Abstract 3103: Overexpression of homeoprotein six1 activates non-canonical TGF-beta signaling to induce epithelial-mesenchymal transition in human papillomavirus type 16-immortalized human keratinocytes.

Abstract

Abstract Inappropriate expression of embryonic genes, particularly homeodomain transcription factors, contributes to tumorigenesis and tumor progression. The overexpression of Six1, a member of the Six family of homeodomain transcription factors, has been found in various human cancers, and is associated with increased tumor progression and metastasis. Previous studies in our laboratory discovered that the expression of Six1 mRNA and protein increased during in vitro progression of human papillomavirus type 16 (HPV16)-immortalized human keratinocytes (HKc/HPV16) toward a differentiation-resistant (HKc/DR) phenotype. However, the precise mechanisms of how Six1 promotes tumor onset at early and late stages of HPV16-mediated transformation remain unknown. In this study, we found that HKc/HPV16 and HKc/DR overexpressing Six1 exhibited a more mesenchymal phenotype compared to vector controls, as characterized by a fibroblastic morphology, and increased migration and invasion. We utilized Whole Human Genome Microarrays (4x44K from Agilent Technologies) to explore the gene expression changes associated with Six1 overexpression in HKc/HPV16 and HKc/DR. We found that overexpression of Six1 down-regulated epithelial-related genes (ex., E-cadherin and occludin) and up-regulated mesenchymal-related genes (ex., N-cadherin, vimentin, and snail), which strongly suggests that Six1 overexpression induces epithelial-mesenchymal transition (EMT). Gene expression changes determined by microarray analysis were confirmed by real time PCR and western blotting. Increased expression of TGF-beta receptors in response to overexpression of Six1 in HKc/DR did not lead to increased Smad-dependent signaling but did activate the Mitogen-activated protein kinase (MAPK) pathway, suggesting that MAPK non-Smad TGF-β signaling may be involved in Six1-mediated EMT. In conclusion, our study demonstrates that Six1 overexpression induces EMT, possibly by activation of the MAPK non-canonical (non-Smad) TGF-β pathway, during HPV16-mediated transformation of human keratinocytes. Citation Format: Hanwen Xu, Lucia Pirisi, Kim E. Creek. Overexpression of homeoprotein six1 activates non-canonical TGF-beta signaling to induce epithelial-mesenchymal transition in human papillomavirus type 16-immortalized human keratinocytes. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3103. doi:10.1158/1538-7445.AM2013-3103