RDGBα, a PI-PA transfer protein regulates G-protein coupled PtdIns(4,5)P2 signalling during Drosophila phototransduction

Abstract

Many membrane receptors activate phospholipase C (PLC) during signalling, triggering changes in the levels of several plasma membrane lipids including phosphatidylinositol (PtdIns), phosphatidic acid (PtdOH) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. It is widely believed that exchange of lipids between the plasma membrane and endoplasmic reticulum (ER) is required to restore lipid homeostasis during PLC signalling, yet the mechanism remains unresolved. RDGBα (hereafter RDGB) is a multi-domain protein with a PtdIns transfer protein (PITP) domain (RDGB-PITPd). We find that, in vitro, the RDGB-PITPd binds and transfers both PtdOH and PtdIns. In Drosophila photoreceptors, which experience high rates of PLC activity, RDGB function is essential for phototransduction. We show that binding of PtdIns to RDGB-PITPd is essential for normal phototransduction; however, this property is insufficient to explain the in vivo function because another Drosophila PITP (encoded by vib) that also binds PtdIns cannot rescue the phenotypes of RDGB deletion. In RDGB mutants, PtdIns(4,5)P2 resynthesis at the plasma membrane following PLC activation is delayed and PtdOH levels elevate. Thus RDGB couples the turnover of both PtdIns and PtdOH, key lipid intermediates during G-protein-coupled PtdIns(4,5)P2 turnover.

Dynamics of Phosphoinositide-Dependent Signaling in Sympathetic Neurons

“…We detected expression of IRBIT in superior cervical ganglia by Western blot (Fig. 8G), in agreement with previous reports showing expression of IRBIT by immunofluorescence (Zaika et al, 2011). When bound to an IP 3 R, IRBIT renders the IP 3 binding domain unavailable for IP 3 .…”

“…Therefore, we bathed the cells with 100 nM tetrodotoxin (TTX). As others have reported (Cruzblanca et al, 1998;del Río et al, 1999;Zaika et al, 2007), upon stimulation of these neurons with 10 M Oxo-M there was only a small Ca 2ϩ rise, suggesting very little release of Ca 2ϩ from intracellular stores (Fig. 8A).…”

“…It has been proposed that M 1 receptors in SCG neurons are too far away from the ER membrane to activate IP 3 Rs (Delmas et al, 2002;Zaika et al, 2011;Zhang et al, 2013). This hypothesis requires a fast local degradation of released IP 3 .…”

“…Given the special needs of the nervous system, it is tempting to imagine that many neurons have faster phosphoinositide dynamics than nonexcitable cells. In sensory neurons and photoreceptors, for example, TRP and other channels require phosphoinositides (Rohacs, 2014;Hille et al, 2015), and therefore the speed of phosphoinositide restoration in these neurons controls the dynamic range for sensory input (Yadav et al, 2015). In the brain, modulatory areas control other brain areas by releasing neurotransmitters and hormones, such as acetylcholine, norepinephrine, or serotonin, acting on G-protein-coupled receptors that activate PLC and hydrolyze PI(4,5)P 2 .…”

“…PI(4,5)P 2 -dependent KCNQ2/3, Ca V 2.2, and Ca V 2.1 channels are widely expressed in the brain, emphasizing the importance for rapid adjustment of phosphoinositide levels for coordinated ion channel activity in the brain. PI(4,5)P 2 depletion in neuronal and cardiac tissues Studies on isolated neurons provide strong evidence for net PI(4,5)P 2 depletion upon activation of muscarinic receptors, leading to closure of PI(4,5)P 2 -dependent ion channels such as KCNQ2/3 or Ca V channels in these cells (Suh and Hille, 2002;Gamper et al, 2004;Zaika et al, 2007;Hille et al, 2015). However, it is not known to what extent natural stimuli cause net PI(4,5)P 2 depletion in intact neuronal tissues.…”