Biomedical subjects

M F Olson

Publications and source records attributed to M F Olson.

21 records · Page 2Linked to original sources

PubMed1992

Heterologous desensitization of the human dopamine D1 receptor in Y1 adrenal cells and in a desensitization-resistant Y1 mutant.

In previous studies, mutant clones (designated Y1DR) were isolated that resisted ACTH-induced homologous desensitization of adenylyl cyclase. The Y1DR mutation also conferred resistance to the homologous desensitization induced by agonist stimulation of transfected beta 2-adrenergic receptors. These observations suggested that ACTH and beta 2-adrenergic agonists homologously desensitized adenylyl cyclase in Y1 cells by a common mechanism. In the present study, parental Y1 cells (Y1DS) and the Y1DR mutant were transfected with the gene encoding the human dopamine D1 receptor and examined for regulation of adenylyl cyclase by dopaminergic agonists. Transformants were isolated from both cell lines and shown to respond to dopamine agonists with increases in adenylyl cyclase activity. Treatment of the Y1DS transformants with ACTH promoted a rapid, homologous desensitization of adenylyl cyclase and had little effect on the responses to dopamine or NaF; treatment of Y1DS with dopaminergic agonists promoted a slower rate of heterologous desensitization that diminished responsiveness of the adenylyl cyclase system to dopamine, ACTH, and NaF. Y1DR cells transfected with the dopamine D1 receptor were resistant to the heterologous desensitization of adenylyl cyclase induced by dopaminergic agonists. These latter observations suggest that the pathways of homologous desensitization and heterologous desensitization converge at a common point in the desensitization pathway defined by the DR mutation in Y1 cells.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1991

Agonist-induced desensitization of adenylyl cyclase in Y1 adrenocortical tumor cells.

Y1 adrenocortical tumor cells (Y1DS) and Y1 mutants resistant to ACTH-induced desensitization of adenylyl cyclase (Y1DR) were transfected with a gene encoding the mouse beta 2-adrenergic receptor (beta 2-AR). Transfectants expressed beta 2-ARs that were able to stimulate adenylyl cyclase activity and steroid biosynthesis. These transfectants were used to explore the basis for the DR mutation in Y1 cells. We demonstrate that beta-adrenergic agonists desensitize the adenylyl cyclase system in transfected Y1DS cells whereas transfected Y1DR cells are resistant to desensitization by beta-adrenergic agonists. The fate of the beta 2-ARs during desensitization was evaluated by photoaffinity labelling with [125I]iodocyanopindolol diazerine. Desensitization of Y1DS transfectants was accompanied by a modest loss in receptor density that was insufficient to account for the complete loss of responsiveness to beta-adrenergic agonists. The extent of receptor loss induced by beta-adrenergic agonists in Y1DR transfectants exceeded that in the Y1DS transfectants indicating that the mutation which protects Y1DR cells from agonist-induced desensitization is prior to receptor down-regulation in the desensitization pathway. From these results we infer that ACTH and isoproterenol desensitize adenylyl cyclase by a common pathway and that receptor loss is not a major component of the desensitization process in these cells.

Adenylyl Cyclases↗

PubMed1991

Regulation of adenylyl cyclase activity by beta-adrenergic agonists in a desensitization-resistant mutant cell line.

Mutant clones resistant to ACTH-induced desensitization of adenylyl cyclase (Y1DR) were previously isolated from the Y1 mouse adrenocortical tumor cell line. In this study, both parental Y1 cells (Y1DS) and a Y1DR mutant were transfected with a gene encoding the mouse beta 2-adrenergic receptor, and transfectants isolated from both Y1DS and Y1DR cells were shown to express beta 2-adrenergic receptors. These transfectants responded to the beta-adrenergic agonist isoproterenol with increases in adenylyl cyclase activity and steroidogenesis and changes in cell shape. The transfectants were analyzed to determine whether the Y1DR mutation was specific for ACTH-induced desensitization of adenylyl cyclase or also affected desensitization of adenylyl cyclase via the beta 2-adrenergic receptor. Treatment of intact Y1DS transfectants with isoproterenol caused a rapid desensitization of the adenylyl cyclase system to further stimulation by the beta-adrenergic agonist. Treatment of intact cells with isoproterenol did not affect ACTH-stimulated adenylyl cyclase activity, indicating that desensitization was agonist specific or homologous. Y1DR transfectants were resistant to the desensitizing effects of isoproterenol in intact cells as well as in cell homogenates. These results indicate that the mutation in Y1DR transfectants affects a component that is common to the pathways of isoproterenol-induced desensitization and ACTH-induced desensitization of adenylyl cyclase. As determined using the hydrophilic beta-receptor antagonist CGP-12177, isoproterenol caused a rapid sequestration of cell surface receptors in both Y1DS and Y1DR transfectants. From these results we infer that the DR phenotype does not arise from mutations affecting receptor sequestration and that receptor number does not limit the response to isoproterenol in these transfectants.

Adenylyl Cyclases↗