Figure 1.

Down-regulation of hTERT/telomerase activity is closely associated with changes in c-Myc and Mad1 expression during the differentiation of HL60 cells. HL60 cells were treated with DMSO for 48 h and analyzed for (a) hTERT mRNA expression by competitive RT-PCR; (b and c) expression of hTERT protein by immunofluorescence and Western blot; (d) telomerase activity by telomeric repeat amplification protocol assay; (e) c-Myc, Max, and Mad1 expression by Northern blot (Top), the ethidium bromide-stained gel visualizing the 18 and 28 S RNA (Middle), and Mnt expression by RT-PCR (Bottom); and (f) EMSA demonstrating DNA binding activities to the hTERT E-box in HL60 extracts. Antibodies used for supershifts are indicated at the top, and protein complexes binding to the hTERT oligo are indicated to the left. Log, logarithmically growing cells; DMSO, DMSO-treated (differentiated) cells; C, competitor for hTERT PCR product; β2-M, β₂-microglobulin, internal control for the hTERT and Mnt RT-PCR.