Sorting for storage in myeloid cells of nonmyeloid proteins and chimeras with the propeptide of myeloperoxidase precursor

• Published in: Journal of leukocyte biology Vol. 71; no. 2; pp. 279 - 288
• Main Authors: Bülow, E., Nauseef, W. M., Goedken, M., McCormick, S., Calafat, J., Gullberg, U., Olsson, I.
• Format: Journal Article
• Language: English
• Published: England Society for Leukocyte Biology 01-02-2002
• Subjects: a1-microglobulin; Antigens; Antigens, CD - metabolism; Basic Medicine; calnexin; calreticulin; CD/metabolism; Cell and Molecular Biology; Cell Differentiation - genetics; Cell Line; Cell- och molekylärbiologi; Chimeric Proteins/genetics/metabolism; fSupport; granule; green fluorescent protein; Human; Humans; Immunohistochemistry; K562 Cells; LAMP-1 protein; Lysosomal Membrane Proteins; Medical and Health Sciences; Medicin och hälsovetenskap; Medicinska och farmaceutiska grundvetenskaper; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Membrane Glycoproteins/genetics/metabolism; Myeloid Cells - metabolism; myeloperoxidase; neutrophil; Non-P.H.S; Non-U.S. Gov't; P.H.S; Peroxidase - genetics; Peroxidase - metabolism; Peroxidase/genetics/metabolism; Protein Precursors - genetics; Protein Precursors - metabolism; Protein Precursors/genetics/metabolism; Protein Transport; Receptors; Receptors, Tumor Necrosis Factor - metabolism; Receptors, Tumor Necrosis Factor, Type I; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; secretion; secretory pathway; Support; Transfection; Trypsin Inhibitor, Kunitz Soybean; tumor necrosis factor receptors; Tumor Necrosis Factor/metabolism; U.S. Gov't; α1‐microglobulin
• ISSN: 0741-5400; 1938-3673; 1938-3673
• DOI: 10.1189/jlb.71.2.279

During formation of polymorphonuclear neutrophils, proteins are synthesized for storage in granules. Whereas sorting of proteins into distinct subtypes of cytoplasmic granules may reflect the coordinated expression of the proteins contained in them, still the mechanism(s) for the retrieval of proteins from the constitutive secretion is unknown. To investigate the mechanisms of retrieval, nonmyeloid secretory proteins were expressed in myeloid cell lines, and their subcellular fate was assessed. The contribution of the propeptide (MPOpro) of the myeloperoxidase (MPO) precursor was investigated by determining the fate of chimeras containing MPOpro. The nonmyeloid protein α1‐microglobulin (α1‐m) was targeted to storage organelles in 32D cells and colocalized with the lysosomal marker LAMP‐1, whereas soluble TNF receptor 1 (sTNFR1) was secreted without granule targeting. Fusion of MPOpro to α1‐m delayed exit from endoplasmic reticulum (ER), but subsequent targeting to dense organelles was indistinguishable from that of α1‐m alone. Fusion proteins between MPOpro and sTNFR1 or green fluorescent protein expressed in myeloid 32D, K562, or PLB‐985 cells did not associate stably with calreticulin or calnexin, molecular chaperones that normally interact transiently with the MPO precursor, but were still efficiently retained in the ER followed by degradation. We conclude that normally secreted, nonmyeloid proteins can be targeted efficiently to storage organelles in myeloid cells, that myeloid cells selectively target some proteins for storage but not others, and that MPOpro may contribute to the prolonged ER retention of the MPO precursor independent of the ER‐molecular chaperones calreticulin and calnexin.