CHOLECYSTOKININ(B) RECEPTOR FROM HUMAN JURKAT LYMPHOBLASTIC T-CELLS IS INVOLVED IN ACTIVATOR PROTEIN-1-RESPONSIVE GENE ACTIVATION

The aim of this study was to analyze the role of cholecystokinin (CCKB ) receptor in human lymphoblastic Jurkat T cells. We investigated the trophic effect resulting from activation of such a receptor by using t he reporter gene strategy, For this purpose, we transiently transfecte d Jurkat T cells with the reporter plasmid p[(TRE)3-tk-Luc] and found that CCK-8 was able to dose-dependently induce luciferase expression r elated to activator protein-1 (AP-1) activation with a maximal respons e identical to that obtained with compounds known to activate AP-1 com plex (quantitatively, the same level of induction was obtained with 1 nM 12-O-tetradecanoylphorbol-13-acetate, 100 mu M diacylglycerol, or 4 nM epidermal growth factor), The involvement of the CCKB receptor in such a stimulation was demonstrated by the inhibiting effect of the se lective CCKB receptor antagonist PD-135,158. This effect was confirmed in COS-7 cells transfected with the cDNA of CCKB receptor cloned from Jurkat T cells. To better understand the AP-1-dependent luciferase ex pression in Jurkat T cells, we tested two specific inhibitors of serin e/threonine phosphatases-1 and -2A: okadaic acid and calyculin A. Thes e compounds strongly increased the phorbol-12-myristate-13-acetate res ponse, whereas we have not observed a contribution of phosphatase inhi bitors on a CCK-8-induced luciferase activity. To confirm that CCKB re ceptors are involved in AP-1 response, we investigated the CCK-8 effec t on interleukin-2 expression, a natural endogenous gene regulated by several factors, including AP-1. In Jurkat T cells activated by phorbo l-12-myristate-13-acetate and phytohemagglutinin, CCK-8 induced IL-2 e xpression. This induction was abolished by PD-135,158, Our results ind icate that CCK-8 exerts a trophic effect in Jurkat T cells through sti mulation of CCKB receptors by modulation of expression of AP-1-regulat ed genes.