Activation of protein kinase C down-regulates IFN-gamma receptors

Proliferation and interferon-gamma receptor expression in psoriatic and healthy keratinocytes are influenced by interactions between keratinocytes and fibroblasts in a skin equivalent model

Epidermal-dermal interactions were studied in a skin equivalent model. Six combinations of keratinocytes and fibroblasts from healthy and psoriatic skin were used. TPA (12-O-tetradecanoylphorbol-13-acetate) was used to determine whether the expression of the IFN-gamma receptors in keratinocytes was related to epidermal differentiation and proliferation. These phenomena were assessed by immunohistochemistry. In all epidermal outgrowths, the epidermal growth factor receptor was expressed throughout the epidermis, cytokeratin 16 suprabasally, and filaggrin and involucrin in its superficial part. The IFN-gamma receptor was expressed throughout the epidermis, but was unevenly distributed. The expression of the IFN-gamma receptor was quantified by confocal laser scanning microscopy both in the whole of epidermis and in areas with the strongest intensity. The total amount varied to a minor degree in the epidermal outgrowths of different origins and was unaffected by TPA. In high-intensity areas interactions between keratinocytes and fibroblasts did influence the amount of IFN-gamma receptor expression and TPA decreased the expression by 13%. There was no correlation between the proliferation rate and the expression of the IFN-gamma receptor. Psoriatic and healthy keratinocytes were equally well differentiated in the skin equivalents. The interferon-gamma receptor was similarly expressed under these conditions. The growth rate, assessed by Ki-67-positive nuclei in the basal layer, was highest in healthy keratinocytes. Keratinocytes from psoriatic lesions increased their growth rate when cocultured with psoriatic fibroblasts compared with normal ones, indicating that fibroblasts may be of importance for epidermal hyperproliferation in psoriatic lesions.

Modulation of murine and human interferon-gamma receptor expression by their ligands or phorbol ester

IFN-gamma receptor expression on murine leukaemic L1210-cells has been studied. With the help of a transfected cell-line expressing the heterologous human receptor it was possible to discern receptor-specific properties like internalization from those regulating their expression on the surface. Recombinant IFN-gamma binds specifically to its homologous receptor at 4 degrees C and is rapidly internalized at physiologic temperatures. For this effect to occur, ligand binding to its receptor at 37 degrees C is necessary and sufficient. This notion is confirmed since a reduction in the number of heterologous human IFN-gamma receptors on the murine cell surface occurred exclusively after treatment with human IFN-gamma. Even weak doses of ligand, insufficient to occupy all receptors, led to a pronounced disappearance of binding sites. However, both receptors are simultaneously up-regulated in the presence of TPA, indicating a separate pathway which is not species-specific. Our findings imply that similar elements of the intracellular signal transduction machinery are involved in the control of MuIFN-gamma and HuIFN-gamma receptor expression. The results indicate also that factors involved in binding, internalization, and regulation of receptor gene expression are not species-specific.

Transduction of the IFN-gamma signal for HLA-DR expression in the promonocytic line THP-1 involves a late-acting PKC activity

Interferon gamma (IFN-gamma) is the most potent known lymphokine for activating macrophages and has been shown to induce expression of HLA-DR in THP-1 cells, a monocytic tumor cell line which expresses many of the properties of monocytes, in a dose- and time-dependent manner. Experiments were designed to examine, by FACS analysis and by measurement of messenger RNA levels, the molecular mechanism regulating the expression of HLA-DR molecules. The expression of HLA-DR molecules induced by IFN-gamma was blocked by the protein kinase C (PKC) inhibitors sphingosine, staurosporine, and H7. H7 when added up to 20 hr after the initial stimulation with IFN-gamma prevented the further expression of HLA-DR. The general kinase inhibitors H8, H9, and HA1004, all less potent PKC inhibitors than H7, did not block the IFN-gamma-induced expression of HLA-DR at the concentrations employed. W7, a calmodulin antagonist, but not a PKC inhibitor, was also unable to prevent the IFN-gamma-induced expression of HLA-DR. Treatment of THP-1 with phorbol 12-myristate 13-acetate (PMA), a direct activator of PKC, alone or with Ca2+ ionophore A23187, was unable to induce HLA-DR expression. However, pretreatment with PMA for 24 hr prior to IFN-gamma stimulation decreased the IFN-gamma-induced expression of HLA-DR without decreasing IFN-gamma receptor levels. These results suggest that PKC plays a significant role in the IFN-gamma-induced signal transduction pathway leading to the expression of HLA-DR in cells of the mononuclear phagocytic lineage, and that PKC activity is required throughout the course of events leading to the actual expression of HLA-DR.

Upregulation of interferon-gamma binding by tumor necrosis factor and lymphotoxin: disparate potencies of the cytokines and modulation of their effects by phorbol ester

Tumor necrosis factor (TNF) and interferon-gamma (IFN-gamma) are immune-modulating cytokines that exert synergistic cytotoxic effects in several types of tumor cells, including ASPC-1 human pancreatic carcinoma cells. Lymphotoxin (LT), is a cytokine that binds to the TNF receptor and mimicks most of the biological actions of TNF. In the present study, we examined ASPC-1 cells for cytokine-mediated modulation of TNF and IFN-gamma receptors. Treatment of ASPC-1 cells with recombinant human IFN-gamma (rhIFN-gamma) did not significantly alter 125I-rhTNF binding. In contrast, treatment with rhTNF led to a dose- and time-dependent increase in 125I-rhIFN-gamma binding and internalization. Scatchard analysis revealed that rhTNF increased the number of 125I-rhIFN-gamma binding sites from 11,000 sites/cell to 23,000 sites/cell without altering receptor affinity. Although rhLT also increased 125I-rhIFN-gamma binding, it was 100-fold less potent than rhTNF. In contrast, rhLT was only 10-fold less potent than rhTNF in displacing 125I-rhTNF from its receptor. The phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) blocked the rhLT- and rhTNF-mediated increase in 125I-rhIFN-gamma binding and markedly decreased 125I-rhTNF binding. These data suggest that both TNF and LT upregulate IFN-gamma receptors in ASPC-1 cells, but that LT is much less efficient than TNF. Further, the TPA-induced attenuation of IFN-gamma receptor upregulation suggests that protein kinase C activation can regulate the TNF/LT-mediated pathways involved in IFN-gamma receptor upregulation.

Effects of mitogenic agents upon glucocorticoid action in human tonsillar T-lymphocytes

The treatment of human tonsillar T-lymphocytes with 4-phorbol 12-myristate 13-acetate (PMA), resulted in about two fold increase in glucocorticoid receptor (GR) number, without any significant change in the receptor affinity. This increase disappeared in the presence of cycloheximide. Alone, PMA and calcium ionophore A23187 did not affect, but together stimulated, like phytohaemagglutinin (PHA), leucine and, in particular, thymidine incorporation. PMA enhanced slightly the stimulatory effect of PHA. Alone, these agents failed to alter the suppressive effect of dexamethasone on thymidine and leucine incorporation; however, PMA-A23187 and PMA-PHA combinations appeared to antagonize the suppression by dexamethasone.

Lymphokine signal transduction

Lymphokines are a group of signalling molecules involved in communication between cells, mainly those of the immune system. The lymphokines are multi-functional and most of them have mitogenic or co-mitogenic activity. An understanding of lymphokine biology is essential to understand how the immune system develops and functions and to provide a rationale for their use in immunotherapy. The potential to understand the cell biology of the lymphokines has recently become more apparent as molecular biological techniques have first of all produced recombinant factors and secondly have provided clues to the signal transduction pathways by cloning receptors, applying site-directed mutational analysis and also probing for specific promoters and enhancers that are activated along the signal pathway. This review discusses the information that has come from the recent analyses which blends with the biochemical analysis of the second messenger systems in an effort to understand the signalling pathways of the lymphokines.

Regulation of gene expression by tumor promoters

Tumor promoters change the program of genes expressed in cells in culture and in the multicellular organism. The growing list of genes that are induced or repressed includes protooncogenes, transcription factors, secreted proteases and viruses. Most of the regulation is at the level of transcription. Several of the cis-acting promoter elements mediating regulation, the transcription factors binding to these elements and their post-translational activation, as well as some of the initial steps of the interaction of cells with tumor promoters have been characterized. The components of the signal transduction chain to the nucleus are, however, still unknown. Mutant and inhibitor studies suggest that the activation or inactivation of certain genes constitute the basis for the development of the tumor promotion phenotype.

Interleukin 2, interleukin 2 receptor, and interferon-gamma synthesis and mRNA expression in phorbol myristate acetate and calcium ionophore A23187-stimulated T cells from elderly humans

The levels of interleukin 2 (IL-2), interleukin 2 receptor (IL-2R), and interferon-gamma (IFN-gamma) specific mRNA and their gene products were examined in phorbol myristate acetate (PMA) and calcium ionophore A23187-costimulated purified T cells from young and elderly humans. In addition, the number of high-affinity IL-2R per activated cell, the high-affinity IL-2R density, and the proliferative response of the cells were measured. Among PMA/A23187-stimulated T cells, there was no statistically significant age-related difference in IL-2 or IL-2R specific mRNA accumulation or in the amount of IL-2 or IL-2R synthesized. IFN-gamma specific mRNA was increased significantly in T cells from elderly individuals and the amount of IFN-gamma synthesized by PMA/A23187-activated T cells was nearly double that produced by cells from young individuals. Quantification of the number of high-affinity IL-2R by [125I]IL-2 binding demonstrated there was no decrease in either the mean number or the dissociation constant of the high-affinity IL-2R on activated T cells of the elderly. Despite producing large amounts of IL-2 and having comparable numbers of both low- and high-affinity IL-2R. PMA/A23187-stimulated T cells from elderly subjects still proliferated less vigorously than did T cells from young persons. The addition of exogenous IL-2 to the cultured cells did not fully correct this age difference. Our findings that the expression of the IL-2, IL-2R, and IFN-gamma genes are not constitutionally defective in the elderly support the hypothesis that the age-related decline in proliferation observed in mitogen-stimulated T cells of the elderly is most likely attributable to alterations in the transmission of signals from the cell membrane to the nucleus.

Analysis of murine interferon-gamma binding to its receptor on intact cells and solubilized membranes. Identification of an 80 kDa receptor

The receptor for murine-interferon-gamma (Mu-IFN-gamma) has been characterized for its molecular size and equilibrium binding constant on a thymoma cell line, EL-4. Binding of 125I-IFN-gamma to intact cells and their solubilized membranes has shown a single class of receptor with Kd values of 1.9 x 10(-9) M and 1.3 x 10(-8) M, respectively. It was shown that solubilization of the Mu-IFN-gamma receptor with a Zwitterionic detergent (Chaps) preserves its binding activity. A direct comparison of the molecular mass of the Mu-IFN-gamma receptor on intact cells versus detergent-solubilized membranes was performed using a radiolabeled photoactivated crosslinking reagent and direct hybridization with 125I-labeled IFN-gamma on Western blots of solubilized receptor. The results indicate that both types of receptors have an identical molecular mass of approximately 80 kDa.

Interferon-gamma is not an antiviral, but a growth-promoting factor for T lymphocytes

The effects of interferon (IFN)-gamma or IFN-alpha/beta on virus yield, (2'-5')oligo(A) synthetase activation, H-2 antigen expression and proliferation of T lymphocytes have been investigated. Under the culture conditions used, vesicular stomatitis virus or Semliki Forest virus replication in T cells was not impaired by the addition of IFN-gamma, whereas it was completely inhibited by the addition of IFN-alpha/beta. In contrast, B cell lines, macrophage-transformed cell lines and fibroblasts were fully protected by both IFN-gamma as well as IFN-alpha/beta following virus infection. The lack of sensitivity of T lymphocytes to the antiviral effects of IFN-gamma was not due to absence of specific membrane receptors, since in saturation binding experiments with 125I-labeled murine IFN-gamma most T cell lines displayed a number of binding sites and a degree of affinity comparable to those found on B cells, which are fully sensitive to IFN-gamma antiviral activity. Analysis of IFN-induced dsRNA-dependent (2'-5')oligo(A) synthetase activity, one of the biochemical markers for cellular responses to IFN, showed that it was not induced in T lymphocytes after IFN-gamma treatment, whereas IFN-alpha/beta induced high levels. Both IFN-gamma and IFN-alpha/beta enhanced H-2 antigen expression on T cells as well as on cells of different histological type. Moreover, when IFN-gamma was tested for its antiproliferative activity on T cells, it was found to consistently potentiate the response of these cells to mitogens or growth factors, rather than inhibit their proliferation. Taken as a whole these results suggest that on T lymphocytes IFN-gamma should not be regarded as an antiviral agent, but rather as a modulator of T cell growth and functional differentiation, transducing intracellular signals dissimilar to those observed with target cells of different origin.

Augmentation of procoagulant activity in monokine stimulated human endothelial cells by calmodulin/protein kinase C inhibitors

The incubation of human umbilical cord endothelial cell cultures with inflammatory mediators results in the induction of procoagulant activity. As many of these mediators activate protein kinase C, the effect of calmodulin and protein kinase C inhibitors on IL-1, TNF, phorbol ester and LPS stimulated procoagulant activity was determined. Incubation of endothelial cell cultures with these inflammatory agents in the presence of phenothiazine derivatives or other classes of calmodulin and protein kinase C antagonists resulted in a 2-4 fold increase in procoagulant activity compared to parallel stimulated cultures in the absence of antagonists. The augmented response of IL-1 stimulated endothelial cells to these antagonists was actinomycin D sensitive.