Down-regulation of p210(bcr/abl) by curcumin involves disrupting molecular chaperone functions of Hsp90.

Objective: To investigate the effects of curcumin (Cur) on p210(bcr/abl) level in K562 cells, and the relationship between these effects and the molecular chaperone functions of heat shock protein 90 (Hsp90).

Methods: Flow cytometry and Western blot were used to examine the abundance of p210(bcr/abl), Hsp90, p23, Hsp70, and p60(Hop) in K562 cells treated with Cur. Reverse transcription polymerase chain reaction (RT-PCR) was used to determine the bcr-abl mRNA level in K562 cells treated with Cur. After co-immunoprecipitation of p210(bcr/abl) and its molecular chaperones, the immunoprecipitate was then subjected to Western blot analysis with anti-Hsp90, anti-Hsp70, anti-p23, and anti- p60(Hop)mAb.

Results: An exposure of K562 cells to Cur produced time-dependent down-regulation of p210(bcr/abl), the inhibition rate of p210(bcr/abl) in K562 cells determined by flow cytometry after treatment with Cur 27.2 micromol/L for 1 h, 6 h, 12 h and 24 h was 31.2%, 63.7%, 81.3% and 94.5%, respectively. In contrast, Cur had almost no influence on bcr-abl mRNA level. Treatment with Cur for 24 h reduced the association of p210(bcr/abl) with Hsp90/p23 complex, while increasing the association of p210(bcr/abl) with Hsp70/ p60(Hop) complex; however, the total protein abundance of Hsp90, p23, and p60(Hop) in K562 cells had no apparent change, while Hsp70 increased greatly.

Conclusions: Down-regulation of p210(bcr/abl) by Cur involves dissociating the binding of p210(bcr/abl) with Hsp90/p23 complex. In contrast, the association of p210(bcr/abl) with Hsp70/ p60(Hop) complex increased.