What is the expected result of the interaction between E7 and wild-type RB?

• A. Increase in G1 cell cycle phase
• B. Decrease in the percentage of cells in G1
• C. No effect on cell cycle
• D. Increase cell apoptosis

Answer: (B)

The interaction between the E7 protein of HPV (Human Papillomavirus) and the wild-type RB (retinoblastoma) protein is crucial in the regulation of the cell cycle. In normal circumstances, RB functions as a tumor suppressor by inhibiting cell cycle progression from the G1 phase to the S phase, preventing cells from dividing uncontrollably. When E7 binds to RB, it effectively inactivates the RB protein, leading to the release of E2F transcription factors that promote the expression of genes necessary for S phase entry.

As a result, the interaction between E7 and RB decreases the ability of RB to restrain the cell cycle, which leads to an increase in the cell population moving from G1 to S phase. This essentially decreases the percentage of cells in G1 because more cells are progressing through the cell cycle and preparing for DNA synthesis. Therefore, the correct answer reflects this mechanism by indicating a decrease in the percentage of cells in G1 as a result of E7's effect on RB.