siRNA “knockdown” of ERα but not ERβ abrogates increased telomerase activity induced by estrogen. In 5 separate experiments, peripheral blood lymphocytes were transfected with either scramble siRNA, siRNA for ERα (ESR1), for ERβ (ESR2), or no siRNA at all (mock) and cultured for 3 days in the presence of PHA, IL-2, and E₂ (1 μM). (A) Representative Western blot indicates that siRNA effectively knocked down ERα expression (> 85%). (B) RT-PCR of a representative experiment indicates that siRNA also knocked down ERβ (59% reduction). (C) Reduction in ERα expression correlated with significant decrease in telomerase activity (*P < .05).