Human papillomavirus 16 E6 oncoprotein interferences with insulin signaling pathway by binding to tuberin

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Tuberous sclerosis complex (TSC) is a genetic disorder caused by mutations in TSC1 or TSC2 tumor suppressor genes.
• The TSC1/TSC2 complex regulates insulin-induced signaling pathways crucial for cell growth.
• High-risk human papillomavirus (HPV) infection, particularly HPV16, is a primary cause of cervical cancer, with the E6 oncoprotein playing a key role in carcinogenesis.

Purpose of the Study:

• To investigate the interaction between HPV16 E6 oncoprotein and the TSC2 tumor suppressor protein, Tuberin.
• To elucidate the functional consequences of this interaction on cellular signaling pathways.
• To identify the specific domains involved in the E6-Tuberin interaction.

Main Methods:

• Co-immunoprecipitation assays to detect protein-protein interactions.
• Western blotting to analyze protein phosphorylation and degradation.
• Site-directed mutagenesis to map interaction domains.

Main Results:

• HPV16 E6 directly interacts with Tuberin (TSC2 product).
• This interaction induces phosphorylation of S6 kinase and S6, independent of insulin.
• HPV16 E6 binding leads to proteasome-mediated degradation of Tuberin.
• Specific motifs (DILG and ELVG) in Tuberin's carboxyl-terminus are essential for E6 binding.
• The interaction region in HPV16 E6 is mapped to its amino-terminal portion, distinct from the p53 binding site.

Conclusions:

• HPV16 E6 disrupts the tumor suppressor function of Tuberin through direct interaction and degradation.
• The E6-Tuberin interaction activates the S6 kinase pathway, promoting cell proliferation and potentially contributing to oncogenesis.
• This study reveals a novel mechanism by which HPV oncogenesis may be linked to cellular growth signaling pathways.