Abstract
In the presence of activated Gs alpha, the beta gamma complex of heterotrimeric G proteins (beta gamma) stimulates adenylyl cyclase (AC) in membranes prepared from cells expressing recombinant AC II or AC IV. Conditional stimulation of AC by beta gamma has been hypothesized to integrate cross-talk between Gs- and non-Gs-coupled regulation of cellular cAMP (Tang, W. J., and Gilman, A. G. (1991) Science 254, 1500-1503). Although observations in cells expressing recombinant receptors, G alpha s, and AC support this hypothesis (Federman, A. D., Conklin, B. R., Schrader, K. A., Reed, R. R., and Bourne, H. R. (1992) Nature 356, 159-161), this mechanism has not been investigated in differentiated cells. Expression of AC II has been reported only in lung, olfactory, and brain tissue. We found that rat lung alveolar type II cells express AC II and IV. Therefore, we hypothesized that beta gamma conditionally stimulates AC in type II cells. Consistent with this hypothesis, we found that the alpha 2-adrenergic agonist UK14304 did not affect basal cAMP in type II cells but potentiated terbutaline-stimulated cAMP accumulation. Treatment of cells with pertussis toxin partially inhibited terbutaline-stimulated cAMP accumulation and completely inhibited the effects of UK14304. In type II cell membranes, purified beta gamma tripled the terbutaline-stimulated increase in AC activity. In contrast, beta gamma inhibited AC activity in the absence of terbutaline. The addition of purified Go alpha blocked beta gamma-induced effects. In summary, type II cells expressing endogenous AC II and IV regulate cAMP accumulation and AC activity in a manner consistent with conditional stimulation by beta gamma. These observations support the overall hypothesis that conditional stimulation of AC by beta gamma integrates cross-talk between signal transduction systems in differentiated cells.
Highlights
From the Cardiovascular Research Institute and the Departments of +pediatrics and 'IIMedicine, University of California, San Francisco, California 94143
We hypothesized that /3,. conditionally stimulates adenylyl cyclase (AC) in type II cells. Consistent with this hypothesis, we found that the u2-adrenergic agonist UK14304 did not affect basal cAMP in type II cells but potentiated terbutaline-stimulated cAMP accumulation
These results suggested to us that pertussis toxin (PTX)-sensitive G proteins contribute to Gsa-stimulated AC activity in type II cells, which is one expected characteristic of an effect mediated by conditional stimulation of AC by 13'1
Summary
Isolation and Culture ofAl veolar Typ e II Cells-We isolated a lveola r type II cells from the lun gs of adult mal e, specific pathogen-free Sprague-Daw ley rats by elastase digesti on a nd "pa nning" cell s on IgGcoate d bacteriolo gic plastic dish es [23]. In all experi me nts, < 1% cellula r lactic acid dehydrogen ase [24] was released into the medium a fte r cells wer e treated with control solut ions , PTX , pertu ssis toxin B-oligomer Measur ement of Adenylyl Cyclase Acti vity-Type II cell s were scra ped from culture dish es in a solut ion of 10 mxt Tri s·H CI, pH 7.7,1 mM EDTA , 1 mxt EGTA , 0.2 mxr phen ylm ethylsulfonyl fluor ide, a nd 5 ug/ml leupeptin a nd wer e disrupted in a gla ss homogen izer. Mat erials-Tissu e culture medium a nd fet al bovin e se rum wer e obtai ned from th e University of Ca liforn ia Cell Cultu re Facility. Henry Bourne (University of Ca liforn ia , San Franci sco)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
