Herein we provide evidence for the coexpression of two distinct
prostacyclin (PGI(2)) receptors (IP) on BEAS-2B human airway epithelial cells. IP receptor heterogeneity initially was suggested by the finding that the rank orders of potency of PGI(2) and three structurally similar analogs [
taprostene,
iloprost, 15-deoxy-16-(m-tolyl)-17,18,19,20-tetranorisocarbacyclin (15-deoxy-
TIC)] for the inhibition of
chemokine (CXCL9 and CXCL10) release and for transcriptional activation/augmentation of cAMP response element and
glucocorticoid response element
luciferase reporters were distinct. Indeed, PGI(2),
taprostene, and
iloprost activated both reporters whereas
15-deoxy-TIC was inert. Conversely,
15-deoxy-TIC, PGI(2), and
taprostene (but not
iloprost) suppressed
chemokine release. Further experiments established that
iloprost did not antagonize the inhibitory effect
taprostene or
15-deoxy-TIC on
chemokine output. Likewise,
15-deoxy-TIC failed to antagonize
taprostene- and
iloprost-induced reporter transactivation. Thus,
iloprost- and 15-deoxy-TIC-induced responses were apparently mediated via pharmacologically distinct receptors. In human embryonic kidney 293 cells overexpressing the human recombinant IP receptor receptor,
15-deoxy-TIC was considerably less potent (>10,000-fold) than
iloprost and
taprostene in promoting cAMP accumulation, yet in BEAS-2B cells, these analogs were equipotent. IP receptor heterogeneity was also supported by the finding that the affinity of the IP receptor antagonist R-3-(4-fluorophenyl)-2-[5-(4-fluorophenyl)-
benzofuran-2-yl-methoxycarbonyl-amino]
propionic acid (
RO3244794) for the receptor mediating inhibition of
chemokine release was approximately 10-fold lower than for the receptor mediating both transcriptional outputs. Finally, small interfering RNAs directed against the IP receptor gene, PTGIR, failed to block the suppression of
chemokine output induced by
taprostene and
15-deoxy-TIC, whereas
taprostene- and
iloprost-induced transcriptional responses were markedly attenuated. Collectively, these results indicate that PGI(2),
taprostene and
15-deoxy-TIC suppress
chemokine release from BEAS-2B cells by interacting with a novel IP receptor that we denote here as the "IP(2)" subtype.