DIFFERENTIAL ACTIVATION OF G(I)-PROTEIN AND G(S)-PROTEIN BY E-TYPE AND I-TYPE PROSTAGLANDINS IN MEMBRANES FROM THE HUMAN ERYTHROLEUKEMIA CELL-LINE, HEL

The group of prostaglandin (PG) E(2)- and prostacyclin receptors consists of different subtypes, which exibit different affinities for prostaglandins and synthetic analogues. PGE(2) activates the E-type PG receptor subtypes EP(1), EP(2) and EP(3), whereas the PGE(2) analogue, sulprostone, binds only to the EP(1) and EP(3) receptor subtypes. The stable PGI(2) analogues, iloprost and cicaprost, both activate the PGI(2) receptor (IF) and iloprost, additionally, bind to the EP(1) subtype. Using these subtype-selective PG receptor agonists, we studied the interaction of PG receptor subtypes with G(s) and G(1)-type heterotrimeric guanine nucleotide-binding proteins (G proteins) in membranes from the human erythroleukaemia cell line, HEL. Sulprostone stimulated high-affinity GTPase in HEL membranes in a pertussis toxin (PTX)-sensitive manner. In contrast, the stimulations induced by PGE(2), iloprost and cicaprost were only partially inhibited by PTX. PGE(2), sulprostone, iloprost and cicaprost stimulated cholera toxin-catalysed ADP-ribosylation as well as labelling with GTP azidoanilide of membrane proteins comigrating with immunologically identified G(i) protein alpha subunits. Furthermore, PGE(2), iloprost and cicaprost enhanced GTP azidoanilide-labelling of G(s) protein alpha subunits, whereas sulprostone did not. We suggest that in HEL cells (1) EP(1) and EP(3) receptor subtypes activate G(i) proteins, that (2) the EP(2) receptor subtype activates G(s) proteins and that (3) the IP receptor activates both G(i) and G(s) proteins.