StarD7 is a fusogenic protein

ANGELETTI, SOFÍA,; SANCHEZ, JULIETA; GENTI- RAIMONDI, SUSANA DEL VALLE; PERILLO, MARÍA ANGELICA

Los Cocos, Córdoba, Argentina

Congreso; XXXVIII Reunión Anual de la Sociedad Argentina de Biofísica; 2009

StarD7 is a novel protein of unknown function that belongs to the START lipid domain family and is expressed in the cytoplasm of human trophoblast cells. We have previously found that StarD7 is able to interact with phosphatidylserine and that StarD7 is partially relocated from the cytoplasm to the plasma membrane during in vitro cytotrophoblast differentiation into syncytiotrophoblast [1,2]. The present work was aimed at elucidating a potential action mechanism for StarD7 that could be derived from its interaction with a lipid-membrane interface. So, we applied an assay based on the labeled lipid fluorescence dequenching induced by a BODIPY-PC dilution with non-labeled lipids. Recombinant StarD7 was able to accelerate the dilution of a labeled lipid from donor to acceptor liposomes in a concentration dependent-manner. Moreover, the size distribution of liposomes was determined with dynamic light scattering. The addition of StarD7 to SUV samples (33 nm) induced the appearance of a population of 41 nm. Taking into account that it was reported that vesicles formed by fusion exhibit a volume 41% bigger than that of the original vesicles [3], it can be concluded that the new vesicles population appeared in the presence of StarD7 may become from SUVs fusion. Besides, we demonstrated a diminish of intercellular desmosomes between adjacent BeWo cells after incubation with recombinant StarD7 at 10 and 20 ìg/ml leading to sincytium formation. Altogether, these findings and previous data suggest that StarD7 is a fusogenic protein that may initiate/facilitate the differentiation of BeWo cells through cell membrane fusion.  [1]. Angeletti,S  et al.. (2004) Surface activity and interaction of StarD7 with phospholipid monolayers. BB Res. Commun. 314 (1): 181-185. [2]. Angeletti S et al. (2008) Expression and Localization of StarD7 in Trophoblast Cells. Placenta 29 (5): 396-404. [3]. Jan Wilschut, Dick Hoekstra. (1991. ) Membrane fusion..