Molecular Characterization of ADP-ribosyl Cyclase Coupled with Receptors

点击翻译按钮获取中文摘要

We previously reported that stimulation of β-adrenergic and angiotensin II receptors modulates activity of ADP-ribosyl cyclase, a synthetic enzyme of cADP-ribose, and showed that cADP-ribose is a critical molecule in sympathetic potentiation of heart contraction, post-natal heart growth, and neuron-glia interaction. In the present study, we used the same strategy to explore the idea mat cADP-ribose is a second messenger downstream of the mGluRs. We first measured ADP-ribosyl cyclase activity in crude membranes from various rat and mouse nervous tissues in the presence or absence of glutamate and/or GTP. Second, the coupling preference of mGluRs to ADP-ribosyl cyclase was examined in NG108-15 neuroblastoma x glioma hybrid cells over-expressing each subtype.Glutamate stimulates ADP-ribosyl cyclase activity in rat or mouse crude membranes of retina via group III mGIuRs or in superior cervical ganglion via group I mGluRs. The retina of mGluR6 deficient mice showed no increase in the ADP-ribosyl cyclase level in response to glutamate. GTP enhanced the initial rate of basal and glutamate-stimutated cyclase activity. GTP-γ-S also stimulated basal activity. To determine whether the coupling mode of mGluRs to ADP-ribosyl cyciase is a feature common to individual cloned mGIuRs, we expressed each mGluR subtype in NG108-15 neuroblastoma x glioma hybrid cells. The glutamate-induced stimulation of the cyclase occurs preferentially in NG108-15 cells over-expressing mGluRs1, 3, 5, and 6. Cells expressing mGluR2 or mGluRs4 and 7 exhibit inhibition or no coupling, respectively. Glutamate-induced activation or inhibition of the cyclase activity was eliminated after pretreatment with cholera or pertussis toxin, respectively. Thus, the subtype-specific coupling of mGIuRs to ADP-ribosyl cyclase via G proteins suggests that some glutamate-evoked neuronal function is mediated by cADP-ribose.