A 28-year-old woman undergoes cervical screening and is found to be HPV-16 positive. Regarding the mechanisms of HPV-mediated malignant transformation, all of the following are true EXCEPT:

Explanation

## HPV-Mediated Malignant Transformation Mechanisms **Key Point:** While HPV E6 and E7 are potent oncoproteins, they do NOT directly activate cellular oncogenes like MYC and RAS. Their primary mechanism is inactivation of tumor suppressors, not oncogene activation. ### Mechanisms of HPV Oncogenesis ```mermaid flowchart TD A[HPV Infection]:::outcome --> B[E6 & E7 Expression]:::action B --> C[E6 inactivates p53]:::action B --> D[E7 inactivates Rb]:::action C --> E[Loss of p53-mediated apoptosis]:::outcome D --> F[Uncontrolled G1/S transition]:::outcome E --> G[Malignant Transformation]:::urgent F --> G ``` ### E6 Oncoprotein Function **High-Yield:** HPV E6 protein: - Binds to p53 tumor suppressor protein - Recruits E6-associated protein (E6AP), a ubiquitin ligase - Targets p53 for **proteasomal degradation** (not transcriptional inactivation) - Results in loss of p53-mediated apoptosis and cell cycle arrest - Allows accumulation of additional mutations ### E7 Oncoprotein Function **High-Yield:** HPV E7 protein: - Binds to hypophosphorylated (active) retinoblastoma (Rb) protein - Prevents Rb-mediated repression of E2F transcription factor - Allows uncontrolled progression through G1/S checkpoint - Leads to premature S-phase entry and DNA synthesis ### Risk Stratification by HPV Type | HPV Type | Classification | E6/E7 Potency | Cancer Risk | | --- | --- | --- | --- | | 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, 68 | High-risk (HR) | Strong | High (cervical, anogenital, oropharyngeal) | | 6, 11, 40, 42, 43, 44, 54, 61, 70, 72, 81, 89 | Low-risk (LR) | Weak | Low (benign warts, RRP) | **Clinical Pearl:** High-risk HPV types have E6 and E7 proteins with significantly higher binding affinity and transforming capacity compared to low-risk types, explaining their strong association with malignancy. ### What E6/E7 Do NOT Do **Warning:** HPV oncoproteins: - ~~Do NOT directly integrate into the host genome~~ (integration is rare and not required for transformation) - ~~Do NOT directly activate MYC or RAS~~ (transformation occurs via tumor suppressor inactivation, not oncogene activation) - ~~Do NOT encode reverse transcriptase~~ (HPV is DNA virus, not retrovirus) **Mnemonic:** **SUPPRESS** — HPV E6/E7 **Suppress** tumor suppressors (p53 and Rb), not activate oncogenes. [cite:Robbins 10e Ch 7]