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Promoter-wide analysis of Smad4 binding sites in human epithelial cells
Daizo Koinuma1, Shuichi Tsutsumi, Naoko Kamimura
1Department of Molecular Pathology, Graduate School of Medicine, University of Tokyo, Bunkyo-ku, Tokyo.
Abstract:
Smad4, the common partner Smad, is a key molecule in transforming growth factor-beta (TGF-beta) family signaling. Loss of Smad4 expression is found in several types of cancer, including pancreatic cancer and colon cancer, and is related to carcinogenesis. Here we identified Smad4 binding sites in the promoter regions of over 25 500 known genes by chromatin immunoprecipitation on a microarray (ChIP-chip) in HaCaT human keratinocytes. We identified 925 significant Smad4 binding sites. Approximately half of the identified sites overlapped the binding regions of Smad2 and Smad3 (Smad2/3, receptor-regulated Smads in TGF-beta signaling), while the rest of the regions appeared dominantly occupied by Smad4 even when a different identification threshold for Smad2/3 binding regions was used. Distribution analysis showed that Smad4 was found in the regions relatively distant from the transcription start sites, while Smad2/3 binding regions were more often present near the transcription start sites. Motif analysis also revealed that activator protein 1 (AP-1) sites were especially enriched in the sites common to Smad2/3 and Smad4 binding regions. In contrast, GC-rich motifs were enriched in Smad4-dominant binding regions. We further determined putative target genes of Smad4 whose expression was regulated by TGF-beta. Our findings revealed some general characteristics of Smad4 binding regions, and provide resources for examining the role of Smad4 in epithelial cells and cancer pathogenesis.
Insights
Researchers mapped Smad4 binding sites in human cells, revealing its distinct genomic locations and interactions with other Smad proteins. This provides insights into Smad4
Area of Science:
- Molecular Biology
- Cancer Research
- Genomics
Background:
- Smad4 is a critical protein in transforming growth factor-beta (TGF-beta) signaling pathways.
- Loss of Smad4 expression is linked to various cancers, including pancreatic and colon cancer, and plays a role in carcinogenesis.
Purpose of the Study:
- To identify Smad4 binding sites in the promoter regions of human genes.
- To characterize the genomic distribution and binding patterns of Smad4 in epithelial cells.
- To understand the relationship between Smad4 binding and gene regulation in the context of TGF-beta signaling.
Main Methods:
- Chromatin immunoprecipitation on a microarray (ChIP-chip) was performed in HaCaT human keratinocytes.
- Analysis of over 25,500 known genes to identify Smad4 binding sites.
- Bioinformatic analysis including distribution analysis and motif analysis of Smad4 binding regions.
Main Results:
- 925 significant Smad4 binding sites were identified.
- Approximately half of Smad4 binding sites overlapped with Smad2/3 binding regions; the remainder were Smad4-dominant.
- Smad4 binding sites were generally located further from transcription start sites compared to Smad2/3.
- AP-1 motifs were enriched in common Smad2/3 and Smad4 binding regions, while GC-rich motifs were enriched in Smad4-dominant regions.
- Putative target genes regulated by TGF-beta were identified.
Conclusions:
- Smad4 exhibits distinct binding characteristics in the genome, differing in location and co-occupancy with other Smads.
- The study provides a comprehensive map of Smad4 binding regions, offering valuable resources for further research.
- These findings contribute to understanding Smad4's role in epithelial cell function and cancer development.
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