MOLECULAR APPROACHES FOR FUNCTIONS AND PHYSIOLOGICAL SIGNIFICANCE OF PROSTAGLANDIN E RECEPTORS

我们之前鉴定了三种小鼠前列腺素（PG） E受体EP3亚型，EP3alpha， EP3beta和EP3gamma，具有不同的cooh末端尾部，通过选择性剪接产生。我们检测了这些同工异构体的Gi活性。ep3α受体表现出明显的不依赖于激动剂的构成活性，ep3β受体没有构成活性，而ep3γ受体表现出充分的构成活性。因此，EP3受体同种异构体在构成性Gi活性上是不同的。在四种PGE受体亚型中，EP2和EP4受体偶联到相同的信号转导途径，即刺激腺苷酸环化酶。然而，EP4受体经历了激动剂诱导的短期脱敏，但EP2受体没有观察到这种脱敏。另一方面，PGE_2被迅速代谢为15-酮-PGE_2。EP4受体明显失去对代谢物的反应，但EP2受体仍有显著的反应。因此，EP2和EP4受体的生理意义可能在于它们对激动剂诱导的短期脱敏的不同敏感性以及它们对激动剂代谢失活的不同敏感性。EP3受体广泛分布于神经系统，并特异性定位于神经元。当EP3受体在PC-12细胞中表达时，在分化的细胞中，EP3激动剂以百日咳毒素不敏感的方式引起神经突收缩。当将C3外泌酶微注射到细胞中时，可以完全抑制EP3激动剂诱导的神经突收缩，这表明EP3受体的形态学作用依赖于Rho活性。

We previously identified three isoforms of the mouse prostaglandin (PG) E receptor EP3 subtype, EP3alpha, EP3beta and EP3gamma, with different COOH-terminal tails, produced through alternative splicing. We examined the Gi activities of these isoforms. The EP3alpha receptor showed marked agonist-independent constitutive Gi activity, the EP3beta receptor had no constitutive activity, and the EP3gamma receptor showed mostly full constitutive activity. Thus, the EP3 receptor isoforms differ in constitutive Gi activity.Among four PGE receptor subtypes, the EP2 and EP4 receptors are coupled to the same signal transduction pathway, stimulation of adenylate cyclase. However, the EP4 receptor underwent short term agonist-induced desensitization, but no such desensitization was observed for the EP2 receptor. On the other hand, PGE_2 is rapidly metabolized to 15-keto-PGE_2. The EP4 receptor markedly lost the response for the metabolite, but the EP2 receptor still had significant response. Therefore, the physiological significance of EP2 and EP4 receptors may lie in their different sensitivities to agonist-induced short term desensitization and their differential susceptibilities to the metabolic inactivation of the agonist.The EP3 receptor is widely distributed in the nervous system and is specifically localized to neurons. when the EP3 receptor was expressed in PC-12 cells, in the differentiated cells, an EP3 agonist caused neurite retraction in a pertussis toxin-insensitive manner. C3 exoenzyme completely inhibited the EP3 agonist-induced neurite retraction when microinjected into the cells, indicating that the morphological effect of the EP3 receptor is dependent on Rho activity.