(A) ELISA shows cytokine levels in culture media collected from the HT-29 CRC cells and CCD-18Co fibroblasts co-cultured for 96 h. Only SDF-1 increased significantly in the co-culture medium (**P<0.01); there were no statistically significant changes in the levels of EGF, bFGF, and IL-6. (B) ELISA shows cytokine levels in the culture media collected from the RKO CRC cells and CCD-18Co fibroblasts co-cultured for 96 h. There were no statistically significant changes in the four cytokines examined. (C) ELISA shows SDF-1 expression in culture media collected from the siRNA negative control (siNC) and β6 knockdown HT-29 CRC cells (siβ6) after co-culture with CAFs for 96 h. Accompanying the decreased expression of β6, SDF-1 expression decreased significantly (**P<0.01). (D) ELISA shows SDF-1 expression in the culture media collected from mock transfected (Mock) and β6 transfected RKO CRC cells (β6 overexpression) after co-culture with CAFs for 96 h. Accompanying the increased expression of β6, SDF-1 expression increased significantly (**P<0.01). (E,F) Transwell invasion chamber assay shows the invasive capacity of HT-29 and RKO CRC cells after co-culture with NFs or CAFs for 24 h in the absence or presence of AMD3100 (a CXCR4 antagonist) pretreatment. The CRC cell invasion capability increased significantly when co-cultured with CAFs (**P<0.01); however, this effect was inhibited by AMD3100 pretreatment. **P<0.01, #P<0.05; data are mean ± S.E.M. from three independent experiments.