## HPV E6 Oncoprotein Mechanism **Key Point:** HPV E6 is the primary oncogenic driver in cervical carcinogenesis, acting through p53 inactivation rather than Rb inhibition (that is E7's role). ### Molecular Mechanism of E6-Mediated Transformation 1. **E6 recruits E6-associated protein (E6AP)** — a cellular ubiquitin ligase 2. **Formation of E6–E6AP–p53 complex** — brings p53 into proximity with the ubiquitination machinery 3. **Ubiquitin-mediated proteasomal degradation of p53** — p53 is tagged with polyubiquitin chains and degraded by the 26S proteasome 4. **Loss of p53 function** — elimination of: - Cell cycle checkpoint (G1/S arrest) - Apoptosis induction in response to DNA damage - DNA repair activation **High-Yield:** This mechanism is distinct from p53 mutation in sporadic cancers; HPV-driven cancers typically have **wild-type p53 that is functionally inactivated** by E6. ### Comparison: E6 vs. E7 Functions | Viral Protein | Target | Mechanism | Consequence | |---------------|--------|-----------|-------------| | **E6** | p53 | Ubiquitin-mediated degradation | Loss of apoptosis, cell cycle arrest | | **E7** | Rb | Direct binding, hyperphosphorylation | Loss of G1/S checkpoint, uncontrolled S-phase entry | **Clinical Pearl:** Both E6 and E7 are required for full malignant transformation; either alone is insufficient. This is why HPV vaccination targeting L1 capsid protein (preventing viral entry) is so effective. **Mnemonic:** **E6 = p53 Executioner** — E6 executes (degrades) p53 via ubiquitin-proteasome pathway. [cite:Robbins 10e Ch 22]
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