FIGURE 4 from HDAC6 Inhibition Releases HR23B to Activate Proteasomes, Expand the Tumor Immunopeptidome and Amplify T-cell Antimyeloma Activity

Effect of HDAC6 inhibitors on the myeloma immunopeptidome. A, Number of peptides eluted from human MHC-I molecules at each indicated peptide lengths (range = 6 to 15 amino acids). RPMI-8226 cells were treated with tubastatin-A, ACY-738 or bortezomib. B, Number of peptides and their fold change after treatment of RPMI-8226 cells with tubastatin-A, ACY-738, or bortezomib. C, The terminal amino acids of the top 50 peptides upregulated by tubastatin-A or ACY-738 treatment were analyzed. Shown is the relative percent of each terminal amino acid for the top 50 peptides upregulated by HDAC6 inhibitor treatment. D, Shown is the number of peptides reduced by treatment of E.G7-Ova cells with bortezomib and the fold decrease relative to untreated cells. E, Shown is the peptide sequence, fold decrease, and gene accession for the 20 peptides most downregulated by bortezomib treatment. Red asterisks indicate peptides upregulated by treatment with both HDAC6 inhibitors. F, The terminal amino acids of the top 50 peptides upregulated by tubastatin-A or ACY-738 treatment were analyzed. Shown is the relative percent of each terminal amino acid for the top 50 peptides upregulated following treatment with each HDAC6 inhibitor. G, Shown are gene accession numbers for the top 20 peptides most downregulated by bortezomib treatment. H, Shown are gene accession numbers for the top 20 peptides most upregulated by either tubastatin-A or ACY-738. Red asterisks indicate genes and peptides that were upregulated following treatment with both of the HDAC6 inhibitors.