VEC trans-endocytosis occurs between HUVECs expressing endogenous VEC and COS7 cells expressing VEC fusion proteins.

<p>(<b>A</b>) Co-culture of COS7 cells expressing VEC-EGFP (COS7-VEC-EGFP) and HUVECs expressing TagRFP657 (HUVEC-TagRFP657). Lower images are higher magnification of the indicated area in upper images. VEC trans-endocytosis occurred between COS7-VEC-EGFP and HUVEC-TagRFP657, due to endogenous VEC in HUVECs. Exogenously expressed VEC molecules in COS7 cells form cell-cell junctions. Arrows show trans-endocytosed VEC-EGFP molecules from COS7 cells by adjacent HUVECs labeled with TagRFP657. Scale bars = 20 µm. (<b>B</b>) Time-course images of co-culture of COS7-VEC-EGFP and HUVECs-VEC-TagRFP657. The interaction between endogenous VEC in HUVECs and over-expressed VEC-EGFP in COS7 cells can induce trans-endocytosis of VEC. Arrows show the trans-endocytosed VEC-EGFP molecules from a COS7 cell that appeared to bud off from cell-cell junctions and be pulled into a HUVEC. Scale bar = 10 µm. See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090736#pone.0090736.s007" target="_blank">Movie S1</a>. (<b>C</b>) Co-culture of COS7 cells expressing VEC-EGFP (COS7-VEC-EGFP) and COS7 cells expressing TagRFP657 (COS7-TagRFP657). Lower images are higher magnification of the indicated area in upper images. No trans-endocytosis occurred between these cells. Scale bars = 20 µm.