No abstract

The PTEN tumour suppressor and pro-apoptotic gene is frequently mutated in human cancers. We show that PTEN transcription is upregulated by Egr-1 after irradiation in wild-type, but not egr-1-/-, mice in vivo. We found that Egr-1 specifically binds to the PTEN 5' untranslated region, which contains a functional GCGGCGGCG Egr-1-binding site. Inducing Egr-1 by exposing cells to ultraviolet light upregulates expression of PTEN messenger RNA and protein, and leads to apoptosis. egr-1-/- cells, which cannot upregulate PTEN expression after irradiation, are resistant to ultraviolet-light-induced apoptosis. Therefore, Egr-1 can directly regulate PTEN, triggering the initial step in this apoptotic pathway. Loss of Egr-1 expression, which often occurs in human cancers, could deregulate the PTEN gene and contribute to the radiation resistance of some cancer cells.

Recent studies are reviewed indicating that the transcription factor early growth response-1 (Egr1) is a direct regulator of multiple tumor suppressors including TGFb1, PTEN, p53, and fibronectin. The downstream pathways of these factors display multiple nodes of interaction with each other, suggesting the existence of a functional network of suppressor factors that serve to maintain normal growth regulation and resist the emergence of transformed variants. Paradoxically, Egr1 is oncogenic in prostate cancer. In the majority of these cancers, PTEN or p53 is inactive. It is suggested that these defects in the suppressor network allow for the unopposed induction of TGFb1 and fibronectin, which favor transformation and survival of prostate tumor epithelial cells, and explain the role of Egr1 in prostate cancer. Egr1 is a novel and logical target for intervention by gene therapy methods, and targeting methods are discussed.