Synaptic Membrane G Proteins Are Complexed with Tubulin In Situ

Abstract

The G proteins G 5 and G~1appear to be capable of binding to tubulin specifically, and it has been suggested that such binding results in G protein activation via direct transfer of GTP. This study was undertaken to demonstrate that consequences of G protein activation by tubulin, i.e., stimulation or inhibition of adenylyl cyclase, were dependent on the G proteins expressed as well as unique aspects of the membrane or cytoskeleton in a given cell type. Membranes from rat 06 glioma cells, which express G5,, but not G~,,1, responded to the addition of tubulin with a stable activation of adenylyl cyclase. Conversely, membranes from rat cerebral cortex, which contain both G5 and G1, responded to exogenous tubulin with a stable inhibition of adenylyl cyclase. Unlike 06 membranes, cerebral cortex membranes are richly endowed with tubulin, and antitubulin antibodies immuno-precipi~atedcomplexes of tubulin and G,1 or G5 from detergent extracts of these membranes. Nearly 90% of the G5,, from Triton X-114 extracts coimmunoprecipitated with tubu~n,suggesting that these proteins exist as a complex in the synaptic membrane. Such complexes may provide the framework for a G protein-cytoskeleton link that participates in the modulation of cellular signal transduction.

Chronic Antidepressant Treatment Prevents Accumulation of Gsα in Cholesterol-Rich, Cytoskeletal-Associated, Plasma Membrane Domains (Lipid Rafts)

“…Tubulin has been shown to interact directly with Gsa (Wang and Rasenick, 1991;Wang et al, 1990;Yan et al, 1996Yan et al, , 2001) and transfer GTP to G protein a subunits. Experiments with a GTP photoaffinity analog suggest that tubulin dimers form complexes with the a subunits of Gs, Gi1, or Gq and activate them through a direct nucleotide transfer (transactivation) mechanism (Popova and Rasenick, 2000;Rasenick and Wang, 1988;Roychowdhury et al, 1993;Yan et al, 2001).…”

Phosphatidylinositol 4,5-Bisphosphate Modifies Tubulin Participation in Phospholipase Cβ1Signaling

“…Association of tubulin with certain G␣ subunits and the subsequent regulation of adenylyl cyclase and PLC␤ 1 signaling has been reported (Popova et al, 1994(Popova et al, , 1997Yan et al, 1996Yan et al, , 2001Popova and Rasenick, 2000). After m1 muscarinic receptor stimulation in vitro (Popova et al, 1997) and in vivo (Popova and Rasenick, 2000), cytosolic tubulin translocates to the plasma membrane.…”

A Specific Domain of Giα Required for the Transactivation of Giα by Tubulin Is Implicated in the Organization of Cellular Microtubules

“…Transducin, however, does not bind to tubulin. Complexes between G s ␣ or G i ␣ and tubulin were co-immunoprecipitated from detergent extracts of synaptic membrane (12)(13)(14)(15). This binding appears to activate the G protein due to a direct transfer of GTP from the E-site in tubulin to G␣ (transactivation) (16 -18).…”