Mf. Belcourt et al., THE INTRACELLULAR LOCATION OF NADH-CYTOCHROME B(5) REDUCTASE MODULATES THE CYTOTOXICITY OF THE MITOMYCINS TO CHINESE-HAMSTER OVARY CELLS, The Journal of biological chemistry, 273(15), 1998, pp. 8875-8881
NADH:cytochrome b(5) reductase activates the mitomycins to alkylating
intermediates in vitro. To investigate the intracellular role of this
enzyme in mitomycin bioactivation, Chinese hamster ovary cell transfec
tants overexpressing rat NADH:cytochrome b(5) reductase were generated
. An NADH:cytochrome b(5) reductase-transfected clone expressed 9-fold
more enzyme than did parental cells; the levels of other mitomycin-ac
tivating oxidoreductases were unchanged. Although this enzyme activate
s the mitomycins in vitro, its overexpression in living cells caused d
ecreases in sensitivity to mitomycin C in air and decreases in sensiti
vity to porfiromycin under both air and hypoxia, Mitomycin C cytotoxic
ity under hypoxia was similar to parental cells. Because NADH:cytochro
me b(5) reductase resides predominantly in the mitochondria of these c
ells, this enzyme may sequester these drugs in this compartment, there
by decreasing nuclear DNA alkylations and reducing cytotoxicity. A cyt
osolic form of NADH:cytochrome b(5) reductase was generated. Transfect
ants expressing the cytosolic enzyme were restored to parental line se
nsitivity to both mitomycin C and porfiromycin in air with marked incr
eases in drug sensitivity under hypoxia. The results implicate NADH:cy
tochrome b(5) reductase in the differential bioactivation of the mitom
ycins and indicate that the subcellular site of drug activation can ha
ve complex effects on drug cytotoxicity.