DECREASED [P-32] GTP-BINDING TO G(S) FOLLOWING NB2 CELL INCUBATION WITH HUMAN GROWTH-HORMONE

We have previously shown that GTP binding protein beta subunit concent ration is maximally increased after 4-7 h incubation with human growth hormone (hGH) in Nb2 node lymphoma cells. beta gamma subunits can alt er G protein actions and changes in beta subunit concentration represe nt available beta gamma subunits. Thus, we studied whether the hGH-sti mulated increase in beta subunit concentration was accompanied by a ch ange in GTP binding to one or more G proteins. Equal numbers of Nb2 ce lls were incubated with hGH (10 ng/ml) for 0-7 h. Membrane was prepare d from the cells for subsequent photoaffinity binding of alpha[P-32]GT P to membrane proteins. A 45 kDa protein identified to be G(s) by immu noprecipitation was the most abundantly alpha-P-32-GTP labeled protein in Nb2 cell membrane. GTP binding to G(s) alpha in Nb2 cell membrane decreased by 37.4+/-11.8% compared to 0 h controls (P = 0.0035; n = 4) after 4 h incubation with hGH. No change in G(s) concentration as det ermined by Western blot was observed over the same time interval. When cells were incubated with both cycloheximide (10(-4) M) and hGH for 4 h, neither the increase in beta subunit concentration nor the decreas e in CTP binding to G(s) was observed. Modulation of beta gamma subuni ts represents a new and novel means by which lactogenic hormones may b e able to modify one or more G proteins and, in turn, multiple signal transduction pathways.