TY - JOUR T1 - Phosphatidylinositol 4,5-Bisphosphate Modifies Tubulin Participation in Phospholipase Cβ<sub>1</sub> Signaling JF - The Journal of Neuroscience JO - J. Neurosci. SP - 1668 LP - 1678 DO - 10.1523/JNEUROSCI.22-05-01668.2002 VL - 22 IS - 5 AU - Juliana S. Popova AU - Arin K. Greene AU - Jia Wang AU - Mark M. Rasenick Y1 - 2002/03/01 UR - http://www.jneurosci.org/content/22/5/1668.abstract N2 - Tubulin forms the microtubule and regulates certain G-protein-mediated signaling pathways. Both functions rely on the GTP-binding properties of tubulin. Signal transduction through Gαq-regulated phospholipase Cβ1(PLCβ1) is activated by tubulin through a direct transfer of GTP from tubulin to Gαq. However, at high tubulin concentrations, inhibition of PLCβ1 is observed. This report demonstrates that tubulin inhibits PLCβ1 by binding the PLCβ1 substrate phosphatidylinositol 4,5-bisphosphate (PIP2). Tubulin binding of PIP2 was specific, because PIP2 but not phosphatidylinositol 3,4,5-trisphosphate, phosphatidylinositol 3-phosphate, phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine, or inositol 1,4,5-trisphosphate inhibited microtubule assembly. PIP2 did not affect GTP binding or GTP hydrolysis by tubulin. Muscarinic agonists promoted microtubule depolymerization and translocation of tubulin to the plasma membrane. PIP2 augmented this process in both Sf9 cells, containing a recombinant PLCβ1 pathway, and SK-N-SH neuroblastoma cells. Colocalization of tubulin and PIP2 at the plasma membrane was demonstrated with confocal laser immunofluorescence microscopy. Although tubulin bound to both Gαq and PLCβ1, PIP2 facilitated the interaction between tubulin and PLCβ1 but not that between tubulin and Gαq. However, PIP2 did augment formation of tubulin–Gαq–PLCβ1 complexes. Subsequent to potentiating PLCβ1 activation, sustained agonist-independent membrane binding of tubulin at PIP2- and PLCβ1-rich sites appeared to inhibit Gαq coupling to PLCβ1. Furthermore, colchicine increased membrane-associated tubulin and also inhibited PLCβ1 activity in SK-N-SH cells. Thus, tubulin, depending on local membrane concentration, may serve as a positive or negative regulator of phosphoinositide hydrolysis. Rapid changes in membrane lipid composition or in the cytoskeleton might modify neuronal signaling through such a mechanism. ER -