Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Monday Speaker Abstracts

FUNCTION OF ABC G1/G4 TRANSPORTERS AND CHOLESTEROL IN CELL-CELL FUSION

Elizabeth Chen ; 1 UT Southwestern Medical Center, Dallas, TX, USA

Cell-cell fusion is critical for the development and physiology of multicellular organisms. It is an asymmetric process in which an invading cell drills actin-propelled membrane protrusions into the receiving cell to promote cell membrane juxtaposition and fusion. Although the protein machinery at the site of fusion, known as the fusogenic synapse, has been extensively studied, the function of lipids in the fusion process remains largely unknown. In a screen for transmembrane proteins involved in cell-cell fusion, we identified a function for the G1/G4 family of ATP-binding cassette transporters (ABC transporters). Overexpression of ABCG1/4 transporters significantly enhanced cell-cell fusion, accompanied by the enrichment of free cholesterol on the outer leaflet of the plasma membrane. In contrast, extracting free cholesterol from the plasma membrane by treating cells with β -methylcyclodextrin inhibited cell-cell fusion, demonstrating a critical function for cholesterol in cell-cell fusion. Using TIRF microscopy, we observed enrichment of free cholesterol associated with the invasive membrane protrusions at the fusogenic synapse. Consistent with this, overexpression of ABCG1/4 transporters in Drosophila S2R+ cells led to an overall increase in the number of membrane protrusions. In contrast, knocking down ABCG1/4 transporters in mouse myoblasts inhibited cell-cell fusion, accompanied by less free cholesterol on the plasma membrane and decreased number of protrusions. Using probes for membrane fluidity and disordered lipid phase, we show that free cholesterol on the outer leaflet significantly increased membrane fluidity and disordered domains. Taken together, our studies revealed a novel function for ABCG1/4 transporters in cell cell fusion and uncovered a critical role for free cholesterol in the fusion process. We further demonstrate that free cholesterol enhances membrane fluidity and thus allowing the formation of membrane protrusions required for cell-cell fusion.

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