The HPV16 E6 binding protein Tip-1 interacts with ARHGEF16, which activates Cdc42

Area of Science:

• Molecular biology
• Cell biology
• Virology

Background:

• Guanidine exchange factor (GEF)-catalyzed activation of Rho proteins, including Cdc42, is implicated in cellular transformation and cancer.
• The human papillomavirus type 16 (HPV16) E6 oncoprotein interacts with Tax-interacting-protein 1 (Tip-1).

Purpose of the Study:

• To identify and functionally analyze novel Tip-1 binding partners.
• To investigate the role of a novel Tip-1 binding GEF in Cdc42 activation in the context of HPV16 E6 expression.

Main Methods:

• Yeast two-hybrid assays and co-immunoprecipitation to identify protein interactions.
• In vitro kinetic analyses and cell-based assays to measure Rho protein activation.
• siRNA gene silencing to assess the functional significance of identified proteins.

Main Results:

• ARHGEF16 was identified as a novel Tip-1 binding protein via its PDZ binding motif.
• ARHGEF16 levels and Cdc42 activation were increased in cells expressing HPV16 E6.
• Recombinant ARHGEF16 activated Cdc42, an effect enhanced by Tip-1 and E6; silencing Tip-1 or ARHGEF16 reduced Cdc42 activation in HPV16 E6-expressing cells.

Conclusions:

• HPV16 E6, Tip-1, and ARHGEF16 cooperate in the activation of Cdc42.
• These findings suggest a mechanistic link between HPV16 E6 expression and elevated Cdc42 activity, potentially contributing to oncogenesis.