Restoration of guanine nucleotide- and fluoride-stimulated activity to an adenylate cyclase-deficient cell line with affinity-purified guanine nucleotide regulatory protein

A guanine nucleotide-binding protein purified from turkey erythrocytes by affinity chromatography confers both F— and guanine nucleotide-stimulation of adenylate cyclase to membranes from CYC- cells, a mutant cell line deficient in these responses. Interaction of turkey erythrocyte membranes with beta-adrenergic agonists before affinity chromatography, which is essential for binding of the guanine nucleotide regulatory protein to the affinity matrix, was also required for recovery of F—stimulation restoring activity in the affinity eluate.

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Desensitization of tumour Leydig cells by lutropin: evidence for uncoupling of the lutropin receptor from the guanine nucleotide-binding protein

Biochemical Journal ◽

10.1042/bj2020739 ◽

1982 ◽

Vol 202 (3) ◽

pp. 739-745 ◽

Cited By ~ 17

Author(s):

Clive J. Dix ◽

Matthias Schumacher ◽

Brian A. Cooke

Keyword(s):

Cyclic Amp ◽

Plasma Membranes ◽

Regulatory Protein ◽

Linear Increase ◽

Guanine Nucleotide ◽

Production Rates ◽

Guanine Nucleotide Binding Protein ◽

Intact Cells ◽

Guanine Nucleotide Binding ◽

Guanine Nucleotide Regulatory Protein

Purified rat Leydig tumour cells were pretreated with lutropin and the effect on the subsequent response to lutropin was determined. Maximal cyclic AMP production was achieved with the same concentration of lutropin in control and lutropin-pretreated cells; however, the maximum stimulated level in pretreated cells was only 30% of controls. The sensitivity to lutropin was decreased in lutropin-pretreated cells [ED50 (dose that produces a response that is 50% of the maximum response) 60±5.7ng/ml and 8±1.8ng/ml (mean±s.d., n=3) for controls], as was the rate of maximal cyclic AMP production (0.58, compared with 1.89pmol/106 cells per min for controls). However, cholera-toxin-stimulated cyclic AMP production was not decreased by lutropin pretreatment, and a potentiation was seen at all time points studied (up to 6h). Pre-incubation with lutropin caused a decrease in specific 125I-labelled human choriogonadotropin binding; however, this decrease was abolished if the cells were washed under acidic conditions (pH3.0 for 2min at 4°C), indicating that occupation but not loss of the lutropin receptors had taken place. The effect of pretreating the cells with lutropin on adenylate cyclase activity in purified plasma membranes was also investigated. In plasma membranes from control cells both guanosine 5′-[β,γ-imido]triphosphate [p(NH)ppG] plus lutropin and NaF plus lutropin caused a 50–60-fold linear increase in cyclic AMP production over 40min compared with 15-fold with p(NH)ppG and 6-fold with lutropin alone. In plasma membranes isolated from lutropin-treated cells the NaF-plus-lutropin- and the p(NH)ppG-stimulated cyclic AMP production rates were unchanged but no effect of lutropin could be demonstrated with or without added p(NH)ppG. In contrast the plasma membranes from dibutyryl cyclic AMP-treated cells had similar cyclic AMP production rates to control cells with all stimulants studied. The present evidence obtained from studies both with intact cells and with isolated plasma membranes indicates that the initial lutropin-induced desensitization of the rat Leydig tumour cell is due to a lesion in the hormone-receptor coupling to the guanine nucleotide regulatory protein. This process is apparently not mediated by cyclic AMP.

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