Changes in gene expression are central to the control of cellular processes such as proliferation, growth arrest, differentiation, and oncogenic transformation. The research in our laboratory focuses on the involvement of the CCAAT/enhancer binding protein (C/EBP) family of transcription factors in controlling these processes. The C/EBP family is composed of five members: C/EBPalpha, beta, gamma, delta and epsilon. With the exception of C/EBPgamma, these proteins function primarily as positive regulators of gene expression. Our research utilizes mouse models - i.e., genetically engineered mice containing targeted disruptions of individual c/ebp genes and cell lines derived from these knockout animals - to investigate the functional roles of C/EBP proteins in animals and cultured cells. A major focus of our research involves the recently discovered role of C/EBPbeta in oncogenic transformation. In collaboration with Robert Smart (North Carolina State University)and Esta Sterneck (NCI-Frederick) we found that C/EBPbeta-deficient mice are completely resistant to the development of skin tumors induced by carcinogens. The tumors that develop in normal mice contain mutations in the Ras proto-oncogene, suggesting that C/EBPbeta is an essential component of the Ras tumorigenesis pathway. Interestingly, mutant animals displayed significantly increased cell death in the epidermis after carcinogen treatment, indicating that C/EBPbeta is involved in suppressing apoptosis in pre-cancerous cells. We are currently determining whether C/EBPbeta is required for transformation of other cell types including macrophages and fibroblasts and whether it plays a pro-survival role in these cells. If C/EBPbeta activity proves to be required for the survival of many types of cancer cells that contain mutations in the Ras signaling pathway, this transcription factor may be an attractive target for novel anti-tumor drugs. To that end, we are conducting studies aimed at understanding the mechanism by which C/EBPbeta is activated in response to oncogenic Ras signaling. We have identified several sites of phosphorylation on C/EBPbeta that are induced by oncogenic Ras and are investigating how these modifications affect C/EBPbeta activity. Another major area of research involves the roles of C/EBPalpha and epsilon in the growth and differentiation of myeloid cells. We are performing this work as a collaborative study with Jonathan Keller (Laboratory of Molecular Immunoregulation). We are using mutant mice and fetal liver-derived hematopoietic precursor cells to examine how specific C/EBP gene deletions affect the functional maturation of myeloid cells in vitro, as well as the development of leukemias in vivo. Additional work is directed toward determining the dimeric status of C/EBP proteins in cells and investigating how changes in dimerization affect their transcriptional activity. We have found that C/EBPgamma is a preferential heterodimeric partner of the other C/EBP family members in vivo and that C/EBPgamma inhibits C/EBP transactivation function in a manner that requires heterodimerization. Transcriptional repression by C/EBPgamma is cell-specific, and we are currently investigating the molecular basis for its variable inhibitory activity in different cell types. To aid in the studies of C/EBPgamma function, we have obtained C/EBPgamma null mice and are using them to analyze the role of this protein in cell growth, survival, and transformation.

Agency
National Institute of Health (NIH)
Institute
Division of Basic Sciences - NCI (NCI)
Type
Intramural Research (Z01)
Project #
1Z01BC010328-03
Application #
6763541
Study Section
(RCGL)
Project Start
Project End
Budget Start
Budget End
Support Year
3
Fiscal Year
2002
Total Cost
Indirect Cost
Name
Basic Sciences
Department
Type
DUNS #
City
State
Country
United States
Zip Code
Staiger, Jennifer; Lueben, Mary J; Berrigan, David et al. (2009) C/EBPbeta regulates body composition, energy balance-related hormones and tumor growth. Carcinogenesis 30:832-40
Spooner, Chauncey J; Sebastian, Thomas; Shuman, Jon D et al. (2007) C/EBPbeta serine 64, a phosphoacceptor site, has a critical role in LPS-induced IL-6 and MCP-1 transcription. Cytokine 37:119-27
Loomis, Kari D; Zhu, Songyun; Yoon, Kyungsil et al. (2007) Genetic ablation of CCAAT/enhancer binding protein alpha in epidermis reveals its role in suppression of epithelial tumorigenesis. Cancer Res 67:6768-76
Spooner, Chauncey J; Guo, Xiangrong; Johnson, Peter F et al. (2007) Differential roles of C/EBP beta regulatory domains in specifying MCP-1 and IL-6 transcription. Mol Immunol 44:1384-92
Lopez, Alex B; Wang, Chuanping; Huang, Charlie C et al. (2007) A feedback transcriptional mechanism controls the level of the arginine/lysine transporter cat-1 during amino acid starvation. Biochem J 402:163-73
Suh, Hyung Chan; Gooya, John; Renn, Katie et al. (2006) C/EBPalpha determines hematopoietic cell fate in multipotential progenitor cells by inhibiting erythroid differentiation and inducing myeloid differentiation. Blood 107:4308-16
Mantena, Srinivasa Raju; Kannan, Athilakshmi; Cheon, Yong-Pil et al. (2006) C/EBPbeta is a critical mediator of steroid hormone-regulated cell proliferation and differentiation in the uterine epithelium and stroma. Proc Natl Acad Sci U S A 103:1870-5
Sebastian, Thomas; Johnson, Peter F (2006) Stop and go: anti-proliferative and mitogenic functions of the transcription factor C/EBPbeta. Cell Cycle 5:953-7
Johnson, Peter F (2005) Molecular stop signs: regulation of cell-cycle arrest by C/EBP transcription factors. J Cell Sci 118:2545-55
Roy, Sanjit K; Shuman, Jon D; Platanias, Leonidas C et al. (2005) A role for mixed lineage kinases in regulating transcription factor CCAAT/enhancer-binding protein-{beta}-dependent gene expression in response to interferon-{gamma}. J Biol Chem 280:24462-71

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