Journal of Leukocyte Biology
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Originally published online as doi:10.1189/jlb.0203066 on July 22, 2003

Published online before print July 22, 2003
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(Journal of Leukocyte Biology. 2003;74:800-809.)
© 2003 by Society for Leukocyte Biology

Artificially controlled aggregation of proteins and targeting in hematopoietic cells

Hanna Rosén1, Ying Gao, Ellinor Johnsson and Inge Olsson

Institution for Laboratory Medecine, Department of Hematology, Lund, Sweden

1Correspondence: Institution for Laboratory Medecine, Department of Hematology, C14, BMC, S-221 84, Lund, Sweden. E-mail: Hanna.Rosen{at}hematologi.lu.se

The targeting mechanisms for granule proteins in hematopoietic cells are largely unknown. Aggregation is believed to be important for protein sorting-for-entry and sorting-by-retention in endocrine and neuroendocrine cells. We asked whether artificially induced multimerization/aggregation of chimeric proteins could affect their sorting in hematopoietic cells. A system was used that permits ligand-controlled intracellular oligomerization of hybrid proteins containing the FK506-binding protein (FKBP). The hybrid proteins ELA-(FKBP)3 with neutrophil elastase (ELA) and (FKBP*)4-FCS-hGH with a furin cleavage site (FCS) and human growth hormone (hGH) were expressed in the myeloblastic 32D and the rat basophilic leukemia (RBL-1) hematopoietic cell lines. ELA alone is normally targeted to secretory lysosomes. However, the hybrid proteins and ligand-induced aggregates of them were constitutively secreted and not targeted. The hGH that was released at the FCS in (FKBP*)4-FCS-hGH was also constitutively secreted. We conclude that protein multimerization/aggregation per se is not enough to facilitate sorting-for-entry to secretory lysosomes in hematopoietic cells and that improperly folded proteins may be eliminated from sorting by constitutive secretion.

Key Words: secretory lysosomes • quality control • multimerization • secretion • storage






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