Identification of Phosphorylated p38 as a Novel DAPK-Interacting Partner during TNFα-Induced Apoptosis in Colorectal Tumor Cells

Death-associated protein kinase (DAPK) is a serine/threonine kinase that contributes to pro-apoptotic signaling on cytokine exposure. The role of DAPK in macrophage-associated tumor cell death is currently unknown. Recently, we suggested a new function for DAPK in the induction of apoptosis during the interaction between colorectal tumor cells and tumor-associated macrophages. Using a cell-culture model with conditioned supernatants of differentiated/activated macrophages (U937) and human HCT116 colorectal tumor cells, we replicated DAPK-associated tumor cell death; this model likely reflects the in vivo tumor setting. in this study, we show that tumor necrosis factor-a exposure under conditions of macrophage activation induced DAPK-dependent apoptosis in the colorectal tumor cell line HCT116. Simultaneously, early phosphorylation of P38 mitogen-activated protein kinase (phospho-p38) was observed. We identified the phospho-P38 mitogen-activated protein kinase as a novel interacting protein of DAPK in tumor necrosis factor-alpha-induced apoptosis. The general relevance of this interaction was verified in two colorectal cell fines without functional p53 (ie, HCT116 p53(-/-) and M29 mutant) and in human colon cancer and ulcerative colitis tissues. Supernatants of freshly isolated human macrophages were also able to induce DAPK and phospho-P38. Our findings highlight the mechanisms that underlie DAPK regulation in tumor cell death evoked by immune cells. (Am J Patbol 2009, 175.557-570; DOI: 10.2353/ajpatb.2009.080853)