Cytokines, Growth Factors and Signal Transduction

Intracellular signaling by cytokines

Our research concerns the mechanisms of cytokine actions, especially those of tumor necrosis factor (TNF). The long-term goal of our studies is to explain the molecular mechanisms whereby TNF produces its many biological actions important in host resistance to cancer and infections, and in the pathogenesis of septic shock, cachexia and inflammatory disorders. Specifically, our studies focus on the elucidation of roles played by members of the family of mitogen activated protein (MAP) kinases in TNF actions. We have recently demonstrated that activation of p38 MAP kinase by cellular stress stimuli (including sodium salicylate, H2O2 or hyperosmolar sorbitol) leads to a selective inhibition of TNF signaling. Activation of p38 MAP kinase results in a rapid inhibition of TNF-induced IkB-a phosphorylation and degradation, a key event in TNF-induced activation of the transcription factor NF-kB. . Interleukin-1 (IL-1)-induced IkB-a phosphorylation and degradation are much less affected by stress stimuli leading to p38 activation. NF-kB is essential for the activation of many genes important in host defenses and inflammation.

Biological functions of TSG-6

TSG-6 (TNF-Stimulated Gene 6), a TNF/IL-1-inducible gene encoding a 34 kDa secretory glycoprotein, is expressed in a variety of cells including leukocytes, fibroblasts, and chondrocytes. TSG-6 was discovered in our laboratory, and we continue to study the properties and functions of TSG-6. Earlier we demonstrated the presence of large amounts of TSG-6 protein in synovial fluids of patients with rheumatoid arthritis and smaller amounts in patients with osteoarthritis (Wisniewski et al. 1993, J. Immunol. 151: 6593). TSG-6 protein was also detected in the serum of patients with sepsis or SLE. TSG-6 irreversibly interacts with Inter-alpha-inhibitor (IaI), a serine protease inhibitor and constituent of normal plasma, resulting in the formation of a stable 120 kDa complex (Wisniewski et al. 1994, Biochemistry 33: 7423). Both TSG-6 and IaI are hyaluronan-binding proteins. We showed that recombinant human TSG-6 protein has a powerful anti-inflammatory effect in the murine air pouch model of acute inflammation (Wisniewski et al., 1996, J. Immunol. 156: 1609). A more recent study produced evidence for the protective effect of TSG-6 in mice with collagen-induced arthritis (CIA), a murine model of chronic inflammation that resembles rheumatoid arthritis in humans (Mindrescu et al.2000, Arthritis & Rheumatism 43: 2668). These and other results indicate that TSG-6 is an endogenous regulator of the inflammatory process. The ultimate goal of these studies is to elucidate the mechanism off the anti-inflammatory action of TSG-6 and to explore the therapeutic potential of recombinant TSG-6 protein.

The Role of TNF-stimulated Gene 6 (TSG-6) in Inflammation

Hans-Georg Wisniewski
Inflammatory processes are associated with the pathogenesis of many diseases, they are part of the response to infection and trauma and play a central role in the development of many autoimmune diseases. Chronic inflammation leads to tissue remodeling and destruction. The proinflammatory cytokines IL-1 and TNF-alpha are the primary mediators of the inflammatory response and act through the activation of a large set of genes in a wide variety of cell types. Among the genes activated by both cytokines is TNF-stimulated gene 6 (TSG-6). The TSG-6 cDNA encodes a secreted 35 kDa glycoprotein which is abundant in synovial fluids of patients with various forms of arthritis and detectable in serum of patients with different inflammatory and autoimmune disorders. The TSG-6 protein consists of two domains, the N-terminal link module and the C-terminal CUB domain. TSG-6 binds to the glycosaminoglycan hyaluronan through its link module, a domain shared with several other hyaluronan-binding proteins. The TSG-6 protein forms a stable complex with components of the plasma protein inter-alpha-inhibitor, a Kunitz-type serine protease inhibitor. Recombinant human TSG-6 protein exerts a potent antiinflammatory effect in a murine model of acute inflammation and in collagen-induced arthritis, a murine model of rheumatoid arthritis. TSG-6-transgenic mice are much less susceptible to develop collagen-induced arthritis than their non-transgenic littermates. Activation of the TSG-6 gene by proinflammatory cytokines, presence of TSG-6 protein at inflammatory sites and its antiinflammatory effect suggest a role for TSG-6 in a negative feed-back control of the inflammatory response. We are studying the physiological and pathophysiological functions of TSG-6 at the molecular and cellular level and in animal models with particular focus on its role in inflammation. The elucidation of the mechanism of TSG-6 action may eventually contribute to a better understanding of inflammatory processes and result in the development of new concepts for the treatment of inflammatory diseases.