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/, 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.