Fig. 2. Mechanistic aspects of TIMP-3 gene therapy. Highly efficient replication-deficient adenoviral vectors engineered to express TIMP-3 infect cells through receptor-mediated endocytosis, traffic to the nucleus and use the host DNA machinery to transcribe and secrete TIMP-3. Recombinant TIMP-3 binds the ECM where it initiates its desired phenotypic effects on cells (indicated by 1-3 in green). TIMP-3 overexpression is associated with anti-angiogenic activity (1), reduction in cell migration and invasion (2) and initiation of apoptosis (3), mediated through modulation of MP activity. The induction of apoptosis occurs though modulation in death receptor/death ligand activity at the cell surface resulting in activation of caspases (in blue). Apoptosis is mediated through a type-2-dependent pathway involving caspase-8, -9 and -3 as well as mitochondrial components. Ultimately, caspase-3-mediated cleavage of death substrates leads to apoptosis.