Friend or foe: Endoplasmic reticulum protein 29 (ERp29) in epithelial cancer

•ERp29 regulates epithelial cell plasticity and the mesenchymal–epithelial transition.•ERp29 shows a tumor suppressive function in primary tumor development.•ERp29 is potentially associated with distant metastasis in cancer.•ERp29 modulates cell survival against genotoxic stress.•Thus, ERp29 displays dual functions as a “friend or foe” in epithelial cancer.

The endoplasmic reticulum (ER) protein 29 (ERp29) is a molecular chaperone that plays a critical role in protein secretion from the ER in eukaryotic cells. Recent studies have also shown that ERp29 plays a role in cancer. It has been demonstrated that ERp29 is inversely associated with primary tumor development and functions as a tumor suppressor by inducing cell growth arrest in breast cancer. However, ERp29 has also been reported to promote epithelial cell morphogenesis, cell survival against genotoxic stress and distant metastasis. In this review, we summarize the current understanding on the biological and pathological functions of ERp29 in cancer and discuss the pivotal aspects of ERp29 as “friend or foe” in epithelial cancer.