Dopaminergic D 1-like receptor-dependent inhibition of tyrosine hydroxylase mRNA expression and catecholamine production in human lymphocytes

Abstract

Activation of human peripheral blood mononuclear cells (PBMC) triggers endogenous production of catecholamines (CA) through protein kinase (PK) C-dependent induction of tyrosine hydroxylase (TH; EC 1.14.16.2), the first and rate-limiting enzyme in the synthesis of CA. Since CA themselves are major mediators of the neural input to the immune system, we have examined their ability to affect PKC-induced TH mRNA expression and CA production in human isolated PBMC. In T- and B-lymphocytes (but not in monocytes) the PKC activator 12- O-tetradecanoylphorbol-13-acetate (TPA) (but not its inactive analogue 4α-phorbol-12,13-didecanoate) induced TH mRNA expression which was followed by an increase in the amount of intracellular CA. Coincubation of human PBMC with dopamine (DA) (but not with norepinephrine or epinephrine) inhibited TPA-induced TH mRNA expression. The effect of DA was concentration-dependent and was mimicked by the dopaminergic D 1-like receptor agonist SKF-38393 but not by the D 2-like receptor agonist bromocriptine. The D 1-like antagonist SCH-23390 shifted to the right the concentration–response curves of both DA and SKF-38393, while neither the D 2-like antagonist domperidone, nor the α 1-adrenoceptor antagonist prazosin, the α 2-adrenoceptor antagonist yohimbine, or the β-adrenoceptor antagonist propranolol affected to any significant extent the inhibitory effect of DA. SKF-38393 also significantly reduced TPA-induced increase of intracellular CA, an effect which was antagonized by SCH-23390. It is thus suggested that in human T- and B-lymphocytes PKC activation leads to TH mRNA expression and subsequent increase of intracellular CA, which can be inhibited by D 1-like receptor activation. Inhibition of intracellular CA production in human PBMC promotes cell survival through reduction of activation-induced apoptosis, and dopaminergic modulation of TH expression and intracellular CA content may thus represent a novel mechanism in the cross-talk between the nervous and the immune system as well as among immune system cells.