Journal of Cell Science 111, 2043-2054 (1998) 2043 Printed in Great Britain © The Company of Biologists Limited 1998 JCS3760 Distinct subcellular localization of calcium binding S100 proteins in human smooth muscle cells and their relocation in response to rises in intracellular calcium Anna Mandinova1, Dan Atar2, Beat W. Schäfer3, Martin Spiess1, Ueli Aebi1 and Claus W. Heizmann3,* 1Maurice E. Müller-Institute, Biocentrum, University of Basel, 4056 Basel, Switzerland 2Division of Cardiology, Department of Internal Medicine, University Hospital, 8032 Zürich, Switzerland 3Division of Clinical Chemistry and Biochemistry, Department of Pediatrics, University of Zürich, 8032 Zürich, Switzerland *Author for correspondence (e-mail:
[email protected]) Accepted 19 May; published on WWW 30 June 1998 SUMMARY Changes in cytosolic Ca2+ concentration control a wide associated with the sarcoplasmic reticulum and with actin range of cellular responses, and intracellular Ca2+-binding stress fibers. In contrast, S100A2 was located primarily in proteins are the key molecules to transduce Ca2+ signaling the cell nucleus. Using a sedimentation assay and via interactions with different types of target proteins. subsequent electron microscopy after negative staining, we Among these, S100 Ca2+-binding proteins, characterized by demonstrated that S100A1 directly interacts with a common structural motif, the EF-hand, have recently filamentous actin in a Ca2+-dependent manner. After attracted major interest due to their cell- and tissue-specific thapsigargin (1 µM) induced increase of the intracellular expression pattern and involvement in various pathological Ca2+ concentration, specific vesicular structures in the processes. The aim of our study was to identify the sarcoplasmic reticulum region of the cell were formed with subcellular localization of S100 proteins in vascular smooth high S100 protein content.