Submitted October 17, 2007
Accepted June 26, 2008
The tetraspanin CD63 is involved in granule targeting of neutrophil elastase
Linda Kallquist, Markus Hansson*, Ann-Maj Persson, Hans Janssen, Jero Calafat, Hans Tapper, and Inge Olsson
Department of Hematology, Lund University, Lund, Sweden
Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam, Netherlands
Department of Clinical Sciences, Section for Clinical and Experimental Infection Medicine, Lund University, Lund, Sweden
* Corresponding author; email: markus.hansson{at}med.lu.se.
Targeting mechanisms of neutrophil elastase (NE) and other luminal proteins stored in myeloperoxidase (MPO)-positive secretory lysosomes/primary granules of neutrophils are unknown. These granules contain an integral membrane protein, CD63 with an adaptor protein-3-dependent granule delivery system. Therefore, we hypothesized that CD63 cooperates in granule delivery of the precursor of NE (proNE). Supporting this hypothesis, an association was demonstrated between CD63 and proNE upon coexpression in COS cells. This also involved augmented cellular retention of proNE requiring intact large extracellular loop of CD63. Furthermore, depletion of CD63 in promyelocytic HL-60 cells with RNA interference or a CD63 mutant caused reduction of cellular NE. However, the proNE steady state level was similar to wild type in CD63-depleted clones making it feasible to examine possible effects of CD63 on NE trafficking. Thus, depletion of CD63 led to reduced processing of proNE into mature NE and reduced constitutive secretion. Furthermore, CD63 -depleted cells showed a lack of morphologically normal granules, but contained MPO-positive cytoplasmic vacuoles with a lack of proNE and NE. Collectively, our data suggest that granule proteins may cooperate in targeting; CD63 can be involved in ER or Golgi export, cellular retention and granule targeting of proNE before storage as mature NE.
