Anoikis of colon carcinoma cells triggered by β-catenin loss can be enhanced by tumor necrosis factor receptor 1 antagonists.

Abstract

Detachment of non-malignant epithelial cells from the extracellular matrix causes their apoptosis, a phenomenon called anoikis. By contrast, carcinoma cells are anoikis-resistant, and this resistance is thought to be critical for tumor progression. Many oncogenes trigger not only anti- but also pr-apoptotic signals. The proapoptotic events represent an aspect of a phenomenon called oncogenic stress, which acts as a safeguard mechanism blocking tumor initiation. In cells that become malignant, oncogene-induced antiapoptotic signals outbalance the proapoptotic ones. It is now thought that treatments blocking the antiapoptotic events but preserving the proapoptotic signals can be particularly effective in killing tumor cells. Whether or not oncogenes induce any proanoikis signals that can be used for enhancing the efficiency of approaches aimed at triggering anoikis of cancer cells has never been explored. β-Catenin is a major oncoprotein that is often activated in colorectal cancer and promotes tumor progression via mechanisms that are understood only in part. We found here that β-catenin triggers both anti- and proanoikis signals in colon cancer cells. We observed that the antianoikis signals prevail and the cells become anoikis-resistant. We further established that one proanoikis signal in these cells is triggered by β-catenin-induced downregulation of an apoptosis inhibitor tumor necrosis factor receptor 1 (TNFR1) and subsequent reduction of the activity of a transcription factor NF-κB (nuclear factor-κB), a mediator of TNFR1 signaling. We also found that the effect of β-catenin on TNFR1 requires the presence of transcription factor TCF1, a β-catenin effector. We demonstrated that ablation of β-catenin in colon cancer cells triggers their anoikis and that this anoikis is enhanced even further if low TNFR1 or NF-κB activity is artificially preserved in the β-catenin-deprived cells. Thus, inhibition of TNFR1 or NF-κB activity can be expected to enhance the efficiency of approaches aimed at blocking β-catenin-driven anoikis resistance of colon carcinoma cells.