Effect of R-MGMT on the cell cycle and transcription. (A) Growth arrest. MCF7 cells were transfected with expression vector (Ctr) or vectors fused with wt or K107L mutant MGMT cDNAs for 24 h () before analysis by FC using dual channels to quantify the fluorescence in the cells from the stainings of MGMT by Mab.3B8 and of DNA by PI. Panels a, b, and c show the distributions of transfected cells stained by MGMT Mab.3B8 (FL1-A, y axis) versus their DNA contents (FL2-A, x axis). Cells with greater MGMT stainings than the control (Ctr), due to the expression of the MGMT cDNAs, are gated (the region R) to generate the histograms (d, e, and f) where the cell populations (events, y axis) were plotted against their DNA contents (x axis) representing G1, S, and G2 phases. The arrow in panel c indicates that a large population of cells expressing the K107L-MGMT proteins are at G1 phase. (B) Inhibition of RNA synthesis. Cells were labeled for 6 h with [3H]uridine after being cultured under full medium (FM) (lane 2), FM with 6BG (lane 1, pretreatment with 60 μM 6BG for 2 h before labeling), Cdex medium (lane 3), Cdex with E2 (lane 4) (pretreatment with 100 nM E2 for 2 h before labeling), or Cdex with E2 and 6BG together (lane 5) (pretreatment with 6BG and E2 together for 2 h before labeling). The labeled total RNAs isolated (2 μg/lane) were resolved on a 1% agarose gel. The top panel is the autoradiograph of the membrane with the labeled RNAs resolved by the agarose gel. The histogram is a summary of the 3H counts from 2 μg of labeled RNAs (averaged from three independent experiments). The bottom panel is the description of the samples. (C) RT-PCR analysis of the levels of PR, pS2, PBGD, and β-actin mRNAs obtained from cells cultured for 24 h, similar to panel B without [3H]uridine labeling. (D) Abbreviations of the wt and Mu (K107L mutant) MGMT full-length (FL) cDNAs used for transfection into the SV-ER cells (). M is the first methionine. (E) Reporter assay. Top panel, immunoblot of the expressed ER (Pab.HC20) and MGMT (Pab.MGMT) proteins in SV-ER cells grown in Cdex medium 24 h after cotransfection with ERE-Luc and MGMT (Wt, Mu, Wt-2A, and Mu-2A) constructs followed by 6 h of treatment with 1 μM E2. SV indicates the parental ER- and MGMT-negative MRC5.SV40 cells. Lower panel, the corresponding luciferase activities in the cell extracts.