Fig. 5

Development of large invasive tumors by transplanted Caco-2-mScarlet cells. A, B Caco-2-mScarlet cell tumors developed three months after transplantation. A Gross (top) and magnified (bottom) views of the Caco-2 cell tumor from the luminal side. B Caco-2 cells (red) formed large tumors, characterized by complex folding of the tumor epithelium. Nuclei were stained with Hoechst33342. C-F Immunofluorescence analysis of large invasive Caco-2 cell tumors. C The dense collagen layer observed at earlier stages was absent at the interface between the large invasive Caco-2 cell tumors and the surrounding stromal cells (indicated by white arrowheads). In these tumors, Caco-2 cells exhibited moderate positivity for COL1A1 (indicated by a white arrow), suggesting the expression of collagen in these cells. D Caco-2 cells within large invasive tumors directly interacted with vimentin (VIM)-positive mesenchymal cells. The vimentin-positive cells infiltrated the folds of the Caco-2 cell sheet (right). E, F Analysis of proliferating cells by EdU staining. In the large tumors, EdU-positive proliferating cells were predominantly located in the peripheral regions (P), with a notable absence in the central regions (C)