This study reports the interactome of HMGB1 in prostate and ovarian cancer cells, which includes a variety of proteins involved in diverse cellular processes. Subcellular fractionation is used to map the distribution of interacting proteins. In the nucleus, HMGB1 interacts directly with NuRD complex subunit RBBP7, as confirmed by yeast two-hybrid. Amongst HMGB1 interacting proteins are also subunits of the THOC complex and the septin complex. THOC5 IP-MS experiments confirmed that THOC proteins interact with septins and also with RAB11.