Abstract

The D2 dopamine receptor isoforms signal to a variety of cellular effectors in both the central nervous system and periphery. Two alternative splice forms of the D2 dopamine receptor exist, the D2s (short) and D2l (long), which has an insertion of 29 amino acids in the third intracellular loop (Dal Taso et al., 1989). In cells of the anterior lobe of the pituitary, D2 dopamine receptors (both forms) are present on lactotroph cells coupled to the inhibition of adenylyl cyclase, activation of voltage-gated calcium channels, and inhibition of potassium channels. We describe here a novel signaling pathway for the D2s, which is the activation of phospholipase D (PLD). GH4C1 cells, a clonal line derived from a rat pituitary tumor, were stably transfected with the gene encoding the D2s, generating GH4-121 cells. Treatment of GH4-121 cells with a dopaminergic agonist resulted in activation of PLD in both a dose-dependent and time-dependent manner. This signaling pathway was not inhibited by prior treatment of cells with pertussis toxin at concentrations that ablate other D2s receptor signaling in this cell line. The stimulation of PLD activity by D2s appeared to correlate with the presence of a specific protein kinase C isoform, PKCε. The D2s stimulation of PLD activity was blocked by preincubation of cells with C3 exoenzyme, indicating that the stimulation of PLD may involve Rho family members. The stimulation of PLD by dopaminergic agonists took place in the absence of any detectable stimulation of phosphoinositide metabolism.