Tissue Homeostasis and Cancer Development

The complex microenvironment contains distinct entities including the structural extracellular matrix, anchored and soluble growth factors and cytokines, and a variety of immune and inflammatory cells. Signals generated within this space dictate cell fate by influencing cell proliferation, differentiation, motility, and cell death. We aim to understand how proteolysis (MMP/TIMP/ADAM), specific growth factors (IGF-II, HGF, TNF), and tumor suppressors and oncogenes impact these signals in tissue homeostasis and tumorigenesis. We use genetic mouse models of human cancers and disease to study the cellular and molecular basis of breast, liver, lung, and bone cancers, and also investigate the role of proteolytic systems in tissue homeostasis in models of heart disease, inflammation and tissue regeneration. A central hypothesis for our work is that cellular microenvironment converges at the cell surface to trigger intracellular signaling pathways and influence cell fate.

In the past two years, we identified TIMP3 as an innate negative regulator of systemic inflammation. Its loss not only increases the proteolytic activity of ADAM17, but also of MT1- MMP known to be central to cell motility and invasion. Multiple organs of timp3-/- mice exhibit greater metastatic dissemination to several cancer cell types. We have also found that Rho C and RANKL are critical for metastasis. Using primary cultures derived from timp3 deficient mice we have shown dysregulated -catenin signaling with specific effects on its target genes (cyclin D1, MMP7) in mammary epithelial and embryonic fibroblasts; and with primary cultures of neonatal cardiac myocyte and fibroblast we have identified a novel concurrent amplification of TGF and TNF signaling due to increased proteolytic activity.

Our ongoing work on TIMP4 in heart disease reveals a differential function for this TIMP following myocardial infarction and pressure overload. Some of our recent discoveries in mouse models are particularly exciting as they hold a high potential for clinical impact, both in breast and bone tumors. A new avenue of our research involves the development of innovative imaging techniques to probe and visualize collagen changes in vivo in mouse models of human diseases.

For more detailed information consult the Khokha lab homepage at http://khokhalab.uhnres.utoronto.ca/

Graduate Students:

• Alison Aiken
• Jackson Hartland
• Sam Molyneux
• Aditya Murthy
  
• Washington Shao

Selected Publications:

• Murphy G, Murthy A, Khokha R. Clipping, shedding and RIPping keep immunity on cue. Trends Immunology, in press.

• Hojilla CV, Kim I, Kassiri Z, Fata JE, Fang H, Khokha R. Metalloproteinase axes increase ‚ beta-catenin signaling in primary mouse mammary epithelial cells lacking TIMP3. J Cell Sci, 120:1050-60, 2007

• Cruz-Munoz W, Sanchez OH, Grappa M, English JL, Hill RP, Khokha R. Enhanced metastatic dissemination to multiple organs by melanoma and lymphoma cells in timp-3(-/-) mice. Oncogene, 25:6489-96. 2006

• English JL, Kassiri Z, Koskivirta I, Atkinson SJ, Di Grappa M, Soloway PD, Nagase H, Vuorio E, Murphy G, Khokha R. Individual Timp deficiencies differentially impact pro-MMP-2 activation. J Biol Chem, 281(15):10337-462005, 2006.

• Smookler DS, Mohammed FF, Kassiri Z, Duncan GS, Mak TW, Khokha R. TIMP3 regulates TNF-dependent systemic inflammation.
  J Immunol. 176(2):721-5, 2006.

• Jones DH, Nakashima T, Sanchez OH, Kozieradzki I, Komarva SV, Sarosi I, Morony S, Rubin E, Sarao R, Hojilla CV, Komnenovic V, Kong YY, Dixon SJ, Sims SM, Khokha R, Wada T, Penninger JM. Regulation of cancer cell migration and bone metastasis by RANKL. Nature 440(7084):692-6, 2006.

• Hakem A, Sanchez-Sweatman O, You-Ten A, Duncan G, Wakeham A, Khokha R, Mak T. RhoC is Dispensable for Embryogenesis and Tumor Initiation but is Essential for Metastasis. Genes Dev, 19:1974-1979, 2005.

• Kassiri Z, Oudit GY, Mohammed FF, Sanchez O, Dawood F, Nuttall RK, Edwards DR, Liu PP, Backx PB, Khokha R. Combination of tumor necrosis factor-alpha ablation and matrix metalloproteinase inhibition prevents heart failure after pressure overload in tissue inhibitor of metalloproteinase-3 knock-out mice. Circ Res, 97(4):380-90, 2005.

• Mohammed FF, Smookler DS, Taylor SEM, Fingleton B, Kassiri Z, Sanchez OH, English JL, Matrisian LM, Au B, Yeh W-C, Khokha R. Abnormal TNF activity in timp-3-/- mice leads to chronic hepatic inflammation and failure of liver regeneration. Nature Genet. 36:969-977, 2004.