Fra-1 is a key driver of colon cancer metastasis and a Fra-1 classifier predicts disease-free survival

Background and Aim: Fra-1 (Fos-related antigen-1) is a member of the AP1 (activator protein-1) family of transcription factors. We have recently shown that Fra-1 is necessary for breast cancer cells to metastasize in vivo, and that breast cancer outcome can be predicted by a classifier comprising genes that are expressed in a Fra-1-dependent fashion. Here, we show that Fra-1 plays an important role also in colon cancer progression. Methods: We compared proliferation rates of parental and Fra-1-depleted colon cancer cells in vitro under 2D, 3D, and attachment-free conditions and in vivo upon subcutaneous and intravenous injections into mice. We also compared RNA expression profiles of colon cancer cells with and without Fra-1 expression. Results: Fra-1 depletion impair colony outgrowth of human colon cancer cells in soft agar and in suspension, whereas it does not affect proliferation on 2D culture plates. Consistent with this, upon subcutaneous injection into mice, tumors formed by Fra-1-depleted colon cancer cells are only three times smaller than those produced by control cells. In contrast, when injected intravenously, Fra-1 depletion causes 200-fold reduction in tumor burden. Consistent with the more aggressive characteristics of Fra-1-proficient tumors, the prognosis of colon cancer patients can be predicted by a Fra-1 classifier generated by comparing RNA profiles of parental and Fra-1-depleted colon cancer cells. Conclusions: Our results demonstrate that Fra-1 is an important determinant of the metastatic potential of human colon cancer cells, and suggest that a Fra-1 classifier can be used as a prognostic predictor in colon cancer patients. Overall design: HT29 cell line, two shRNAs against Fra-1, one empty vector control, three biological replicates

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Iskit S, Schlicker A, Wessels L, Peeper DS