Abstract
Abstract Objective: Protein Kinase D1 (PKD1) is an important modulator of several signal-transduction pathways in benign and malignant human diseases. Currently the role of PKD1 in colon cancer, which is the second-leading cause of cancer-related deaths, is not well established. We have found previously that advance stage prostate cancer has suppressed expression. This led us to analyze PKD1 expression patterns in various other cancer tissue samples including colon cancer. Materials and Methods: Tissue microarrays containing colon cancer samples with corresponding normal tissues were used to investigate the expression profile of PKD1 using immunohistochemistry. To determine PKD1 mediated effects on oncogenic β-catenin signaling in colon cancer, human colorectal adenocarcinoma cell line SW480. Stable transformants of SW480 were created with GFP and SW480-PKD1-GFP, PKD1 overexpression leads to attenuation of β-catenin/T cell factor (TCF) transcription activity measured by luciferase reporter assays. To determine the effect of PKD1 overexpression on other cancer associated genes, RT-PCR array (that had 84 cancer related genes) analysis was performed in SW480-GFP and SW480-PKD1-GFP cells. Results: Our expression analysis determined a significant decrease in PKD1 expression in advanced Dukes stage (II, III and IV) colon cancer samples as compared to non-neoplastic colon samples. We have also noticed downregulation and aberrant localization of β-catenin in colon cancer samples compared to non-neoplastic colon samples. Therefore, we also determined the function of PKD1 in oncogenic β-catenin signaling in colon cancer. Our confocal microscopy analyses demonstrates that PKD1 up-regulation caused translocation of β-catenin from the nucleus to the plasma membrane. PKD1 overexpression also reduced β-catenin/TCF interaction in the nucleus and suppressed the expression of its downstream signaling proteins. Phenotypic changes in the stable transformants were measured via proliferation assays, anchorage independent growth, anchorage dependent growth, cellular motility and invasion. The overexpression of PKD1 markedly suppressed cell proliferation in SW480 cells. The SW480-PKD1-GFP cells formed fewer colonies compared with SW480-GFP cells. The SW480-PKD-GFP cells showed very minimal or no motility and invasion compared to SW480-GFP cells. Our RT-PCR array data shows that PKD1 overexpression also modulates expression of tissue inhibitor of metalloproteinase 3 (TIMP3), interferon α, interferon β and tumor necrosis factor receptor (TNFR). Conclusion: In conclusion, PKD1 is down regulated in colon cancer and its downregulation is correlated with aberrant β-catenin subcellular localization. Our data suggest that the altered PKD1 expression may induce β-catenin dependent and independent signaling in colon cancer and suppression of PKD1 may play a critical role in colon carcinogenesis and colon cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2907. doi:10.1158/1538-7445.AM2011-2907
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