Abstract 1493: The Twist box is required for Twist1-induced prostate cancer metastasis.

The Twist1 gene has diverse roles during development and pathologic states such as cancer. Twist1 is best known for its roles in cancer by inducing an epithelial-mesenchymal transition (EMT) transcriptional program implicated in facilitating tumorigenesis, tumor progression and treatment resistance. Twist1 is a bHLH transcription factor that has both repressor and transactivation functions, but the importance of these different activities for Twist1 cancer phenotypes are unknown. We hypothesized Twist1 may mediate these various functions using distinct structural domains and/or motifs. We disrupted the putative transactivation domain in the Twist box of Twist1 by mutating a critical phenylalanine residue (F191) to glycine. We then created stable isogenic prostate cancer cell lines overexpressing wildtype and F191G versions of Twist1. We assessed the role of the Twist box using in vitro and in vivo assays, which mimic the various stages of cancer progression to metastasis. These include loss of homotypic cell-cell contacts, cell migration and invasion, anoikis resistance and soft agar colony formation. We also observed biophysical cell traction forces on a fabricated substratum and finally performed experimental lung metastasis assays. The overexpression of Twist1 in prostate cancer cells lead to an EMT biomarker phenotype and the F191G mutant lacked expression of some of these markers. The F191G mutant was deficient for transcriptional activity using promoter reporter based assays. Using single cell measurements we found that Twist1 expressing Myc-CaP cells exert more force on the substratum than vector control cells. Additional in vitro assays suggest Twist1 can confer cellular properties associated with increased tumor aggressiveness including increased migration/invasion, cell death/anoikis resistance and in vitro tumorigenic potential by soft agar colony formation. The Twist box mutant, F191G, displayed compromised activity compared to wildtype Twist1 in many of the in vitro assays described above revealing that the Twist box is necessary for many of the pro-metastatic functions of Twist1. We compared the gene expression profile of Twist1 and F191G overexpressing prostate cancer cells by microarray and observed that the F191G mutant had an expression profile that was similar to wildtype Twist1 but attenuated. Lastly, Twist1 overexpression compared to vector control prostate cancer cells showed an increased frequency of metastatic lung tumors using the experimental lung metastasis assay. Interestingly, Twist1 overexpression also resulted in the appearance of extra-thoracic metastases. The F191G mutant was less able to confer prostate cancer cells the ability to colonize metastatic lesions in the lung and resulted in no extra-thoracic metastases. Our results show that F191G mutation behaves as loss of function and is necessary for Twist1-induced metastasis of prostate cancer cells. Citation Format: Rajendra P. Gajula, Sivarajan T. Chettiar, Russell D. Williams, Saravanan Thiyagarajan, Yoshinori Kato, Khaled Aziz, Ruoqi Wang, Nishant Gandhi, Aaron T. Wild, Farhad Vesuna, Jinfang Ma, Tarek Salih, Jessica Cades, Elana Fertig, Shyam Biswal, Timothy F. Burns, Christine Chung, Charles M. Rudin, Venu Raman, Joseph M. Herman, Russell K. Hales, Steven An, Phuoc T. Tran. The Twist box is required for Twist1-induced prostate cancer metastasis. [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 1493. doi:10.1158/1538-7445.AM2013-1493