Altered beta-adrenoceptor function associated to protein kinase C activation in hyperproliferative T lymphocytes

Involvement of thyroid hormones in the alterations of T-cell immunity and tumor progression induced by chronic stress

BACKGROUND

Stress alters the neuroendocrine system, immunity, and cancer. Although the classic stress hormones are glucocorticoids and catecholamines, thyroid hormones have also been related to stress. We recently reported that chronic restraint stress impairs T-cell mediated immunity and enhances tumor growth in mice.

METHODS

To study the participation of these hormones on the stress-induced alterations of the immune function and lymphoma growth, mice were subjected to acute or chronic stress, with or without thyroxin supplementation. Hormone levels, immune status, and cancer progression were evaluated.

RESULTS

Differential endocrine alterations were observed in response to acute and chronic stress. Although corticosterone and noradrenaline levels were increased by acute stress, they were restored after prolonged exposure to the stressor. Instead, thyroid hormone levels were only reduced in chronically stressed animals in comparison with control subjects. Correlating, chronic but not acute stress impaired T-cell reactivity. Thyroxin replacement treatment of chronic restraint stress-exposed mice, which restored the euthyroid status, reversed the observed reduction of T-cell lymphoproliferative responses. Moreover, therapeutic thyroid replacement also reversed the alterations of lymphoma growth induced by chronic stress in syngeneic mice bearing tumors as well as Interleukin-2 production and specific cytotoxic response against tumor cells. Finally, we found that the isoforms theta and alpha of the protein kinase C are involved in these events.

CONCLUSIONS

These results show for the first time that thyroid hormones are important neuroendocrine regulators of tumor evolution, most probably acting through the modulation of T-cell mediated immunity affected by chronic stress.

Thyroid hormones increase inducible nitric oxide synthase gene expression downstream from PKC-ζ in murine tumor T lymphocytes

Regulation of cell proliferation by thyroid hormone (TH) has been demonstrated, but the effect of THs and the mechanisms involved in lymphocyte activity have not been elucidated. Differential expression of PKC isoenzymes and high nitric oxide synthase (NOS) activity have been described in tumor T lymphocytes. We have analyzed the direct actions of TH on normal T lymphocytes and BW5147 T lymphoma cells in relation to PKC and NOS activities. THs increased tumor and mitogen-induced normal T lymphocyte proliferation. PKC isoenzyme-selective blockers impaired these effects in both cell types, indicating the participation of Ca2+-dependent and -independent isoenzymes in normal and tumor cells, respectively. TH actions were blunted by extra- and intracellular Ca2+ blockers only in normal T lymphocytes, whereas NOS blockers impaired TH-induced proliferation in T lymphoma cells. Incubation for 24 h with TH induced a rise in total and membrane-associated PKC activities in both cell types and led to a rapid and transient effect only in tumor cells. THs increased atypical PKC-ζ expression in BW5147 cells and classical PKC isoenzymes in mitogen-stimulated normal T cells. TH augmented NOS activity and inducible NOS protein and gene expression only in tumor cells. Blockade of PKC and the atypical PKC-ζ isoform inhibited TH-mediated stimulation of inducible NOS and cell proliferation. These results show, for the first time, that differential intracellular signals are involved in TH modulation of lymphocyte physiology and pathophysiology.

Different mitogen-mediated Beta-adrenergic receptor modulation in murine T lymphocytes depending on the thyroid status

OBJECTIVE

The aim of this work was to analyze beta-adrenergic receptor (betaAR) regulation of T-lymphocyte proliferation in mice according to different thyroid hormone statuses.

METHODS

T cells from eu-, hypo- (by propylthiouracil treatment) and hyperthyroid (by thyroxine, T4 administration) mice were purified and specific radioligand binding assays were performed. The effects of the beta-agonist isoproterenol (ISO) on intracellular levels of cyclic AMP (cAMP) were determined. Mitogen-induced T-cell proliferation was measured by [(3)H]-thymidine incorporation. Finally, protein kinase C (PKC) activity in cytosol and membrane fractions were determined using radiolabelled enzymatic substrates.

RESULTS

Adecrease or a non-significant increase in betaAR number was found on T lymphocytes from hypo- and hyperthyroid mice compared to euthyroid controls. ISO stimulation of cAMP levels was lower in hypothyroid and higher in hyperthyroid T lymphocytes compared to controls. T-selective mitogen-induced proliferation was increased in T4-treated animals, but decreased in hypothyroid mice. During the peak of proliferation, downregulation of betaAR was observed in all animals. However, a higher or a lower decrease was observed in hyper- and hypothyroid T cells, respectively. In parallel, a higher translocation of PKC activity was observed in hyperthyroid cells, and a lower one was found in hypothyroid lymphocytes with respect to controls.

CONCLUSIONS

These results indicate that intracellular signals triggered by mitogen activation, namely PKC, would be related to differential betaAR downregulation in T lymphocytes depending on the thyroid hormone status, contributing to the distinct proliferative responses found in hypo- or hyperthyroidism compared to the euthyroid state.

Modulatory effect of the adrenergic system upon fibroblast proliferation: participation of beta 3-adrenoceptors

1. The beta3-adrenoceptor agonist ZD 7114, like the non-selective beta-adrenoceptor agonist isoprenaline, but unlike the beta1-adrenoceptor agonist dobutamine and the beta2-adrenoceptor agonist salbutamol, produced an increment on mouse embryonic fibroblast proliferation. The half-maximal stimulation of cell growth occurred at substantially lower concentrations with the beta3-adrenoceptor agonist (EC50: 5.5 x 10(-8) m) than with isoprenaline (EC50: 1.25 x 10(-6) m). 2. The selective beta3-adrenoceptor antagonist SR 5923 OA prevented the beta3-stimulated fibroblast proliferation. Conversely, practolol and butoxamine did not prevent fibroblast growth. 3. Additionally, a decrease of cAMP was obtained in fibroblasts cells upon stimulation with isoprenaline and ZD 7114. 4. The expression of beta-adrenoreceptors on fibroblast cells was also studied by radioligand binding. The Ki values in the presence of beta1- and beta2-adrenoceptor antagonist was two-fold higher than the Ki values for beta3 adrenoceptor antagonist indicating the presence of A3-receptor subtype. 5. Inhibitors of different intracellular coupling pathways including phospholipase C (U 73122), protein kinase C (staurosporine), calcium/calmodulin (trifluoroperazine) and calcium channel (verapamil), prevented the stimulatory actions of the selective beta3-adrenoceptor agonist ZD 7114. 6. The presence of beta3-adrenoceptors on embryonic mouse fibroblast cells may play a role in the modulation of cell growth and biologic activity. The mechanism by which ZD 7114 triggers cell proliferation and function, involves the activation of phospholipase C, PKC, calcium/calmodulin and the influx of calcium.

Noradrenaline and α-adrenergic signaling induce thehsp70gene promoter in mollusc immune cells

Expression of heat shock proteins (hsp) is a homeostatic mechanism induced in both prokaryotic and eukaryotic cells in response to metabolic and environmental insults. A growing body of evidence suggests that in mammals, the hsp response is integrated with physiological responses through neuroendocrine signaling. In the present study, we have examined the effect of noradrenaline (NA) on the hsp70 response in mollusc immune cells. Oyster and abalone hemocytes transfected with a gene construct containing a gastropod hsp70 gene promoter linked to the luciferase reporter-gene were exposed to physiological concentrations of NA, or to various α- and β-adrenoceptor agonists and antagonists. Results show that NA and α-adrenergic stimulations induced the expression of luciferase in transfected mollusc immunocytes. Furthermore, exposure of hemocytes to NA or to the α-adrenoceptor agonist phenylephrine (PE) resulted in the expression of the inducible isoform of the hsp70 protein. Pertussis toxin (PTX), the phospholipase C (PLC) inhibitor U73122, the protein kinase C (PKC) inhibitor calphostin C, the Ca2+-dependent PKC inhibitor Gö 6976 and the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor LY294002 blocked the PE-mediated induction of the hsp70 gene promoter. These results suggest that α-adrenergic signaling induces the transcriptionnal upregulation of hsp70 in mollusc hemocytes through a PTX-sensitive G-protein, PLC, Ca2+-dependent PKC and PI 3-kinase. Thus, a functional link exists between neuroendocrine signaling and the hsp70 response in mollusc immune cells.