Abstract 5314: An oncogenic splice variant of the KLF6 tumor suppressor gene is associated with poor survival and is a potent driver of breast cancer metastasis

Breast cancer is a leading causes of cancer death in women worldwide. It is a heterogeneous and genetically complex disease has left a significant proportion of patients with inadequate treatment options. Since metastasis and drug resistance pose significant challengea in breast cancer treatment, elucidating the mechanisms of these processes is critical for understanding the key drivers of disease progression and for the development of targeted therapies. Accumulating evidence from our laboratory and other groups suggest that the tumor suppressor gene, KLF6, and its oncogenic splice variant, KLF6-SV1, play a role in breast cancer progression, dissemination, and chemoresistance. Here we demonstrate that in multiple independent clinical cohorts of over 1200 breast cancer patients with defined clinical outcome, high KLF6-SV1 mRNA levels in the primary tumor associated with poor survival and disease recurrence. Specifically, upregulated KLF6-SV1 expression in the primary tumors correlated with poor survival independent of disease stage and grade. Thus, we hypothesized that KLF6-SV1 is an early driver/molecular determinant of invasive breast cancer. In order to investigate the functional/biological relevance of KLF6-SV1 in breast cancer development and progression, we performed a series of experiments using retroviral-based overexpression in multiple non-tumorigenic, tumorigenic, and metastatic breast cancer cell lines. We demonstrated that overexpression of KLF6-SV1 increased mesenchymal marker gene expression, cellular survival, invasion, as well as the migratory potential of KLF6-SV1 transduced cells. Interestingly, KLF6-SV1 did not increase growth rate of these mammary epithelial cell lines, similar to the clinical data which showed an absence of a correlation between KLF6-SV1 expression and primary tumor size. In a 3D model KLF6-SV1 upregulation disrupted mammary acinar morphogenesis promoting complex multiacinar structures. To assay whether the KLF6-SV1-induced EMT phenotype conferred increased metastatic potential in vivo, we injected tumorigenic cells expressing high levels of KLF6-SV1 subcutaneously into immunodeficient mice. Strikingly, KLF6-SV1 overexpression alone drove the entire metastatic cascade resulting in dissemination to many organs including the liver, kidney, heart, lung, and spleen. Furthermore, KLF6-SV1 overexpression in a metastatic breast cancer cell line increased metastasis to the lungs and liver in an orthotopic model of the disease. This is consistent with our clinical data in which high KLF6-SV1 expression was correlated with decreased overall survival and metastasis free survival. Together these findings suggest a role for the KLF6-SV1 splice variant as a driver of breast cancer metastasis and validate its potential utility as a novel biomarker and therapeutic target for breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5314. doi:1538-7445.AM2012-5314