Figure 4.
The temporal order of changes in cell cycle regulators indicated blocking of G1/S transition by syncytin-1 knockdown in BeWo cells. (A) Western blot analysis of cell cycle regulators. Compared to the corresponding controls, increased levels of p15 protein, and decreased levels of CDK4, E2F1, PCNA, and c-Myc, proteins, were observed as early as 40 hour post-transfection in cells transfected with SsiRNA1. A reduced level of CDK1 was detected at 48 hour post-transfection. The comparable levels of β-actin protein indicated a roughly equal loading of total protein. Measurement of mRNA levels with real-time PCR indicated the following changes in the syncytin-1 knockdown group: increase of p15 (B), decrease of E2F1 (D), PCNA (E), and c-Myc (F), mRNA levels, at 40 hour post-transfection. No change in CDK4 mRNA levels was detected at any time points examined (C). The decrease of CDK1 mRNA levels was not observed until 48 hour post-transfection (G). (*, p < 0.05; **, p < 0.01)