| Ca2+ is a key second messenger in many intracellular signaling pathways. Ca2+ signals control many cellular functions ranging from short-term responses such as contraction and secretion to longer-term regulation of cell growth and proliferation. Stromal interaction molecules (STIMs) function as Ca2+ sensors that detect changes in Ca2+ content in intracellular Ca2+ stores. STIM1 is conserved, ubiquitously expressed, and functions as an endoplasmic reticulum (ER) Ca2+ sensor that migrates from the ER Ca2+ store to the plasma membrane where it activates calcium-release-activated calcium (CRAC) channels when the ER Ca2+ store is low. STIM1 is a potential tumor suppressor; defects in STIM1 may cause rhabdomyosarcoma and rhabdoid tumors. STIM1 can either homodimerize or form heterodimers with STIM2. STIM2 possesses a high sequence identity to STIM1 and can function as an inhibitor of STIM1-mediated plasma membrane store-operated Ca2+ entry. However, further investigation is required to elucidate the true physiological function of STIM2. |
