The nuclear, 75 kDa form of early growth response protein-1/nerve growth factor-induced A protein is primarily restricted to LH beta-subunit-expressing cells in rat anterior pituitary

Objective: Early growth response protein-1 (Egr-1)/nerve growth factor-indu ced A (also known as Zif- 268, Krox-24, TIS8, ZENK) is a zinc-finger transc ription factor which, although expressed in a range of organ systems, has b een shown to be essential only in the maintenance of fertility through acti ons within the endocrine system, In the present study we have investigated the anatomical basis for actions of Egr-1 in the adult anterior pituitary g land. Design: Using female rats and mice as experimental models, rye have used im munocytochemical and microscopic analysis to make observations of the cellu lar and sub-cellular localization of Egr-1 protein. Methods: Immuno-(Western) blotting was first used to characterize the anter ior pituitary proteins detected by a commercially available Egr-1 antibody. Subsequently the antibody was used both singly and in combination with an LH beta -subunit antibody for immunocytochemical localization studies in pi tuitary sections, Results: The Egr-1 antiserum detected a single, major (primarily nuclear) 7 5 kDa protein band in Western blots of anterior pituitary extracts. Nuclear localization was confirmed by immunocytochemistry, which also demonstrated that the 75 kDa protein is localized to a minority subpopulation of anteri or pituitary cells in both rat and mouse. Dual immunocytochemical localizat ion showed that the Egr-1 protein is primarily restricted to the nuclei of LH beta -subunit-expressing cells. Conclusions: Sub-cellular localization of Egr-1 to the nucleus is consisten t with a direct role in transcriptional regulation of anterior pituitary fu nction in the adult rat. Furthermore, a selective role in the physiological control of gonadotrophin gene expression is indicated.