INVESTIGADORES
SUHAIMAN Laila
congresos y reuniones científicas
Título:
PIP2 PROMOTES MEMBRANE CURVATURE AND IS A SIGNALING HUB IN HUMAN SPERM ACROSOME EXOCYTOSIS
Autor/es:
ALTAMIRANO, KARINA N; SUHAIMAN, LAILA; LUCCHESI, O; RUETE, CELESTE; DEL POPOLO, MARIO G; BELMONTE, SILVIA A
Lugar:
Mendoza
Reunión:
Simposio; II International Symposium on Traslational Medicine y XIII Jornadas de Investigacion de la Fac. de Ccias. Médicas; 2019
Institución organizadora:
FCM,FCEN-UNcuyo-UBA-Univ Friburg
Resumen:
The human sperm has a secretory vesicle that undergoes exocytosis when challenged with different stimuli known as acrosome reaction (AR). The exocytosis requires the fusion of the outer acrosome membrane (OAM) and plasma membrane in multiple points generating hybrid vesicles.We reported that diacylglycerol (DAG) stimulates AR by feeding into a PKC and PLD1-dependent positive loop that supplies PIP2. We hypothesize that PIP2 synthesis is required to produce DAG and IP3, and to induce a change in the OAM curvature.We explored by coarse-grained Molecular Dynamics simulations the correlation between membrane curvature and local lipid composition. By TEM, we demonstrated that PIP2 increase induces deep acrosomal membrane invaginations; although it was not able to induce acrosome swelling, AR or membrane disruption. However, for the AR to proceed, PIP2 needs to be synthesized and hydrolyzed. Recent publication proposed the following signaling pathway: cAMP?>Epac?>Rap1?>PLCε. This PLC catalyzes the hydrolysis of PIP2 , generating IP3, which binds IP3-sensitive channels and releases Ca2+ from the acrosome. Given that we demonstrated that DAG induces the AR in the absence of cAMP and extracellular calcium, we asked about the mechanism triggered by DAG. By using Far-IFI we showed that DAG activates Rap1 suggesting the existence of an exchange factor for this small GTPase. Then, we thought about a nucleotide exchange factor activated by DAG (RasGRP1), described to activate Rap1 in secretory cells. By WB and IFI we demonstrated the presence and localization of RasGRP1 in human sperm. Further, we tested RasGRP1 in exocytosis assays. We observed that it triggered the AR in a dose-dependent manner. Our findings highlight the dual role of PIP2 in exocytosis. It is controlling the membrane curvature and constitutes a hub in the signaling pathway to exocytosis. We present direct evidence showing the presence and function of RasGRP1 which adds an alternative pathway to exocytosis.