An endogenous glycosylphosphatidylinositol-specific phospholipase D releases basic fibroblast growth factor-heparan sulfate proteoglycan complexes from human bone marrow cultures.
Basic fibroblast growth factor (bFGF) is a hematopoietic cytokine that stimulates stromal and stem cell growth. It binds to a glycosylphosphatidylinositol (GPI)-anchored heparan sulfate proteoglycan on human bone marrow (BM) stromal cells. The bFGF-proteoglycan complex is biologically active and is released by addition of exogenous phosphatidylinositol-specific phospholipase C. In this study, we show the presence of an endogenous GPI-specific phospholipase D (GPI-PLD) that releases the bFGF-binding heparan sulfate proteoglycan and the variant surface glycoprotein (a model GPI-anchored protein) from BM cultures. An involvement of proteases in this process is unlikely, because released proteoglycan contained the GPI anchor component, ethanol-amine, and protease inhibitors did not diminish the release. The mechanism of release is likely to involve a GPI-PLD and not a GPI-specific phospholipase C, because the release of variant surface glycoprotein did not reveal an epitope called the cross-reacting determinant that is exposed by phospholipase C-catalyzed GPI anchor cleavage. In addition, phosphatidic acid (which is specifically a product of GPI-PLD-catalyzed anchor cleavage) was generated during the spontaneous release of the GPI-anchored variant surface glycoprotein. We also detected GPI-PLD-specific enzyme activity and mRNA in BM cells. Therefore, we conclude that an endogenous GPI-PLD releases bFGF-heparan sulfate proteoglycan complexes from human BM cultures. This mechanism of GPI anchor cleavage could be relevant for mobilizing biologically active bFGF in BM. An endogenous GPI-PLD could also release other GPI-anchored proteins important for hematopoiesis and other physiologic processes.
Brunner
G
G
Department of Cell Biology, New York University Medical Center, NY 10016.
Metz
C N
CN
Nguyen
H
H
Gabrilove
J
J
Patel
S R
SR
Davitz
M A
MA
Rifkin
D B
DB
Wilson
E L
EL
D000328:Adult; D001853:Bone Marrow / Q000378:metabolism*; D002478:Cells, Cultured; D010450:Endopeptidases / Q000502:physiology; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000235:genetics / Q000502:physiology*; D006410:Hematopoiesis; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate / Q000378:metabolism*; D006801:Humans; D010739:Phospholipase D / Q000235:genetics / Q000502:physiology*; D011509:Proteoglycans / Q000378:metabolism*
D010450:Endopeptidases; D016222:Fibroblast Growth Factor 2; D017261:Glycosylphosphatidylinositols; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate; D010739:Phospholipase D; D011509:Proteoglycans