Function and mechanism of EndoU - PROJECT SUMMARY RNA-binding proteins (RBPs), including enzymes that act on RNA, impact all aspects of cellular function. However, the roles, molecular mechanisms and integration with the cellular regulatory networks are still unknown for most RBPs. The goal of this study is to elucidate the function, molecular mechanism, and regulation of a novel endoribonuclease, EndoU. Uniquely, the RNase activity of EndoU in vitro and in cell culture is directly activated by Ca2+ ions, suggesting a role in the cellular responses to this key second messenger. Importantly, EndoU misregulation is associated with uterine, cervical, skin, bronchial, and lung squamous cell cancers. It is heavily downregulated in esophageal, oral squamous, and cervical cancer, and is a strong prognostic marker in head/neck and colorectal cancers. EndoU is cytoplasmically expressed in distinct cell types sharing a major, driving role of programmed cell death in their development: thymocytes, B cells, squamous epithelial cells, and placental syncytiotrophoblasts. We hypothesize that EndoU controls survival/differentiation decisions during thymocyte development by cleaving target RNAs in response to changes in intracellular calcium levels. We specifically aim to fill the knowledge gap in understanding EndoU’s cellular role, RNA targeting repertoire, and the mechanism of EndoU activity and its Ca2+-dependent conformational control.
