Ligand Bias at Metabotropic Glutamate 1a Receptors: Molecular Determinants That Distinguish β-Arrestin-Mediated from G Protein-Mediated Signaling
Ligand Bias at Metabotropic Glutamate 1a Receptors: Molecular Determinants That Distinguish β-Arrestin-Mediated from G Protein-Mediated Signaling
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DOI：
10.1124/mol.112.078444
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发表时间：
2012-08-01
影响因子：
3.6
通讯作者：
Wroblewski, Jarda T.
中科院分区：
文献类型：
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作者：
Emery, Andrew C.;DiRaddo, John O.;Wroblewski, Jarda T.
代谢性谷氨酸1a(MGlu1a)受体是一种G蛋白偶联受体，与磷脂酰肌醇(PI)的水解、β-arrestin-1介导的持续的细胞外信号调节激酶(ERK)磷酸化和细胞保护信号有关。在此之前，我们报道了该受体存在配基偏向，因为谷氨酸诱导了这两种作用，而奎斯奎宁只诱导了PI的水解。在目前的研究中，我们发现谷氨酸、天冬氨酸和L-半胱氨酸等mGlu1受体激动剂是无偏的，并激活了这两条信号通路，而喹乙醇和(S)-3，5-二羟基苯甘氨酸只刺激PI的水解。竞争性拮抗剂仅抑制PI的水解，而不抑制依赖β-arrestin的途径，而非竞争性mGlu1受体拮抗剂则阻断这两条途径。对mGlu1a受体配体结合域的突变分析表明，Thr188残基是PI水解酶所必需的，但不是保护性信号，而Arg323和Lys409残基是β-arrestin-1介导的持续ERK磷酸化和细胞保护信号所必需的，但不是PI水解酶所必需的。因此，配体偏向的机制似乎涉及不同模式的激动剂与受体配体结合域的相互作用。尽管一些mGlu1a受体激动剂偏向于PI水解，但我们鉴定了两种内源性化合物，戊二酸和琥珀酸，它们是完全偏向于β-arrestin介导的保护性信号的新的mGlu1受体激动剂。药理学研究表明，在产生这两种作用时，谷氨酸与mGlu1受体以两种不同的方式相互作用，因为竞争性的mGlu1受体拮抗剂阻断PI水解并不抑制细胞保护信号。偏向于PI水解的奎斯奎酯不能抑制谷氨酸诱导的保护作用，偏向保护作用的戊二酸不干扰谷氨酸诱导的PI水解。综上所述，这些数据表明mGlu1受体的配基偏差是由于不同的受体-谷氨酸相互作用模式所致，这些模式不同地耦合到PI水解和β-arrestin介导的细胞保护信号，并揭示了作用于mGlu1受体的新的内源性激动剂的存在。
The metabotropic glutamate 1a (mGlu1a) receptor is a G protein-coupled receptor linked with phosphoinositide (PI) hydrolysis and with beta-arrestin-1-mediated sustained extracellular signal-regulated kinase (ERK) phosphorylation and cytoprotective signaling. Previously, we reported the existence of ligand bias at this receptor, inasmuch as glutamate induced both effects, whereas quisqualate induced only PI hydrolysis. In the current study, we showed that mGlu1 receptor agonists such as glutamate, aspartate, and L-cysteate were unbiased and activated both signaling pathways, whereas quisqualate and (S)-3,5-dihydroxyphenylglycine stimulated only PI hydrolysis. Competitive antagonists inhibited only PI hydrolysis and not the beta-arrestin-dependent pathway, whereas a noncompetitive mGlu1 receptor antagonist blocked both pathways. Mutational analysis of the ligand binding domain of the mGlu1a receptor revealed that Thr188 residues were essential for PI hydrolysis but not for protective signaling, whereas Arg323 and Lys409 residues were required for beta-arrestin-1-mediated sustained ERK phosphorylation and cytoprotective signaling but not for PI hydrolysis. Therefore, the mechanism of ligand bias appears to involve different modes of agonist interactions with the receptor ligand binding domain. Although some mGlu1a receptor agonists are biased toward PI hydrolysis, we identified two endogenous compounds, glutaric acid and succinic acid, as new mGlu1 receptor agonists that are fully biased toward beta-arrestin-mediated protective signaling. Pharmacological studies indicated that, in producing the two effects, glutamate interacted in two distinct ways with mGlu1 receptors, inasmuch as competitive mGlu1 receptor antagonists that blocked PI hydrolysis did not inhibit cytoprotective signaling. Quisqualate, which is biased toward PI hydrolysis, failed to inhibit glutamate-induced protection, and glutaric acid, which is biased toward protection, did not interfere with glutamate-induced PI hydrolysis. Taken together, these data indicate that ligand bias at mGlu1 receptors is attributable to different modes of receptor-glutamate interactions, which are differentially coupled to PI hydrolysis and beta-arrestin-mediated cytoprotective signaling, and they reveal the existence of new endogenous agonists acting at mGlu1 receptors.