Alteration in the intracellular Na ⁺ /K ⁺ ratio regulates gene expression through the shift of G-quadruplex dynamics in living cells

Alteration in the intracellular Na ⁺ _i /K ⁺ _i ratio can play an important regulatory role in many mammalian cells. Here, we demonstrated that the expression of some early response genes does depend on the intracellular Na ⁺ _i /K ⁺ _i ratio and that the inhibition of DNA-binding activity of transcription factors c-Fos and c-Jun attenuates the upregulation of Zfp36 and Egr1 genes in HeLa cells. Both replacement of intracellular Na ⁺ and K ⁺ by Li ⁺ and the dissipation of Na ⁺ _i /K ⁺ _i gradient demonstrated a similar effect on the transcription of Fos , Jun , Zfp36 , and Ptgs2 . Oligonucleotide sequences from the Fos , Kit , and Myс promoters with an ability to fold into G-quadruplexes (G4s) change their conformations differently depending on the ratio of Na ⁺ , K ⁺ , and Li ⁺ ions in vitro . Fluorescence lifetime imaging microscopy studies using DNA G4-specific dye DAOTA-M2 revealed that changes in compositions and ratios of monovalent metal cations in HeLa cells were accompanied by alterations in intranuclear G4s dynamics. The data demonstrate that these structures may be considered as intracellular sensors of monovalent metal cations regulating gene expression through the shift of G4s dynamics.