Abstract
AIM: We previously revealed that Ca(＋＋)-activated calmodulin binds to ABCA1 by the region near the PEST sequence and retards its calpain-mediated degradation to increase HDL biogenesis. Calmodulin activity is reportedly modulated also by other nutritional divalent cations; thus, we attempted to determine whether Zn(＋＋) is involved in the regulation of ABCA1 stability through the modulation of calmodulin activity. METHODS: The effects of Zn(＋＋) on ABCA1 expression was investigated in J774 mouse macrophage cell-line cells and HepG2 human hepatoma cell-line cells. RESULTS: Zn(＋＋) increased ABCA1 expression, not by increasing the mRNA but by attenuating its decay rate, more prominently in the presence of cAMP. Accordingly, it enhanced cell cholesterol release with extracellular apolipoprotein A-I. Calmodulin binding to ABCA1 was increased by Zn(＋＋) and Ca(＋＋). Zn(＋＋) suppressed calpain-mediated hydrolysis of the peptide of ABCA1 cytosolic loop, including the PEST sequence and the calmodulin-binding site, in a calmodulin- dependent fashion, in the presence of the minimum amount of Ca(＋＋) to activate calpain, but not calmodulin. Calpain activity was not directly inhibited by Zn(＋＋) at the concentration for enhancing calmodulin binding to ABCA1. CONCLUSION: Nutritional divalent cation Zn(＋＋) is involved in the regulation of ABCA1 activity and biogenesis of HDL through the modulation of calmodulin activity. The results were consistent with previous clinical findings that Zn(＋＋) increased plasma HDL in the conditions of sympathetic activation, such as type 2 diabetes and chronic hemodialysis.