Binding of HIV-1 Tat to p53 decreases levels of PTEN. (A) Proposed mechanistic circuit for intracellular HIV-1 Tat: HIV-1 Tat may increase cell survival by preventing PTEN from binding to p53. Binding of HIV-1 Tat to p53 may result in reduced levels of both p53 by destabilization and PTEN by downregulation of PTEN expression. (B) In vitro binding assay: Lysates containing p53-FLAG were incubated with BSA (control) or HIV-1 Tat protein and then mixed with lysate containing PTEN V5-tag. Proteins bound to p53 were immunoprecipitated using anti-FLAG immobilized antibody and analyzed for PTEN-V5 tag levels by Western blotting. Ratios of PTEN-V5 levels normalized by p53-FLAG levels are shown.