Protein kinases A and C rapidly modulate expression of human lung fibroblast B2 bradykinin receptor affinity forms

Abstract

WI-38 and IMR90 human lung fibroblasts express B2 receptors for the peptide mediator bradykinin. These G-protein-coupled receptors which control cell growth, protein synthesis, and prostaglandin E2 (PGE2) production occur in three affinity forms, high (H, KD 440 pM), intermediate (I, KD 5.6 nM), and low (L, KD 42 nM). Utilizing specific monoclonal antireceptor antibodies which are able to distinguish among these B2 bradykinin receptor forms, we demonstrate regulated differential enhancement of their expression in fibroblasts. Activation of cellular second messenger regulatory pathways based on protein kinase C or protein kinase A drives B2 receptor affinity form expression in opposite directions, both of which are relevant to the levels of human bradykinin generation in vivo in the tissues of origin for these fibroblasts. On a spontaneous basis WI-38 human lung fibroblasts most frequently express the L form alone or the I+L forms concurrently. Activation of protein kinase C augments expression of both I and L affinity receptors within 30 min, increasing receptor number and enhancing PGE2 production. In contrast, activation of protein kinase A by 8-bromo-cAMP or forskolin enhances receptor expression and PGE2 production instead at the I to H types of affinity forms within 30 min. The effects of both kinase systems are blocked by serine/threonine (Ser/Thr) protein kinase inhibitors, indicating a role for phosphorylation at Ser or Thr residues in determining the cellular expression of bradykinin B2 receptor affinity forms. An increase in immunoprecipitable I form bradykinin receptors is detectable within 20 to 30 min after activation of either protein kinase C or protein kinase A. This time frame emphasizes the ability of human fibroblasts for rapid mobilization of B2 receptor affinity forms. Regulated expression of this repertoire of bradykinin B2 receptors at the level of receptor number and concurrent activity allows fibroblasts a sensitive means to adjust their responses to their cellular environment utilizing Ser/Thr phosphorylation events.