A 32-year-old woman undergoes cervical cytology screening and a Pap smear shows cells with a characteristic perinuclear halo and enlarged, hyperchromatic, irregular nuclei resembling raisins. These cells are marked as **A** in the cervical epithelium diagram. Which of the following best describes the oncogenic mechanism by which the causative agent of these findings leads to cervical cancer?

Explanation

## Why "Both HPV E6 and E7 proteins act synergistically to disable p53 and Rb pathways" is right The koilocytes marked **A** are the pathognomonic cytologic hallmark of HPV infection, characterized by perinuclear halo (cytoplasmic clearing) and raisinoid nuclei. The oncogenic mechanism of high-risk HPV (types 16, 18, 31, 33, 45, 52, 58) involves two critical viral oncoproteins working together: E6 inactivates p53 (eliminating cell cycle arrest and apoptosis), while E7 inactivates Rb (releasing E2F and driving uncontrolled G1→S progression). This dual mechanism is the hallmark of HPV-driven malignant transformation and is the reason high-risk HPV is necessary for cervical cancer development. (Robbins 10e Ch 22; Harrison 21e Ch 81) ## Why each distractor is wrong - **"HPV E6 protein degrades p53, abolishing cell cycle checkpoint control and apoptosis"**: While E6 does degrade p53, this option describes only one half of the oncogenic mechanism. E6 alone is insufficient; E7's inactivation of Rb is equally critical for transformation. The question asks for the best description of the mechanism, which requires both proteins. - **"HPV E7 protein inactivates Rb, releasing E2F and permitting unrestricted G1→S progression"**: This correctly describes E7's function but omits E6's role in p53 degradation. Neither viral protein alone is sufficient for full malignant transformation; both are required. - **"HPV L1 capsid protein directly integrates into the host genome, causing chromosomal instability"**: L1 is a structural capsid protein, not an oncoprotein. HPV integration (when it occurs) is mediated by disruption of the viral genome itself, not L1. This is a common distractor confusing structural and regulatory viral proteins. **High-Yield:** Koilocytes = perinuclear halo + raisinoid nuclei = HPV infection; high-risk HPV E6 (p53) + E7 (Rb) = cervical cancer; low-risk HPV 6, 11 = genital warts only. [cite: Robbins 10e Ch 22; Harrison 21e Ch 81]