B. Halvorsen et al., PROTEOGLYCANS IN MACROPHAGES - CHARACTERIZATION AND POSSIBLE ROLE IN THE CELLULAR UPTAKE OF LIPOPROTEINS, Biochemical journal, 331, 1998, pp. 743-752
The murine macrophage cell line J774 was incubated with [S-35]sulphate
. The cell-associated S-35-labelled macromolecules were shown to be pr
oteoglycans and glycosaminoglycans in similar amounts. The possible pr
esence of cell-surface proteoglycans was investigated by incubating [S
-35]sulphate-labelled cells with trypsin for 15 min. The released mate
rial contained approx. 70 % free glycosaminoglycan chains and 30 % pro
teoglycans. The latter component was demonstrated by HNO2 treatment to
contain heparan sulphate. In the total cell fraction not treated with
trypsin a small but significant portion was shown to be chondroitin s
ulphate proteoglycan, The cell-associated glycosaminoglycans contained
both chondroitin sulphate and heparan sulphate. To investigate possib
le biological functions of cell-surface proteoglycans in macrophages,
cells were incubated with NaClO3 to inhibit sulphation of proteoglycan
s and beta-D-xyloside to abrogate proteoglycan expression. The uptake
of oxidized I-125-tyraminylcellobiose-labelled low-density lipoprotein
(I-125-TC-LDL) was typically two to three times higher than that of n
ative I-125-TC-LDL in untreated J774 cells. The cellular uptake at 37
degrees C of native I-125-TC-LDL was decreased 25% after both NaClO3 a
nd xyloside treatment, whereas the uptake of oxidized I-125-TC-LDL was
decreased 35 % after both types of treatment. The mRNA levels for the
scavenger receptor A-II and the LDL receptor were not affected by NaC
lO3 or xyloside treatment, Furthermore, fluid-phase endocytosis, measu
red as uptake of horseradish peroxidase, and receptor-mediated endocyt
osis, measured as uptake of I-125-TC-ovalbumin, were not affected by N
aClO3 treatment of J774 cells. Removal of cell-surface chondroitin sul
phate with chondroitinase ABC decreased only the binding of native I-1
25-TC-LDL, whereas removal of heparan sulphate with heparitinase decre
ased the binding of both oxidized and native I-125-TC-LDL. Addition of
lipoprotein lipase increased the uptake of oxidized I-125-TC-LDL 1.7
times and the uptake of native I-125-TC-LDL 2.1 times. The binding of
the former was more sensitive to NaClO3 treatment than the latter. The
results presented support the notion that some of the uptake pathways
for lipoproteins in the foam-cell-forming macrophages depend on the p
resence of cell-surface heparan sulphate and chondroitin sulphate.