ROS and SOCE: recent advances and controversies in the regulation of STIM and Orai

Store-operated Ca2+ entry (SOCE) is a widespread mechanism in cells to raise cytosolic Ca2+ and to refill Ca2+ stores. T cells critically rely on SOCE mediated by stromal interaction molecules (STIM) and Orai molecules for their activation and regulation of gene transcription; cells such as muscle cells, neurons or melanocytes probably utilize SOCE for the transmission of inducible receptor-mediated function as well as for generalized Ca2+ homeostasis mechanisms. Exposure to environmental or cell-intrinisic reactive oxygen species (ROS) can affect several components involved in Ca2+ homeostasis and thus alter multiple pathways. While all cells have a capacity to produce intracellular ROS, exposure of immune and skin cells to extracellular oxidative stress is particularly high during inflammation and/or with UV exposure. This review briefly summarizes cell-intrinsic sources of ROS and focuses on current findings and controversies regarding the regulation of STIM and Orai by oxidative modifications. We also introduce melanocytes as a new model system to study the function of STIM and Orai isoforms under physiological conditions that include exposure to UV light as an activating stimulus.