Endocrine Abstracts

The anti-inflammatory actions of glucocorticoids are mediated in part by inhibition of nuclear factor kappa B (NFkappaB) activation. Reports that NFkappaB activation within anterior pituitary folliculo-stellate (FS) cells provokes the release of interleukin-6 (IL-6) [1] which acts a paracrine mediator of ACTH release [2], raise the possibility that NFkappaB is a potential target for the negative feedback actions of glucocorticoids upon the hypothalamo-pituitary-adrenal axis. Accordingly, we have examined the effects of the synthetic glucocorticoid, dexamethasone, on the lipopolysaccharide (LPS)-induced activation of NFkappaB and release of IL-6 from FS cells, using a murine FS cell line (TtT/GF) as a model. Preliminary studies using reverse transcriptase polymerase chain reaction demonstrated expression of the components necessary for LPS-induced activation of NFkappaB in the cell line, namely the toll-like receptors Tlr4 and Tlr2, CD14 and MD-2. LPS (100nanogram per millilitre) readily stimulated IL-6 release from the cells. Its effects were first apparent after 4 hours contact, persisted for 24 hours and were prevented by inclusion of dexamethasone (1 micromolar) in the medium. The increase in IL-6 release was preceded by an acute phase of NFkappakappaB activation (evident from 30 minutes to 2 hours of LPS contact), as shown by nuclear translocation of the p65 subunit of the NFkappakappaB dimeric complex from the cytosol and degradation of the inhibitory protein of NFkappaB, IkappaBalpha. Furthermore, treatment with dexamethasone inhibited LPS-induced nuclear translocation of p65 and increased the expression of IkappaBalpha protein. These results show for the first time that the NFkappaB system in FS cells is glucocorticoid sensitive and support the premise that inhibition of NFkappaB activation provides a potential mechanism for feedback inhibition of ACTH release, particularly in conditions of immune or inflammatory stress.

Generously supported by Pfizer and the BBSRC

1. Lohrer et al. 2000. Endocrinology.141(12): 4457-65.

2. Bethin et al. 2000. Proc Natl Acad Sci USA. 97(16): 9317-22.