The loss of MAGI1 in primary tumors induces tumor cell proliferation. (A) Primary tumor growth of MCF7shLuc and MCF7shMAGI1 cells injected subcutaneously in nude mice. Primary tumor growth was assessed by measuring the tumor volume over time until the tumors were too big and the mice had to be euthanized. Bars correspond to the mean ± Standard Error to the Mean (SEM; n = 8 mice per group). Unpaired two-tailed Student’s t-test; *p < 0.05. (B,C) Representative immunohistochemical staining of Ki67 in primary tumors obtained after subcutaneous engraftment of either MCF7shLuc (B) or MCF7shMAG1 cells (C). Brown staining indicates positive immunoreactivity. Scale bar = 250 µM. In the magnified area, the red * highlights an increased number of mitotic cells in the MCF7shMAGI1-derived primary tumor. (D,E) Quantification of the immunohistochemical analysis in (B,C), showing the percentage of primary tumor cells stained positively for Ki67 (D) and the normalized mean intensity of Ki67 positive cells (E) in MCF7shMAGI1 and MCF7shLuc primary tumors. Bars correspond to the mean ± SD (n = 4 for shLuc and n = 5 for shMAGI1). Unpaired two-tailed Student’s t-test; **p < 0.01 and ***p < 0.001.