Abstract 2392: Transcriptional repression of VEGF by Znf24, a C2H2 zinc finger protein

Abstract

Abstract Vascular endothelial growth factor (VEGF) is a key regulator during the formation of new blood vessels during angiogenesis. It functions to promote the proliferation and migration of endothelial cells under both physiological conditions such as embryogenesis and pathological conditions such as tumor growth. VEGF has been shown to play an important role in the development and metastasis of breast as well as other human cancers. To date, many trans-activating factors of VEGF have been described, whereas transcriptional repression of VEGF remains less studied. We have previously reported the identification of a SCAN-domain containing C2H2 zinc finger protein, Znf24, which functions to repress the transcription of VEGF. In this study we explore the mechanism by which Znf24 represses VEGF transcription. We have generated a series of VEGF promoter constructs bearing deletions from the 5′ end. Reporter gene assays in the breast cancer cell line MDA-MB-231 have revealed a proximal region of the VEGF promoter essential for Znf24-induced repression. To determine whether Znf24 represses VEGF transcription through direct binding to the VEGF promoter, we have performed electrophoretic mobility shift assays (EMSA) using the VEGF proximal promoter region as a probe. We have found that Znf24 protein binds to this proximal region, suggesting that VEGF is a direct downstream target of Znf24. To begin to investigate Znf24 functions in vivo, we have conducted immunohistochemistry assays using human breast cancer tissue microarrays representing different stages of disease progression and tumor sizes, as well as matched normal breast tissues. We have determined that Znf24 protein levels are significantly decreased in malignant tissues compared to normal adjacent tissues. A potential negative correlation between Znf24 protein levels and tumor sizes is also observed, suggesting that Znf24 may serve as a negative regulator of tumor growth. Our data suggest that Znf24 represses VEGF transcription through direct binding to the VEGF promoter and that it may function as a negative regulator of tumor growth by inhibiting tumor angiogenesis. (Supported by NIH P01 CA045548 and the Simeon J. Fortin Charitable Foundation) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2392.