FUNCTIONAL CHARACTERIZATION OF STARD7, A NOVEL GESTATIONAL TUMOR START DOMAIN CONTAINING PROTEIN.

ANGELETTI SOFÍA; RENA VIVIANA; GENTI DE RAIMONDI SUSANA

Villa Giardino. Córdoba

Congreso; XV Jornadas de la Sociedad de Biología de Córdoba; 2005

Sociedad de Biología de Córdoba

The StAR-related lipid transfer (START) domain is defined as a motif of around 200 amino acids implicated in lipid/sterol binding. In a previous study, we identified the StarD7 transcript encoding one of the 15 family members with START domain present in the human genome. In addition, we demonstrated that StarD7 recombinant protein forms stable Gibbs and Langmuir monolayers at the air-buffer interface, showing marked surface activity and interaction with phospholipid monolayers, mainly with phosphatidylserine, cholesterol and phosphatidylglycerol (Biochem. Biophys. Res. Comm. 314: 181, 2004). To gain an insight about the role of this novel protein in the physiology of the cell, we transiently transfected Cos-7 cell line with pcDNA/TO/c-myc plasmid containing a wild type StarD7 cDNA and both NH2- and C-terminal deleted versions. Western blot and immunofluorescence assays of the transfected cells were performed with two different antibodies obtained against overexpressed StarD7 and StarD7-C-terminal amino acids, respectively. The specificity of these antibodies was verified with an antibody against c-myc epitope. The results obatined demonstrate that wild type StarD7-c-myc protein, as well as the mutant ones, are localized in the cytoplasm. These localizations were confirmed through subcellular fractionation and subsequent western blot assays. Furthermore, it was demonstrated that antibodies recognize preferentially a 40 kDa protein present in different cell lines, such as JEG-3, Caco-2 y C2BBe1. We also investigated the expression of StarD7 in JEG-3 cell line exposed to methotrexate (1μM). This drug induces differentiation of JEG-3 cells, which resulted in the enhancement of StarD7 expression. Our findings suggest that StarD7 may play a functional role in the process of trophoblast differentiation throught phospholipids uptake and transport.