G-protein biased signaling agonists of Dopamine D3 receptor promote distinct activation patterns of ERK1/2

Dopamine D3 receptors (D3R) have a causal role in neurological and psychiatric disorders. We have developed a novel class of G-protein biased (GPB) signaling D3R agonists with minimal β-arrestin2 (βarr2) recruitment and demonstrated efficacy in rodent model of Parkinson's disease. This contrasts with unbiased (UB) D3R agonists like Pramipexole which recruit both β-arrestin and G-proteins for signaling. In this study, we investigated the effects of GPB and UB agonists on D3R mediated activation of mono and dual phosphorylation of ERK1/2. We used the neuronal-like SH-SY5Y cells stably expressing D3R and βarr2 knockdown (βarr2KD) to delineate the roles of G and βarr2 on phosphorylation patterns of ERK1/2 induced by D3R agonists. Results indicate GPB and UB agonists promote similar early and late phase mono activation patterns of ERK1/2. On the contrary, GPB and UB agonists promote either early or early and late phase dual activation of ERK1/2, respectively. The early phase dual activation of ERK1/2 is predominantly promoted by G while the late phase dual activation by βarr2 recruitment. PKC plays a significant role in both the early and late phase dual phosphorylation of ERK1/2. βarr2KD significantly increased short- and long-term dual phosphorylation levels of ERK1/2 induced by GPB agonists which was inhibited by a combination of G and PKC inhibitors. Interestingly, βarr2KD significantly reduced the short and long-term dual phosphorylation of ERK1/2 by UB agonists. Overall, this study highlights that biased signaling agonists of D3R have differential effects on ERK1/2 which may be advantageous to develop better drugs.