| Popis: |
Cell cycle regulators and signal transduction pathways can influence apoptotic sensitivity of tumor cells, and we previously described an association between EGFr overexpression, reduced DNA repair activity, and increased apoptotic sensitivity of ME-180 cervical carcinoma cells toward cis-diammedichloroplatinum (cDDP; K. Nishikawa, et al., Cancer Res., 52: 4758-4765, 1992). In the present study, the characteristics of ME-180 cells selected for high or low apoptotic sensitivity to cDDP (or camptothecin) were examined and compared to determine whether signal transduction components and cell cycle regulation were distinct in these isogenic drug response variant populations. As ME-180 cells progressed from high to low cDDP sensitivity [IC50 approximately 80 ng/ml in cDDP sensitive (PT-S) to approximately 2000 ng/ml in cDDP-resistant (Pt-R) cells], there was a significant decrease in EGFr expression that paralleled the relative reduction in cDDP apoptotic responsiveness (approximately 30-fold). cDDP-resistant cells had the slowest rate of growth and more effectively reduced DNA adduct levels following cDDP exposure than parental cells. Cellular levels of the cell cycle inhibitor p21WAF1 inversely correlated with cDDP responsiveness with high levels of p21WAF1 expressed in drug-resistant Pt-R cells in the absence of elevated p53. cDDP stimulated a 2-fold increase in p53 levels in both drug-sensitive and drug-resistant cells but caused a delayed reduction in p21WAF1 levels, suggesting p53-independent regulation of p21WAF1 in ME-180 cells. Activation of EGFr in Pt-R cells stimulated cell cycle progression (2-fold), reduced p21WAF1 levels (2-fold), and increased sensitivity to cDDP (3-fold), suggesting that receptor signaling enhanced the efficacy of cDDP to induce cell death by relieving cell cycle restriction. These results demonstrate that the transition of ME-180 cells from a drug-sensitive to drug-resistant phenotype correlates with reciprocal changes in EGFr and p21WAF1 expression and provides additional evidence that the pathways controlled by these proteins may contribute to some forms of drug resistance. |
