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Mechanisms of Adrenocorticotropin-Induced Activation of Extracellularly Regulated Kinase 1/2 Mitogen-Activated Protein Kinase in the Human H295R Adrenal Cell Line

Centre for Endocrinology, Barts and the London School of Medicine, London EC1M 6BQ, United Kingdom

Address all correspondence and requests for reprints to: Dr. P. J. King, Centre for Endocrinology, John Vane Science Centre, William Harvey Research Institute, Charterhouse Square, London EC1M 6BQ, United Kingdom. E-mail: p.j.king{at}qmul.ac.uk.

The role of ACTH in stimulating or inhibiting growth of adrenal cells has been a subject of some controversy. Reports that ACTH may stimulate ERK/MAPK in Y1 cells have suggested a role for cAMP in this process. In attempting to extend this work, the ACTH responses in the human H295R cell line have been studied. This cell line makes only a very modest cAMP response to ACTH, yet the ERK1/2 response is highly reproducible and immediate but not prolonged. It is minimally reduced by the protein kinase A inhibitor, H89, but unaffected by protein kinase C and calcium inhibitors. Inhibition of epidermal growth factor receptor or other tyrosine kinase receptor transactivation was without effect, as was inhibition of c-Src activity or c-Src phosphorylation. The most effective inhibitor of this pathway was dansylcadaverine, an inhibitor of receptor internalization. These findings imply that ACTH-induced ERK1/2 activation in H295R cells is dependent on a mechanism distinct from that by which most G protein-coupled receptors activate ERK1/2 but that nevertheless seems to depend on receptor internalization.