Cross-talk between Rac1 and Cdc42 GTPases regulates formation of filopodia required for dengue virus type-2 entry into HMEC-1 cells

This study investigates how dengue virus type-2 (DENV-2) enters human microvascular endothelial cells (HMEC-1) through manipulation of the host cell's actin cytoskeleton. Using fluorescence microscopy, drug inhibitors, and dominant-negative protein expression, researchers demonstrate that DENV-2 binding triggers activation of Rac1 and Cdc42 GTPases, which reorganize actin filaments into dynamic filopodia—finger-like cellular protrusions at the cell periphery. These filopodia are essential for virus internalization; when their formation is blocked using Rac1 inhibitors or dominant-negative mutants, viral entry and productive infection are severely reduced. Notably, virus binding to cell surface receptors occurs independently of actin organization, but subsequent steps require proper cytoskeletal dynamics. The study also reveals that myosin II motor activity contributes to filopodial stability. Microtubule disruption has no effect on infection. This research demonstrates a novel mechanism where DENV-2 exploits coordinated signaling between two Rho-family GTPases to remodel the host actin cytoskeleton, enabling viral particle transport and cellular entry.

Key findings

• DENV-2 binding to HMEC-1 cells induces rapid actin reorganization into filopodia through activation of Rac1 and Cdc42 GTPases, which is required for viral entry and productive infection
• Virus binding to cell surface receptors occurs independently of actin organization, but filopodia formation is essential for subsequent internalization steps
• Inhibition of Rac1 or expression of dominant-negative Rac1/Cdc42 mutants blocks filopodia formation and reduces infection to 2-3% of control levels
• Myosin II ATPase activity stabilizes filopodia and contributes to viral infection efficiency
• Microtubule disruption does not affect DENV-2 infection, indicating specificity of the actin cytoskeleton requirement