RGS Proteins Determine Signaling Specificity of Gq-coupled Receptors

Abstract

Regulators of G protein signaling (RGS) proteins accelerate GTP hydrolysis by G␣ subunits, thereby attenuating signaling. RGS4 is a GTPase-activating protein for G i and G q class ␣ subunits. In the present study, we used knockouts of G q class genes in mice to evaluate the potency and selectivity of RGS4 in modulating Ca 2؉ signaling transduced by different G q -coupled receptors. RGS4 inhibited phospholipase C activity and Ca 2؉ signaling in a receptor-selective manner in both permeabilized cells and cells dialyzed with RGS4 through a patch pipette. Receptor-dependent inhibition of Ca 2؉ signaling by RGS4 was observed in acini prepared from the rat and mouse pancreas. The response of mouse pancreatic acini to carbachol was about 4-and 33-fold more sensitive to RGS4 than that of bombesin and cholecystokinin (CCK), respectively. RGS1 and RGS16 were also potent inhibitors of G q -dependent Ca 2؉ signaling and acted in a receptor-selective manner. RGS1 showed approximately 1000-fold higher potency in inhibiting carbachol than CCK-dependent signaling. RGS16 was as effective as RGS1 in inhibiting carbachol-dependent signaling but only partially inhibited the response to CCK. By contrast, RGS2 inhibited the response to carbachol and CCK with equal potency. The same pattern of receptorselective inhibition by RGS4 was observed in acinar cells from wild type and several single and double G q class knockout mice. Thus, these receptors appear to couple G q class ␣ subunit isotypes equally. Difference in receptor selectivity of RGS proteins action indicates that regulatory specificity is conferred by interaction of RGS proteins with receptor complexes.

The RGSZ2 Protein Exists in a Complex with μ-Opioid Receptors and Regulates the Desensitizing Capacity of Gz Proteins

“…This has been reported for different RGS proteins in regulating Gq proteins activated by distinct receptors (Xu et al, 1999); RGS3 and muscarinic m3 receptor; RGS5 and angiotensin AT1a receptor (Wang et al, 2002); RGS8 towards muscarinic m1 and substance P receptors (Saitoh et al, 2002); RGS-R4 subfamily and subtypes of muscarinic acetylcholine receptors (Roy et al, 2003;Bernstein et al, 2004). In the present study, we show that both RGSZ1 and RGSZ2 co-precipitate with m-opioid receptors, and that the association between RGSZ and Ga subunits is altered by a morphine challenge.…”

A regulator of G protein signaling interaction surface linked to effector specificity

“…Since most of the RGS residues in direct contact with G ␣ are well conserved across the entire family, these residues are unlikely to determine RGS-G protein specificity alone. Rather, additional regulatory proteins, such as effectors (11), G␤ proteins (9,(35)(36)(37)(38), or G proteincoupled receptors (7,39) may be involved. Since five classspecific residues (r77, r117, r121, r122, r124, and r125) cluster above the RGS-G ␣ interface to form an active site common to all members of the family, a reasonable hypothesis is that this is the binding site for additional proteins that mediate specificity (Fig.…”

“…For example, RGS4, RGS16, and RGS1, but not RGS2, have much greater effects on G q -mediated Ca 2ϩ responses in rat pancreatic acinar cells when activated by carbachol than when activated by cholecystokinin (7), suggesting RGS-receptor interaction. G ␤␥ has been shown to inhibit the GTPase-accelerating protein (GAP) activities of RGS4 (8,9), RGSZ1 (8), and the effector PLC-␤1 (9).…”

RGSZ1 and GAIP Regulate μ- but Not δ-Opioid Receptors in Mouse CNS: Role in Tachyphylaxis and Acute Tolerance

“…There is increasing evidence that certain RGS proteins show receptor selectivity (Xu et al, 1999;Wang et al, 2002). Thus, these regulatory proteins might determine the characteristics of the signals triggered by agonists acting at a given receptor.…”