MODULATION OF TAT GENE INDUCTION BY GLUCOCORTICOIDS INVOLVES A NEUTRALIZING SEQUENCE

Recent studies have indicated that two elements in addition to the glu cocorticoid response element (GRE) are involved in the induction of th e endogenous TAT gene in Fu5-5 rat hepatoma cells. The first is the 21 bp glucocorticoid modulatory element (GME) at -3648 bp, which causes reporter constructs to display both a left shift in the dose-response curve for glucocorticoids and increased percentages of agonist activit y for antiglucocorticoids. The second is a negative element at -3340 t o -3050 that blocks the action of the GME. This last observation raise d the question of how GME activity can be expressed in Fu5-5 cells in the intact TAT gene that contains both the GME and the negative elemen t. The present study identifies a third element, a ''neutralizing'' se quence, that restores the activity of the GME even when otherwise inac tivated by the negative element. This neutralizing sequence was locate d within the region surrounding the GREs of the TAT gene but is separa te from the GREs. The activity of the individual GME and negative elem ents was found to depend upon spacing. However, in combination with th e natural GRE, the native TAT gene spacing of the GME and negative ele ments was able to reproduce the activity of the intact gene. Thus, a t otal of three additional elements (an activator, a negative element, a nd a neutralizer) appear to cooperate with the GREs in glucocorticoid induction of the TAT gene in Fu5-5 cells. While such a grouping of ele ments may be novel among steroid regulated genes, it is a not uncommon occurrence for the transcriptional control of other genes. (C) 1998 E lsevier Science Ltd. All rights reserved.