FIGURE 4.

Molecular interaction between Bcl-xL and Bnip3 in chondrocytes. A, Bcl-xL was immunoprecipitated (IP) from ATDC5 cells left untreated or treated with 20 mm P_i. The immunoprecipitated materials were Western blotted with anti-Bnip3 antibody. Bnip3 was associated with Bcl-xL after 6 h of P_i treatment. Bnip3 was detected as two bands (arrows). The top band is the immunoglobulin heavy chain. B, susceptibility to apoptosis of primary chondrocytes by Bcl-xL knockdown was partially restored by the simultaneous silencing of Bnip3. Western blot analysis shows efficient gene knockdown of Bcl-xL and Bnip3 through RNAi. The results are expressed as the means ± S.D. of six cultures. Experiments were repeated at least three times, and the representative data are presented. ^*, significantly different, p < 0.05. GFP, green fluorescent protein. C, overexpression of Bnip3 promoted the P_i-induced cell death of primary chondrocytes, which was rescued by simultaneous transduction of Bcl-xL, whereas overexpression of Bcl-2 or Mcl-1 had little effect. The results are expressed as the means ± S.D. of six cultures. Experiments were repeated at least three times and the representative data are presented. ^*, significantly different, p < 0.05.