Abstract. Matrix-degrading proteases play a key role in normal development, wound healing, many diseases such as rheumatoid arthritis and, in particular, tumour invasion. In invasive tumours, these enzymes are expressed by fibroblasts of the tumour stroma. Their expression and activity are tightly regulated at several levels, an important one being transcription. Previous in vitro and in vivo findings pointed to a major role of the Ets-1 transcription factor for this level of regulation. In the present study, we tried to prove this role in fibroblasts. We stimulated wild-type mouse fibroblasts with physiological doses of basic fibroblast growth factor (bFGF, known to induce different proteases and expressed by tumour cells) and compared the results to those obtained in Ets-1 -/-fibroblasts derived from Ets-1 knock-out mice. We found that basal Ets-1 levels are necessary not only for a fast induction of MMPs 2, 3 and 13 by bFGF but also for maintenance of the bFGF-induced expression of tissue inhibitors of metalloproteinases (TIMPs) 1, 2 and 3, which are known not only to inhibit but also participate as activators of certain pro-MMPs.

Abstract. The transcription factor Ets-1 plays several distinct critical roles in tumour development and progression by acting both in neoplastic cells and in the tumour stroma. Increased expression of Ets-1 in tumours is often associated with a worse prognosis. Stromal fibroblasts attribute an important part to the behaviour of malignant tumours. In this study we investigated the role of Ets-1 in the tumour stroma. It is well known that ets-1 expression in fibroblasts -one of the main components of the tumour stroma -can be induced by basic fibroblast growth factor (bFGF). We applied suppression subtractive hybridization (SSH) to identify genes that are differentially expressed between bFGF stimulated wild-type fibroblasts and fibroblasts with reduced Ets-1 expression. We selected clones up-or down-regulated in bFGF stimulated wild-type fibroblasts using SSH and functionally characterized them by reference to public databases using NCBI BLAST tools. Expression levels of genes corresponding to subtracted clones were analyzed using RT-PCR. Known genes were associated with diverse functions; novel Ets-1 regulated genes identified by SSH not only encoded components involved in matrix degradation (as cathepsin and PAI-2) but also constituents of the extracellular matrix (ECM) including α-2-Type I collagen, TGF-β induced protein, lumican and decorin. Our findings identify several potential novel target genes of Ets-1, and they provide potentially important insights into the role of Ets-1 in stromal fibroblasts for both remodelling and different functionalities of the ECM.

Abstract. Tyrosine phosphorylation is one of the key covalent modifications that occurs in multicellular organisms as a result of intercellular communication. The family of tyrosine kinases (PTKs) are responsible for part of the cellular phosphorylation and are involved in a broad variety of cellular functions including differentiation, proliferation, migration, invasion, angiogenesis and survival under physiological as well as pathological conditions. Aberration in PTK signalling occurs in inflammatory diseases and diabetes, and aberrant expression can lead to benign proliferative conditions as well as to various forms of cancer. Indeed, more than 70% of the known oncogenes and proto-oncogenes involved in cancer code for PTKs. Therefore, these enzymes are now used as targets in the treatment of different tumours. Ets-1 is a transcription factor expressed in a number of human malignancies with demonstrated roles within both neoplastic cells and tumour stroma. These roles include stimulation of tumour cell proliferation and invasion as well as tumour angiogenesis. Database searches have revealed that ETS binding sites are present in several promoters of PTK-encoding genes. We investigated the role of Ets-1 in transcriptional regulation of a panel of 89 PTKs in epithelial HeLa tumour cells. In this study, HeLa cells stably overexpressing and underexpressing Ets-1 were used for real-time PCR analysis of all known human PTKs. The results suggest that Ets-1 is an essential transcription factor that cannot be substituted by other members of the ETS family. Transcription of most PTKs was found to be increased by Ets-1. In contrast Ets-1 seems to act as a transcriptional repressor of other PTKs. The data presented here underscore the importance of Ets-1 in tumour development and progression.

Abstract.The transcription factor Ets-1 is known to be involved in a broad variety of cellular functions such as cell proliferation, migration, invasion, apoptosis and angiogenesis. In nearly all these reports, the full-length Ets-1 (p51) is commonly considered to be the active form and the role of the Ets-1ΔVII splice variant (p42) has not been addressed. Therefore, we studied the functional effects of p42 Ets-1 in comparison to p51 Ets-1 expression in a well-characterized mouse fibroblast cell line. Furthermore, the specific role of Ets-1 was evaluated using mouse fibroblasts with a reduced Ets-1 expression caused by RNAi and compared to fibroblasts with a binding inhibition of the whole ETS transcription factor family by stably overexpressing the ETS DNA binding domain as transdominant-negative mutant. Our results demonstrate that p42 Ets-1 has quite different functions and target genes compared to p51 Ets-1 (e.g. TIMP-4, MMP-3, MMP-9, MMP-13). In some cases (e.g. in cytokine expression) p42 Ets-1 is a functional transcription factor which acts in the same manner as a transdominant-negative approach.

Abstract. We previously reported that the inactivation of the Ets 1 transcription factor by a specific decoy strategy reduces rat C6 glioma cell proliferation and mmp-9 expression. In the present study, we analysed the effects of the dominantnegative form of Ets 1 (Ets-DB) on rat C6 glioma cell proliferation, migration, invasion, in vivo tumor growth on the chicken chorioallantoic membrane (CAM) and mmp-9 expression. In addition, we examined differences in gene expression between Ets-DB expressing and control cells using suppression subtractive hybridization (SSH). We found that retrovirus mediated expression of Ets-DB inhibited cellular proliferation, migration, invasion, mmp-9 expression, cellular growth in soft agar, and in vivo growth in the chicken chorioallantoic membrane assay. SSH analysis revealed expression of different genes in Ets-DB expressing cells involved in basic cellular processes. Each of these genes contained binding sites for different Ets-factors within their promoters. Finally, we found that, in addition to Ets 1, Elk-1, Elf-1, Fli-1 and Etv-1 are further Ets family members expressed in rat C6 glioma cells. Our results indicate that Ets transcription factors play important roles for basic properties of rat C6 glioma cells. Targeting of these factors might therefore become a useful experimental tool for therapeutic strategies against malignant gliomas.