HPV-16 E7 Interacts with the Endocytic Machinery via the AP2 Adaptor μ2 Subunit

Area of Science:

• Oncology
• Virology
• Cell Biology

Background:

• Human papillomavirus (HPV) E7 protein is a key driver of HPV-induced malignancy, primarily by disrupting cell cycle regulation and promoting cell proliferation.
• HPV E7 targets pRB tumor suppressors for degradation, a process influenced by phosphorylation and an acidic patch near the LXCXE motif.

Purpose of the Study:

• To investigate the novel interactions of HPV-16 E7 with cellular machinery beyond pRB.
• To elucidate the role of HPV-16 E7 in clathrin-mediated endocytosis and its contribution to cellular transformation.

Main Methods:

• Investigated HPV-16 E7 interaction with the AP2 complex using mutational analysis.
• Assessed the role of specific amino acid residues (e.g., Y25) in E7 for AP2-μ2 binding.
• Examined the impact of CKII phosphorylation on E7-AP2 interaction.
• Studied the effect of E7-AP2 association on EGFR internalization and cellular transformation under nutrient-limited conditions.

Main Results:

• HPV-16 E7 directly binds to the AP2-μ2 subunit via residues 25-YEQL-28, overlapping but distinct from the pRB LXCXE motif.
• Point mutations at Y25 indicate E7-AP2 interaction is independent of pRB binding.
• CKII phosphorylation of serines 31 and 32 facilitates E7 binding to AP2.
• E7-AP2 complex formation contributes to cellular transformation, partly by inhibiting AP2-mediated EGFR endocytosis.

Conclusions:

• HPV-16 E7 targets clathrin-mediated endocytosis by interacting with the AP2 complex.
• This novel interaction, involving a conserved AP2 recognition motif in E7, contributes to malignant transformation.
• E7's modulation of endocytic pathways, including EGFR trafficking, is a critical mechanism in HPV-induced oncogenesis.