Rapid homeostatic response of H4IIE cells to zinc deprivation is not due to changes in total amount of ZnT‐1 protein

Abstract

Earlier studies with H4IIE (rat hepatoma) cells have shown that in the presence of an extracellular metal chelator DTPA (diethylenetriaminepentaacetic acid), efflux of zinc is shut down rapidly. Zinc efflux in cells is controlled by the SLC30 group of membrane transporters known as ZnTs. ZnT-1 is the only member of this family located in the plasma membrane. We have earlier reported that DTPA did not significantly change the concentration of ZnT-1 mRNA in transformed cells. To further understand the mechanism of DTPA-induced zinc retention, protein expression of ZnT-1 was assessed in H4IIE cells, at different time points, in the presence of either zinc or DTPA. Cells were incubated with or without 100μM ZnSO4 or 50μM DTPA for 2 h or 48 h and ZnT-1 protein concentrations were estimated using Western Blot analysis. Zinc increased (15%) whereas DTPA reduced (39%) the expression of ZnT-1 after 48 h treatment. However, ZnT-1 protein concentrations were not affected by either zinc or DTPA, after 2 h of treatment, the time at which zinc efflux was altered in our earlier studies. Thus we conclude that the rapid homeostatic response of cells to DTPA is not due to a change in the total amount of ZnT-1 protein, but could be due to a reduction in its plasma membrane localization.