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Glucocorticoid treatment facilitates cyclic adenosine 3',5'-monophosphate-dependent protein kinase response in
Abstract:
Late passage cultures of a clonal osteogenic sarcoma line (ROS 17/2.8) failed to respond to PTH with activation of cAMP-dependent protein kinase isoenzymes despite showing a sensitive and dose-dependent increase in cAMP after treatment with the hormone. When cells were treated with hydrocortisone or dexamethasone, protein kinase responsiveness to PTH was readily demonstrated; such treatment also resulted in enhanced cAMP production. Forskolin preincubation resulted in a cAMP response to PTH of similar magnitude to that seen with hydrocortisone but no activation of cAMP-dependent protein kinase occurred. Thus, the effect of glucocorticoid cannot be explained merely by the increased amplitude and sensitivity of the cAMP response which developed with glucocorticoid treatment in these cells. The data indicate that cellular activation of cAMP-dependent protein kinase does not automatically follow cAMP generation and that information transfer can be restored by pharmacological means.
Insights
Glucocorticoids restore parathyroid hormone (PTH) signaling in osteogenic sarcoma cells by enabling protein kinase activation, not just increasing cyclic AMP (cAMP) levels. This reveals a crucial step in cellular information transfer.
Area of Science:
- Molecular Endocrinology
- Cellular Signaling
- Biochemistry
Background:
- Osteogenic sarcoma cell lines (ROS 17/2.8) exhibit impaired protein kinase activation in response to parathyroid hormone (PTH).
- Cyclic AMP (cAMP) generation is observed with PTH treatment, but downstream signaling is disrupted in late passage cultures.
Purpose of the Study:
- To investigate the mechanism by which glucocorticoids restore PTH-induced protein kinase activation in ROS 17/2.8 cells.
- To determine if enhanced cAMP production alone explains the restoration of signaling by glucocorticoids.
Main Methods:
- Treatment of late passage ROS 17/2.8 cells with PTH, hydrocortisone, dexamethasone, and forskolin.
- Measurement of intracellular cAMP levels.
- Assay of cAMP-dependent protein kinase isoenzyme activation.
Main Results:
- Late passage ROS 17/2.8 cells showed PTH-stimulated cAMP increase but failed to activate cAMP-dependent protein kinase.
- Hydrocortisone or dexamethasone treatment restored PTH-induced protein kinase activation and enhanced cAMP production.
- Forskolin preincubation increased cAMP response to PTH but did not activate protein kinase, indicating glucocorticoid effects are beyond cAMP elevation.
Conclusions:
- Glucocorticoid treatment facilitates information transfer from cAMP generation to protein kinase activation in response to PTH.
- The restoration of signaling by glucocorticoids is not solely due to increased cAMP levels or sensitivity.
- Cellular activation of cAMP-dependent protein kinase is a distinct step following cAMP generation, which can be pharmacologically modulated.