Arsenic specifically suppresses hTERT mRNA levels independent of cell type. The expression of hTERT and c-myc was measured by real-time PCR and normalized to actin in b and human phosphoprotein in a, c, and d. hTERT mRNA levels are expressed as percent of untreated control. (a) Arsenic diminished hTERT mRNA expression in a dose-dependent fashion. Experiments were performed after 12 days of arsenic exposure. (b) Two days of arsenic (0.75 μM) but not vincristine (Vin; 0.075 nM) or doxorubicin (Dox; 50 nM) diminishes hTERT mRNA levels. (c) Cell lines other than NB4 also had decreased hTERT mRNA levels after arsenic treatment. NB4 cells were especially sensitive as 0.75 μM for 8 days had resulted in more than 98% inhibition of hTERT expression. The other cell lines were treated with 2 μM arsenic for 14 days. (d) c-myc expression was also decreased in all four cell lines with arsenic exposure.