Abstract A21: DACH1 blocks prostate cancer cell growth and interleukin-6 signaling

In Drosophila, eye development is coordinately regulated by the retinal determination gene network (RDGN), mainly consisting of dachshund (dac), eyes absent (eya), and sin oculis (so). The mammalian homologues are Dach, Eya, and Six, respectively. RDGN, although best known for its role in eye specification, is essential for the development of many organs including retinal, kidney, brain, and limb in both flies and mammals. Recently, coordinate abnormal expression of the DACH1/Eya/Six complex has been observed in human tumors supporting a tumor promoting role of Six and Eya family members, and a tumor-suppressor function of DACH. Oncogenes sustain host-cell interactions, promoting invasiveness, recruiting inflammatory mediators and developing angiogenic networks. Ras and Myc promote tumor angiogenesis through up-regulation of VEGF and the inflammatory mediator, interleukin-8(IL-8) and interleukin-6 (IL-6). Our previous studies demonstrate DACH1 inhibits migration of MCF10A cells transformed with distinct oncogenes (Ha-Ras, c-Raf, c-Myc, and ErbB2) as well as the highly metastatic MDA-MB-231 human breast cancer cell line. An unbiased proteomic approach to identify candidate proteins regulated by DACH1 expression, using antibody array analysis, demonstrated DACH1 expression correlated with reduced secretion of IL-8 and the related chemokines IL-1, IL-6, GRO, and MIP1 (α, β, γ) from Ras or c-Myc transformed MCF-10A cells and repressed IL-8 promoter activity. Altered expressions of the IL-6 and IL-8 genes are seen in many cancers including prostate cancer. Hormone-resistant prostate carcinoma cell lines produce large amounts of IL-6 and IL-8 compared to hormone responsive prostate cancer cell lines. The expression of IL-8 and IL-6 are linked to poor prognosis and metastatic phenotype in prostate cancer. Recent finding demonstrated that IL-6 regulates the dynamic equilibrium between cancer stem cells and non-stem cancer cells in human breast and prostate cancer. IL-6 alone can transform non-tumorigenic benign prostate epithelial cells and further progress to invasive phenotype. To explore the role of DACH1 in androgen resistant prostate cancer, PC3 cells stably expressing DACH1 were established. DACH1 inhibited proliferation evaluated by MTT assay and growth curve. Microarray analyses demonstrated DACH1 inhibited mRNA expression of GRO, IL-6, IL-8 by 75%, 80% and 90%, respectively. However, there was no change of mRNA expression for IL-6 and IL-8 receptor. It has been reported that stable expression IL-6 in SV40T immortalized non-tumorigenic prostate epithelial cell line p69 induced EMT and acquired malignant phenotypes through autocrine loop IL6 and IGF-1R signaling. To further test the functional interaction of DACH1 with IL-6, a table cells expressing IL-6 alone or IL-6 with DACH1 were deployed. Ectopic expression of DACH1 attenuated activation of IGF-1 R by IL-6 as evaluated by phosphorylation of IGF-1R. Subcutaneous implantation study showed a 60% inhibition of in vivo tumor growth by DACH1. Together, our studies suggest that loss expression of DACH1 is an important cause of prostate tumorigenesis and restoration of DACH1 expression provides a potential therapeutic application. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A21.