The characterization of the induction of lipocortin I by administration of dexamethasone and thyroid hormone in a thymic epithelial cell lne

Riley, Henry Drinker
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Lipocortin I, a putative phospholipase A2 inhibitor, has been previously reported to be either unresponsive or induced at the level of transcription or translation by glucocorticoid administration depending on which cell line or model system was under investigation. using a thymic epithelial cell line I show in this dissertation the rapid induction in serum free conditions of lipocortin I mRNA by dexamethasone. Using a lipocortin I cDNA probe, hybridization to Northern blots of RNA shows that induction occurs within 30 minutes of treatment with nanomolar amounts of dexamethasone, and continues to rise for at least three hours. It is demonstrated that this induction is dose dependent. Immunoblots employing a polyclonal antibody to lipocortin I establishes that there is also an increase in lipocortin I protein following dexamethasone treatment. I also discovered that lipocortin I mRNA is induced by the picomolar administration of thyroid hormone (T3) in serum free conditions. Northern blot analysis using lipocortin I cDNA indicates an increase in mRNA within 30 minutes which continues to increase for up to four hours. This induction is also shown to be dose dependent. Immunoblots show an increase of lipocortin I protein following T3 administration. Through the use of nuclear run-off experiments I demonstrate that the induction of lipocortin I mRNA by both hormones is the result of an increase in the transcriptional activity of the gene and not stabilization of the message. Under continuous culture conditions both hormones attenuate the response to the other. This result is discussed in relationship to the ambiguity surrounding the inducibility of lipocortin I mRNA and protein found in the current literature. Finally the thymic epithelial cell line is transfected with inducible constructs containing the complete coding region of the cDNA for lipocortin I in either sense or antisense orientations. The cells containing the sense orientation show a greatly increased number and size of Hassall's corpuscles. These structures are found in the thymic medulla in vivo and are thought to be sites of thymic hormone production and secretion.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1990.
Includes bibliographical references (leaves 68-76)
xi, 76 leaves, bound ill. 29 cm
Lipocortins, Dexamethasone -- Physiological effect, Epithelial cells, Serum-free culture media
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Biomedical Sciences (Biochemistry); no. 2563
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