Modulation of D 3 R Splicing, Signaling, and Expression by D 1 R through PKA→PTB Phosphorylation.

The D 1 R and D 3 R receptors functionally and synergistically interact in striatonigral neurons. Dopaminergic denervation turns this interaction antagonistic, which is correlated with a decrement in D 3 nf isoform and an increment in D 3 R membranal expression. The mechanisms of such changes in D 3 R are attributed to the dysregulation of the expression of their isoforms. The cause and mechanism of this phenomenon remain unknown. Dopaminergic denervation produces a decrement in D 1 R and PKA activity; we propose that the lack of phosphorylation of PTB (regulator of alternative splicing) by PKA produces the dysregulation of D 3 R splicing and changes D 3 R functionality. By using in silico analysis, we found that D 3 R mRNA has motifs for PTB binding and, by RIP, co-precipitates with PTB. Moreover, D 1 R activation via PKA promotes PTB phosphorylation. Acute and 5-day D 1 R blockade decreases the expression of D 3 nf mRNA. The 5-day treatment reduces D 3 R, D 3 nf, and PTB protein in the cytoplasm and increases D 3 R in the membrane and PTB in the nucleus. Finally, the blockade of D 1 R mimics the effect of dopaminergic denervation in D 1 R and D 3 R signaling. Thus, our data indicate that through PKA→PTB, D 1 R modulates D 3 R splicing, expression, and signaling, which are altered during D 1 R blockade or the lack of stimulation in dopaminergic denervation.