Fig. 4

Cancer cell-cell fusion model which is focused predominantly on the expression of the fusogen syncytin-1 and includes some basal similarities to physiological fusion events. In this model it is assumed that a cancer cell with a re-organised actin cytoskeleton expresses syncytin-1 and a PS-binding receptor, which recognises ASCT2 and PS, respectively. A basal syncytin-1 expression could be attributed to promotor mutation and/or hypomethylation (TF = transcription factor). The majority of expressed syncytin-1 will remain in the cytosol. In some cells, syncytin-1 may translocate to the plasma membrane, which may be facilitated by altered cytoskeletal structures. The corresponding cell exhibits Ca²⁺-PLS activity, which is engaged by Ca²⁺ to shuttle PS and subsequently enable plasma membrane merger and cell fusion (modified according to [166])