The retinoblastoma protein, RB, is a negative regulator of cell proliferation and apoptosis. The anti- proliferation function of RB underlies its tumor suppression activity. The anti-apoptotic function of RB should promote tumor development, however, this aspect of the RB activity has not been investigated. We have obtained in vivo evidence for the tumor promoting potential of RB using a mouse strain we have generated. In this mouse strain, we mutated two codons in the Rb gene to inactivate a caspase cleavage site at the C- terminus of RB. The resulting Rb-MI allele encodes a caspase-resistant RB-MI protein that protects cells from tumor necrosis factor (TNF)-induced apoptosis. TNF activates caspase-8 to cleave Bid and thus causing mitochondria leakage and cell death. We have shown that TNF-induced Bid cleavage is impaired in Rb-MI cells, resulting in a reduced death response. In vivo, the intestinal epithelial cells of Rb-MI mice are resistant to TNF-dependent apoptosis induced by endotoxin. Furthermore, Rb-MI promotes spontaneous colon tumors in the p53-null genetic background. These results establish a strong correlation between Rb- Ml-mediated protection from TNF-induced apoptosis and the development of intestinal tumors. TNF is an inflammatory cytokine that orchestrates the systemic response to infections and injuries. Discovered as a physiological factor that can kill tumor cells, TNF has been shown to also promote tumor growth, particularly those associated with chronic inflammation in the liver and the gut. The mechanisms underlying the switch between tumor-promotion versus tumor-suppression by TNF are not fully understood. We propose that the RB-dependent anti-apoptotic mechanism, which is constitutively activated in Rb-MI cells, can promote TNF- dependent tumor development under conditions of inflammation. To test this hypothesis, we will pursue four specific aims:
Aim 1 -To investigate the effect of Rb-MI on inflammation-associated tumor development in mouse models;
Aim 2 - To investigate the effect of caspase-8 deficiency on inflammation-associated colon cancer;
Aim 3 - To characterize the protein binding functions of RB and RB-MI;
Aim 4 -To investigate the regulation of caspase-8 by RB. The proposed study will generate new mouse models for colon cancer and elucidate the RB-dependent anti-apoptotic pathway. Results from the proposed research will facilitate the development of new strategies to reduce the risk of inflammation-associated cancer.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
3R01CA058320-20S2
Application #
8469107
Study Section
Cancer Molecular Pathobiology Study Section (CAMP)
Program Officer
Hildesheim, Jeffrey
Project Start
1994-05-03
Project End
2014-02-28
Budget Start
2012-06-01
Budget End
2014-02-28
Support Year
20
Fiscal Year
2012
Total Cost
$72,087
Indirect Cost
$25,567
Name
University of California San Diego
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
804355790
City
La Jolla
State
CA
Country
United States
Zip Code
92093
Han, Jinbo; Sridevi, Priya; Ramirez, Michael et al. (2013) ýý-Catenin-dependent lysosomal targeting of internalized tumor necrosis factor-ýý suppresses caspase-8 activation in apoptosis-resistant colon cancer cells. Mol Biol Cell 24:465-73
Han, Jinbo; Soletti, Rossana C; Sadarangani, Anil et al. (2013) Nuclear expression of *-catenin promotes RB stability and resistance to TNF-induced apoptosis in colon cancer cells. Mol Cancer Res 11:207-18
Spehlmann, Martina E; Manthey, Carolin F; Dann, Sara M et al. (2013) Trp53 deficiency protects against acute intestinal inflammation. J Immunol 191:837-47
Ludwig, Kirsten; Tse, Edison S; Wang, Jean Yj (2013) Colon cancer cells adopt an invasive phenotype without mesenchymal transition in 3-D but not 2-D culture upon combined stimulation with EGF and crypt growth factors. BMC Cancer 13:221
Bourgo, Ryan J; Thangavel, Chellappagounder; Ertel, Adam et al. (2011) RB restricts DNA damage-initiated tumorigenesis through an LXCXE-dependent mechanism of transcriptional control. Mol Cell 43:663-72
Zeitlin, Samantha G; Chapados, Brian R; Baker, Norman M et al. (2011) Uracil DNA N-glycosylase promotes assembly of human centromere protein A. PLoS One 6:e17151
Knudsen, Erik S; Wang, Jean Y J (2010) Targeting the RB-pathway in cancer therapy. Clin Cancer Res 16:1094-9
Francis, Sarah M; Bergsied, Jacqueline; Isaac, Christian E et al. (2009) A functional connection between pRB and transforming growth factor beta in growth inhibition and mammary gland development. Mol Cell Biol 29:4455-66
Huang, XiaoDong; Masselli, Anja; Frisch, Steven M et al. (2007) Blockade of tumor necrosis factor-induced Bid cleavage by caspase-resistant Rb. J Biol Chem 282:29401-13
Borges, H L; Hunton, I C; Wang, J Y J (2007) Reduction of apoptosis in Rb-deficient embryos via Abl knockout. Oncogene 26:3868-77

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