Figure 5.

Secreted GDF15 from senescent fibroblasts mediates pro‐oncogenic effects on epithelial cells through activating the MAPK and PI3K pathways. (a, b) The phosphorylation of p38, ERK, and AKT was induced in colon epithelial cells (LT97, AA/C1, Caco‐2, and HT‐29) that were co‐cultured with senescent CCD‐18Co(A) or s1005395(B) cells compared to the epithelial cells grown with normal fibroblasts (S=senescent, N=normal). (c, f) The phosphorylation of p38, ERK, and AKT was reduced in colon epithelial cells, including LT97(C), AA/C1(D), Caco‐2(E), and HT‐29(F) when they were co‐cultured with senescent fibroblast cell line CCD‐18Co after shGDF15 knockdown (S=senescent, N=normal). In all experiments, colon epithelial cell lines and colon fibroblasts were co‐cultured for three days. (g) Human recombinant GDF15 (rhGDF15) induced the phosphorylation of p38, ERK, and AKT in all four colon epithelial cells (LT97, AA/C1, Caco‐2, and HT‐29). Colon epithelial cell lines were treated with rhGDF15 (20 ng/ml) for three days. The medium with rhGDF15 was refreshed every day. DPBS (0.1%) was used as a vehicle control treatment. (h–j) Cell proliferation (h), migration (i), and invasion (j) were reduced in colon epithelial cells (LT97, AA/C1, Caco‐2, and HT‐29) treated with U0126 (ERK inhibitor), SB203580 (p38 inhibitor), and LY294002 (AKT inhibitor). In cell proliferation, migration, and invasion assay, colon epithelial cell lines and senescent fibroblasts were co‐cultured in the presence of inhibitors, including U0126 (5 µM), SB203580 (10 µM), and LY294002 (10 µM). DMSO (0.1%) served as the vehicle control treatment (n = 2 independent experiments). The statistical significance was determined using a Student's t test. Statistically significant differences are indicated: *p < 0.05, **p < 0.01, ***p < 0.001