PAR1 and PAR2 Couple to Overlapping and Distinct Sets of G Proteins and Linked Signaling Pathways to Differentially Regulate Cell Physiology

Abstract

The protease-activated receptors (PAR1 and PAR2) are unusual G protein-coupled receptors that are activated by distinct serine proteases and are coexpressed in many different cell types. Limited recent evidence suggests these closely related receptors regulate different physiological outputs in the same cell, although little is known about the comparative signaling pathways used by these receptors. Here we report that PAR1 and PAR2 couple to overlapping and distinct sets of G proteins to regulate receptorspecific signaling pathways involved in cell migration. In functionally PAR-null COS-7 cells, ectopically expressed PAR1 and PAR2 both form stable complexes with G␣ q , G␣ 11 , G␣ 14 , G␣ 12 , and G␣ 13 . It is surprising that PAR1 but not PAR2 coupled to G␣ o , G␣ i1 , and G␣ i2 . Consistent with these observations, PAR1 and PAR2 stimulation of inositol phosphate production and RhoA activation was blocked by specific inhibitors of G q/11 and G 12/13 signaling, respectively. Both receptors stimulated extracellular signal-regulated kinase (ERK) 1/2 phosphorylation, but only PAR1 inhibited adenylyl cyclase activity, and pertussis toxin blocked PAR1 effects on both adenylyl cyclase and ERK1/2 signaling. Neu7 astrocytes express native PAR1 and PAR2 receptors that activate inositol phosphate, RhoA, and ERK1/2 signaling. However, only PAR1 inhibited adenylyl cyclase activity. PAR1 and PAR2 also stimulate Neu7 cell migration. PAR1 effects on ERK1/2 phosphorylation and cell migration were blocked both by pertussis toxin and by the mitogen-activated protein kinase kinase/ERK inhibitor [1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene (U0126)], whereas PAR2 effects were only blocked by U0126. These studies demonstrate that PAR1 and PAR2 physically and functionally link to overlapping and distinct profiles of G proteins to differentially regulate downstream signaling pathways and cell physiology.

Neutrophil Elastase Acts as a Biased Agonist for Proteinase-activated Receptor-2 (PAR2)

“…The inhibition of the NE-triggered MAPK signal by inhibitors of Rho-associated kinase indicate that this response is occurring through the coupling of the receptor to the G␣ 12/13 . The ability of PAR 2 to engage G␣ 12/13 has been reported in a number of other cells (31,32), but the implications of selectively activating this arm of PAR 2 signaling by NE remain to be fully understood.…”

Proteinase-activated receptors (PARs) as targets for antiplatelet therapy

“…Classical heterotrimeric guanine nucleotide-binding protein (G protein) dependent pathways downstream of PAR activation have been well characterized for each PAR subtype [24]. PAR1 and PAR2 functionally couple to multiple G proteins including the Gαq/11, Gαi/o and Gα12/13 subfamilies [25][26][27]. Despite cleavage by thrombin, PAR3 does not signal conventionally via G proteins like the other PARs [10].…”

G protein coupled receptor signaling complexes in live cells

“…Whether these receptor oligomers are preassembled in complex with inactive G proteins is unclear, as evidence exists both for 16 - 19 and against 20 , 21 this idea. Preassembly of GPCR/G protein likely depends on the particular GPCR and G protein in question.…”