Telomerase repression in HMEC is mediated by pRb-family proteins. (A) Relative levels of pRb, p107, and p130 mRNAs in HMEC stably transduced at passage 2 with a control vector or a vector encoding shRNAs against these three transcripts were determined by quantitative RT-PCR. Mean values and SD (n=3) are shown. Values significantly different from controls (p < 0.05, Student’s t-test) are denoted with a *. (B) HMEC expressing shRb/107/130, shp16, or vector controls were harvested and pRb, p107, p130 and p16 levels were determined by immunoblotting. (C) Total population doublings of HMEC expressing shRB/107/130, shp16, or control viruses are plotted versus time. (D) hTERT mRNA levels were assayed at passage 5 by Taqman PCR. Mean mRNA levels ± SD (n=3) are presented relative to each other after normalization using mRNA levels of TATA binding protein (TBP).