B₂ kinin receptor upregulation by cAMP is associated with BK-induced PGE₂ production in rat mesangial cells

In the rat mesangial cell (MC), activation of the bradykinin B₂ receptor (B₂R) by bradykinin (BK) is associated with both phospholipase C (PLC) and A₂ (PLA₂) activities and with inhibition of adenosine 3',5'- cyclic monophosphate (cAMP) formation leading to cell contraction. Because cAMP plays an important role in the regulation of gene expression in general, we investigated the effect of increasing the intracellular cAMP concentration ([cAMP](i)) in mesangial cells on the B₂ mRNA expression, on the density of B₂ receptor binding sites, on the BK-induced increase in both the free cytosolic Ca²⁺ concentration ([Ca²⁺](i)), and in the prostaglandin E₂ (PGE₂) production. Forskolin, PGE₂, and cAMP analog, 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), were used to increase [cAMP](i). Twenty-four-hour treatment with forskolin, PGE₂, and 8-BrcAMP resulted in significant increases in B₂ receptor binding sites, which were inhibited by cycloheximide. The maximum B₂ receptor mRNA expression (160% above control) was observed in cells treated during 24 h with forskolin and was prevented by actinomycin D. In contrast, the D-myo-inositol 1,4,5-trisphosphate (IP₃) formation and the BK-induced increase in [Ca²⁺](i), reflecting activation of PLC, were not affected by increased levels of [cAMP](i). However, the BK- induced PGE₂ release, reflecting PLA₂ activity, was significantly enhanced. These data bring new information regarding the dual signaling pathways of B₂ receptors that can be differentially regulated by cAMP.