HDAC9 and synovial sarcoma: To answer this question we exposed two synovial sarcoma (Syo-1 and K-SS1) and two rhabdomyosarcoma cell lines (RMS and RD) to Tv6 for 6 h in the presence of HDAC inhibitors, and analyzed sirtuin enzymatic activity using a four-amino-acid (QPKK) acetylated peptide as substrate (see material and methods).