Collagenase digests were performed with 1 mg/ml type II collagenase and 1 mg/ml BSA (Sigma) in Hank’s balanced salt solution for 40 min (cells were exposed to SAHA or vehicle during this incubation). Cells were then harvested and cross-linked with 1% formaldehyde for 15 min. Cells were lysed (1% SDS, 10 mM EDTA, 50 mM Tris-HCl pH 8.0) and sonicated to generate 200 to 500 bp DNA fragments. Libraries were prepared and sequenced on an Illumina HiSeq 2000 using standard Illumina protocols