Determining the role of RGS proteins in opioid biochemistry and behavior
Smith, Chelsea E.
MetadataShow full item record
Opioids are potent analgesic drugs prescribed to treat pain that ranges from moderate to severe. They have unwanted side effects, can lead to tolerance and dependence, and display addictive properties. Opioids function by acting on mu opioid receptors (MORs) located throughout the CNS. MOR is coupled to inhibitory heterotrimeric G proteins of the Gαi/o family, which have many downstream signaling effects, including inhibition of adenylyl cyclase. Regulators of G protein signaling (RGS) proteins negatively modulate this receptor-mediated G protein signaling. One of the remaining questions regarding the effects of RGS proteins on MOR signaling is which, if any, Gαi/o protein subtype serves as the site of action for RGS protein inhibition of opioid signaling. To evaluate the role of one Gα subunit, Gαo, in the effects of RGS proteins on opioid signaling, MOR-mediated biochemistry was evaluated in mice that express an RGS- insensitive (RGSi), mutant Gαo protein (Gαo -RGSi). In particular, MOR expression and function was measured using saturation radioligand binding with agonist [3H]DAMGO and MOR agonist-stimulated [35S]GTPγS binding, respectively, while G protein expression was evaluated by Western blot. Mice possessing the knock-in mutation showed no changes in total MOR expression, but showed decreased agonist-stimulated G protein activation. This loss in stimulation could be attributed to a decrease in the expression of Gαo, Gαz, Gβ1-4 and Gγ2 proteins in the Gαo-RGSi +/GS mice. These changes in G protein expression and activity are likely a result of compensation in response to the increased signaling produced by the RGSi mutation. Thus, it will be difficult to use these mice as a model for studying RGS proteins due to these compensatory changes in the opioid signaling system. Nevertheless, this,shows that RGS proteins play an essential role in the basic control of MOR signaling.