Modulation of mitogen-activated protein kinase cascades by differentiation-1 protein: Acquired drug resistance of hormone independent prostate cancer cells

Purpose: The inhibitor of differentiation-1 protein (Id-1) is over expressed in multidrug resistance prostate cancer cells. We determined the effect of Id-1 expression and its underlying pathways on the development of multidrug resistance in prostate cancer. Materials and Methods: AT3 cells were transfected with the Id-1 gene or a blank vector. Id-1 mRNA expression was determined by reverse transcriptase-polymerase chain reaction and Id-1 protein content was detected by immunoblot and flow cytometry. Cellular cytotoxicity was determined by MTT (microculture 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay (Sigma Chemical Co., St. Louis, Missouri). The activation and expression of mitogenactivated protein kinase (MAPK) were measured by transactivation assay and Western blotting, respectively. Results: Id-1 overproduction drove AT3 cells to become resistant to chemotherapeutic agents but did not induce mdr-1 gene expression. The p38MAPK and c-jun N-terminal kinase (JNK) pathways were suppressed, which correlated with increased Id-1 expression. No significant change in extracellular signal-regulated kinase (ERK) activation was observed in Id-1 transfectants compared with that of AT3 or vector control. Treatment of Id-1 expressing cells with p38MAPK and JNK inhibitors resulted in decreased doxorubicin induced apoptosis. In contrast, Id-1 expressing cells treated with ERK inhibitor made cells more sensitive to drug induced apoptosis. Conclusions: Up-regulation of Id-1 was found in prostate cancer multidrug resistant cells. Sustained ERK activation, and JNK and p38MAPK inhibition by Id-1 in cells may confer drug resistance. These changes in MAPKs could be a mechanism for the acquisition of multidrug resistance in prostate cancer.