Macrophages are sentinel immune cells that survey the tissue microenvironment, releasing cytokines in response to both exogenous insults and endogenous events such as tumorigenesis. Macrophages mediate tumor surveillance and therapy-induced tumor regression; however, Tumor Associated Macrophages (TAMs) and their products may also promote tumor progression. Whereas NF-κB is prominent in macrophage-initiated inflammatory responses, little is known about the role of p53 in macrophage responses to environmental challenge including chemotherapy or in TAMs. Here, we report that NF-κB and p53, which generally have opposing effects in cancer cells, co-regulate induction of pro-inflammatory genes in primary human monocytes and macrophages. Using Nutlin-3 as a tool, we demonstrate that p53 and NF-κB rapidly and highly induce IL-6 by binding to its promoter. Transcriptome analysis revealed global p53/NF-κB co-regulation of immune response genes including several chemokines, which effectively induced human neutrophil migration. Additionally, we show that p53, activated by tumor cell paracrine factors, induces high basal levels of macrophage IL-6 in a TAM model system (Tumor-conditioned Macrophages [TCMs]). Compared to normal macrophages, TCMs exhibited higher p53 levels, enhanced p53 binding to the IL-6 promoter and reduced IL-6 levels upon p53 inhibition. Taken together, we describe a mechanism by which human macrophages integrate signals through p53 and NF-κB to drive pro-inflammatory cytokine induction. Our results implicate a novel role for macrophage p53 in conditioning the tumor microenvironment and suggest a potential mechanism by which p53-activating chemotherapeutics, acting upon p53-sufficient macrophages and precursor monocytes, may indirectly impact tumors lacking functional p53.

The integrity of DNA is constantly challenged throughout the life of a cell by both endogenous and exogenous stresses. A well-organized rapid damage response and proficient DNA repair, therefore, become critically important for maintaining genomic stability and cell survival. When DNA is damaged, the DNA damage response (DDR) can be initiated by alterations in chromosomal structure and histone modifications, such as the phosphorylation of the histone H2AX (the phosphorylated form is referred to as γ-H2AX). γ-H2AX plays a crucial role in recruiting DDR factors to damage sites for accurate DNA repair. On repair completion, γ-H2AX must then be reverted to H2AX by dephosphorylation for attenuation of the DDR. Here, we report that the wild-type p53-induced phosphatase 1 (Wip1) phosphatase, which is often overexpressed in a variety of tumors, effectively dephosphorylates γ-H2AX in vitro and in vivo. Ectopic expression of Wip1 significantly reduces the level of γ-H2AX after ionizing as well as UV radiation. Forced premature dephosphorylation of γ-H2AX by Wip1 disrupts recruitment of important DNA repair factors to damaged sites and delays DNA damage repair. Additionally, deletion of Wip1 enhances γ-H2AX levels in cells undergoing constitutive oncogenic stress. Taken together, our studies show that Wip1 is an important mammalian phosphatase for γ-H2AX and shows an additional mechanism for Wip1 in the tumor surveillance network. Cancer Res; 70(10); 4112-22. ©2010 AACR.