FOS PROMOTER IS OVERACTIVE OUTSIDE OF GENOME CONTEXT AND WEAKLY REGULATED BY CHANGES IN THE Na+i/K+i RATIO

Changes in the Na+ and K+ intracellular concentrations affect expression of the FOS gene. Here, we obtained a genetic construct coding for the TurboGFP-dest1 protein under control of the human FOS promoter (-549 to +155) and studied its expression in HEK293T cells exposed to monovalent metal cations. Amplification of the FOS promoter sequence from genomic DNA was efficient only in the presence of Li+ ions. Incubation of cells with ouabain or in a medium containing Li+ ions instead of Na+ ions caused intracellular accumulation of Na+ and Li+ ions, respectively. In addition, both stimuli increased the levels of endogenous FOS mRNA and the average fluorescence intensity of TurboGFP-dest1 in transfected cells. The mRNA levels of TurboGFP-dest1 were significantly higher than the FOS mRNA levels and were little affected by the stimuli.