RGS-Rz and RGS9-2 proteins control mu-opioid receptor desensitisation in CNS: the role of activated Gαz subunits

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

“…These observations suggest that the enhancement of m agonist signaling produced in RGSZ2 or RGSZ1 knockdown mice intensified the desensitization of m-opioid receptors. This phenomenon diminishes after reducing the levels of Gaz, but not Gai2 subunits (Garzón et al, 2004;Sánchez-Blázquez et al, 2005). Thus, Gz proteins appear to play an important role in morphine-induced acute tolerance.…”

“…Equal loading was verified by probing the blots with an anti-b-actin antibody (CSA-400, Stressgen, Victoria, Canada), either in the same or parallel blots. The separated proteins were transferred to 0.2 mm polyvinylidene difluoride membranes (Bio-Rad), and the membranes were incubated at 61C for 24 h with polyclonal antisera diluted in TBS-0.05% Tween 20 (TTBS): anti-Gao (GC/2, NEI-804) 1 : 1000; anti-Gaz, anti-Gai2, and anti-Gai1 (1 : 2000; Garzón et al, 1997a), as well as affinity-purified IgGs raised against RGSZ2 and RGSZ1 (1 : 3000; Garzón et al, 2004;Sánchez-Blázquez et al, 2005). Antibody binding was detected with a goat anti-rabbit IgG (H þ L) horseradish peroxidase conjugate antiserum (BioRad, #170-6515) diluted 1 : 5000 in TTBS and exposed to the membranes for 3 h. The secondary antibody was visualized with the ECL plus Western Blotting Detection System (RPN2132, Amersham Biosciences), and chemiluminescence was detected using a Peltier cooled CCD camera (À351C; high signal-to-noise ratio; dynamic range up of 3.4 OD) and a ChemiImager IS-5500 (Alpha Innotech, San Leandro, California).…”

“…These results suggest that the knockdown of the RGSZ2 proteins desensitizes certain effectors that are regulated by m receptor-activated GaGTP subunits, leading to the rapid attenuation of agonist-evoked signals. The effects of high doses of morphine that remained in these animals were probably promoted by the activation of G proteins that exhibit a low capacity to promote m receptor desensitization (eg of Gi2) on effectors that still show receptor regulation (Garzón et al, 2004;Sánchez-Blázquez et al, 2005). This was particularly relevant when higher doses of morphine were administered to mice with impaired RGSZ2 function.…”

“…As a result, the activity of DAMGO is less intense than might be expected from the level of G protein activation. The differences observed between morphine and DAMGO in promoting m receptor desensitization could reside in the differential activation of Gi2 and Gz proteins in promoting analgesia (Garzón et al, 1997a, b), Gz being more active in this phenomena (Garzón et al, 2004;Sánchez-Blázquez et al, 2005). Furthermore, the knockdown of RGSZ2 promoted no changes on the analgesic activity of the d receptor agonists RGSZ2 proteins regulate l-opioid receptors J Garzó n et al tolerance paradigm.…”

“…In the central nervous system (CNS), Gz proteins are more effective in mediating the desensitization of m-opioid receptors than Gi2 proteins (Garzón et al, 2004;Sánchez-Blázquez et al, 2005). Moreover, RGSZ1 regulates Gz proteins following their activation by m receptors, as does GAIP, albeit to a much lesser extent (Garzón et al, 2004).…”