Chromatin in IgH gene promoters of cHL cells has a “closed” structure that can be opened by inhibition of DNA methylation. (A) L428, L1236, or KM-H2 cells were incubated for 72 hours in the presence of 500 ng of DNA methylation inhibitor 5-aza-dC (right). Local methylation at the V_H promoter chromatin was analyzed by antidimethylated histone 3 lysine 9 antibodies by ChIP analysis. Signals obtained for the IgH promoter, the involucrin promoter, and the histone H2B promoter are shown. (B) Histone H3-K9 methylation was assessed by ChIP at the V_H promoter regions of Ig-producing B-JAB and Namalwa cells. As controls, the histone H2B promoter and the involucrin promoter were used.