Zinc chloride stimulates DNA synthesis of mouse embryonic stem cells: Involvement of PI3K/Akt, MAPKs, and mTOR

Although zinc is one of the most important trace elements in the body, the mechanisms underlying zinc-induced cell proliferation have yet to be unraveled. Thus, we investigated the effect of zinc chloride (ZnCl₂) on mouse embryonic stem (ES) cell proliferation and related signaling pathways. ZnCl ₂ (40 μM) significantly increased [³H]-thymidine incorporation after 12 h of treatment. At moderate concentrations (≥4 μM), ZnCl₂ increased cell cycle regulatory protein levels, [ ³H]-thymidine incorporation, and total cell numbers, but higher doses of ZnCl₂ (≥200 μM) blocked this proliferative effect. ZnCl₂ induced the phosphorylation of Akt, c-Jun N-terminal kinases/stress-activated protein kinases (JNK/SAPK), p44/42 MAPKs, and mammalian target of rapamycin (mTOR) in a time-dependent manner. Pretreatment of LY 294002 (a PI3K inhibitor, 10^-6 M), wortmannin (a PI3K inhibitor, 10^-7 M), or an Akt inhibitor (10^-5 M), which inhibited the activation of JNK/SAPK and p44/42 MAPKs, blocked the ZnCl₂-induced expression of cyclins and cyclin-dependent kinases (CDKs). Furthermore, pretreatment with PD 98059 (a p44/42 inhibitor, 10^-5 M) or SP 600125 (a JNK inhibitor, 10^-6 M) inhibited ZnCl₂-induced activation of mTOR, p70S6K, and 4E-BP1. In addition, rapamycin (an mTOR inhibitor, 10^-8 M) blocked the ZnCl₂-induced increase in [³H]-thymidine incorporation and cell cycle regulatory protein expression. In conclusion, ZnCl₂ stimulated ES cell proliferation through the PI3K/Akt, p44/42 MAPKs, JNK/SAPK, and mTOR signal pathways.