Carcinogenesis Advance Access originally published online on August 13, 2008
Carcinogenesis 2008 29(11):2195-2202; doi:10.1093/carcin/bgn194
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Adiponectin stimulates Wnt inhibitory factor-1 expression through epigenetic regulations involving the transcription factor specificity protein 1
1 Department of Pharmacology
2 Department of Medicine
3 Research Center of Heart, Brain, Hormone and Healthy Aging, University of Hong Kong, Hong Kong, China
4 Howard Hughes Medical Institute, University of Washington School of Medicine, Seattle, WA 98195, USA
5 School of Biological Sciences, University of Auckland, Auckland 1003, New Zealand
* To whom correspondence should be addressed. Department of Pharmacology, University of Hong Kong, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong, China. Tel: +852 28192864; Fax: +852 28170859; Email: yuwanghk{at}hku.hk
Adiponectin (ADN) is an adipokine possessing growth inhibitory activities against various types of cancer cells. Our previous results demonstrated that ADN could impede Wnt/beta-catenin-signaling pathways in MDA-MB-231 human breast carcinoma cells [Wang,Y. et al. (2006) Adiponectin modulates the glycogen synthase kinase-3 beta/beta-catenin signaling pathway and attenuates mammary tumorigenesis of MDA-MB-231 cells in nude mice. Cancer Res., 66, 11462–11470]. Here, we extended our studies to elucidate the effects of ADN on regulating the expressions of Wnt inhibitory factor-1 (WIF1), a Wnt antagonist frequently silenced in human breast tumors. Our results showed that ADN time dependently stimulated WIF1 gene and protein expressions in MDA-MB-231 cells. Overexpression of WIF1 exerted similar inhibitory effects to those of ADN on cell proliferations, nuclear beta-catenin activities, cyclin D1 expressions and serum-induced phosphorylations of Akt and glycogen synthase kinase-3 beta. Blockage of WIF1 activities significantly attenuated the suppressive effects of ADN on MDA-MB-231 cell growth. Furthermore, our in vivo studies showed that both supplementation of recombinant ADN and adenovirus-mediated overexpression of this adipokine substantially enhanced WIF1 expressions in MDA-MB-231 tumors implanted in nude mice. More interestingly, we found that ADN could alleviate methylation of CpG islands located within the proximal promoter region of WIF1, possibly involving the specificity protein 1 (Sp1) transcription factor and its downstream target DNA methyltransferase 1 (DNMT1). Upon ADN treatment, the protein levels of both Sp1 and DNMT1 were significantly decreased. Using silencing RNA approaches, we confirmed that downregulation of Sp1 resulted in an increased expression of WIF1 and decreased methylation of WIF1 promoter. Taken together, these data suggest that ADN might elicit its antitumor activities at least partially through promoting WIF1 expressions.
Abbreviations: ADN, adiponectin; DMEM, Dulbecco’s modified Eagle’s medium; DNMT1, DNA methyltransferase 1; FBS, fetal bovine serum; GSK-3β, glycogen synthase kinase-3 beta; mRNA, messenger RNA; MSP, methylation-specific polymerase chain reaction; PCR, polymerase chain reaction; siRNA, small interfering RNA; Sp1, specificity protein 1; WIF1, Wnt inhibitory factor-1
Co-first author. Received April 13, 2008; revised July 21, 2008; accepted August 8, 2008.