Cholecystokinin type B receptor-mediated inhibition of A-type K+ channels enhances sensory neuronal excitability through the phosphatidylinositol 3-kinase and c-Src-dependent JNK pathway

Shear stress differentially activates extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) by mechanisms involving Gαi2 and Gβ/γ proteins, respectively, in bovine aortic endothelial cells (BAEC). The early events in this signaling mechanism by which G proteins regulate ERK and JNK in response to shear stress have not been defined. Here we show that BAEC endogenously express a G protein-dependent form of phosphatidylinositol 3-kinase, PI3Kγ, and its activity is stimulated by shear stress. PI3Kγ activity was measured in vitro using BAEC that were transiently transfected with an epitope-tagged PI3Kγ (vsv-PI3Kγ). Exposure of BAEC to shear stress rapidly and transiently stimulated the activity of vsv-PI3Kγ (maximum by 15 s, with a return to basal after 1-min exposure to 5 dyn/cm2 shear stress). Activity of vsv-PI3Kγ was stimulated by shear stress intensities as low as 0.5 dyn/cm2. Treatment of BAEC with an inhibitor of PI3K, wortmannin, inhibited shear-dependent activation of JNK but had no effect on that of ERK. Furthermore, expression of a kinase-inactive mutant (PI3KγK799R) in BAEC inhibited the shear-dependent activation of JNK but not ERK. Taken together, these results suggest that PI3Kγ selectively regulates the shear-sensitive JNK pathway. This differential and novel signaling pathway may be responsible for coordinating various mechanosensitive events in endothelial cells.

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Insulin-Like Growth Factor-1 Receptor-Mediated Inhibition of A-type K+ Current Induces Sensory Neuronal Hyperexcitability Through the Phosphatidylinositol 3-Kinase and Extracellular Signal-Regulated Kinase 1/2 Pathways, Independently of Akt

Endocrinology ◽

10.1210/en.2013-1559 ◽

2014 ◽

Vol 155 (1) ◽

pp. 168-179 ◽

Cited By ~ 24

Author(s):

Hua Wang ◽

Jianzhong Qin ◽

Shan Gong ◽

Bo Feng ◽

Yuan Zhang ◽

...

Keyword(s):

Trigeminal Ganglion ◽

Kinase Inhibitor ◽

Delayed Rectifier ◽

Phosphatidylinositol 3 Kinase ◽

Neuronal Hyperexcitability ◽

Type K ◽

K Current ◽

Trigeminal Ganglion Neurons ◽

Ganglion Neurons ◽

Phosphatidylinositol 3

Although IGF-1 has been implicated in mediating hypersensitivity to pain, the underlying mechanisms remain unclear. We identified a novel functional of the IGF-1 receptor (IGF-1R) in regulating A-type K+ currents (IA) as well as membrane excitability in small trigeminal ganglion neurons. Our results showed that IGF-1 reversibly decreased IA, whereas the sustained delayed rectifier K+ current was unaffected. This IGF-1–induced IA decrease was associated with a hyperpolarizing shift in the voltage dependence of inactivation and was blocked by the IGF-1R antagonist PQ-401; an insulin receptor tyrosine kinase inhibitor had no such effect. An small interfering RNA targeting the IGF-1R, or pretreatment of neurons with specific phosphatidylinositol 3-kinase (PI3K) inhibitors abolished the IGF-1–induced IA decrease. Surprisingly, IGF-1–induced effects on IA were not regulated by Akt, a common downstream target of PI3K. The MAPK/ERK kinase inhibitor U0126, but not its inactive analog U0124, as well as the c-Raf-specific inhibitor GW5074, blocked the IGF-1–induced IA response. Analysis of phospho-ERK (p-ERK) showed that IGF-1 significantly activated ERK1/2 whereas p-JNK and p-p38 were unaffected. Moreover, the IGF-1–induced p-ERK1/2 increase was attenuated by PI3K and c-Raf inhibition, but not by Akt blockade. Functionally, we observed a significantly increased action potential firing rate induced by IGF-1; pretreatment with 4-aminopyridine abolished this effect. Taken together, our results indicate that IGF-1 attenuates IA through sequential activation of the PI3K- and c-Raf-dependent ERK1/2 signaling cascade. This occurred via the activation of IGF-1R and might contribute to neuronal hyperexcitability in small trigeminal ganglion neurons.

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