Timp-1 Interaction With Alpha V Beta 3 Integrin Confers Resistance To Human Osteosarcoma Cell Line Mg-63 Against Tnf-Alpha-Induced Apoptosis

Tumor necrosis factor-alpha (TNF-alpha) is a pleiotropic cytokine affecting diverse cellular responses. TNF-alpha is cytotoxic in many systems, but it can also act as an anti-apoptotic signal to promote cell survival pathways activated through integrins and extracellular matrix components. This is particularly evident in cancer cells. To unravel the basis of resistance to TNF-alpha-induced apoptosis, human osteosarcoma MG-63 cell line was used. Our data showed that resistance to apoptosis was accompanied by high levels of TIMP-1 expression in part mediated by NF-kappa B activation, whereas under apoptotic conditions, in the presence of cycloheximide (CHX), TIMP-1 and alpha v beta 3 integrin protein levels were significantly reduced. Silencing TIMP-1 using siRNA led to increased apoptosis following treatment with TNF-alpha, whereas exogenously-added recombinant TIMP-1 reduced the extent of apoptosis. Immunoprecipitation and confocal microscopy experiments demonstrated that TIMP-1 interacted with alpha v beta 3 integrins. The biological role of this interaction was revealed by the use of echistatin, an antagonist of alpha v beta 3 integrin. In the presence of echistatin, decreased protection against apoptosis by recombinant TIMP-1 was observed.