Effect of therapeutic concentration of lithium on live HEK293 cells; increase of Na + /K + -ATPase, change of overall protein composition and alteration of surface layer of plasma membrane.

BACKGROUND: The effect of long-term exposure of live cells to lithium cations (Li) was studied in HEK293 cells cultivated in the presence of 1mM LiCl for 7 or 21days. The alteration of Na+ /K+ -ATPase level, protein composition and biophysical state of plasma membrane was determined with the aim to characterize the physiological state of Li-treated cells.

METHODS: Na+ /K+ -ATPase level was determined by [3 H]ouabain binding and immunoblot assays. Overall protein composition was determined by 2D electrophoresis followed by proteomic analysis by MALDI-TOF MS/MS and LFQ. Li interaction with plasma membrane was characterized by fluorescent probes DPH, TMA-DPH and Laurdan.

RESULTS: Na+ /K+ -ATPase was increased in plasma membranes isolated from cells exposed to Li. Identification of Li-altered proteins by 2D electrophoresis, MALDI-TOF MS/MS and LFQ suggests a change of energy metabolism in mitochondria and cytosol and alteration of cell homeostasis of calcium. Measurement of Laurdan generalized polarization indicated a significant alteration of surface layer of isolated plasma membranes prepared from both types of Li-treated cells.

CONCLUSIONS: Prolonged exposure of HEK293 cells to 1mM LiCl results in up-regulation of Na+ /K+ -ATPase expression, reorganization of overall cellular metabolism and alteration of the surface layer/polar head-group region of isolated plasma membranes.

GENERAL SIGNIFICANCE: Our findings demonstrate adaptation of live HEK293 cell metabolism to prolonged exposure to therapeutic concentration of Li manifested as up-regulation of Na+ /K+ -ATPase expression, alteration of protein composition and change of the surface layer of plasma membrane.