Thyrotropin effect on the availability of Ni regulatory protein in FRTL-5 rat thyroid cells to ADP-ribosylation by pertussis toxin

Publisher Website
Google Scholar
Abstract
Incubation of FRTL‐5 rat thyroid cell membranes with [32P]NAD and pertussis toxin results in the specific ADP‐ribosylation of a protein of about 40 kDa. This protein has the same molecular mass of the αi subunit of the adenylate cyclase regulatory protein Ni and is distinct from proteins ADP‐ribosylated by cholera toxin in the same membranes. Prior treatment of FRTL‐5 cells with pertussis toxin results in the ADP‐ribosylation of Ni, as indicated by the loss of the toxin substrate in the ADP‐ribosylation assay performed with membranes prepared from such cells. Preincubation of FRTL‐5 cells with thyrotropin causes the same loss; cholera toxin has no such effect. Pertussis toxin, as do thyrotropin and cholera toxin, increases cAMP levels in FRTL‐5 cells. Forskolin together with thyrotropin, cholera toxin or pertussis toxin causes a further increase in cAMP levels. Petussis toxin and thyrotropin are not additive in their ability to increase adenylate cyclase activity, whereas both substances are additive with cholera toxin. A role of Ni in the thyrotropin regulation of the adenylate cyclase activity in thyroid cells is proposed.