Control of epithelial cell migration and invasion by the IKKß- and CK1α-mediated degradation of RAPGEF2.

Epithelial cell migration is crucial for the development and regeneration of epithelial tissues. Aberrant regulation of epithelial cell migration has a major role in pathological processes such as the development of cancer metastasis and tissue fibrosis. Here, we report that in response to factors that promote cell motility, the Rap guanine exchange factor RAPGEF2 is rapidly phosphorylated by I-kappa-B-kinase-ß and casein kinase-1α and consequently degraded by the proteasome via the SCF(ßTrCP) ubiquitin ligase. Failure to degrade RAPGEF2 in epithelial cells results in sustained activity of Rap1 and inhibition of cell migration induced by HGF, a potent metastatic factor. Furthermore, expression of a degradation-resistant RAPGEF2 mutant greatly suppresses dissemination and metastasis of human breast cancer cells. These findings reveal a molecular mechanism regulating migration and invasion of epithelial cells and establish a key direct link between IKKß and cell motility controlled by Rap-integrin signaling.

Atypical E2fs control lymphangiogenesis through transcriptional regulation of Ccbe1 and Flt4.

Lymphatic vessels are derived from venous endothelial cells and their formation is governed by the Vascular endothelial growth factor C (VegfC)/Vegf receptor 3 (Vegfr3; Flt4) signaling pathway. Recent studies show that Collagen and Calcium Binding EGF domains 1 protein (Ccbe1) enhances VegfC-dependent lymphangiogenesis. Both Ccbe1 and Flt4 have been shown to be indispensable for lymphangiogenesis. However, how these essential players are transcriptionally regulated remains poorly understood. In the case of angiogenesis, atypical E2fs (E2f7 and E2f8) however have been recently shown to function as transcriptional activators for VegfA. Using a genome-wide approach we here identified both CCBE1 and FLT4 as direct targets of atypical E2Fs. E2F7/8 directly bind and stimulate the CCBE1 promoter, while recruitment of E2F7/8 inhibits the FLT4 promoter. Importantly, inactivation of e2f7/8 in zebrafish impaired venous sprouting and lymphangiogenesis with reduced ccbe1 expression and increased flt4 expression. Remarkably, over-expression of e2f7/8 rescued Ccbe1- and Flt4-dependent lymphangiogenesis phenotypes. Together these results identified E2f7/8 as novel in vivo transcriptional regulators of Ccbe1 and Flt4, both essential genes for venous sprouting and lymphangiogenesis.

Regulation of E2F1 by the von Hippel-Lindau tumour suppressor protein predicts survival in renal cell cancer patients.

Biallelic mutations of the von Hippel-Lindau (VHL) gene are the most common cause of sporadic and inherited renal cell carcinoma (RCC). Loss of VHL has been reported to affect cell proliferation by deregulating cell cycle-associated proteins. We report that the VHL gene product (pVHL) inhibits E2F1 expression at both mRNA and protein level in zebrafish and human RCC cells, while loss of VHL increases E2F1 expression in patient kidney tumour tissue and RCC cells, resulting in a delay of cell cycle progression. RCCs from von Hippel-Lindau patients with known germline VHL mutations express significantly more E2F1 compared to sporadic RCCs with either clear-cell (cc) or non-cc histology. Analysis of 138 primary RCCs reveals that E2F1 expression is significantly higher in tumours with a diameter ≤7 cm and with a favourable American Joint Committee on Cancer (AJCC) stage. The expression of E2F1 in RCC significantly correlates with p27 expression, suggesting that increased expression of E2F1 in RCC induces tumour cell senescence via p27. Cox regression analysis shows significant prediction of E2F1 expression for disease-free survival and overall survival, implying that E2F1 expression in kidney tumour is a novel prognostic factor for patients with RCC.

HIF proteins connect the RB-E2F factors to angiogenesis.

Recently, we showed that E2F7 and E2F8 (E2F7/8) are critical regulators of angiogenesis through transcriptional control of VEGFA in cooperation with HIF. (1) Here we investigate the existence of other novel putative angiogenic E2F7/8-HIF targets, and discuss the role of the RB-E2F pathway in regulating angiogenesis during embryonic and tumor development.

E2F7 and E2F8 promote angiogenesis through transcriptional activation of VEGFA in cooperation with HIF1.

The E2F family of transcription factors plays an important role in controlling cell-cycle progression. While this is their best-known function, we report here novel functions for the newest members of the E2F family, E2F7 and E2F8 (E2F7/8). We show that simultaneous deletion of E2F7/8 in zebrafish and mice leads to severe vascular defects during embryonic development. Using a panel of transgenic zebrafish with fluorescent-labelled blood vessels, we demonstrate that E2F7/8 are essential for proper formation of blood vessels. Despite their classification as transcriptional repressors, we provide evidence for a molecular mechanism through which E2F7/8 activate the transcription of the vascular endothelial growth factor A (VEGFA), a key factor in guiding angiogenesis. We show that E2F7/8 directly bind and stimulate the VEGFA promoter independent of canonical E2F binding elements. Instead, E2F7/8 form a transcriptional complex with the hypoxia inducible factor 1 (HIF1) to stimulate VEGFA promoter activity. These results uncover an unexpected link between E2F7/8 and the HIF1-VEGFA pathway providing a molecular mechanism by which E2F7/8 control angiogenesis.