FOS Promoter is Overactive Outside of Genome Context and Weakly Regulated by Changes in the Na⁺_i/K⁺_i Ratio

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Andrey M. Gorbunov¹, Dmitrii A. Fedorov¹, Olga E. Kvitko¹, Olga D. Lopina¹, Elizaveta A. Klimanova^1,a*

¹Faculty of Biology, Lomonosov Moscow State University, 119234 Moscow, Russia

^* To whom correspondence should be addressed.

Received: February 10, 2025; Revised: March 31, 2025; Accepted: May 13, 2025

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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.

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KEY WORDS: lithium, sodium, ouabain, FOS, transcription

DOI: 10.1134/S0006297925600371

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