DR396, an apoptotic DNase γ inhibitor, attenuates high mobility group box 1 release from apoptotic cells

High mobility group box1 (HMGB1) is a non-histone chromatin chromosomal protein playing an important role in chromatin architecture and transcriptional regulation. Recently, HMGB1 has been shown to be secreted into extracellular milieu in necrosis and apoptosis, and involved in inflammatory responses. However, the mechanism by which apoptotic cells release HMGB1 is unclear. In this study, to investigate the mechanism of HMGB1 release, we searched inhibitors of HMGB1 release from apoptotic cells. As a result, three compounds, 4-(4,6-dichloro-[1,3,5]-triazin-2-ylamino)-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)-benzoic acid (DR396), Pontacyl Violet 6R (PV6R), and Fmoc-D-Cha-OH (FDCO) in our in-house chemical library were found to inhibit HMGB1 release from staurosporine (STS)-induced apoptotic HeLa S3 cells. Interestingly, these three compounds have been previously categorized into apoptotic DNase γ inhibitors. Therefore, we examined whether apoptotic nucleosomal DNA fragmentation is involved in the release of HMGB1 during apoptosis. Expectedly, DR396, which is the most potent and specific inhibitor of DNase γ, was found to almost completely inhibit both HMGB1 release and internucleosomal DNA cleavage in HeLa S3 cells transfected with DNase γ expression vector and stably expressing DNase γ (HeLa S3/γ cells). These results clearly suggest that nucleosomal DNA fragmentation catalyzed by DNase γ is critical in the release of HMGB1 from apoptotic cells.