I would also like to thank members of the Chen lab; you have always accepted me and served me well as my adopted lab. The next step in tumor progression involves the recruitment and infiltration of nonmalignant cells into the tumor. The tumor microenvironment refers to the various cell types present in the tumor, as well as the tumor stroma, blood vessels, secreted molecules, and local microenvironmental conditions (ie, hypoxic, necrotic, etc.).
Immune cells present in the tumor microenvironment include lymphocytes, macrophages known as tumor-associated macrophages (TAMs), neutrophils, and myeloid-derived suppressor cells (MDSCs). Those cells that can survive in the bloodstream and spread to a secondary site usually reach the capillary bed and adhere to the endothelium of microvessels [23]. However, for this, these cells must overcome the same pressures of the primary tumor, i.e.
In addition, MDSCs directly promote tumor angiogenesis by differentiating into endothelial cells and directly incorporating into tumor endothelium in vivo [18]. C/EBPα is a founding member of the CCAAT/enhancer binding protein family of transcription factors, all of which bind a similar DNA consensus motif. Following the cloning of the C/EBPα gene, detailed studies led to the discovery of the basic-leucine zipper (bZIP) class of DNA-binding and dimerization domain proteins [ 42 ].
Without dimerization, DNA binding cannot occur and the specificity of DNA binding results from the amino acid sequence of the basic region [ 44 ].
CMPHSC
MEPGMP
1+CD11b+ cells from tumor-bearing mice, and in tumor-free mice, C/EBPα expression was found to be more than 4-fold decreased in tumor cells. In an experiment where the same number of MDSCs were injected with tumor cells in mice, ablation of C/EBPα led to an improvement in the pro-tumor phenotype of MDSCs: tumor growth and tumor angiogenesis were significantly increased. MDSCs are recruited to tumors, where they promote tumor growth through mechanisms of immune suppression and angiogenesis in the tumor microenvironment.
Wild-type (C/EBPαflox/flox) and myeloid conditional null (C/EBPαflox/flox;LysMCre) mice were injected with 1x 105 3LL or B16 tumor cells in the hind limb. We observed a significant increase in the total number of colonies in bone marrow isolated from C/EBPα conditional null mice ( Figure 5A,B ). We found that tumor conditions significantly reduced the number of total colonies ( Figure 6A ) as well as the number of myeloid progenitors (CFU-M and CFU-G) in Cebpaflox/flox;LysMCre+/+ mice compared to control tumor-bearing mice. Figure 6B) Interestingly, there was no difference in the percentage of each individual colony type between wild-type and CN mice.
Thus, TNF-α appears to be involved in the recruitment of MDSCs from the bone marrow and. We observed an increase in the number and percentage of myeloid progenitors in the bone marrow and a. In tumor-bearing mice, we observed the opposite: C/EBPα conditional null mice had fewer myeloid progenitors in the bone marrow and more circulating white blood cells.
Instead, there were fewer total colonies and less of each progenitor in the bone marrow of C/EBPα conditional null tumor-bearing mice. Thus, it appears that increased myeloid progenitor production in the bone marrow resulted in greater MDSC expansion in tumor-bearing mice. Perhaps the increase in white blood cells observed in the peripheral blood of C/EBPα conditional null tumor-bearing mice was a result of increased MDSC production and expansion in these mice.
Taken together, these data support the hypothesis that signals in the tumor microenvironment, including hypoxia and TNF-α secretion, downregulate C/EBPα expression in myeloid lineage cells, resulting in MDSC proliferation and expansion. Cebpaflox/flox;LysMCre+/+ conditional null mice and Cebpaflox/flox;LysMCre-/- littermates with 3LL tumors subcutaneously in the hind leg. We sought to determine whether MDSCs were responsible for increased tumor angiogenesis and accelerated tumor growth in the conditional null animals.
/EBPαflox/flox;LysMCre, CN) mice were injected with 1x 105 3LL tumor cells in the hind limb. After analyzing tumor vascularity by staining tumor sections with CD31 antibody, we observed a significant increase in vascular density in tumors co-injected with Gr1+CD11b+ MDSCs from.
C/EBP! CN
These data provide molecular evidence supporting a negative role of C/EBPα in the pro-angiogenic properties of MDSCs by. Taken together, our findings reveal dual negative roles for C/EBPα in the expansion and pro-angiogenic gene expression in MDSCs. Yang L, DeBusk L, Fukuda K, Fingleton B, Green-Jarvis B, et al. 2004) Expansion of myeloid immunosuppressor Gr+ CD11b+ cells in tumor-bearing host directly promotes tumor angiogenesis. 2000) Initial stages of tumor cell-induced angiogenesis: evaluation via skin window chambers in rodent models.
Gabrilovich DI, Bronte V, Chen SH, Colombo MP, Ochoa A, et al. 2007) The terminology problem for myeloid-derived suppressor cells. Rodriguez P, Zea A, DeSalvo J, Culotta K, Zabaleta J, et al. Arginine consumption by macrophages modulates CD3 {zeta} chain expression in T lymphocytes. Pabst T, Mueller B, Zhang P, Radomska H, Narravula S, et al. 2001) Dominant-negative mutations of CEBPA, encoding CCAAT/enhancer binding protein-α (C/EBPα), in acute myeloid leukemia.
Timchenko NA, Harris TE, Wilde M, Bilyeu TA, Burgess-Beusse BL, et al. (1997) Ti CCAAT/enhancer-binding a protina nga alpha ket mangregula ti p21 a protina ken panagadu ti hepatocyte kadagiti kappasngay a tukak. Müller C, Alunni-Fabbroni M, Kowenz-Leutz E, Mo., ken dagiti dadduma pay Fukuchi Y, Shibata F, Ito M, Goto-Koshino Y, Sotomaru Y, et al.(2006) Komprehensibo a panaganalisar ti panagbalbaliw ti linia ti myeloid babaen ti panagusar kadagiti utot a mangiyebkas ti maiduron a porma ti C/EBPα.
Zhang D, Hetherington C, Meyers S, Rhoades K, Larson C, et al. 1996) CCAAT enhancer-binding protein (C/EBP) and AML1 (CBF alpha2) synergistically activate the macrophage colony-stimulating factor receptor promoter. Zhang P, Iwama A, Datta M, Darlington G, Link D, et al. 1998 ) Upregulation of interleukin 6 and granulocyte colony-stimulating factor receptors by transcription factor CCAAT enhancer binding protein α (C/EBPα) is critical for granulopoiesis. Radomska H, Huettner C, Zhang P, Cheng T, Scadden D, et al. 1998) CCAAT/enhancer binding protein alpha is a regulatory switch sufficient for induction of granulocytic development from bipotential myeloid.
Seifeddine R, Driem A, Blanc E, Fulchignoni-Lataud M-C, Belda M-ALF, et al. 2008) Hypoxia Regulates CCAAT/Enhancer Binding Protein-α Expression in Breast Cancer Cells. Zhang D, Zhang P, Wang N, Hetherington C, Darlington G, et al. 1997 ) Absence of granulocyte colony-stimulating factor signaling and neutrophil development in CCAAT enhancer-binding protein α-deficient mice. Burchert A, Cai D, Hofbauer LC, Samuelsson MKR, Slater EP, et al. 2004) Interferon consensus sequence binding protein (ICSBP; IRF-8).
Schepers H, Wierenga ATJ, Van Gosliga D, Eggen BJL, Vellenga E, et al. 2007) Reintroduction of C/EBP into leukemic CD34+ stem/progenitor cells impairs self-renewal and partially restores myelopoiesis. Marigo I, Bosio E, Solito S, Mesa C, Fernandez A, et al. 2010) Tumor-induced tolerance and immunosuppression depend on the C/EBPβ transcription factor (Supplementary information).
