R. Felix et al., SYNTHESIS OF MEMBRANE-BOUND AND MATRIX-BOUND COLONY-STIMULATING FACTOR-I BY CULTURED OSTEOBLASTS, Journal of cellular physiology, 166(2), 1996, pp. 311-322
Colony-stimulating factor-1 (CSF-1) is synthesized as a secreted or me
mbrane-bound molecule. We investigated whether osteoblastic cells prod
uce these forms of CSF-1. Glutaraldehyde-fixed cell layers supported p
roliferation of the macrophage cell line BAC1.2F5, suggesting the pres
ence of membrane- or/and matrix-associated CSF-1. Furthermore, CSF-1 a
ctivity could be either extracted from the matrix or released from the
cell membrane. A neutralizing antiserum against CSF-1 inhibited these
activities. After labeling the cellular proteins with [S-35] met/cys
or [S-35] SO42- CSF-1 was immunoprecipitated and analyzed by SDS-PAGE.
Under nonreducing conditions, bands with MW more than 200, 200, 100,
and 50 kd were detected. These bands shifted to lower MW under reducin
g conditions. Treatment with chondroitin lyase ABC decreased the MW of
the 200 kd monomer, proving the proteoglycan structure. Much smaller
quantities of CSF-1 were found in the matrix extract than in the condi
tioned medium. Transforming growth factor beta (TGF-beta) increased bo
th the synthesis of CSF-1 and its accumulation in the matrix. CSF-1 re
leased with trypsin from the membrane fraction yielded on SDS-PAGE a b
and with MW of 60 and 30 kd under nonreducing and reducing conditions,
respectively. Transcripts encoding both the secreted and the membrane
-associated forms of the cytokine were detected in osteoblasts by reve
rse transcription polymerase chain reaction. These data indicate that
osteoblastic cells produce the secreted forms, either remaining in the
culture supernatant, or being associated to the matrix, and the membr
ane associated form of CSF-1. (C) 1996 Wiley-Liss, Inc.