MOLECULAR APPROACHES FOR FUNCTIONS AND PHYSIOLOGICAL SIGNIFICANCE OF PROSTAGLANDIN E RECEPTORS

我们以前确定了三种亚型的小鼠前列腺素（PG）E受体EP 3亚型，EP 3 α，EP 3 β和EP 3 γ，具有不同的COOH末端的尾巴，通过选择性剪接产生。我们检查了这些异构体的Gi活性。EP 3 α受体表现出显著的激动剂非依赖性组成型Gi活性，EP 3 β受体没有组成型活性，EP 3 γ受体表现出大部分完全组成型活性。在四种PGE受体亚型中，EP 2和EP 4受体与相同的信号转导途径偶联，即刺激腺苷酸环化酶。然而，EP 4受体经历了短期激动剂诱导的脱敏，但没有观察到这样的脱敏EP 2受体。另一方面，PGE_2迅速代谢为15-酮-PGE_2。EP 4受体对代谢产物的反应明显丧失，但EP 2受体仍有明显的反应。因此，EP 2和EP 4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和它们对激动剂的代谢失活的不同敏感性。当EP 3受体在PC-12细胞中表达时，在分化的细胞中，EP 3激动剂以百日咳毒素不敏感的方式引起神经突收缩。C3外切酶完全抑制EP 3激动剂诱导的神经突起收缩时，微量注射到细胞中，表明EP 3受体的形态学效应依赖于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.