The prostaglandin E-prostanoid (EP), receptor signals primarily through the
inhibitory G protein G(i), thereby decreasing intracellular cAMP levels. T
o study the signal transduction properties of the rabbit EP3 receptor, five
splice variants were expressed in HEK293tsA201 cells: 72A, 74A, 77A, 80A a
nd the novel splice Variant NT, which lacks the C-terminal sequence. The ab
ility of the EP3 receptor splice variants to modulate expression of a beta-
galactosidase reporter gene under the control of a promoter containing cAMP
response elements (CRE) was assessed. Each splice variant induced sulprost
one-mediated increase in beta-gatactosidase enzymatic activity with EC50 ra
nging from 0.8 nM for the NT splice variant to 3.1 nM for the 77A splice va
riant. Substitution of either Asp(338) with Ala, or Arg(329) with Ala or Gl
u in the 77A splice variant resulted in a loss of receptor-evoked increases
in P-galactosidase activity, whereas substitution of Lys(300) with alanine
had no effect on signal transduction. These phenotypes correlate with the
inhibition of cAMP generation by direct cAMP measurement. Signal transducti
on was insensitive to pretreatment of cells with pertussis toxin, suggestin
g that a nonG(i)/G(o) pathway is activated by the EP3 receptor. Direct meas
urement of second messenger levels confirmed that there was no increase in
cAMP levels mediated by the 77A splice variant, however, there was a modest
increase in intracellular Ca2+. Partial blockade of the reporter activity
with kinase inhibitors demonstrates that CRE activation is mediated in part
by a Ca2+-dependent kinase pathway. These data suggest that the EP, recept
or signals through a novel cAMP response element binding protein/CRE pathwa
y.