Breast cancer (BC) is the second leading cause of cancer deaths among women. DEK is a known oncoprotein that is highly expressed in over 60% of breast cancers and is an independent marker of poor prognosis. However, the molecular mechanisms by which DEK promotes tumor progression are poorly understood. To identify novel oncogenic functions of DEK, we performed RNA-Seq analysis on isogenic Dek-knockout and complemented murine BC cells. Gene ontology analyses identified gene sets associated with immune system regulation and cytokine-mediated signaling and differential cytokine and chemokine expression was confirmed across Dek-proficient versus Dek-deficient cells. By exposing murine bone marrow-derived macrophages (BMDM) to tumor cell conditioned media (TCM) to mimic a tumor microenvironment, we showed that Dek-expressing breast cancer cells produce a cytokine milieu, including up-regulated Tslp and Ccl5 and down-regulated Cxcl1, Il-6, and GM-CSF, that drives the M2 polarization of macrophages. We validated this finding in primary murine mammary tumors and show that Dek expression in vivo is also associated with increased expression of M2 macrophage markers in murine tumors. Using TCGA data, we verified that DEK expression in primary human breast cancers correlates with the expression of several genes identified by RNA-Seq in our murine model and with M2 macrophage phenotypes. Together, our data demonstrate that by regulating the production of multiple secreted factors, DEK expression in BC cells creates a potentially immune suppressed tumor microenvironment, particularly by inducing M2 tumor associated macrophage (TAM) polarization.

Self-renewing hematopoietic stem cells and multipotent progenitor cells are responsible for maintaining hematopoiesis throughout an individual's lifetime. For overall health and survival, it is critical that the genome stability of these cells is maintained and that the cell population is not exhausted. Previous reports have indicated that the DEK protein, a chromatin structural protein that functions in numerous nuclear processes, is required for DNA damage repair in vitro and long-term engraftment of hematopoietic stem cells in vivo. Therefore, we investigated the role of DEK in normal hematopoiesis and response to DNA damaging agents in vivo. Here, we report that hematopoiesis is largely unperturbed in DEK knockout mice compared with wild-type (WT) controls. However, DEK knockout mice have fewer radioprotective units, but increased capacity to survive repeated sublethal doses of radiation exposure compared with WT mice. Furthermore, this increased survival correlated with a sustained quiescent state in which DEK knockout restricted hematopoietic progenitor cells (HPC-1) were nearly three times more likely to be quiescent following irradiation compared with WT cells and were significantly more radioresistant during the early phases of myeloid reconstitution. Together, our studies indicate that DEK functions in the normal hematopoietic stress response to recurrent radiation exposure.

Breast cancer is the second leading cause of cancer deaths among women. DEK is a known oncoprotein found to be highly expressed in more than 60% breast cancers and is found to be an independent marker of poor prognosis. However, the molecular mechanisms by which DEK promotes tumor progression are poorly understood. To elucidate the oncogenic functions of DEK, we performed RNA-seq analysis on isogenic Dek-knockout and complemented murine breast cancer cells, which indicated dysregulation of immune signaling. Among the target genes identified and confirmed was an upregulation of thymic stromal lymphopoietin (TSLP) in Dek expressing murine breast cancer cells. TSLP was previously shown by Han et al to amplify the alternative (M2) activation of macrophages. M2-like macrophages are tumor promoting, they recycle iron for cell growth and encourage tissue remodeling and repair activities like angiogenesis. To test the immune modulating functions of Dek-expressing breast cancer cells, we treated bone marrow derived macrophages (BMDM) with tumor cell conditioned media. We found that in vitro, Dek expressing cancer cells induced an M2-like polarization of macrophages, as determined by the expression of M2-associated genes, enhanced migration, and iron recycling phenotypes, which was accompanied by inhibited ERK1/2 signaling. We found this phenotypic trend to be true in vivo, as well. In sectioned mammary tumors from MMTV-RontgDek+/+ and MMTV-RontgDek−/− mice, we see lower levels of iron staining in Dek+/+ tumors than in Dek−/− tumors using Prussian blue staining that co-localized with F4/80 macrophage marker staining. This suggested that Dek expression in the tumors induced an iron recycling, M2-like phenotype in tumor associated macrophages. Furthermore, we observed increased TSLP expression and angiogenesis, as determined by CD31 staining, in Dek-expressing tumors in vivo. These findings suggest that tumor Dek expression may promote breast cancer progression by inducing M2-like macrophage polarization in a murine breast cancer model. Citation Format: Miranda Shephard, Nicholas Pease, Lisa M. Privette Vinnedge. Expression of the DEK oncogene in breast cancer cells promotes M2 polarization of tumor associated macrophages [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2836.

Breast cancer is the most common cancer and the second leading cause of cancer deaths among women. DEK is a known oncoprotein found to be highly expressed in more than 60% breast cancers and is found to be an independent marker of poor prognosis. However, the molecular mechanisms by which DEK promotes tumor progression are poorly understood. To elucidate the oncogenic functions of DEK, we performed RNA-seq analysis on isogenic Dek-knockout and complemented murine breast cancer cells, which indicated dysregulation of immune signaling. Among the target genes identified and confirmed was an upregulation of thymic stromal lymphopoietin (TSLP) in Dek expressing breast cancer cells. TSLP was previously shown by Han et al to amplify the alternative (M2) activation of macrophages. M2-like macrophages are tumor promoting, they recycle iron for cell growth and encourage tissue remodeling and repair activities like angiogenesis. Classically (M1) activated macrophages are tumor suppressing and are typically associated with response to infection. To test the immune modulating functions of Dek-expressing breast cancer cells, we treated bone marrow derived macrophages (BMDM) with tumor cell conditioned media. We found that in vitro, Dek expressing cancer cells induced an M2-like polarization of macrophages, as determined by the expression of M2-associated genes, enhanced migration, and iron recycling phenotypes, which was accompanied by inhibited ERK1/2 sighnaling. We found this phenotypic trend to be true in vivo, as well. In sectioned mammary tumors from MMTV-RontgDek+/+ and MMTV-RontgDek-/- mice, we see lower levels of iron staining in Dek+/+ tumors than in Dek-/- tumors using Prussian blue staining that co-localized with F4/80 macrophage marker staining. This suggested that Dek expression in the tumors induced an iron recycling, M2-like phenotype in tumor associated macrophages. These findings suggest that tumor Dek expression may promote breast cancer progression by inducing M2-like macrophage polarization in a murine breast cancer model. Citation Format: Miranda S. Shephard, Nicholas A. Pease, Jon Cheek, Lisa M. Privette Vinnedge. Expression of the DEK oncogene in breast cancer cells promotes M2 polarization of tumor associated macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3471.