Differential dysregulation of -TrCP1 and -2 by HIV-1 Vpu leads to inhibition of canonical and non-canonical NF-B pathways in infected cells

The HIV-1 Vpu protein is expressed late in the virus lifecycle to promote infectious virus production and avoid innate and adaptive immunity. This includes the inhibition of the NF-B pathway which, when activated, leads to the induction of inflammatory responses and the promotion of antiviral immunity. Here we demonstrate that Vpu can inhibit both canonical and non-canonical NF-B pathways, through the direct inhibition of the F-box protein -TrCP, the substrate recognition portion of the Skp1-Cul1-F-box (SCF)-TrCP ubiquitin ligase complex. There are two paralogues of -TrCP (-TrCP1/BTRC and -TrCP2/FBXW11), encoded on different chromosomes, which appear to be functionally redundant. Vpu, however, is one of the few -TrCP substrates to differentiate between the two paralogues. We have found that patient-derived alleles of Vpu, unlike those from lab-adapted viruses, trigger the degradation of -TrCP1 while co-opting its paralogue -TrCP2 for the degradation of cellular targets of Vpu, such as CD4. The potency of this dual inhibition correlates with stabilisation of the classical IB and the phosphorylated precursors of the mature DNA-binding subunits of canonical and non-canonical NF-B pathways, p105/NFB1 and p100/NFB2, in HIV-1 infected CD4+ T cells. Both precursors act as alternative IBs in their own right, thus reinforcing NF-B inhibition at steady state and upon activation with either selective canonical or non-canonical NF-B stimuli. These data reveal the complex regulation of NF-B late in the viral replication cycle, with consequences for both the pathogenesis of HIV/AIDS and the use of NF-B-modulating drugs in HIV cure strategies.