Steady-state levels of G-protein beta-subunit expression are regulated by treatment of cells with bacterial toxins

Cultures of 3T3-L1 cells were incubated with either 10 ng/ml cholera toxin or 10 ng/ml pertussis toxin from 4 days prior to the initiation of differentiation and throughout the subsequent incubation. Toxin concentrations were sufficient to completely prevent the labelling of alpha-subunits with [32P]NAD+ and pertussis toxin and to prevent by more than 90% the labelling with [32P]NAD+ and cholera toxin in membranes prepared from these cells. Neither toxin prevented the differentiation to the adipocyte phenotype. Neither toxin prevented the increases in the relative amounts of G-proteins which occur upon differentiation. Both toxins dramatically decreased the amount of beta-subunits. As measured by quantitative immunoblotting with antisera specific for both the 35 kDa and 36 kDa beta-subunits, levels of beta-subunit were decreased by more than 50% of steady-state level of control cells. Thus, bacterial toxins which modifies G-protein alpha-subunits are capable of modulating the levels of beta-subunits in vivo. The basis for the regulation of G-protein subunit expression by bacterial toxins is under study