| A large family of structurally related molecules called the tumor necrosis factor (TNF) family is intimately connected to immune regulation. Binding of TNF-related ligands to their cognate receptors can induce various biological responses such as cellular proliferation, differentiation, survival or death. Two recently described cytokines, APRIL (A PRoliferation Inducing Ligand) and BLyS (B Lymphocyte Stimulator, also called BAFF, THANK, TALL-1, zTNF4), form a new subfamily of TNF-like ligands. They are expressed in hematopoietic cells and implicated in immune regulation as well. However, APRIL was originally cloned as a factor that dictates tumor growth as (i) it increases tumor growth rates both in vitro and in vivo, (ii) a variety of tumor cells express APRIL endogenously and (iii) blocking APRIL function largely prevents tumor growth in vivo. Two receptors of the TNF family, BCMA and TACI, have been described to bind APRIL, but neither appears to be responsible for the induction of tumor proliferation. Similarly, the immune regulatory effects of APRIL cannot be attributed solely to BCMA and TACI. It is therefore clear that a third receptor exists that is largely responsible for the tumor stimulatory capacity of APRIL and possibly mediates some immune effects of APRIL as well. These findings constitute the basis of this proposal, which will have three main lines: APRIL and its role in immunology. 1. The first line of research in this project is a continuation on the results we obtained with our transgenic APRIL mice that show that APRIL serves a role in T and B cell immunity. We will set out to analyse this in more detail using our transgenics in combination with several TCR transgenics. Moreover, we will analyse the endogenous expression and function of APRIL during different immune reactions. As most of these studies are hampered by the availability of effective tools, like monoclonal antibodies, our first objective will be to generate these tools. 2. APRIL and its role in tumor biology. The second line of research is focused on the tumor promoting potential of APRIL. We will analyse the signaling pathways induced in APRIL-stimulated tumors to further our understanding on the molecular mechanisms that govern APRIL-dependent tumor growth. Our APRIL transgenic mice will also be used to study the effect of ectopic APRIL expression on spontaneous and chemically or retrovirally induced lymphoma formation. Furthermore, we will employ different approaches, including the moAb, to block APRIL's function in several of our tumor model systems and then study tumor growth, morphology and immunogenicity. 3. APRIL receptor identification and functional analysis. The third line of research proposed in this project is to identify the APRIL receptor that mediates tumor cell proliferation. Initially, we will screen lymphoid and tumor cells for APRIL binding. The latter will be compared with the non-transformed tissue to determine whether the receptor is ectopic expressed on the tumors or whether it is tissue specific. Alongside we will employ a purification strategy of this receptor from tumor cells. We have access to all the tools needed for this purification through a collaboration with Dr M. Hahne (Madrid, Spain). This, combined with our in-house mass spectrometry facility, provides the right conditions for the identification. Identification of this receptor will be followed by a detailed analysis of its expression, its signal transduction and its endogenous function. More importantly, its regulation and function in tumor cell growth will be analysed using monoclonal antibodies directed against the receptor. Taken together these experiments will provide valuable information on the endogenous role of APRIL in the immune system as well as its tumor promoting capacity. This, combined with the tools to be generated and the possible identification of the third APRIL receptor, will allow us to determine the feasibility of anti-tumor therapies using APRIL or its tumor receptor as a target. |
