ABSTRACT
Aldosterone can elicit rapid nongenomic effects both in vivo and in vitro, often mediated by signal transduction cascades. However, it is not understood how these rapid effects are initiated. In this study we show that aldosterone leads to rapid activation of mitogen activated protein kinases ERK1/2 in the cortical collecting duct cell line M-1. Inhibitors of transcription and translation could not block this activation, which suggests an extranuclear (nongenomic) mechanism. Although it is known that M-1 cells do not contain a transcriptionally functional MR, it is not known whether a closely related protein still could mediate the effects, or an unrelated nonclassic receptor. To test this hypothesis, the effects of four classical mineralocorticoid receptor antagonists were studied. None of the compounds could block the response to aldosterone. Altogether, the data suggest that rapid aldosterone effects in M-1 cells are initiated by a receptor different from the classical mineralocorticoid receptor.
Subject(s)
Aldosterone/pharmacology , Mineralocorticoid Receptor Antagonists , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinases/metabolism , Aldosterone/metabolism , Animals , Butadienes/pharmacology , Cell Line , Cycloheximide/pharmacology , Dactinomycin/pharmacology , Dose-Response Relationship, Drug , Enzyme Activation/drug effects , Enzyme Inhibitors/pharmacology , Flavonoids/pharmacology , Hydrocortisone/pharmacology , Kidney Cortex/cytology , Kidney Cortex/metabolism , Kidney Tubules, Collecting/cytology , Mice , Mineralocorticoid Receptor Antagonists/pharmacology , Mitogen-Activated Protein Kinase 1/antagonists & inhibitors , Mitogen-Activated Protein Kinase 3 , Mitogen-Activated Protein Kinases/antagonists & inhibitors , Nitriles/pharmacology , Phosphorylation , Proto-Oncogene Proteins c-raf/metabolismABSTRACT
Steroids may exert their action in living cells by several ways: 1). the well-known genomic pathway, involving hormone binding to cytosolic (classic) receptors and subsequent modulation of gene expression followed by protein synthesis. 2). Alternatively, pathways are operating that do not act on the genome, therefore indicating nongenomic action. Although it is comparatively easy to confirm the nongenomic nature of a particular phenomenon observed, e.g., by using inhibitors of transcription or translation, considerable controversy exists about the identity of receptors that mediate these responses. Many different approaches have been employed to answer this question, including pharmacology, knock-out animals, and numerous biochemical studies. Evidence is presented for and against both the participation of classic receptors, or proteins closely related to them, as well as for the involvement of yet poorly understood, novel membrane steroid receptors. In addition, clinical implications for a wide array of nongenomic steroid actions are outlined.