INVOLVEMENT OF C-JUN IN THE CONTROL OF GLUCOCORTICOID RECEPTOR TRANSCRIPTIONAL ACTIVITY DURING DEVELOPMENT OF CHICKEN RETINAL TISSUE

The ability of the glucocorticoid receptor (GR) to induce gene express ion in embryonic chicken retinal tissue increases dramatically during development, although the quantity of the receptor molecules does not change greatly with age. This study examines the possible involvement of c-Jun in the developmental control of GR activity. Expression of c- Jun in retinal tissue was high at early embryonic ages and declined du ring development. Elevation of c-Jun expression in retina of mid-devel opmental ages by treatment with 12-0-tetradecanoyl-phorbol-13-acetate (TPA), or by introduction of a c-Jun expression vector, caused a prono unced decline in the inducibility of the endogenous glutamine syntheta se gene and the transiently transfected CAT constructs pDELTAG46TCO an d pGS2.1CAT, that are controlled by a minimal consensus glucocorticoid response element (GRE) promoter and the glutamine synthetase promoter , respectively. The effect of c-Jun was dose dependent and could be re versed by overexpression of GR. C-Jun-evoked repression of GR activity could be relieved by overexpression of Jun D. Overexpression of Jun D could also elevate the responsiveness of early embryonic retina to gl ucocorticoids and cause a 5-fold increase in pDELTAG46TCO induction. T he effect of Jun D could be reversed by overexpression of c-Jun. Expre ssion of c-Jun might therefore be important for repression of GR activ ity at early embryonic ages.