Previously we demonstrated that the histamine H2 receptor can activate both the adenylate cyclase and phosphoinositide/protein kinase (PKC) signaling pathways. Although dual coupling occurs via separate GTP-dependent mechanisms the structural components of the H2 receptor directing differential signaling have not been established. We explored this question by attempting to confer to the beta2-adrenergic receptor (betaAR), which is known to stimulate cAMP formation, the ability to activate PKC through the construction of beta2/H2 chimeric receptors. Intracytoplasmic domains of the human beta2 adrenergic receptor were substituted with the corresponding sequences of the human H2 receptor and stably expressed in HEK-293 cells. Binding of [(3)H]-CGP to chimeric wild type beta2 receptors was comparable. Substitution of the second intracellular loop (2i) of the betaAR led to a significant decrease in coupling to adenylate cyclase while leading to a 139.5 +/- 9.4% control increase in epinephrine mediated PKC activation. Introduction of the H2 receptor 3i also led to a decrease in betaAR mediated cAMP generation but provided the latter with the ability to stimulate PKC (182.2 +/- 8% of control). Concomitant expression of both 2i and 3i led to a substantial increase in epinephrine mediated PKC activation (201.8 +/- 10.5% of control). Addition of the carboxyl terminal tail did not facilitate stimulation of PKC. In summary, the third intracellular loop of the H2 receptor plays an essential role in activating PKC with maximal efficiency conferred by the second intracellular domain.
Copyright 2000 Academic Press.