Oxygen sensing in neuroendocrine cells and other cell types: pheochromocytoma (PC12) cells as an experimental model

A steady supply of oxygen is an absolute requirement for mammalian cells to maintain normal cellular functions. To answer the challenge that oxygen deprivation represents, mammals have evolved specialized cell types that can sense changes in oxygen tension and alter gene expression to enhance oxygen delivery to hypoxic areas. These oxygensensing cells are rare and difficult to study in vivo. As a result, pheochromocytoma (PC12) cells have become a vital in vitro model system for deciphering the molecular events that confer the hypoxia-resistant and oxygen-sensing phenotypes. Research over the last few years has revealed that the hypoxia response in PC12 cells involves the interactions of several signal transduction pathways (Ca2+/calmodulin-dependent kinases, Akt, SAPKs, and MAPKs) and transcription factors (HIFs, CREB, and c-fos/junB). This review summarizes the current understanding of the role these signal transduction pathways and transcription factors play in determining the hypoxic response.