Cyclic nucleotide signalling systems in vascular smooth muscle cells and immune system cells with special reference to phosphodiesterases PDE3 and PDE4

Abstract: The cyclic nucleotide signalling systems are important in vascular smooth muscle and in the immune system, and are of interest from a pharmacological point of view. Drugs which interfere with the cyclic nucleotide levels have profound effects on heart, blood vessels and airways and have actual or potential use in several important diseases, such as heart failure, hypertension, arteriosclerosis, asthma and autoimmune diseases. In this work, cyclic nucleotide phosphodiesterases (PDEs) (which degrade cyclic nucleotides) are studied. Inhibitors of the PDE isoenzymes PDE3 have vasorelaxing and positive inotropic effects, whereas PDE4-inhibitors have a suppressing effect in the immune system. The present studies focus on the expression and regulation of PDE3 and PDE4 in vascular smooth muscle cells and immune system cells and their importance for regulation of proliferation in immune system cells. In vascular smooth muscle cells, PDE3 was found to be phosphorylated and activated in in vivo response to elevated cAMP. It could also be phosphorylated in vitro by cAMP-dependent protein kinase (PKA). Activity of PDE4 in vascular smooth muscle cells increased 3-5-fold within 15 min in response to elevated cAMP. The data support activation by PKA-dependent phosphorylation of both PDE3 and PDE4 in vascular smooth muscle cells. A PDE3A from a vascular smooth muscle cDNA library was cloned and sequenced. The sequence was the same as the cardiac PDE3A, except for a 51 truncation. Thus, the vascular PDE3A is coded by the same gene as the cardiac. Expression yielded an active PDE with similar characteristics as the vascular smooth muscle enzyme. If the truncation reflects presence of an alternative form of PDE3A is not known. Autoreactive T- lymphocyte clones all expressed PDE3 and PDE4 with individual PDE4 / PDE3 ratios. PDE3B and 4A-D were detected in all clones. Antigen stimulation induced a marked increase in both PDE3- and PDE4-activities, which was maximal after 2-3 days (a few days before proliferation peak). Both PDE3- and PDE4-inhibitors inhibited antigen-stimulated proliferation. The combination was usually more effective than each inhibitor alone. T-cells transformed with human T-lymphotropic virus - 1 (HTLV-1) in general exhibited increased PDE4 / PDE3 ratios and, in some cell lines, strongly increased PDE4 activity. The effect of isoenzyme-specific PDE-inhibitors on the proliferation of these cells varied between different cell lines, but in some HTLV-I-positive cell lines, a PDE4-inhibitor strongly inhibited proliferation.