Abstract LB-129: Loss of Rab25 expression promotes tumor formation and angiogenesis in esophageal squamous cell carcinoma
Authors: Tong Carol Man , Tang Kwan Ho , Guan Xin Yuan , Ma Stephanie 
Published: June 2012

Abstract
Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies worldwide and is particularly prevalent in some areas of Asian countries. With the advent of next-generation sequencing technologies, it is now possible for us to integrate and analyze large amounts of data at genome-wide scale, with the goal for a better understanding of cellular function and disease development. In order to elucidate the molecular mechanisms that drive tumorigenesis in ESCC, we employed a high-throughput sequencing technology named RNA-Seq (RNA sequencing) to identify dysregulated gene expression in 14 patient-derived ESCC or adjacent non-tumor (NT) clinical specimens of Chinese origin. The expression of Rab25, a family member of Ras-associated binding GTPases, was found to be downregulated in tumour tissues significantly. By both qPCR and immunohistochemistry analysis on a tissue microarray, expression of Rab25 was found to be significantly decreased in a larger cohort of ESCC tumors compared with NT counterparts. Patients with higher levels of Rab25 expression were also significantly associated with a better overall survival.
Consistently, absent or downregulated Rab25 expression was also detected in all ESCC cell lines examined as compared to a pooled normal tissue control. Rab25 expression in ESCC cell lines could be restored by demethylation treatment with 5-aza-dC, suggesting Rab25 is silenced via epigenetic alterations. Rab25 functions as an important mediator of vesicle trafficking, regulating cell polarity and distribution of membrane proteins, which are important for the maintenance of normal epithelial lining of the esophagus. We hypothesized that loss of Rab25 expression could lead to dysregulation in the maintenance of this normal epithelium and thus result in tumor development. The tumor suppressive function of Rab25 and the tumorigenic effect of its loss were evaluated by lentiviral-based overexpression and shRNA-knockdown of Rab25 in ESCC cell lines. In vivo studies found Rab25 to suppress tumor formation and angiogenesis in nude mice. Rab25-knockdwon cells gave rise to significantly more and larger tumors as compared to negative control cells. Immunohistochemical staining of resected xenografts revealed an increase in microvessel density and tumor proliferation as shown by higher expressions of endothelial marker CD34 and proliferation marker PCNA, respectively, in Rab25-knockdown cells as compared to negative controls. Similarly, conditioned medium from Rab25-knockdown cells enhanced tube-forming capability of HUVECs, suggesting potential regulation of angiogenic factors by Rab25-mediated pathway. Work on the identification of potential angiogenic factors regulated by Rab25 is now currently underway using a human angiogenesis antibody array. In summary, Rab25 functions as an important tumor suppressor gene in ESCC development by regulating angiogenesis.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-129. doi:10.1158/1538-7445.AM2011-LB-129