Histone deacetylase inhibitors abrogate IL-1α/OSM-induced expression of key metalloproteinase genes. Cells were starved of serum for 24 hours before stimulation with I/O, a combination of IL-1α (5 ng/ml) and oncostatin M (OSM) (10 ng/ml) for 6 hours in the absence or presence of either trichostatin A (TSA) ((a) as shown or (b, c) 500 ng/ml) or NaBy ((a) as shown; (b, c) 10 mM). Total RNA was isolated and subjected to quantitative RT-PCR for expression of the genes (a, b) MMP1 and MMP13 and (c) ADAMTS4, ADAMTS5, and ADAMTS9. Data were normalised to the 18 S rRNA housekeeping gene; means and ranges are plotted. Absolute numbers are primer/probe-set-dependent and so cannot be compared between genes. (a) SW1353 chondrosarcoma cells; (b, c) primary human chondrocytes; (b) (inset) expression of COL2A1 and aggrecan by conventional RT-PCR. I/O, O/I, a combination of IL-1α and OSM; NaBy, sodium butyrate.