The ability of retinoids to inhibit cancer cell growth and induce gene expression is well known. Our objectives were (1) to determine if retinol and retinoic acid (RA) inhibited the migration and invasion of RA-resistant colon cancer cells and (2) to determine if retinol and RA mediated migration and invasion transcriptionally. Two RA-resistant colon cancer cell lines, HCT-116 and SW620, were serum starved 48 h before seeding 1 x 10^5 cells/well on uncoated Boyden chambers (migration) or Matrigel-coated Boyden chambers (invasion). The upper portion of the chambers contained 0 (control), 1, or 10 microM RA or retinol. An 8 micrometer pore-sized filter separated the cells from a lower chamber containing chemoattractant. Fetal bovine serum (10%) and 20 ng/ml hepatic growth factor served as chemoattractants for the migration and invasion assays, respectively. Cell migration was measured after 8 h and invasion after 24 h by propidium iodide staining. All data are reported as mean ÑÂ± SEM for n=3. Although RA-resistant, the HCT-116 and SW620 cell lines showed a similar dose response to RA and retinol treatment in both migration and invasion assays, despite the inability of RA to inhibit cell growth. In HCT-116 cells, 1 microM RA or retinol decreased migration to 60.6 +/− 12.9% and 35.4 +/− 15.2% of control, respectively. At 10 microM, HCT-116 cell migration was inhibited to 41.4 +/− 15.7% of control for RA and 27.9 +/− 17.1% for retinol. Treatment with 1 microM RA or retinol reduced SW620 migration to 80.9 +/− 7.2% and 36.5 +/− 8.9% of control, respectively. Ten microM RA or retinol reduced SW620 migration to 65.9 +/− 8.1% and 36.4 +/− 7.2% of control, respectively. The ability of HCT-116 cells to invade was decreased to 66.9 +/− 6.9% and 52.6 +/− 15.9% of control by 1 microM RA and retinol, respectively. Ten microM RA and retinol decreased cell invasion to 45.0 +/− 7.3% and 40.0 +/− 6.7% of control, respectively. SW620 cell invasion was decreased slightly by 1 microM RA and retinol to 77.1 +/− 16.3 and 81.2 +/− 19.0 % of control, respectively. Ten microM RA or retinol inhibited invasion to a greater extent, to 56.8 +/− 11.7 % of control and 46.0 +/− 15.0% of control, respectively. To determine if cell migration and invasion were mediated transcriptionally or translationally, cells were treated with retinoids and 2 micrograms/ml actinomycin D, 10 microM of a retinoic acid receptor (RAR) pan-antagonist, or 10 micrograms/ml cycloheximide. Treatment with actinomysin D, RAR antagonist, or cycloheximide did not affect cell migration or invasion. In conclusion, RA and retinol inhibited the migration and invasion of RA-resistant colon cancer cells via a RAR-independent mechanism, most likely involving post-transcriptional modification. Supported by Research Scholar Grant # 03-233-01-CNE from the American Cancer Society.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]