Arsenic inhibits the transcription of hTERT. (a) Half-life of hTERT mRNA is unaltered by arsenic. Control and arsenic-exposed (0.75 μM arsenic for 2 days) NB4 cells were treated with actinomycin D (5 μg/ml). RNA was collected at the time points indicated and real-time PCR was performed to detect the expression of hTERT, c-myc, and huPo. Both c-myc and huPo mRNA decayed in control and arsenic-treated samples and thus served as positive controls for this assay. hTERT mRNA decay was not increased by arsenic. (b) hTERT expression in control (lower arrowhead) and arsenic-treated (upper arrowhead) samples was well within the linear range on the standard curve of real-time PCR. (c) Nuclear run-on reaction showed diminished transcription of hTERT in NB4 cells treated with 0.75 μM for 8 days. c-myc transcription rate also decreased to 40%. huPo served as control.