Andrade Erika C, Musante Veronica, Horiuchi Atsuko, Matsuzaki Hideo, Brody A Harrison, Wu Terence, Greengard Paul, Taylor Jane R, Nairn Angus C
Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut 06508.
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520.
J Neurosci. 2017 Mar 8;37(10):2709-2722. doi: 10.1523/JNEUROSCI.4559-15.2017. Epub 2017 Feb 6.
ARPP-16 (cAMP-regulated phospho-protein of molecular weight 16 kDa) is one of several small acid-soluble proteins highly expressed in medium spiny neurons of striatum that are phosphorylated in response to dopamine acting via D1 receptor/protein kinase A (PKA) signaling. We show here that ARPP-16 is also phosphorylated and by microtubule-associated serine/threonine kinase 3 (MAST3 kinase), an enzyme of previously unknown function that is enriched in striatum. We find that ARPP-16 interacts directly with the scaffolding A subunit of the serine/threonine protein phosphatase, PP2A, and that phosphorylation of ARPP-16 at Ser46 by MAST3 kinase converts the protein into a selective inhibitor of B55α- and B56δ-containing heterotrimeric forms of PP2A. Ser46 of ARPP-16 is phosphorylated to a high basal stoichiometry in striatum, suggestive of basal inhibition of PP2A in striatal neurons. In support of this hypothesis, conditional knock-out of ARPP-16 in CaMKIIα::cre/floxed ARPP-16/19 mice results in dephosphorylation of a subset of PP2A substrates including phospho-Thr75-DARPP-32, phospho-T308-Akt, and phospho-T202/Y204-ERK. Conditional knock-out of ARPP-16/19 is associated with increased motivation measured on a progressive ratio schedule of food reinforcement, yet an attenuated locomotor response to acute cocaine. Our previous studies have shown that ARPP-16 is phosphorylated at Ser88 by PKA. Activation of PKA in striatal slices leads to phosphorylation of Ser88, and this is accompanied by marked dephosphorylation of Ser46. Together, these studies suggest that phospho-Ser46-ARPP-16 acts to basally control PP2A in striatal medium spiny neurons but that dopamine acting via PKA inactivates ARPP-16 leading to selective potentiation of PP2A signaling. We describe a novel mechanism of signal transduction enriched in medium spiny neurons of striatum that likely mediates effects of the neurotransmitter dopamine acting on these cells. We find that the protein ARPP-16, which is highly expressed in striatal medium spiny neurons, acts as a selective inhibitor of certain forms of the serine/threonine protein phosphatase, PP2A, when phosphorylated by the kinase, MAST3. Under basal conditions, ARPP-16 is phosphorylated by MAST3 to a very high stoichiometry. However, the actions of MAST3 are antagonized by dopamine and cAMP-regulated signaling leading to disinhibition of ARPP-16 and increased PP2A action.
ARPP - 16（分子量为16 kDa的环磷酸腺苷调节磷蛋白）是几种小的酸溶性蛋白之一，在纹状体的中等棘状神经元中高度表达，这些神经元会因多巴胺通过D1受体/蛋白激酶A（PKA）信号传导而发生磷酸化。我们在此表明，ARPP - 16也会被微管相关丝氨酸/苏氨酸激酶3（MAST3激酶）磷酸化，MAST3激酶是一种功能未知但在纹状体中富集的酶。我们发现ARPP - 16直接与丝氨酸/苏氨酸蛋白磷酸酶PP2A的支架A亚基相互作用，并且MAST3激酶使ARPP - 16的Ser46位点磷酸化后，该蛋白会转变为PP2A含B55α和B56δ的异源三聚体形式的选择性抑制剂。ARPP - 16的Ser46位点在纹状体中以高基础化学计量比被磷酸化，这表明纹状体神经元中PP2A存在基础抑制。为支持这一假设，在CaMKIIα::cre/floxed ARPP - 16/19小鼠中条件性敲除ARPP - 16会导致包括磷酸化苏氨酸75 - DARPP - 32、磷酸化T308 - Akt和磷酸化T202/Y204 - ERK在内的一部分PP2A底物去磷酸化。条件性敲除ARPP - 16/19与在食物强化的渐进比率程序中测量的动机增加有关，但对急性可卡因的运动反应减弱。我们之前的研究表明，ARPP - 16在Ser88位点被PKA磷酸化。纹状体切片中PKA的激活会导致Ser88位点磷酸化，同时伴随着Ser46位点的显著去磷酸化。总之，这些研究表明，磷酸化的Ser46 - ARPP - 16在纹状体中等棘状神经元中对PP2A起基础控制作用，但多巴胺通过PKA作用会使ARPP - 16失活，导致PP2A信号传导的选择性增强。我们描述了一种在纹状体中等棘状神经元中富集的新型信号转导机制，该机制可能介导神经递质多巴胺对这些细胞的作用。我们发现，在纹状体中等棘状神经元中高度表达的蛋白ARPP - 16，在被MAST3激酶磷酸化后，可作为丝氨酸/苏氨酸蛋白磷酸酶PP2A某些形式的选择性抑制剂。在基础条件下，ARPP - 16被MAST3磷酸化的化学计量比非常高。然而，MAST3的作用会被多巴胺和环磷酸腺苷调节的信号传导拮抗，导致ARPP - 16去抑制和PP2A作用增强。
