title: Secretion of annexin V from cultured cells requires a signal peptide.
abstract: Annexin V is an intracellular protein that lacks a hydrophobic signal peptide. However, there are several studies reporting the extracellular presence of annexin V. In this study, we designed transgenes of annexin V with or without an attached secretory signal peptide and investigated the secretion of the transgene products in COS-7 cells. The signal peptide, targeted annexin V to the endoplasmic reticulum (ER), the Golgi and culture media of transfected cells. In contrast, without the signal peptide, annexin V was present only in the cytoplasm and was not detected in the medium. To confirm our results we also evaluated the presence of extracellular annexin V in two cultured cell lines: BeWo, a choriocarcinoma cell model of placental trophoblasts, and human umbilical vein endothelial cells (HUVEC). Our results showed that annexin V was immunolocalized on the surfaces of both cells but could not be detected in the culture medium of either cell type. Our results suggest that the secretion of annexin V required the recombinant addition of a hydrophobic signal peptide and that the limited quantities of endogenous cell surface annexin V on BeWo and HUVEC cells is most likely derived from adjacent damaged cells.
authors.affiliation: Department of Molecular and Cellular Physiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267-0576, USA.
authors.forename: X
authors.initials: X
authors.lastname: Wang
authors.forename: B
authors.initials: B
authors.lastname: Campos
authors.forename: M A
authors.initials: MA
authors.lastname: Kaetzel
authors.forename: J R
authors.initials: JR
authors.lastname: Dedman
mesh_terms: D000818:Animals; D000838:Anions; D017304:Annexin A5 / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002462:Cell Membrane / Q000737:chemistry; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D002822:Choriocarcinoma / Q000737:chemistry / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000737:chemistry; D004730:Endothelium, Vascular / Q000737:chemistry / Q000378:metabolism; D005260:Female; D006801:Humans; D010743:Phospholipids / Q000032:analysis; D011247:Pregnancy; D021382:Protein Sorting Signals / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000032:analysis / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D014471:Umbilical Veins; D014594:Uterine Neoplasms / Q000737:chemistry / Q000378:metabolism
chemical_list: D000838:Anions; D017304:Annexin A5; D017077:Culture Media, Conditioned; D010743:Phospholipids; D021382:Protein Sorting Signals; D011994:Recombinant Proteins