STUB1/CHIP promotes ubiquitination and degradation of HIV-1 Vif to restore the cellular level of APOBEC3G protein.

HIV-1 accessory protein Vif is required for neutralization of cellular restriction factor APOBEC3G through its ubiquitination and proteasomal degradation which allows replication of HIV-1 in non-permissive cells. This function of Vif is required for maintaining the genomic integrity of HIV-1. We here report that the Vif interacts with the cellular E3 ubiquitin ligase CHIP and the level of Vif protein gets reduced by the expression of CHIP. Reduction of Vif by CHIP expression is due to its increased rate of degradation as shown by cycloheximide (CHX) chase assay. CHIP expression also resulted in the ubiquitination of Vif protein in a dose dependent manner. The role of CHIP in the ubiquitination and degradation was confirmed by the endogenous knockdown of CHIP using CRISPR Cas9 method. Loss of endogenous CHIP protein showed the stabilization of Vif with concomitant destabilization of APOBEC3G. As expected Vif mediated ubiquitination of APOBEC3G was also reduced in CHIP knockdown cells. These results established that CHIP functions as a negative regulator of Vif protein which in-turn stabilizes APOBEC3G.