2005 Abstracts: Tumor Suppressive Effects of HPP1 Overexpression in Colon Cancer
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Tumor Suppressive Effects of HPP1 Overexpression in Colon Cancer
David Shibata, H. Lee Moffitt Cancer Center and Resesarch Institute, Tampa, FL; Li Zhang, Kun Cai, Fumiaki Sato, Stephen Meltzer, University of Maryland School of Medicine, Baltimore, MD; Timothy Yeatman, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL
Introduction: HPP1 is a novel gene that is inactivated by promoter methylation in tumors of the colon and rectum, stomach and pancreas. However, direct biologic evidence implicating the loss of HPP1 in the development of a malignant phenotype is limited. Structural homologies suggest potential effects on cell growth and apoptosis. We have sought to investigate the phenotypic effects of HPP1 overexpression in a colon cancer cell line.
Methods: We have introduced full-length HPP1 into the non-expressing HCT116 cell line. Empty vector transfections were used as comparative controls. Alterations in doubling time were calculated using standard techniques while changes in cell proliferation were quantified using a tetrazolium salt-based assay. Effects on apoptosis were analyzed using TUNEL staining. Results: Upregulation of HPP1 in the HCT116 cell line was confirmed by a 36-fold increase in HPP1 mRNA expression as documented by quantitative real-time RT-PCR. The HPP1 transfectant (HT) displayed an alteration in morphology as well as a qualitative reduction in growth. HT demonstrated a 20% increase in cell doubling time over the control transfectant (20.0 +/- 0.4 vs. 16.7 +/- 0.4 hours; p<0.0001). HPP1 overexpression resulted in a 26% reduction in cell proliferation as compared to control (Optical Density: 0.57 +/- 0.02 vs. 0.76 +/- 0.01; p=0.001). HT demonstrated a 3-fold increase in apoptotic cells as compared to control. (p<0.0001) Conclusions: HPP1 overexpression results in a significant attenuation of cell growth and proliferation as well as an increase in cellular death. Our study provides further evidence to support the role of HPP1 as a tumor suppressor gene in colorectal neoplastic progression.
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