GLUTATHIONE-REDUCTASE IN HUMAN AND MURINE LUNG-TUMORS - HIGH-LEVELS OF MESSENGER-RNA AND ENZYMATIC-ACTIVITY

The enzyme glutathione reductase (GR) (GSSG + NADPH + H+ --> 2 GSH + N ADP+) plays a key role in the cellular defense against oxidative stres s. High levels of GR activity are often associated with tumor growth a nd/or resistance mechanisms against drug and radiation therapy. In ord er to investigate the molecular basis of elevated glutathione reductas e activities we studied the enzyme at the DNA, mRNA and protein levels in murine experimental tumor cell lines and in human lung tumors. A m odified ultracentrifugation procedure was developed which allowed the simultaneous isolation of DNA and total cellular RNA. Out of 11 human bronchial carcinomas obtained from patients without prior chemotherapy , five tumors showed a GR activity which was 2.4 to 3.8 times higher t han in the respective control tissues. In each case the elevated enzym e activity was accompanied by an elevated GRmRNA level. For none of th e tumors, GR gene rearrangement or amplification was observed by South ern blot analyses. The mouse tumor cell lines ASB XIV, Lewis lung carc inoma and EAT cells, also showed high levels of GRmRNA whereas this mR NA was hardly detectable in normal mouse lung tissue.