LGR4 regulates tumorigenicity in human breast cancer cells. A, B) shLGR4 MDA-MB-231 or control (ctrl) MDA-MB-231 cells were injected orthotopically into 9 mice per group. The tumor volumes were monitored until 7 wk (A). The tumor weights were measured at 49 d when the mice were euthanized (B). Error bars are means ± sd. **P < 0.01, ***P < 0.001. C, D) shLGR4 MDA-MB-231 or ctrl MDA-MB-231 cells were injected subcutaneously into 6 nude mice per group. The tumor volumes were recorded up to 31 d (C). The tumor weights were recorded at 31 d when the mice were euthanized (D). Error bars are means ± sd. *P < 0.05, **P < 0.01, ***P < 0.001. E) LGR4 knockdown decreased PCNA expression in xenograft tumors. The tumors from panel C were excised and sectioned for PCNA staining. Representative images are shown (3 images from each of 3 mice). Scale bars, 50 µm (top); 10 µm (bottom).