Transforming growth factor-ß (TGF-ß) signals through membrane-bound serine/threonine kinase receptors, which upon stimulation phosphorylate Smad-proteins and thereby trigger their nuclear translocation and transcriptional activity. Although the three isoforms of TGF-ß are highly homologous at the level of sequence, analysis of their in vivo function by gene knock outs revealed striking differences suggesting that there is no significant redundancy between TGF-ß1, -ß2 and -ß3. While signaltransduction by TGF-ß1 has been well character-ized, receptor binding and activation by the TGF-ß2 isoform is still unclear. We have shown that TßRII-B, an alternatively spliced variant of TßRII is a TGF-ß2 binding receptor which interacts with all known TGF-ß receptors through the ligands TGF-ß1 or TGF-ß2. This receptor mediates TGF-ß2-signaling directly via the Smad-pathway in the absence of any Type III receptor (Betaglycan).
TßRII-B shows a ubiquitous expression pattern as examined by northern-blot-analysis. The expression of TßRII-B at the cell surface was shown in cells such as osteoblasts and osteosarcomas, to C2C12 myoblasts and to the multipotent fibroblastic cell line C3H10T1/2. The focus of current studies is to understand the mechanisms of the interaction between TGFß2 and TßRII-B in immunological and functional approaches and how the signaling cascade differs from TßRIII-dependent TGFß2-signaling. In addition we examine TGF-ß isoform specific signalling pathways which might be independent or parallel to the Smad pathway.

The biological significance of growth inhibition by TGF-ß becomes apparent upon malfunction of this mechanism during tumor progression. TGF-ß has a strong antiproliferative activity which is lost in different forms of cancer due to mutations in the TGF-ß receptor genes as well as in the genes for the Smads. Upon this TGF-ß resistance of tumor cells, the level of endogenously expressed and secreted TGF-ß raises dramatically, causing angiogenesis in the vicinity of the tumor as well as immunosuppression.
In order to study the immunosuppressive role of TGF-ß we are investigating TGF-ß induced signalling specifically on cytotoxic T-cells. The effect of TGF-ß is being studied on the level of T-cell differentiation, proliferation and activation towards specific target cells. In order to manipulate the TGF-ß pathway we are establishing retro- and adenoviral transduction of primary murine splenocytes and T-cell lines, expressing specific TGF-ß signalling molecules. The aim of this project is to understand the effect of TGF-ß secreted from the tumor on mature T-cells in order to develop genetherapeutic strategies for the "redirected-killing of specific tumor cells".

The figure shows FACS-analysis of primary murine spleen cells which were transduced to express GFP. In the upper panel, the Dot Blot depicts the single spleen cells sorted for size (X-axis) and granularity (Y-axis). The gated cells represent the proliferating spleen cells. In the lower panel, histograms show GFP-expression (X-axis) and cell number (Y-axis). The blue histogram shows non-transduced control cells. In red, transduced cells are shown.

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Several members of the TGF-ß superfamily play key roles in the development, repair and survival of neurons. TGF-ß2 and -ß3 are most prominently expressed along growing axonal tracts both in the peripheral and central nervous system. Rat pheochromocytoma cells (PC12 cells) have been used as a model system for differentiation of neuronal cells. After stimulation with nerve growth factor (NGF), they stop growing, form processes, and exhibit other markers characteristic of neurons such as electrical excitability after appropriate stimuli and formation of synaptic vesicles.
We are studying the effect of TGF-ß on neurite growth from sensory neurons and PC12 cells, which have been treated with NGF. In order to investigate both the NGF and TGF-ß pathways we expressed mutant signalling proteins of either pathway and analysed the effect by reportergen-assays, in vivo-phosphorylation and by the phenotypic alterations of the cells. We have generated a series of stable cell lines expressing dominant negative forms of the TGF-ß signalling molecules under the control of a doxycycline-inducible promoter. Our data suggest crosstalk between the NGF-induced signalling cascade and the TGF-ß pathway leading to neuronal differentiation in PC12 and sensory neurons.

The figure shows rat pheochromocytoma cells (PC12), that represent a model system for the differentiation of neuronal cells. Treatment with Nerve Growth Factor (NGF) results in growth arrest and in the induction of a differentiation program with the characteristics of neurite outgrowth and the formation of synaptic-like vesicles.
The neurite outgrowth is demonstrated in the photographs above which show PC12 cells that were cultivated either in growth media without NGF or in media supplemented with 50 ng/ml NGF for 6 days.

Transforming growth factor-ß (TGF-ß) signals through membrane-bound serine/threonine kinase receptors, which upon stimulation phosphorylate Smad-proteins and thereby trigger their nuclear translocation and transcriptional activity. Although the three isoforms of TGF-ß are highly homologous at the level of sequence, analysis of their in vivo function by gene knock outs revealed striking differences suggesting that there is no significant redundancy between TGF-ß1, -ß2 and -ß3. While signaltransduction by TGF-ß1 has been well characterized, receptor binding and activation by the TGF-ß2 isoform is still unclear. We have shown that TßRII-B, an alternatively spliced variant of TßRII is a TGF-ß2 binding receptor which interacts with all known TGF-ß receptors through the ligands TGF-ß1 or TGF-ß2. This receptor mediates TGF-ß2-signaling directly via the Smad-pathway in the absence of any Type III receptor (Betaglycan). TßRII-B shows a restricted expression pattern as examined by RT-PCR and immunoprecipitation after affinity labeling with TGF-ß. The expression of TßRII-B at the cell surface is restricted to cells such as osteoblasts and osteosarcomas, to C2C12 myoblasts and to the multipotent fibroblastic cell line C3H10T1/2. The distinct expression of TßRII-B in cells originating from tissues where the isoform TGF-ß2 has a predominant role may reflect the importance of this receptor in TGF-ß isoform specific signalling.
The focus of current studies are to understand the role of this specific TGF-ß type II receptor in the process of bone formation as well as TGF-ß isoform specific signalling pathways which might be independent or parallel to the Smad pathway.