Regulation of protein tyrosine kinases in tumour cells by the transcription factor Ets-1

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.