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Volume 272, Number 16, Issue of April 18, 1997 pp. 10790-10796
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

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Dexamethasone Induces Neuropeptide Y (NPY) Expression and Impairs Insulin Release in the Insulin-producing Cell Line RINm5F
RELEASE OF NPY AND INSULIN THROUGH DIFFERENT PATHWAYS

(Received for publication, November 27, 1996, and in revised form, January 29, 1997)

Ulrika Myrsén-Axcrona , Sven Karlsson ^¶ , Frank Sundler and Bo Ahrén ^¶

From the  Department of Physiology and Neuroscience, Section of Neuroendocrine Cell Biology, Lund University, 221 85 Lund and ^¶ Department of Medicine, Lund University, 205 02 Malmö, Sweden

Neuropeptide Y (NPY) occurs in adrenergic as well as in non-adrenergic nerves innervating the islets of Langerhans and inhibits glucose-stimulated insulin secretion. Recently we demonstrated that NPY is expressed within islet beta cells of the rat pancreas following treatment with dexamethasone in vivo. In this study we examined the cellular expression of NPY following dexamethasone treatment of the insulin-producing cell line RINm5F, which under control conditions does not express or release NPY. The cells were cultured with or without dexamethasone (100 nM) for 5 days. Over the 5-day culture period, dexamethasone time dependently induced an increased release of NPY with a concomitant decrease in the release of insulin. Northern blot and in situ hybridization revealed a corresponding time-dependent increase in the amount of NPY transcripts and in the number of cells labeled for NPY mRNA, whereas immunocytochemistry for NPY revealed only a few immunoreactive cells, indicating a rapid release of the formed peptide. Following 5 days of culture with dexamethasone, acute stimulation with D-glyceraldehyde (10 mM) or KCl (20 mM) Ca²⁺ dependently stimulated the release of insulin. In contrast neither stimulation with D-glyceraldehyde or KCl nor removal of extracellular Ca²⁺ affected the release of NPY. Furthermore the D-glyceraldehyde- and KCl-induced increase in cytosolic Ca²⁺, evident in control RINm5F cells, was impaired after dexamethasone treatment. We conclude that RINm5F cells show steroid-sensitive plasticity and express NPY after dexamethasone treatment concomitantly with a decreased insulin secretion and impaired increase in cytosolic Ca²⁺ upon depolarization with KCl or stimulation with D-glyceraldehyde. We also conclude that NPY and insulin secretion are regulated differently and suggest that the inability of the removal of extracellular Ca²⁺ to inhibit NPY secretion and the failure of D-glyceraldehyde and KCl to stimulate NPY secretion reflect a constitutive release of this peptide from the cells in contrast to the regulated release of insulin.

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