RUNX3 Inhibits Cell Proliferation and Induces Apoptosis by TGF-beta-Dependent and -Independent Mechanisms in Human Colon Carcinoma Cells

Background: Genes involved in the TGF-beta signaling pathway are often altered in several types of cancers. The TGF-beta-resistant human colon cancer cell line HT-29 has inactivated T beta RII and deficient expression of RUNX3 and Smad4, which are involved in the TGF-beta signaling pathway. Methods: Western blot and immunocytochemistry were performed to confirm gene expression, the MTT assay to detect cell growth, flow cytometry to investigate the cell cycle and the TUNEL to detect cell apoptosis. Results: In the absence of TGF-beta, Bim was upregulated, cell growth was inhibited and apoptosis was induced. TGF-beta treatment did not affect RUNX3 expression; however, the increase in Bim expression was significant and time dependent. Interestingly, Smad4 but not Smad2/3 was also upregulated upon exposure to TGF-beta. This was not the case after TGF-beta treatment of parent HT-29 cells. As expected, TGF-beta further inhibited cell growth and induced apoptosis in HT-29/RUNX3+ cells. Conclusion: Our data demonstrate that RUNX3 is involved in TGF-beta-dependent and -independent cell growth inhibition and apoptosis induction pathways. Copyright (C) 2009 S. Karger AG, Basel