Published online Sep 15, 2003. doi: 10.3748/wjg.v9.i9.1915
Revised: April 23, 2003
Accepted: May 16, 2003
Published online: September 15, 2003
AIM: To investigate and determine the mechanism and signal pathway of tetradecanoylphorbol-1, 3-acetate (TPA) in degradation of RXRα.
METHODS: Gastric cancer cell line, BGC-823 was used in the experiments. The expression level of RXRα protein was detected by Western blot. Nuclear and cytoplasmic protein fractions were prepared through lysis of cell and centrifugation. Localization and translocation of RXRα were observed under laser-scanning confocal microscope through labeling specific anti-RXRα antibody and corresponding immunofluorescent antibody as secondary antibody. Different inhibitors were used as required.
RESULTS: In BGC-823 cells, RXRα was expressed in the nucleus. When cells were treated with TPA, expression of RXRα was repressed in a time-dependent and TPA-concentration-dependent manner. Meanwhile, translocation of RXRα from the nucleus to the cytoplasm occurred, also in a time-dependent manner. When cells were pre-incubated with proteasome inhibitor MG132 for 3 hrs, followed by TPA for another 12 hrs, TPA-induced RXRα degradation was inhibited. Further observation of RXRα translocation in the presence of MG132 showed that MG-132 could block TPA-induced RXRα redistribution. Conversely, when RXRα translocation was inhibited by LMB, an inhibitor for blocking protein export from the nucleus, TPA could not repress expression of RXRα.
CONCLUSION: TPA could induce the degradation of RXRα protein in BGC-823 cells, and this degradation is time- and TPA-concentration-dependent. Furthermore, the degradation of RXRα by TPA is via a proteasome pathway and associated with RXRα translocation from the nucleus to the cytoplasm.