ABSTRACT
Bcl-3 is an atypical member of the inhibitor of kappa light polypeptide gene enhancer in B-cells (IκB) family. It associates with p50/nuclear factor-κB1 (NF-κB1) and p52/NF-κB2 homodimers in nuclei where it modulates transcription in a context-dependent manner. A subset of B-cell tumors exhibits recurrent translocations of Bcl-3, resulting in overexpression. Elevated expression without translocations is also observed in various B-cell lymphomas and even some solid tumors. Here we investigated the role of Bcl-3 in azoxymethane/dextran sulfate sodium (AOM/DSS)-induced colon tumors, a mouse model for colitis-associated colorectal cancers in humans. Contrary to expectations, Bcl-3 suppressed colorectal tumor formation: Bcl-3-deficient mice were relatively protected from DSS-induced epithelial damage and developed more polyps after AOM/DSS treatment, although polyp size was unaffected. DSS-challenged mutant mice exhibited increased recruitment of myeloid-derived suppressor cells, consistent with protection of the epithelium. Loss of Bcl-3 in intestinal epithelial cells was sufficient to increase tumorigenesis. The added tumor burden in mutant mice was dependent on tumor necrosis factor-α (TNFα), a tumorigenic, NF-κB-mediated signaling pathway that was dampened by Bcl-3. These findings reveal a tumor-suppressive role for Bcl-3 in this inflammation-associated cancer model. Bcl-3 thus functions as a tumor promoter or suppressor, depending on the cellular and environmental context.
Subject(s)
Cell Transformation, Neoplastic/genetics , Colonic Neoplasms/etiology , Colonic Neoplasms/pathology , Inflammation/complications , Intestinal Mucosa/metabolism , Intestinal Mucosa/pathology , Proto-Oncogene Proteins/genetics , Transcription Factors/genetics , Animals , B-Cell Lymphoma 3 Protein , Cell Transformation, Neoplastic/metabolism , Colitis/chemically induced , Colitis/complications , Colonic Neoplasms/metabolism , Colonic Polyps/etiology , Colonic Polyps/metabolism , Colonic Polyps/pathology , Dextran Sulfate/adverse effects , Disease Models, Animal , Epithelial Cells/metabolism , Germ-Line Mutation , Mice , Mice, Knockout , Organ Specificity/genetics , Proto-Oncogene Proteins/metabolism , Signal Transduction , Transcription Factors/metabolism , Tumor Necrosis Factor-alpha/metabolismABSTRACT
The activation of protein tyrosine kinase(s) (PTK) is a critical event required for the development of NK cell-mediated cytotoxicity. Here we demonstrate that the adaptor protein shc undergoes tyrosine phosphorylation during the generation of antibody-dependent cellular cytotoxicity (ADCC) and natural killing. In addition, we report that, upon direct or antibody-dependent target cell interaction, shc coprecipitates with the Src homology 2 (SH2)-containing inositol phosphatase, SHIP. To gain information on the functional role of shc in NK cytotoxicity, we overexpressed wild-type or dominant negative shc constructs in the human NKL cell line. Our findings show a consistent shc-mediated down-regulation of ADCC and natural killing. Such functional effect correlates with a perturbation of the phosphoinositide (PI) metabolism by means of a shc-mediated negative regulation of inositol 1,4,5 triphosphate (IP3) generation and intracellular calcium flux upon CD16 ligation. Furthermore, our data show that dominant-negative shc-mediated perturbation of shc/SHIP interaction leads to inhibition of ligand-dependent SHIP recruitment to CD16 zeta chain. We suggest that shc plays a role of negative adaptor by modulating SHIP recruitment to activation receptors involved in the generation of NK cytotoxic function.
