Loss of STAT3 occurred in part through the ubiquitin-proteasome pathway however curcumin and FLLL32 did not inhibit the 20S proteasome in OSA cell lines. A) OSA8 was treated with DMSO, curcumin, FLLL32, or the proteasome inhibitor MG132 for 4 hours prior to collection. Protein lysates were generated and STAT3 was immunoprecipitated. Protein was separated by SDS-PAGE and western blotting for ubiquitin and STAT3 was performed. Experiments were repeated two times. Densitometry analysis was performed using Image J (Rasband, W. S., Image J, U. S. National Institutes of Health, Bethesda, Maryland, USA, http://rsb.info.nih.gov/ij/ webcite, 1997-2009). B) Canine (OSA8) or human (SJSA) OSA cells were serum starved for 2 hours then treated with DMSO, 10 μM curcumin, 10 μM FLLL32, or 10 μM MG132 for 4 hours. Cells were collected, washed with cold PBS, and prepared for use in the 20S Proteasome Activity Assay Kit (Millipore, Billerica, MA). Experiments were repeated two times.
Fossey et al. BMC Cancer 2011 11:112 doi:10.1186/1471-2407-11-112