Wnt inhibitory factor-1, a Wnt antagonist, is silenced by promoter hypermethylation in malignant pleural mesothelioma Sonny Batra a , Yihui Shi a , Kristopher M. Kuchenbecker a , Biao He a , Noemi Reguart a,b , Iwao Mikami a , Liang You a , Zhidong Xu a , Yu-Ching Lin a , Genevie `ve Cle ´ment a , David M. Jablons a, * a Thoracic Oncology Laboratory, Department of Surgery, Comprehensive Cancer Center, University of California, San Francisco, CA, USA b Medical Oncology Service, Institut Catala ` d’Oncologia, Hospital Germans Trias i Pujol, Barcelona, Spain Received 11 February 2006 Available online 24 February 2006 Abstract Wnt inhibitory factor-1 (WIF-1) is a secreted protein that antagonizes Wnt signaling. We recently demonstrated the importance of aberrant activation of the Wnt signaling pathway in various cancers including malignant pleural mesothelioma. In this study, we revealed downregulated WIF-1 expression in cell lines and primary tissue when compared to normal mesothelial cell lines and adjacent pleura, respectively. We observed hypermethylation in four of four mesothelioma cell lines, but not in two normal mesothelial cell lines. In pri- mary tissue samples, we observed methylation in three paired tumor specimens compared to their adjacent normal pleura and methyl- ation in eight of nine unpaired tumor tissue samples. Taken together, our studies suggest that WIF-1 silencing due to its promoter hypermethylation is an important mechanism underlying the constitutively activated Wnt signaling in mesothelioma. New therapies toward inhibition of the Wnt pathway through WIF-1 might be promising for the future treatment of malignant mesothelioma. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Wnt inhibitory factor-1; Wnt signaling; Promoter hypermethylation Malignant pleural mesothelioma is an aggressive and highly lethal tumor closely associated with asbestos expo- sure [1]. The median survival time after diagnosis ranges from 7 to 19 months and median survival after standard therapeutic regimens such as chemotherapy, radiation, and surgery remains dismal [2]. In the United States, approximately 3000 new patients are diagnosed per year and the incidence of this disease is increasing [3]. New ther- apies based on an improved understanding of molecular mechanisms of mesothelioma are therefore in great need. The Wnt genes encode a family of 19 secreted glycopro- teins that play an important role in embryogenesis and oncogenesis [4,5]. Aberrant Wnt activation has been impli- cated in various human cancers, including colorectal cancer [6], melanoma [7] non-small cell lung cancer (NSCLC) [8], leukemia [9], and mesothelioma [10]. However, the molec- ular mechanism underlying constitutive activation of Wnt signaling in oncogenesis is not yet fully understood. In the Wnt signaling pathway, b-catenin is a key media- tor. In the absence of Wnt signals, cytosolic b-catenin is recruited to a multi-protein ‘‘destruction complex’’ that consists of casein kinase 1, adenomatous polyposis coli, Axin, and glycogen synthase kinase-3b (GSK-3b) [11–14]. In the resting state, b-catenin is phosphorylated by GSK- 3b and is subsequently targeted for degradation via the ubiquitin proteosome pathway [15–17]. Binding of Wnt ligands to their Frizzled receptors triggers the Wnt/b-cate- nin pathway, also termed the canonical Wnt pathway, through phosphorylation and increased activity of Dishev- elled (Dvl) [18–20]. Dvl activity alters the composition of the ‘‘destruction complex’’ with a net result of decreasing its affinity for b-catenin, which subsequently translocates 0006-291X/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2006.02.084 * Corresponding author. Fax: +1 415 502 3179. E-mail address: jablonsd@surgery.ucsf.edu (D.M. Jablons). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 342 (2006) 1228–1232 BBRC