Role of receptor kinase in β1-adrenergic receptor signaling, and hypertrophy/heart failure

刺激α_1肾上腺素受体(α_1AR)可激活新生大鼠心肌细胞中丝氨酸/苏氨酸蛋白激酶c-jun氨基末端激酶(JNK)。JNK属于丝裂原活化蛋白激酶家族成员，是介导细胞外信号起源于细胞表面至细胞核的关键分子之一。在心肌细胞中，G蛋白偶联受体的刺激激活了包括JNK在内的丝裂原激活的蛋白激酶，并触发了肥大反应。Gα_q、Gα_&lt；12&gt；和Gα_&lt；13&gt；的羧基末端区域的表达抑制了JNK的激活。Gα_q和Gα；12/13&gt；的参与进一步得到了证据的支持，即Gα_q；q/11&gt；特异性的G蛋白信号转导调节域的表达被G蛋白偶联受体激酶2(GRK2)的G蛋白信号转导结构域或p115-α的G蛋白信号转导结构域所抑制。RGS结构域含有~12 5个氨基酸，与激活形式的Gα亚基相互作用。表达G-α和G-α_I特异性RGS蛋白，但不能抑制JNK1的激活。GRK2的羧基末端区域与Gβγ结合并阻断其功能，但不影响JNK2的激活。这些结果表明，Gα和Gα_q而不是Gβγ介导了α_1AR诱导的JNK的激活。EGTA、BAPTA-AM或尼群地平处理细胞几乎完全抑制JNK的激活。α_1AR刺激缓慢并逐渐增加对尼群地平敏感的细胞内钙离子浓度。细胞内Ca~(2+)的这种增加也被p115-RGS的表达所抑制，表明Gα_&lt；12/13&gt；参与了这一过程。这些结果表明，Gα_(12/13)通过L型钙通道增加钙内流，从而激活JNK。

Stimulation of α_1-adrenregic receptor (α_1AR) activates c-Jun NH_2-terminl kinase (JNK), a serine/threonine protein kinase, in rat neonatal myocytes. JNK belongs to a member of mitogen-activated protein kinase family, and is one of the key molecules mediating extracellular signal originating at cell surface to nucleus. In cardiomyocytes, stimulation of G protein-coupled receptors activates mitogen-activated protein kinases including JNK, and triggers hypertrophic responses. JNK activation is inhibited by the expression of carboxyl terminal regions of Gα_q, Gα_<12> and Gα_<13>. Involvement of Gα_q and Gα_<12/13> is further supported by the evidence that the JNK activation is inhibited by the expression of Gα_<q/11>-specific regulator of G protein signaling (RGS) domain of G protein-coupled receptor kinase 2 (GRK2) or Gα_<12/13>-specific RGS domain of p115-rhoGEF (p115-RGS). RGS domain contains 〜125 amino acids, and interacts with activated forms of specific Gα subunits. The expression of Gα_<q/11>- and Gα_i-specific RGS protein, RGS4, but not the treatment with PTX inhibits the JNK activation. Carboxyl terminal region of GRK2 that binds to Gβγ and blocks the function does not affect the JNK activation. These results suggest that Gα_<12/13> and Gα_q but not Gβγ mediate the α_1AR-induced JNK activation. The treatment of cells with EGTA, BAPTA-AM or nitrendipine almost completely inhibits the JNK activation. α_1AR stimulation slowly and gradually increases the intracellular Ca^<2+> that is sensitive to nitrendipine. This increase in the intracellular Ca^<2+> is also inhibited by the expression of p115-RGS, indicating the involvement of Gα_<12/13>. These results indicate that Gα_<12/13> activates JNK by the increased Ca^<2+> entry through L-type Ca^<2+> channel in rat neonatal myocytes.