title: Expression of the receptor tyrosine kinase Ret on the plasma membrane is dependent on calcium.
abstract: Mutations in the Ret receptor tyrosine kinase are responsible for a variety of human syndromes, including multiple endocrine neoplasia 2 and Hirschsprung's disease. Ret is expressed as a 150-kDa precursor form in the endoplasmic reticulum and a 170-kDa mature form at the plasma membrane. Here we show that expression of p170(ret) is dependent on calcium. Depletion of extracellular calcium completely blocks p170(ret) expression, which is not caused by a decrease in half-life of p170(ret) at the plasma membrane but by a defect in processing of p150(ret) into p170(ret). This processing defect can be mimicked by treating the cells with thapsigargin, a drug that releases calcium from internal stores, indicating that reduction in luminal calcium is responsible for the processing defect. We propose that a relatively high concentration of luminal calcium is necessary for the proper folding of Ret in the endoplasmic reticulum.
authors.affiliation: Laboratory for Physiological Chemistry, Utrecht University, P.O. Box 80042, 3508 TA Utrecht, The Netherlands.
authors.forename: D H
authors.initials: DH
authors.lastname: van Weering
authors.forename: T C
authors.initials: TC
authors.lastname: Moen
authors.forename: I
authors.initials: I
authors.lastname: Braakman
authors.forename: P D
authors.initials: PD
authors.lastname: Baas
authors.forename: J L
authors.initials: JL
authors.lastname: Bos
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D029721:Drosophila Proteins; D004721:Endoplasmic Reticulum / Q000201:enzymology; D006801:Humans; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D029721:Drosophila Proteins; D011518:Proto-Oncogene Proteins; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; D002118:Calcium