Figure 4.

Down‐regulated MMP‐9 expression by honokiol through the degradation of ubiquitin/proteasome system in H1299 cells. (a) H1299 cells were treated with honokiol (0, 2.5, 5, 7.5, 10 μM) for 24 hr, the total mRNAs were harvested, and the mRNA level of MMP‐9 was detected by RT‐PCR assay. (b) H1299 cells were treated with or without 5 μM MG132 for 30 min before 10 μM honokiol incubation for 24 hr. After treatment, the expression of MMP‐9 protein was assayed by Western blotting or (c) the ubiquitination of MMP‐9 was analyzed by immunoprecipitation analysis with an anti‐MMP‐9 antibody. The immunoprecipitates were then analyzed the expression of ubiquitin by Western blotting