HIV-1 TAT protein disturbs the signaling cascade that leads to acrosomal exocytosis in human sperm

PACHECO GUINAZU, ANAHI BELEN; MASONE, DIEGO; BEAUMELLE, BRUNO; RESA JURIN, LUCAS ARMANDO; ALTAMIRANO, KARINA N; BELMONTE SILVIA A

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

SAIB-SAIC-SAB-SAI-SAFE-SAA-SAFIS-SAH-SAP

The acrosome reaction (AR) is a regulated calcium-dependent exocytosis necessary for fertilization. Fertility parameters in HIV-seropositive men are abnormal. The HIV-1 transactivating protein (Tat) is released by infected cells and extracellular Tat enters uninfected cells by endocytosis inducing toxic effects. This protein impairs neurons secretion contributing to HIV pathogenesis. The aim of this work was to determine if HIV-1 Tat was able to enter a non-endocytic cell like sperm affecting gamete function. First, we incubated spermatozoa with recombinant wild type Tat (WT-Tat). By WB and indirect immunofluorescence, we demonstrated that Tat, at physiological concentrations, pass through human sperm membranes. To elucidate the mechanisms involved in Tat internalization we challenged sperm with Tat mutants. We observed that a W11 residue is required in this process. WT-Tat strongly impaired progesterone (Pg)-induced AR as measured by exocytosis assays. Considering that HIV-1 Tat binds phosphatidylinositol (4,5)-bisphosphate (PIP2) with high affinity and that our laboratory has shown that PIP2 plays a key role in the sperm exocytic cascade we tested a Tat mutant unable to bind PIP2. As expected, the mutant did not affect sperm exocytosis. To confirm that the inhibitory effect of Tat on the AR is due to its ability to bind the phospholipid, we rescued Tat-induced inhibition of secretion by adding PIP2. This suggests that Tat is sequestering PIP2. We assumed that Pg-induced AR inhibition will occur due to lack of IP3 synthesis. To test this argument, we resorted to the agonist of IP3 receptors, adenophostin that rescued Pg-induced exocytosis after Tat inhibition. These findings suggest that Tat requires the W11 residue to permeate through the plasma membrane and when inside the sperm a strong interaction with PIP2 avoids the AR to proceed. Our findings may provide some clues to elucidate the unsolved issues concerning to male fertility in HIV patients.