Restoration of sensitivity of cultured hepatoma cells to cyclic nucleotides shows permissive effect of dexamethasone

The impact of endogenous annexin A1 on glucocorticoid control of inflammatory arthritis

OBJECTIVES

To establish the role and effect of glucocorticoids and the endogenous annexin A1 (AnxA1) pathway in inflammatory arthritis.

METHODS

Ankle joint mRNA and protein expression of AnxA1 and its receptors were analysed in naive and arthritic mice by real-time PCR and immunohistochemistry. Inflammatory arthritis was induced with the K/BxN arthritogenic serum in AnxA1(+/+) and AnxA1(-/-) mice; in some experiments, animals were treated with dexamethasone (Dex) or with human recombinant AnxA1 or a protease-resistant mutant (termed SuperAnxA1). Readouts were arthritic score, disease incidence, paw oedema and histopathology, together with pro-inflammatory gene expression.

RESULTS

All elements of the AnxA1 pathway could be detected in naive joints, with augmentation during ongoing disease, due to the infiltration of immune cells. No difference in arthritis intensity of profile could be observed between AnxA1(+/+) and AnxA1(-/-) mice. Treatment of mice with Dex (10 µg intraperitoneally daily from day 2) afforded potent antiarthritic effects highly attenuated in the knockouts: macroscopic changes were mirrored by histopathological findings and pro-inflammatory gene (eg, Nos2) expression. Presence of proteinase 3 mRNA in the arthritic joints led the authors to test AnxA1 and the mutant SuperAnxA1 (1 µg intraperitoneally daily in both cases from day 2), with the latter one being able to accelerate the resolving phase of the disease.

CONCLUSION

AnxA1 is an endogenous determinant for the therapeutic efficacy of Dex in inflammatory arthritis. Such an effect can be partially mimicked by application of SuperAnxA1 which may represent the starting point for novel antiarthritic therapeutic strategies.

Chromatin structures of the rat tyrosine aminotransferase gene relate to the function of its cis-acting elements

The relationship between DNase I-hypersensitive sites (HSs) and transcriptional enhancers of the rat tyrosine aminotransferase (TAT) gene was examined by comparing HSs in and around the TAT gene with the activity of the corresponding DNA sequences in transient transfection assays. In this manner, we identified two HSs as liver-specific enhancers. Of three hepatoma cell lines examined, only one sustained TAT mRNA levels comparable to those of liver. In this cell line, both enhancers were strongly active, and strong hypersensitivity in chromatin over the enhancers was evident. The other two hepatoma cell lines had reduced levels of TAT mRNA and no or altered hypersensitivity over either the enhancers or the promoter. One of these lines carried a negative regulator of the TAT gene, the tissue specific extinguisher Tse-1. This cell line exhibited all HSs characteristic of the strongly active gene except at the promoter; however, one enhancer was inactive even though hypersensitive in chromatin. In a TAT-nonexpressing cell line, inactivity of both enhancers correlated with absence of the respective HSs. We conclude that although hypersensitivity in chromatin necessarily accompanies cell-type-specific enhancer activity, the occurrence of cell-type-specific HSs does not imply that the underlying sequences harbor enhancers active in transient transfection assays.

Chromatin structures of the rat tyrosine aminotransferase gene relate to the function of its cis-acting elements

The relationship between DNase I-hypersensitive sites (HSs) and transcriptional enhancers of the rat tyrosine aminotransferase (TAT) gene was examined by comparing HSs in and around the TAT gene with the activity of the corresponding DNA sequences in transient transfection assays. In this manner, we identified two HSs as liver-specific enhancers. Of three hepatoma cell lines examined, only one sustained TAT mRNA levels comparable to those of liver. In this cell line, both enhancers were strongly active, and strong hypersensitivity in chromatin over the enhancers was evident. The other two hepatoma cell lines had reduced levels of TAT mRNA and no or altered hypersensitivity over either the enhancers or the promoter. One of these lines carried a negative regulator of the TAT gene, the tissue specific extinguisher Tse-1. This cell line exhibited all HSs characteristic of the strongly active gene except at the promoter; however, one enhancer was inactive even though hypersensitive in chromatin. In a TAT-nonexpressing cell line, inactivity of both enhancers correlated with absence of the respective HSs. We conclude that although hypersensitivity in chromatin necessarily accompanies cell-type-specific enhancer activity, the occurrence of cell-type-specific HSs does not imply that the underlying sequences harbor enhancers active in transient transfection assays.

Regulation of the synthesis of tyrosine aminotransferase: the relationship to mRNATAT

The activity of the hepatic enzyme tyrosine aminotransferase (TAT) is the sum of many diverse regulatory factors. These include the developmental stage of the animal, the hormonal and nutritional environment of the animal (or tissue culture cell), other extrinsic and intrinsic regulatory cycles and factors (including cytoplasmic substances), and chromatin structure. Although TAT is subject to a number of post-translational modifications, alterations in catalytic activity always parallel changes in enzyme amount. In a few instances this is due to a selective change in TAT degradation, but most are due to changes in the rate of aminotransferase synthesis. Recent studies have shown that TAT synthesis is generally directly correlated with the activity, and presumably amount, of the mRNA that codes for tyrosine aminotransferase.

Unlinked control of multiple glucocorticoid-induced processes in HTC cells

HTC cell variants chosen for their lack of tyrosine aminotransferase (EC 2.6.1.5) (TAT) induction by glucocorticoids were tested for interrelated effects on other glucocorticoid responses: TAT induction by dibutyryl cyclic AMP (dBcAMP) +/- dexamethasone, glutamine synthetase (GS) induction, cyclic nucleotide phosphodieterase (PDE) suppression, inhibition of alpha-aminoisobutyric acid (AIB) uptake, inhibition of plasminogen activator (PA), and induction of mouse mammary tumor virus (MTV). Loss of TAT induction by steroid was accompanied by loss of TAT induction by dBcAMP and of PDE suppression by steroid. In addition, subclones of MTV-infected cells were examined for the effect of the virus on glutamine synthetase (GS) and TAT induction. The virus had no effect on their induction in wild-type cells and no effect on GS induction in the variants. One MTV-infected subclone from a TAT variant, however, showed significant return of TAT induction.

The role of glucocorticoid hormones as biological amplifiers

Recent research in hormone action has been aimed at studying single effects in well-defined systems. As exemplified in several chapters of this book, it has been possible to deduce a general mechanism of action of the glucocorticoids using this approach. Most hormones, and the glucocorticoids in particular, do not act as independent agents in the intact animal. Although the best known example of how glucocorticoids interact with other hormones is the amplification of the effect of those whose action is mediated by cAMP, these steroids also augment the effects of a variety of other hormones and effectors. Such interactions are of interest in clinical medicine as well, since glucocorticoid hormones are used in combination with other drugs in a number of conditions, including the treatment of asthma, allergies, and certain kinds of shock and cancer. Neither the biochemical nor the pharmacologic basis for the effects of the glucocorticoids is known. In some cases the actions of other hormones are not observed unless the tissue has first been exposed to glucocorticoids. In these instances the glucocorticoids are said to exert a "permissive effect," since they allow a process to proceed at a maximal rate even though the steroid itself has no effect on this process. There is no doubt that such examples exist, as documented above: thus the concept of a "permissive effect" does have utility. The term fails to describe the more general role the glucocorticoids play, since in many instances the steroid also has a direct effect on the process itself, or optimizes a process in which the primary effector is not as yet known. Because of these cases, and because the historically more general usage first proposed by INGLE [1] seems to have been forgotten, use of the term "permissive effect" has been avoided in this chapter. An ultimate goal in glucocorticoid hormone research is to identify the mechanisms involved in the amplification effect these hormones exert. Now that the actions of these hormones and of the hormones they interact with are being defined, such work is within the realm of feasibility.

Pleiotropic drug resistance in cystic fibrosis fibroblasts: increased resistance to cyclic AMP

In previous studies, cystic fibrosis (CF) fibroblasts were demonstrated to be resistant to the cytotoxic effects of ouabain, dexamethasone, and the sex hormones, dihydrotestosterone, 17beta-estradiol, and progesterone. We now show that CF fibroblasts also exhibit greatly increased resistance to the cytotoxic effects of exogenous dibutyryl cyclic AMP (cAMP), as well as to isoproterenol and theophylline, drugs which are known to increase endogenous levels of cAMP. CF cells were also shown to have normal amounts of (3H)cAMP binding to protein kinase as well as normal amounts of cAMP-stimulated protein kinase activity. Phosphodiesterase in CF cells was also found to be stimulated by cAMP to the same degree as in normal cells. These findings suggest that there is no detectable protein kinase deficiency in CF cells. cf cells thus appear to be unlike some cAMP-resistant mutants described by others which are defective in protein kinase activity and cAMP regulation of phosphodiesterase levels. The cross-resistance of CF fibroblasts to ouabain, steroid hormones, and cAMP may provide a unique opportunity to study the biochemical events involved in the metabolism of these drugs as well as the basic biochemical defect in a common human genetic disease.

Studies of cyclic AMP action using mutant tissue culture cells

S49 mouse lymphoma cell mutants, each with a specific defect in its ability to generate or respond to cyclic AMP, have been isolated. Analysis of the properties of these cells has begun to provide information on complex and significant biologic problems related to the cyclic AMP system.

Activity of protein kinase dependent on adenosine 3':5'-monophosphate and of its thermostable protein inhibitor in rat hepatoma (HTC) cells. Unlikely role in the permissive action of glucocorticoids

Normal expression of a variety of hormonal effects which depend on cyclic AMP (adenosine 3':5'-monophosphate) requires the presence of glucocorticoids. Our hypothesis was that glucocorticoids control directly or indirectly the activity of cyclic-AMP-dependent protein kinase. This has been investigated in cultured hepatoma (HTC) cells in which N6,O2'-dibutyryladenosine 3':5'-monophosphate increases the activity of tyrosine transaminase only after glucocorticoid treatment. In these cells, we have determined the concentration and half-life of protein kinase, the sensitivity of this enzyme in vitro to cyclic AMP and to its thermostable protein inhibitor, the state of dissociation of protein kinase holoenzyme in vivo and its sensitivity, in the intact cell, to dibutyryladenosine 3':5'-monophosphate and to the inhibitor diamide, and we have also determined the concentration of endogenous thermostable protein inhibitor of protein kinase. None of these parameters were influenced by glucocorticoids under conditions where these hormones stimulate the activity of tyrosine transaminase and restore sensitivity to dibutyryladenosine 3':5'-monophosphate. It is concluded that the permissive action of glucocorticoids probably results from a control of cyclic-AMP-dependent processes exerted at a level beyond the protein kinase system.

The influence of culture conditions on the induction of tyrosine aminotransferase by cyclic nucleotides in rat hepatoma cells

The increase in tyrosine aminotransferase activity which occurs in rat hepatoma tissue culture (HTC) cells in response to cyclic AMP analogs has been shown to be an enzyme induction, similar to the larger response observed in certain other hepatoma cells and in liver. A specific antibody to tyrosine aminotransferase has been used to show that the number of enzyme molecules and the rate of enzyme synthesis are increased by N6,O2'-dibutyryl cyclic AMP in HTC cells. The effect on tyrosine aminotransferase is also produced by various 8-substituted derivatives of cyclic AMP and occurs whether or not the enzyme has been preinduced with a glucocorticoid. The response of the enzyme is greater when HTC cells are maintained in monolayer than in suspension cultures. Neither cell growth nor serum is required for the response.

Effects of TSH and cyclic AMP on the human thyroid cells cultured in a chemically defined medium

In a serum-free, chemically defined medium human thyroid cells elongated remarkably and resembled fibroblastic cells. They retained the cyclic AMP response to TSH and the supplement of medium with TSH or dibutyryl cyclic AMP permitted the preservation of epithelial nature by the cells. Cyclic AMP of the cells of epithelial nature was higher than those of fibroblastic appearance.