Annexin 1-dependent actions of glucocorticoids in the anterior pituitary gland: roles of the N-terminal domain and protein kinase C.
Annexin 1 (ANXA1) is an important mediator of glucocorticoid action in the neuroendocrine system. As the activity of this protein in other systems is modulated by phosphorylation of its N-terminal domain, we have explored the significance of this domain and its phosphorylation status to ANXA1 actions within the pituitary gland, using an established in vitro preparation. Two N-terminal peptides, ANXA1(Ac2-26) and ANXA1(Ac1-50), inhibited forskolin-evoked ACTH and prolactin release; however, they lacked the potency and full efficacy of the parent molecule (ANXA1(1-346)), whereas other shorter N-terminal sequences were without effect. A chimeric protein comprising ANXA1(1-44) and the C-terminal core of ANXA5 (ANXA5(20-320)) also produced a partial inhibition of peptide release. Protein kinase C (PKC) blockade (PKC(19-36)) abolished the inhibitory effects of dexamethasone on forskolin-evoked peptide release and attenuated the antisecretory actions of ANXA1(Ac2-26.) ANXA5, which sequesters PKC in other systems, produced similar effects. PKC(19-36) also blocked the dexamethasone- induced translocation of a serine phosphorylated species of ANXA1 from the cytoplasm to the outer cell surface. These results suggest that 1) the N-terminal domain plays a fundamental role in effecting the inhibitory actions of ANXA1 on pituitary peptide release; 2) PKC-dependent mechanisms are essential for both the cellular exportation and the biological activity of ANXA1; and 3) ANXA1 exported from the cells is serine phosphorylated.
John
Christopher
C
Department of Neuroendocrinology, Division of Neuroscience and Psychological Medicine, Faculty of Medicine, Imperial College of Science Technology and Medicine, Hammersmith Hospital Campus, Du Cane Road, London W12 ONN, UK.
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Patricia
P
Solito
Egle
E
Morris
John
J
Christian
Helen
H
Flower
Roderick
R
Buckingham
Julia
J
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017305:Annexin A1 / Q000737:chemistry / Q000494:pharmacology*; D017304:Annexin A5 / Q000494:pharmacology; D015153:Blotting, Western; D003907:Dexamethasone / Q000494:pharmacology*; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism; D011493:Protein Kinase C / Q000737:chemistry / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013329:Structure-Activity Relationship
D017305:Annexin A1; D017304:Annexin A5; D010446:Peptide Fragments; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D011388:Prolactin; D011493:Protein Kinase C