Open AccessDefective guanyl nucleotide-binding protein beta gamma subunits in a forskolin-resistant mutant of the Y1 adrenocortical cell line.
Author(s) -
Jane Mitchell,
John K. Northup,
Bernard P. Schimmer
Publication year - 1992
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.89.19.8933
Subject(s) - adenylyl cyclase , forskolin , heterotrimeric g protein , g alpha subunit , g protein , gs alpha subunit , mutant , beta (programming language) , gi alpha subunit , pertussis toxin , gtp binding protein regulators , protein subunit , alpha (finance) , adenylate cyclase toxin , adcy9 , gtp' , microbiology and biotechnology , adcy10 , camp dependent pathway , chemistry , biology , biochemistry , receptor , enzyme , gene , medicine , construct validity , nursing , patient satisfaction , computer science , programming language
Forskolin-resistant mutants derived from Y1 adrenocortical cells display decreased responsiveness both to receptor and postreceptor stimulators of adenylyl cyclase and decreased amounts of the alpha subunits of the GTP-binding proteins (G proteins) that mediate stimulation (Gs) and inhibition (Gi) of adenylyl cyclase--namely, Gs alpha and Gi alpha-2. This phenotype is suggestive of a mutation that affects the processing or plasma membrane incorporation of G protein alpha subunits. Since the membrane attachment of heterotrimeric G proteins has been ascribed in part to the beta gamma subunits, we examined the quantity and functional activity of beta gamma subunits in wild-type Y1 and forskolin-resistant Forsk-10r-9 and Forsk-10r-3 cells. We now show that two assays previously used to examine the activity of purified beta gamma subunits--namely, to support either rhodopsin-catalyzed guanyl nucleotide exchange on Gt alpha or pertussis toxin-catalyzed ADP-ribosylation of Gt alpha--can be used with detergent extracts of cells. In both assays the beta gamma activity in Forsk-10r-9 and Forsk-10r-3 extracts was decreased by 53-76% compared with wild-type Y1 extracts. When normalized for immunoreactive beta subunit, the beta gamma activity in the Forsk-10r-9 samples was decreased by 55-57% compared with the wild-type Y1 samples. These results suggest that a mutation of one of the G protein beta or gamma subunits may result in the multiple defects of adenylyl cyclase activity and apparent loss of G protein alpha subunits seen in the forskolin-resistant mutant cells. The frequency with which these spontaneous mutations arise in the Y1 cell line suggests that they may contribute more generally to genetic abnormalities in signal transduction.