Apolipoprotein A-I Synthesis and Secretion Are Increased in Hep G2 Cells Depleted of Copper by Cupruretic Tetramine

Abstract

Two amine chelators, namely N,N′-bis(2-aminoethyl)-1,3-propanediamine-4 HCl (2,3,2-tetramine) and diamsar, were used at various levels to deplete copper (Cu) from cultured Hep G2 cells. For cells cultured at 0.63 µmol of Cu/L, maximal depletions were attained after 24 h of incubation with 10 µmol of either chelator/L, which resulted in an average significant depletion of 45% of cellular Cu. In addition, when cells were cultured continuously for four passages at 0.63 µmol Cu/L with 20 µmol of 2,3,2-tetramine/L, cellular Cu was significantly depleted more than 40% compared with controls. Furthermore, after two passages of 2,3,2-tetramine treatment, cells were pulsed for 10 min with [3H]leucine and chased up to 2 h. At the end of the pulse, the amount of [3H]leucine incorporated into apolipoprotein A-I was twofold greater (P < 0.05) in treated than in control cells. No difference was detected for the synthesis of apolipoprotein B and total protein. During the chase, the cellular depletion curves for apolipoprotein A-I, apolipoprotein B and total protein were not altered by 2,3,2-tetramine treatment. From 30 to 120 min of the chase, the amount of nascent apolipoprotein A-I degraded was small and not altered, but that secreted into the medium was 56% higher (P < 0.05) in the Cu-depleted than in the control cells.