Structure of RGS4 Bound to AlF4−-Activated Giα1: Stabilization of the Transition State for GTP Hydrolysis

López-Fando

et al. 2004

105

In the CNS, the regulators of G-protein signaling (RGS) proteins belonging to the Rz subfamily, RGS19 (Ga interacting protein (GAIP)) and RGS20 (Z1), control the activity of opioid agonists at m but not at d receptors. Rz proteins show high selectivity in deactivating Gaz-GTP subunits. After reducing the expression of RGSZ1 with antisense oligodeoxynucleotides ( Knockdown of GAIP and of the GAIP interacting protein C-terminus (GIPC) led to changes in agonist effects at m but not at d receptors. The impairment of RGSZ1 extended the duration of morphine analgesia by at least 1 h beyond that observed in control animals. CTOP (Cys 2 , Tyr 3 , Orn 5 , Pen 7 -amide) antagonized morphine analgesia when given during the period in which the effect of morphine was enhanced by RGSZ1 knockdown. Thus, in naive mice, morphine tachyphylaxis originated in the presence of the opioid agonist and during the analgesia time course. The knockdown of RGSZ1 facilitated the development of tolerance to a single dose of morphine and accelerated tolerance to continuous delivery of the opioid. These results indicate that m but not d receptors are linked to Rz regulation. The m receptor-mediated activation of Gz proteins is effective at recruiting the adaptive mechanisms leading to the development of opioid desensitization.

Section: Discussionmentioning

confidence: 94%

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

Garzón

López-Fando

et al. 2004

105

“…However, the members of the RGS-Rz subfamily exhibit the distinctive feature of binding with similar affinities to the activated GaGTP subunits as well as to the transition state . This is accomplished through binding to the Nterminal helix of activated Ga subunits Wang et al, 1998), an interaction that is not observed between Gai and RGS4 (Tesmer et al, 1997).…”

Section: Discussionmentioning

confidence: 99%

“…Both are required for RGS binding to the transition state of Ga and for its subsequent GAP activity. The loops between a3 and a4, a5, and a6, and the residues at the end of a7 and at the beginning of the a8 helix form the Ga interaction surface (Tesmer et al, 1997). Other RGS residues not involved in contact with Ga may mediate RGS-effector interactions, as occurs in the RGS9-1 and phosphodiesterase (PDE)g-Gat complex.…”

Section: Discussionmentioning

confidence: 99%

Sumoylated RGS-Rz Proteins Act as Scaffolds for Mu-Opioid Receptors and G-Protein Complexes in Mouse Brain

Bermúdez

Sánchez‐Blázquez

et al. 2006

The RGSZ1 and RGSZ2 proteins, members of the RGS-Rz subfamily of GTPase-activating proteins (GAP), are involved in Mu-opioid receptor desensitization. The expression of these proteins, as well as of their main target the Gz protein, is virtually restricted to the nervous tissue. In synaptosomal membranes, these Rz proteins undergo post-translational modifications such as glycosylation and phosphorylation, and they may covalently attach to small ubiquitin-like modifier (SUMO) proteins. While RGSZ1 exists in conjugated and non-conjugated forms, RGSZ2 is mostly conjugated to SUMO-1, SUMO-2 and SUMO-3 proteins. These sumoylated forms of the GAPs readily associated with Mu-opioid receptors but they associated only poorly with Delta receptors. Furthermore, Gai2 and Gaz subunits co-precipitated with the sumoylated forms of RGSZ1/Z2 proteins, but to a lesser extent with the Ser phosphorylated SUMO-free form of RGSZ1. Upon Mu-opioid receptor activation, there is a strong increase in the association of Ga proteins with RGSZ2 proteins that persists for intervals longer than 24 h. This effect probably accounts for their role in Mu-opioid receptor desensitization. Only a moderate increase was observed with RGSZ1, the non-sumoylated form of which probably acts as an efficient GAP for these Ga subunits. Therefore, sumoylation regulates the biological activity of RGS-Rz proteins and it is likely that it serves to switch their behavior, from that of a GAP for activated Ga subunits to that of a scaffold protein for specific signaling proteins.

“…The extreme N-terminal helix of Ga subunits is crucial for its interaction with RGS-Rz proteins (Wang et al, 1998;Tu et al, 1997). This interaction does not occur between Gai1 and RGS4 (Tesmer et al, 1997) and could account for the binding of GaGTP to RGS-Rz proteins. In this scenario, the capacity of certain RGS proteins to bind to receptor-activated GaGTP subunits could reduce Gamediated activation of downstream effectors.…”

Section: Discussionmentioning

confidence: 99%

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

Garzón

López-Fando

et al. 2005

104

The regulator of G-protein signaling RGS17(Z2) is a member of the RGS-Rz subfamily of GTPase-activating proteins (GAP) that efficiently deactivate GazGTP subunits. We have found that in the central nervous system (CNS), the levels of RGSZ2 mRNA and protein are elevated in the hypothalamus, midbrain, and pons-medulla, and that RGSZ2 is glycosylated in synaptosomal membranes isolated from CNS tissue. In analyzing the function of RGSZ2 in the CNS, we found that when the expression of RGSZ2 was impaired, the antinociceptive response to morphine and [D-Ala 2 , N-MePhe 4 , Gly-ol 5 ]-enkephalin (DAMGO) augmented. This potentiation involved m-opioid receptors and increased tolerance to further doses of these agonists administered 24 h later. High doses of morphine promoted agonist desensitization even within the analgesia time-course, a phenomenon that appears to be related to the great capacity of morphine to activate Gz proteins. In contrast, the knockdown of RGSZ2 proteins did not affect the activity of d receptor agonists, [D-Pen 2,5 ]-enkephalin (DPDPE), and [D-Ala 2 ] deltorphin II. In membranes from periaqueductal gray matter (PAG), both RGSZ2 and the related RGS20(Z1) co-precipitated with m-opioid receptors. While a morphine challenge reduced the association of Gi/o/z with m receptors, it increased their association with the RGSZ2 and RGSZ1 proteins. However, only Gaz subunits co-precipitated with RGSZ2. Doses of morphine that produced acute tolerance maintained the association of Ga subunits with RGSZ proteins even after the analgesic effects had ceased. These results indicate that both RGSZ1 and RGSZ2 proteins influence m receptor signaling by sequestering Ga subunits, therefore behaving as effector antagonists.