Nina Adam

Critical role of the disintegrin metalloprotease ADAM17 for intestinal inflammation and regeneration in mice.

The protease a disintegrin and metalloprotease (ADAM) 17 cleaves tumor necrosis factor (TNF), L-selectin, and epidermal growth factor receptor (EGF-R) ligands from the plasma membrane. ADAM17 is expressed in most tissues and is up-regulated during inflammation and cancer. ADAM17-deficient mice are not viable. Conditional ADAM17 knockout models demonstrated proinflammatory activities of ADAM17 in septic shock via shedding of TNF. We used a novel gene targeting strategy to generate mice with dramatically reduced ADAM17 levels in all tissues. The resulting mice called ADAM17ex/ex were viable, showed compromised shedding of ADAM17 substrates from the cell surface, and developed eye, heart, and skin defects as a consequence of impaired EGF-R signaling caused by failure of shedding of EGF-R ligands. Unexpectedly, although the intestine of unchallenged homozygous ADAM17ex/ex mice was normal, ADAM17ex/ex mice showed substantially increased susceptibility to inflammation in dextran sulfate sodium colitis. This was a result of impaired shedding of EGF-R ligands resulting in failure to phosphorylate STAT3 via the EGF-R and, consequently, in defective regeneration of epithelial cells and breakdown of the intestinal barrier. Besides regulating the systemic availability of the proinflammatory cytokine TNF, our results demonstrate that ADAM17 is needed for vital regenerative activities during the immune response. Thus, our mouse model will help investigate ADAM17 as a potential drug target.

Unraveling Viral Interleukin-6 Binding to gp130 and Activation of STAT-Signaling Pathways Independently of the Interleukin-6 Receptor

ABSTRACT Human herpesvirus 8 encodes a viral version of interleukin-6 (vIL-6) which shows 25% sequence homology with human IL-6. In contrast to human IL-6, which first binds to the IL-6 receptor (IL-6R) and only subsequently associates with the signal transducing receptor subunit gp130, vIL-6 has been shown to directly bind to gp130 without the need of IL-6R. As a functional consequence, vIL-6 can activate far more target cells in the body since all cells express gp130, but only cells such as hepatocytes and some leukocytes express IL-6R. We sought to understand which amino acid sequences within the vIL-6 protein were responsible for its ability to bind and activate gp130 independent of IL-6R. As a first approach, we constructed chimeric IL-6 proteins in which all known gp130 interacting sites (sites II and III) were sequentially transferred from vIL-6 into the human IL-6 protein. To our surprise, human IL-6 carrying all gp130 interacting sites from vIL-6 did not show IL-6R-independent gp130 activation. Even more surprisingly, the loop between helix B and C of vIL-6, clearly shown in the crystal structure not to be in contact with gp130, is indispensable for direct binding to and activation of gp130. This points to an IL-6R induced change of site III conformation in human IL-6, which is already preformed in vIL-6. These data indicate a novel activation mechanism of human IL-6 by the IL-6R that will be important for the construction of novel hyperactive cytokine variants.

Viral Interleukin-6: Structure, pathophysiology and strategies of neutralization

Viral Interleukin-6 (vIL-6) is encoded by Human herpes virus 8 (HHV8), also known as Kaposis sarcoma (KS)-associated herpes virus (KSHV). HHV8 infection is found in patients with KS, primary effusion lymphoma (PEL) and plasma cell-type of multicentric Castlemans disease (MCD), with a high incidence observed in HIV infected individuals. vIL-6 shares about 25% identity with its human counterpart. Human IL-6 (hIL-6) binds to the human IL-6 receptor (hIL-6R) and the hIL-6/hIL-6R complex associates with the signaling receptor subunit gp130. Upon dimerization of gp130 intracellular signaling is initiated. All cells in the body express gp130 but only some cell types express the hIL-6R. Human IL-6 does not stimulate cells, which do not express hIL-6R. However, a naturally occurring soluble form of the hIL-6R (shIL-6R) can bind hIL-6 and the complex of hIL-6/shIL-6R can stimulate cells, which only express gp130 but no hIL-6R. This process, which has been named trans-signaling, leads to a dramatic increase in the spectrum of hIL-6 target cells during inflammation and cancer. vIL-6, in contrast to hIL-6, can directly bind to and activate gp130 without the need of the hIL-6R. Therefore, at least in theory, vIL-6 can stimulate every cell in the human body. This review highlights the properties of vIL-6 regarding structural features, implications for pathophysiology, and strategies of neutralization. Furthermore, mechanisms of activation of gp130 by hIL-6, vIL-6, and by forced dimerization will be discussed.