|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1994 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 1993 : ¥1,200,000 (Direct Cost : ¥1,200,000)
We have isolated cDNAs for three subtypes of prostaglandin (PG) E receptor, EP1, EP2 and EP3, and three isoforms of EP3 with different COOH-terminal tails, EP3alpha, beta and gamma, which are produced through alternative splicing and differ in selectivity of G protein coupling. EP1 is coupled to unknown G protein other than Gi or Gs, and exerts Ca^<2+> influx through Ca^<2+>-permeable channel independent of phospholipase C pathway, resulting in activation of protein kinase C (PKC) and inhibition of Na+ ion reabsorption in kidney. The activation of PKC in turn suppressed the EP1-mediated Ca^<2+> influx, and prolonged PKC activation down-regulated the level of EP1 mRNA.Thus, PKC is not only a mediator of EP1 signals but also a feedback regulator of EP1.
EP3 not only inhibited adenylate cyclase but also stimulated Ca^<2+> influx via Gi. This is due to activation of IP_3-responsive Ca^<2+> permeable channel, resulting from phospholipase C-beta activation by betagamma subunits released from Gi. PGE_2 extracellular Ca^<2+>-dependently induces contraction of uterus through EP3. This action is mediated by the mechanism mentioned above.
In situ hybridization studies have revealed that three subtypes are expressed in different segments of the nephron, suggesting that PGE_2 exerts multiple functions via these subtypes expressed in different kidney regions. The diversity of the cellular responses to PGE_2 in mainly based on the different expression of functionally different PGE receptor subtypes and isoforms produced through altarnative splicing.