A. Zyad et al., RESISTANCE TO TNF-ALPHA AND ADRIAMYCIN IN THE HUMAN BREAST-CANCER MCF-7 CELL-LINE - RELATIONSHIP TO MDR1, MNSOD, AND TNF GENE-EXPRESSION, Cancer research, 54(3), 1994, pp. 825-831
The molecular basis of cross-resistance to tumor necrosis factor (TNF)
and Adriamycin has been investigated using the breast adenocarcinoma
cell line MCF7/p, its Adriamycin-resistant counterpart MCF7Adr(R), and
the MDR1 gene-transduced MCF-7 cells (MCF7/MDR1). While the parental
cell line MCF7/p was TNF-sensitive, MCF7Adr(R) was TNF-resistant. The
TNF resistance exhibited by MCF7Adr(R) cells was not due to a lack of
TNF receptor expression because both cell lines express comparable lev
els of p75 and p55 receptors as revealed by immunofluorescence analysi
s. NF-kappaB translocation, which is an essential transducing signal o
f the TNF-induced lysis pathway, does not appear to be involved in thi
s resistance as assessed by gel shift experiments. In order to determi
ne the role of MDR1 gene expression in the development of this cross-r
esistance, MCF7/p cells transfected by the MDR1 gene were examined. Ou
r data showed that the expression of the MDR1 gene in these cells resu
lted in a relative resistance of these cells to Adriamycin without aff
ecting their susceptibility to TNF killing. The implication of the man
ganese superoxide dismutase and endogenous TNF expression in the cross
-resistance by MCF7Adr(R) cells to Adriamycin and TNF has also been in
vestigated. Northern blot analysis indicated that following TNF stimul
ation, the expression of 4-kilobase and 1-kilobase manganese superoxid
e dismutase mRNAs were 9- to 10-fold induced in MCF7Adr(R) cells as co
mpared to MCF7/p and MCF7/MDR1 cells. This suggests a possible involve
ment of this enzyme in the Adriamycin-induced resistance to TNF. Altho
ugh TNF-treatment of MCF7/p and MDR-cells induced endogenous TNF expre
ssion in these cells. the level of mRNA induction was selectively enha
nced in MCF7Adr(R) cells (7- to 8-fold greater in MCF7Adr(R) cells as
compared to MCF7/p and MCF7/MDR1 cells). Collectively, these data indi
cate that the expression of the MDR1 gene in MCF7/p cells following ge
ne transfection is not sufficient for the acquisition of TNF resistanc
e by MCF7/MDR1 cells. Furthermore, our data provide the first evidence
that Adriamycin-induced resistance to TNF in MCF7Adr(R) cells may, in
part, involve an overexpression of endogenous TNF and manganese super
oxide dismutase genes.