and PKC theta, are Ca(2+)-independent, whereas the two atypical PKCs (zeta and lambda) lack the Ca(2+)-binding region and are not activated by diacylglycerol. Here we show that cultured human endothelial cell line EA.hy926 as well as freshly isolated human umbilical vein endothelial cells express members of all PKC subfamilies. No traces of PKC gamma or delta were detected in endothelial cells. On the contrary the classical PKCs (alpha and beta), the novel PKC epsilon, as well as the atypical PKC zeta are present at the mRNA level in human endothelial cells and the corresponding proteins are also detected by immunoblotting.

Interferon-gamma induces a phospholipase D-dependent release of arachidonic acid from endothelial cell membranes: a mechanism for protein kinase C activation

Interferon-gamma (IFN-gamma) induces MHC class II expression on endothelial cells in a protein kinase C (PKC)-dependent manner. Here we show that IFN-gamma induces a sixfold arachidonic acid (AA) release from cultured rat microvascular endothelial cell membranes compared with non-treated cells. Since this result suggests that AA could act as a second messenger for IFN-gamma, we analysed its capacity to directly activate PKC. We have previously shown that IFN-gamma induces a transient, multiphasic activation of PKC via the action of the phospholipase D (PLD) pathway. Here we show that AA is able to activate PKC. In an attempt to characterize the source of the liberated AA after IFN-gamma induction in endothelial cells we used a panel of enzyme inhibitors. The IFN-gamma-induced release of AA could not be modified by interfering either with the phospholipase A2 (PLA2) pathway using bromophenacyl bromide (BPB), or with the phospholipase C (PLC) pathway using neomycin. The phosphatidic acid phosphatase (PAPase) inhibitor propranolol, inhibiting the generation of diacylglycerol (DAG) and further AA from phosphatidic acid (PA), could totally down-regulate the IFN-gamma-induced release of AA. Since PA is produced solely by the action of PLD from phosphatidylcholine (PC) we conclude that the AA originated from the cell membrane-associated PC. In summary, we show here that IFN-gamma causes the liberation of cell membrane-associated, PC-linked AA. This AA could directly activate PKC in a similar multiphasic manner to IFN-gamma, suggesting that it is a true second messenger for IFN-gamma in cultured endothelial cells.

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.

TNF alpha-induced expression of endothelial adhesion molecules, ICAM-1 and VCAM-1, is linked to protein kinase C activation

The role of protein kinase C (PKC) in TNF alpha-induced activation of endothelial adhesion molecules ICAM-1 and VCAM-1 was analysed. Phorbol myristate acetate, which is known to activate PKC, was able to mimic TNF alpha-induced up-regulation of ICAM-1 and partly also VCAM-1 expression. Similarly a PKC inhibitor, H7, but not another kinase inhibitor, HA1004, inhibited TNF alpha-induced enhancement of ICAM-1 expression at both the mRNA and the protein level. Moreover we were able to measure a transient PKC activation peak at 16 min after TNF alpha induction in endothelial cells analysed by phorbol-dibutyrate binding. These results indicate that the TNF alpha-induced effect on the regulation of endothelial adhesion molecule expression is at least partly mediated by PKC activation.