Effects of cell proliferation on the uptake of transferrin-bound iron by human hepatoma cells

The effects of cellular proliferation on the uptake of transferrin-bound iron (Tf-Fe) and expression of transferrin receptor-1 (TfR1) and transferrin receptor-2 (TfR2) were investigated using a human hepatoma (HuH7) cell line stably transfected with TfR1 antisense RNA expression vector to suppress TfR1 expression. At transferrin (Tf) concentrations of 50 nmol/L and 5 μmol/L, when Tf-Fe uptake occurs by the TfR1- and TfR1-independent (NTfR1)-mediated process, respectively, the rate of Fe uptake by proliferating cells was approximately 250% that of stationary cells. The maximum rate of Fe uptake by the TfR1- and NTfR1-mediated process by proliferating cells was increased to 200% and 300% that of stationary cells, respectively. The maximum binding of Tf by both TfR1- and NTfR1-mediated processes by proliferating cells was increased significantly to 160% that of stationary cells. TfR1 and TfR2-α protein levels expressed by proliferating cells was observed to be approximately 300% and 200% greater than the stationary cells, respectively. During the proliferating growth phase, expression of TfR1 messenger RNA (mRNA) increased to 300% whereas TfR2-α mRNA decreased to 50% that of stationary cells. In conclusion, an increase in Tf-Fe uptake by TfR1-mediated pathway by proliferating cells was associated with increased TfR1 mRNA and protein expression. An increase in Tf-Fe uptake by NTfR1-mediated pathway was correlated with an increase in TfR2-α protein expression but not TfR2-α mRNA. In concluion, TfR2-α protein is likely to have a role in the mediation of Tf-Fe uptake by the NTfR1 process by HuH7 hepatoma cell in proliferating and stationary stages of growth. (H epatology 2003;38:967-977.)