CCNE1 and HIV-1 infection: The CCNE2, as the substrate of CDC4 was reported to act as a dependency factor to induce HIV Tat activity by encoding protein Cyclin E1, Cdk2 and Cyclin E. It is speculated that HIV-1 hijacks CDC4 to sequester it to prevent the degradation of CCNE2, facilitating HIV-1 infection in the target cells [46].