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. It was previously found that StarD7 is able to interact with phosphatidylserine. We have previously shown that StarD7 is partially relocated from the cytoplasm to the plasma membrane during in vitro cytotrophoblast differentiation into syncytiotrophoblast. This study further investigates the function of StarD7 in trophoblasts. MTT-based cell proliferation assays were preformed in triplicate using BeWo cells that were incubated with increasing concentrations of recombinant StarD7 protein (0, 5, 10 or 20 mg/ml). Cell viability was determined by propidium iodide staining and detection of LDH in the culture supernatants. Statistical analysis was by t-test and a P value < or ¼ 0.05 was considered to be significant. Syncytialization of BeWo cells was assessed by immunostaining for desmoplakin. The proliferation of BeWos was significantly inhibited by incubation with StarD7 at 5, 10 and 20 mg/ml. Incubation of BeWos with StarD7 did not cause a significant increase in cell death as measured by either propidium iodide or LDH release at any of the concentrations we tested. Fluorescent microscopy suggested that there were few intracellular desmosomes between adjacent BeWo cells after treatment with StarD7 at 20 mg/ml. BeWo cultures treated with StarD7 at these concentrations had similar levels of intracellular desmosomes to those found in control cultures treated with
Keywords: START lipid domain, Trophoblast proliferation arrest, Syncytialization, Cell fusion