J. Fellenberg et al., MODULATION OF RESISTANCE TO ANTI-APO-1-INDUCED APOPTOSIS IN OSTEOSARCOMA CELLS BY CYTOKINES, International journal of cancer, 72(3), 1997, pp. 536-542
The CD95/APO-I/Fas receptor/ligand system plays a crucial role in grow
th control by mediating apoptosis in lymphoid and non-lymphoid cells,
To investigate the role of CD95-mediated apoptosis in osteosarcoma, we
studied 3 human osteosarcoma cell lines (HOS/TE 85, MG 63 and Saos-2)
and osteoblasts derived from bone biopsies. In contrast to osteoblast
-like cells, all cell lines were resistant to anti-APO-1-induced apopt
osis despite constitutive CD95 expression at intermediate levels. Bloc
king of macromolecular synthesis by cycloheximide or actinomycin D or
modulation of CD95 expression by cytokines (TNF-alpha and/or gamma-int
erferon) restored sensitivity to anti-APO-l-induced cell death, PCR an
alysis of the CD95 transcripts revealed the production of a truncated
splice variant that codes for a soluble form of the CD95 receptor. Syn
thesis and secretion of soluble CD95 protein into the culture supernat
ant was demonstrated by Western blot analysis, Treatment with sensitiz
ing cytokines led to up-regulation of full-length CD95 transcripts and
the encoded membrane-bound CD95 protein but not the truncated mRNA sp
lice variant and the corresponding soluble receptor, as shown by PCR a
nd Western blot analysis. The biological activity of soluble CD95 secr
eted by osteosarcoma cells was demonstrated by the ability of osteosar
coma supernatants to protect the sensitive T-cell line Jurkat from ant
i-APO-1-mediated apoptosis, Our results suggest that the production of
soluble CD95 by osteosarcoma cell lines that may block physiological
death signals and the production of membrane-bound CD95 are differentl
y regulated by cytokines via modulation of RNA splicing. (C) 1997 Wile
y-Liss, Inc.