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Externalization of Annexin I from A Folliculo-Stellate-Like Cell Line

Department of Human Anatomy and Genetics (L.C., A.N., J.F.M., H.C.C.), University of Oxford, Oxford OX1 3QX, United Kingdom; and Department of Neuroendocrinology (J.C.B.), Division of Neuroscience and Psychological Medicine, Faculty of Medicine, Imperial College of Science Technology and Medicine, Hammersmith Hospital Campus, London W12 0NN, United Kingdom

Address all correspondence and requests for reprints to: Dr. H. C. Christian, Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, United Kingdom. E-mail: helen.christian{at}anat.ox.ac.uk.

Our recent studies on rat pituitary tissue suggest that the annexin I-dependent inhibitory actions of glucocorticoids may not be exerted directly on endocrine cells but indirectly via folliculo-stellate (FS) cells. FS cells contain glucocorticoid receptors and abundant annexin I. We have studied the localization of annexin I in FS cells and the ability of dexamethasone to induce annexin I secretion by an FS (TtT/GF) cell line, using Western blotting and immunofluorescence microscopy. Exposure of TtT/GF cells to dexamethasone (0.1 µM, 3 h) caused an increase in the amount of annexin I protein in the intracellular compartment and attached to the surface of the cells. In nonpermeabilized cells, immunofluorescence labeling revealed that annexin I immunoreactivity was associated with the cell surface and concentrated in focal patches on the ends of cytoplasmic processes; dexamethasone (0.1 µM, 3 h) increased both the number and intensity of these foci. Immunogold electron microscopy confirmed in anterior pituitary tissue the presence of immunoreactive-annexin at the surface of FS cell processes contacting endocrine cells. These data support our hypothesis that annexin I is released by FS cells in response to glucocorticoids to mediate glucocorticoid inhibitory actions on pituitary hormone release via a juxtacrine mechanism.

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