MOLECULAR-CLONING AND CHARACTERIZATION OF SCAMPER, A SPHINGOLIPID CA2-MEDIATING PROTEIN FROM ENDOPLASMIC-RETICULUM( RELEASE)

Release of Ca2+ stored in endoplasmic reticulum is a ubiquitous mechan ism involved in cellular signal transduction, proliferation, and apopt osis. Recently, sphingolipid metabolites have been recognized as media tors of intracellular Ca2+ release, through their action at a previous ly undescribed intracellular Ca2+ channel. Here we describe the molecu lar cloning and characterization of a protein that causes the expressi on of sphingosyl-phosphocholine-mediated Ca2+ release when its complem entary RNA is injected into id Xenopus oocytes. SCaMPER (for sphingoli pid Ca2+ release-mediating protein of endoplasmic reticulum) is an 181 amino acid protein with two putative membrane-spanning domains. SCaMP ER is incorporated into microsomes upon expression in Sf9 cells or aft er translation in vitro. It mediates Ca2+ release at 4 degrees C as we ll as 22 degrees C, consistent with having ion channel function. The E C(50) for Ca2+ release from Xenopus oocytes is 40 mu M, similar to sph ingosyl-phosphocholine-mediated Ca2+ release from permeabilized mammal ian cells. Because Ca2+ release is not blocked by ryanodine or La3+, t he activity described here is distinct from the Ca2+ release activity of the ryanodine receptor and the inositol 1,4,5-trisphosphate recepto r. The properties of SCaMPER are identical to those of the sphingolipi d-gated Ca2+ channel that we have previously described. These findings suggest that SCaMPER is a sphingolipid-gated Ca2+-permeable channel a nd support its role as a mediator of this pathway for intracellular Ca 2+ signal transduction.