The time-course of agonist-induced solubilization of trimeric Gqα/G11α proteins resolved by two-dimensional electrophoresis

Prolonged agonist stimulation results in specific transfer ofactivated Gα subunits of Gqα/G11α family from particulatemembrane fraction to soluble (cytosol) cell fraction isolated as250 000 x g supernatant. In this study, we have used 2Delectrophoresis for more defined resolution of Gα subunits ofGqα/G11α family and followed the time course of solubilizationeffect. The small signal of soluble G proteins was alreadydetected in control, hormone-unexposed cells. Hormonestimulation resulted in a slow but continuous increase of bothintensity and number of immunoreactive signals/spots of these Gproteins (10, 30, 60, 120 and 240 min). At longer times ofagonist exposure (>2 hours), a marked increase of Gqα/G11αproteins was detected. The maximal level of soluble Gqα/G11αproteins was reached after 16 hours of continuous agonistexposure. At this time interval, eight individual immunoreactivesignals of Gqα/G11α proteins could be resolved. The relativeproportion among these spots was 15:42:10:11:7:7:2:5.Solubilization of this class of Gα proteins was thus observed afterprolonged agonist stimulation only, induced by ultra highconcentration of hormone and in cells expressing a large numberof GPCRs. Our data therefore rather indicate tight/persistingbinding of Gqα/G11α proteins to the membrane.