The extracellular microenvironment converges at the cell surface to trigger intracellular signaling pathways and influence cell fate. The complex cellular microenvironment is constituted of distinct entities including the structural extracellular matrix; anchored or soluble growth factors and cytokines; as well as a variety of immune cells which either reside in or later infiltrate the tissue. Signals generated within this microenvironment dictate cell fate including proliferation, differentiation, motility, and cell death. We focus on understanding how proteolysis (MMPs/TIMPs), specific growth factors (IGF-II, HGF, TNF), tumor suppressors (PTEN) and oncogenes (Viral SV40 T antigen, mammalian protooncogenes) impact these signals during tissue homeostasis and tumorigenesis.
TIMPs are natural inhibitors of metalloproteinases, including MMP (matrix metalloproteinases), ADAM (a disintegrin and metalloproteinase) and ADAM-TS (ADAM with thrombospondin domain) enzymes. Using genetically altered (transgenic and knockout mice) mice subjected to site-specific tumor models for breast, liver, prostate, uterine, bone and lung we ask how proteolytic activity impacts the different stages of tumor development and progression in these organs. We also utilize a battery of physiological systems to uncover the natural function of these genes during normal cell function. Coupling the knowledge of the normal function with that derived from tumor models is providing new insights into the critical regulatory role of the TIMP genes in determining the cell fate in both normal and malignant tissues.
In the last year, we have demonstrated that TIMP3 is an innate negative regulator of inflammation in vivo: systemic, hepatic or following arthritic joint disease (Smookler et al., J Immunology, 2006; Mohammed et al., Nat Genet. 2004; Mahmoodi et al., Am J Path. 2005). We showed that it regulates TNF bioactivity and signaling by controlling ADAM17- (TACE) mediated shedding of cell surface bound TNF. In a pressure overload model of heart disease that mimics high blood pressure, TIMP3 couples the regulation of cytokine homeostasis (specifically TACE mediated TNF shedding) with the homeostasis of the extracellular matrix (via MMP mediated remodeling). Single and double knockouts in timp3-/-x tnf -/- crosses allowed us to further show that simultaneous dual dysregulation of MMP and TNF activities are both necessary and sufficient for heart disease resulting from pressure overload, and that deleting TNF completely abrogates the disease in this model (Kassiri et al, Circ Res 2005; Kassiri and Khokha, Throm Hemostasis 2005).? Our collaborative efforts have revealed the same importance for the TIMP3 regulation of MMPs and TNF in 2 other important human diseases so far; type II diabetes and vascular inflammation (Federici et al., J Clin Invest. 2005).
Liver regeneration offers an ideal system to study cell division in vivo. Timp1 deficiency or its overexpression directly affects hepatocyte cell cycle progression by altering the bioavailability of HGF and its subsequent signaling through the c-Met receptor (Mohammed et al., Hepatology 2005). In contrast, Timp3 null mice fail to regenerate liver despite the accelerated entry of quiescent hepatocytes into the cell cycle. Here, excessive and sustained TNF bioactivity is responsible for failed liver regeneration due to hepatocyte apoptosis (Mohammed et al., Nat Genet. 2004). These findings form a platform to investigate the proteolytic regulation of the bioavailability of many key growth factors in the process of liver regeneration (Mohammed and Khokha, Trends Cell Biol. 2005).
In cancer models, we have demonstrated that a Timp3 deficiency in the host, but not in the tumor cell, affects tumorigenesis, angiogenesis and metastasis (Cruz et al., Oncogene, 2006a; Cruz et al., Oncogene, 2006b), and this inhibitors controls MT1-MMP activity which is a critical invasion-promoting protease (English al at, JBC, 2006). Also, the TIMP3 regulation of the ectodomain release of the pro-angiogenic molecule VCAM-1 is reminiscent of its key role in the liver regeneration and heart disease models (Singh et al., Cardiovas Res. 2005). Further, rhoC has emerged to be essential for metastatic dissemination of mammary tumors (Hakem et al., Genes Dev. 2005) and rankl for cancer cell migration and metastasis to bone (Jones et al., Nature 2006).