HIV-1 TAT PROTEIN DISTURBS THE SIGNALING CASCADE THAT LEADS TO ACROSOMAL EXOCYTOSIS IN HUMAN SPERM

ANAHÍ BELÉN PACHECO GUIÑAZÚ; DIEGO MASONE; LUCAS RESA JURIN; SILVIA ALEJANDRA BELMONTE

Buenos Aires

Congreso; Reunion conjunta de sociedades de biosciencia; 2017

Sociedad Argentina de Investigación Bioquímicas y Biología Molecular (SAIB)

The acrosome reaction (AR) is a regulated calcium-dependent exocytosis necessary forfertilization. Fertility parameters in HIV-seropositive men are abnormal. The HIV-1 transactivatingprotein (Tat) is released by infected cells and extracellular Tat enters uninfected cells byendocitosis inducing toxic effects. This protein impairs neurons secretion contributing to HIVpathogenesis. The aim of this work was to determine if HIV-1 Tat was able to enter a nonendocyticcell like sperm affecting gamete function. First, we incubated spermatozoa withrecombinant wild type Tat (WT-Tat). By WB and indirect immunofluorescence, we demonstratedthat Tat, at physiological concentrations, pass through human sperm membranes.To elucidate themechanisms involved in Tat internalization we challenged sperm with Tat mutants. We observedthat 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 bindsphosphatidylinositol (4,5)-bisphosphate (PIP2) with high affinity and that our laboratory has shownthat PIP2 plays a key role in the sperm exocytic cascade we tested a Tat mutant unable to bindPIP2. As expected, the mutant did not affect sperm exocytosis. To confirm that the inhibitory effectof Tat on the AR is due to its ability to bind the phospholipid, we rescued Tat-induced inhibition ofsecretion by adding PIP2. This suggests that Tat is sequestering PIP2. We assumed that PginducedAR inhibition will occur due to lack of IP3 synthesis. To test this argument, we resorted tothe 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 plasmamembrane 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 fertilityin HIV patients.