Histone acetylation status in response to SIRT1 activity. Cells were transfected with expression vectors for different NFκB subunits. Expression vector for SIRT1 was used as a positive control. Histones were isolated after 24 hours and acetylation status was assessed by western blot. Transfection with empty vector was used as a reference control. ( A ) Detection was carried out with an antibody specific for acetylated histone H4K16 and with another antibody binding to histone H4 independently of the acetylation status (total H4). ( B ) Detection films of blots were scanned and quantified in silico. Values of H4K16 were normalized to total H4 and fold changes relative to control were calculated. n = 3. *P >0.05 versus empty vector.