Purification and characterization of TEF1, a transcription factor that controls the human transforming growth...

Transforming growth factor-alpha (TGF-alpha) is a member of the epidermal growth factor family. It activates signal transduction pathways leading to cell proliferation through the interaction with cell surface epidermal growth factor receptor. The overexpression of TGF-alpha has been found in many types of cancers and is thought to be involved in the genesis and maintenance of these tumors. Recent results also implicate this growth factor in the development of certain diabetic complications, such as atherosclerosis. The function of TGF-alpha can be tightly controlled at the level of transcription of its gene. We have previously characterized the proximal TGF-alpha promoter and identified two neighboring regulatory elements that appeared to cooperate with each other in the regulation of TGF-alpha transcription. The transcription factor that functions through the distal element was identified as AP-2, a protein that was found to be induced by the oncoprotein, Ras. However, what factor binds and controls the proximal regulatory element (PRE) is still unclear. Here, we report the purification and preliminary characterization of the PRE-binding transcription factor TEF1 by sequence-specific DNA-affinity chromatography from rat kidney nuclear extracts. The purified TEF1 migrates on the SDS-PAGE at a molecular mass of about 36 kDa. It specifically interacts with the PRE and was able to strongly activate transcription from the TGF-alpha promoter in HeLa cell nuclear extracts in an in vitro transcription assay. The UV cross-linking experiment confirmed that this 36 kDa protein is indeed the protein that specifically binds the PRE. We also show that the spacing between the AP-2 and the TEF1 sites in the TGF-alpha promoter has little effect on the transcription from the TGF-alpha promoter. The purification of TEF1 furthers our understanding of how TGF-alpha expression is regulated and may help us understand the upstream signaling events that lead to the elevated expression of this growth factor.