The glucose-regulated protein (GRP) system in mammalian cells is induced by glucose deprivation, anoxia, the calcium ionophore A23187, and 2-deoxyglucose. In Chinese hamster ovary cells the major 97, and 170 kDa.Removal of each of these four GRP-inducing stresses leads to the coordinate repression of GRPs and induction of the major heat shock proteins at 70 and 89 kDa. The application of each of these four GRP-inducing conditions leads to a significnt induction of resistance to the drug doxorubicin. Removal of each GRPinducing condition results in the rapid disappearance of this resistance in a manner that correlates with the repression of the GRPs. 2). In addition to glucose deprivation, this system can be induced by 2-deoxyglucose (3), the calcium ionophore A23187 (4), chronic anoxia (5), and viral infection (6). The GRP system represents a subset of a group of stress proteins that also includes the major heat shock proteins. In the case of the heat shock proteins, it has been shown that the application of a heat shock proteininducing stress results in concomitant expression of a heatresistant state referred to as thermotolerance (7-11). GRPs, however, are not associated with thermotolerance (12).Independent of these studies, it is also recognized that two conditions that induce GRPs, chronic anoxia and 2-deoxyglucose, lead to resistance to the drug doxorubicin (13-16). Based on these studies we consider here the hypothesis that GRP induction confers resistance to this chemotherapeutic agent in analogy to studies relating heat shock proteins and heat resistance. To test this hypothesis, we first used glucose deprivation, the most common method of GRP induction. We report that this treatment as well as A23187 induce resistance to doxorubicin. Finally, with all four inducers, there is a good temporal correlation between the application of the GRP-inducing stress and the induction of cellular resistance to doxorubicin and between the removal of the GRP-inducing stress and repression of cellular resistance to doxorubicin.The development of drug resistance is a major limiting factor in determining the success of cancer chemotherapy, and the investigation of mechanisms of resistance has attracted considerable attention (17-19). Since hypoxia and nutrient deprivation can occur during tumor development, this information suggests an alternative approach to the study of the mechanism(s) by which resistance to this chemotherapeutic agent may occur and connects this protective phenomenon with conditions associated with the expression of a major stress protein system. METHODSChinese hamster ovary (CHO) cells initially obtained from Los Alamos National Laboratory were maintained as monolayer cultures at 370C in Ham's F-10 medium (GIBCO) supplemented with 15% (vol/vol) newborn calf serum. The RIF-1 cell line was cultured in the a modification of minimal essential medium with 10% (vol/vol) fetal calf serum as described (20,21). In situ studies were performed by collecting cultured cells and then intradermally inocula...

No abstract

No abstract