Serglycin proteoglycan is required for secretory granule integrity in mucosal mast cells.
SG (serglycin) PGs (proteoglycans) are strongly implicated in the assembly of MC (mast cell) granules. However, this notion has mainly been on the basis of studies of MCs of the connective tissue subtype, whereas the role of SG PG in mucosal MCs has not been explored. In the present study, we have addressed the latter issue by using mice with an inactivated SG gene. Bone marrow cells were differentiated in vitro into the mucosal MC phenotype, expressing the markers mMCP (mouse MC protease) -1 and -2. Biosynthetic labelling experiments performed on these cells revealed an approximately 80% reduction of 35SO4(2-) incorporation into PGs recovered from SG-/- cells as compared with SG+/+ counterparts, indicating that SG is the dominating cell-associated PG of mucosal MCs. Moreover, the absence of SG led to defective metachromatic staining of mucosal MCs, both in vivo and in the in vitro-derived mucosal MCs. Ultrastructural analysis showed that granules were present in similar numbers in SG+/+ and SG-/- cells, but that their morphology was markedly affected by the absence of SG, e.g. with electron-dense core formation only seen in SG+/+ granules. Analysis of the MC-specific proteases showed that mMCP-1 and mMCP-7 were completely independent of SG for storage, whereas mMCP-2 showed a partial dependence. In contrast, mMCP-4 and -6, and carboxypeptidase A were strongly dependent on SG for storage. Together, our data indicate that SG PG is of crucial importance for assembly of mature mucosal MC granules, but that the specific dependence on SG for storage varies between individual granule constituents.
Braga
Tiago
T
Swedish University of Agricultural Sciences, Department of Molecular Biosciences, The Biomedical Centre, Box 575, 751 23 Uppsala, Sweden.
Grujic
Mirjana
M
Lukinius
Agneta
A
Hellman
Lars
L
Abrink
Magnus
M
Pejler
Gunnar
G
D000818:Animals; D001854:Bone Marrow Cells / Q000502:physiology*; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D007413:Intestinal Mucosa / Q000502:physiology*; D008407:Mast Cells / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009092:Mucous Membrane / Q000502:physiology; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D022142:Secretory Vesicles / Q000502:physiology* / Q000648:ultrastructure; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
D017077:Culture Media, Conditioned; D011509:Proteoglycans; D011994:Recombinant Proteins; D033921:Vesicular Transport Proteins; C075430:serglycin