Association of the G Proteinα q/α11-Subunit with Cytoskeleton in Adrenal Glomerulosa Cells: Role in Receptor-Effector Coupling1

In 3-day primary cultures of rat glomerulosa cells, a 30-min preincubation with either 10 μm colchicine (a microtubule-disrupting agent) or 10 μm cytochalasin B (a microfilament-disrupting agent) decreased angiotensin II (Ang II)-induced inositol phosphate accumulation by 50%. Moreover, both drugs decreased inositol phosphate production induced by fluoroaluminate (a nonspecific activator of all G proteins), indicating that both microtubules and microfilaments are essential for phospholipase C activation. Analysis of microfilament- and microtubule-enriched fractions and immunoprecipitation of actin and tubulin revealed that the αq/α11-subunit of the Gq/11 protein was associated with both structures. Ang II stimulation induced a rapid translocation ofα q/α11, microfilaments, and microtubules to the membrane and induced a time-dependent increase in the level ofα q/α11 associated with both microfilaments and microtubules. Moreover, double immunofluorescence staining clearly showed a colocalization of theα q/α11-subunit of the Gq/11 coupling protein and microfilament distribution. These associations and plasma membrane redistribution under Ang II stimulation indicate that microfilaments and microtubules are both involved in phospholipase C activation and inositol phosphate production. Moreover, our results indicate that the αq/α11 protein is closely associated with cytoskeletal elements and is found both at the plasma membrane level as well as on intracellular stress fibers.