ABSTRACT
Cancer progression is associated with epigenetic alterations, such as changes in DNA methylation, histone modifications or variants incorporation. The p400 ATPase, which can incorporate the H2A.Z variant, and the Tip60 histone acetyltransferase are interacting chromatin-modifying proteins crucial for the control of cell proliferation. We demonstrate here that Tip60 acts as a tumor suppressor in colon, since mice heterozygous for Tip60 are more susceptible to chemically induced preneoplastic lesions and adenomas. Strikingly, heterozygosity for p400 reverses the Tip60-dependent formation of preneoplastic lesions, uncovering for the first time pro-oncogenic functions for p400. By genome-wide analysis and using a specific inhibitor in vivo, we demonstrated that these effects are dependent on Wnt signaling which is antagonistically impacted by p400 and Tip60: p400 directly favors the expression of a subset of Wnt-target genes and regulators, whereas Tip60 prevents ß-catenin acetylation and activation. Taken together, our data underline the physiopathological importance of interplays between chromatin-modifying enzymes in the control of cancer-related signaling pathways.
Subject(s)
Colonic Neoplasms/metabolism , Colonic Neoplasms/pathology , Histone Acetyltransferases/physiology , Histones/metabolism , Inositol 1,4,5-Trisphosphate Receptors/physiology , Trans-Activators/physiology , Wnt Proteins/metabolism , Acetylation , Animals , Blotting, Western , Cells, Cultured , Chromatin/metabolism , Chromatin Immunoprecipitation , Colonic Neoplasms/genetics , Disease Progression , Female , Gene Expression Profiling , Histone Acetyltransferases/metabolism , Lysine Acetyltransferase 5 , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Precancerous Conditions/genetics , Precancerous Conditions/metabolism , Precancerous Conditions/pathology , Protein Processing, Post-Translational , RNA, Messenger/genetics , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Wnt Proteins/genetics , beta Catenin/metabolismABSTRACT
Class switch recombination (CSR) occurs between highly repetitive sequences called switch (S) regions and is initiated by activation-induced cytidine deaminase (AID). CSR is preceded by a bidirectional transcription of S regions but the relative importance of sense and antisense transcription for CSR in vivo is unknown. We generated three mouse lines in which we attempted a premature termination of transcriptional elongation by inserting bidirectional transcription terminators upstream of Sµ, upstream of Sγ3 or downstream of Sγ3 sequences. The data show, at least for Sγ3, that sense transcriptional elongation across S region is absolutely required for CSR whereas its antisense counterpart is largely dispensable, strongly suggesting that sense transcription is sufficient for AID targeting to both DNA strands.
Subject(s)
Cytidine Deaminase/genetics , DNA, Antisense/genetics , Immunoglobulin Class Switching/genetics , Immunoglobulin Switch Region/genetics , Recombination, Genetic , Transcription, Genetic , Animals , B-Lymphocytes/physiology , Cells, Cultured , Enzyme-Linked Immunosorbent Assay , Flow Cytometry , Immunoglobulins/genetics , Mice , Polyadenylation , Polymerase Chain ReactionABSTRACT
DNA polymerase (Pol) is an error-prone repair DNA polymerase that has been shown to create genetic instability and tumorigenesis when overexpressed by only 2-fold in cells, suggesting that a rigorous regulation of its expression may be essential in vivo. To address this question, we have generated mice which express a transgene (Tg) bearing the Pol cDNA under the control of the ubiquitous promoter of the mouse H-2K gene from the major histocompatibility complex. These mice express the Tg only in thymus, an organ which normally contains the most abundant endogenous Pol mRNA and protein, supporting the idea of a tight regulation of Pol in vivo. Furthermore, we found no tumor incidence, suggesting that the single Pol overexpression event is not sufficient to initiate tumorigenesis in vivo.