Elucidating the role of foxo transcription factors on lithium induced growth arrest in hepatocellular carcinoma cells

Lithium is one of the most effective drugs for the treatment of bipolar disorder for years. Many studies have shown that lithium has neuroprotective effect and has aca¬pacity to inhibit cell proliferation. Specifically, it can inhibit cell growth by inducing G2/M arrest in different cell lines including hepatocellular carcinoma cells. Up to now, many mammalian enzymes have been identified as a target of lithium; however, how lithium exerts these diverse effects is unclear. In this study, we aimed to elucidate the role FOXO transcription factors in lithium induced growth arrest in hepatocellular carci¬noma cells. The possible role of FOXO was observed by luciferase reporter assay and real time PCR. There was an increase in FOXO promoter activity along with an increase in lithium induced GADD45a expression. To test the possible molecular mechanisms for FOXO regulation, FOXO regu-latory kinases were analyzed by Western Blotting and an increase in MST activity was observed after lithium treatment. The increase in MST ac¬tivity after lithium treatment sug-gests probable mechanism that lithium can activate FOXO to induce cell cycle arrest with the help of MST. To determine the FOXO and MST dependency in lithium induced growth arrest, stably FOXO and MST ex¬pressed cells were generated. It was found that lithium induces MST activation and MST increases the GADD45a expression through FOXO or another way. It was also found that the role of MST in lithium actions could be independent of its kinase activity. The experimental data and findings obtained from this study possess the potential of unco¬vering the molecular mechanisms lithium induced cell cycle arrest in hepatocellular car¬cinoma cells. The exploration of molecular mechanisms in-volved in lithium mediated HCC growthinhibition may provide new insights for therapy of liver tumors.