HDAC9 and Miyoshi myopathy: We further dissected the mechanism of HDAC-mediated gene repression in MM cells in acidic conditions, using DR4. DR4 expression was curtailed (Figures 4C, 4D and 4E), and histone H3K9 in a DR4 gene promoter was deacetylated in MM cells (Figure 5A) in acidic conditions.