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Topological control of p21WAF1/CIP1 expression in normal and neoplastic tissues
W S el-Deiry1, T Tokino, T Waldman
1Oncology Center, Johns Hopkins University School of Medicine, Baltimore, Maryland 21231, USA.
Abstract:
The p53-regulated gene product p21WAF1/CIP1 is the prototype of a family of small proteins that negatively regulate the cell cycle. To learn more about p21WAF1/CIP1 regulation in vivo, monoclonal antibodies were developed for immunohistochemistry. These revealed that p21WAF1/CIP1 expression followed radiation-induced DNA damage in human skin in a pattern consistent with its regulation by p53. A detailed comparison of the human, rat, and mouse p21WAF1/CIP1 promoter sequences revealed that this induction was probably mediated by conserved p53-binding sites upstream of the transcription start site. In unirradiated tissues, p21WAF1/CIP1 expression was apparently independent of p53 and was observed in a variety of cell types. Moreover, there was a striking compartmentalization of p21WAF1/CIP1 expression throughout the gastrointestinal tract that correlated with proliferation rather than differentiation. As epithelial cells migrated up the crypts, the Ki67-expressing proliferating compartment near the crypt base ended abruptly, with the coincident appearance of a nonproliferating compartment expressing p21WAF1/CIP1. In colonic neoplasms, this distinct compartmentalization was largely abrogated. Cell cycle inhibitors are thus subject to precise topological control, and escape from this regulation may be a critical feature of neoplastic transformation.
Insights
The cell cycle inhibitor p21WAF1/CIP1 shows regulated expression in response to DNA damage and in specific tissue compartments. Its disrupted compartmentalization in colon cancer suggests a role in neoplastic transformation.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- p21WAF1/CIP1 is a key regulator of the cell cycle, controlled by p53.
- Understanding p21WAF1/CIP1 in vivo regulation is crucial for cell cycle control research.
Purpose of the Study:
- To investigate the in vivo regulation of p21WAF1/CIP1.
- To explore the role of p53 in p21WAF1/CIP1 expression.
- To examine p21WAF1/CIP1 compartmentalization in normal and neoplastic tissues.
Main Methods:
- Development of monoclonal antibodies for immunohistochemistry.
- Analysis of p21WAF1/CIP1 expression in human skin following radiation-induced DNA damage.
- Comparative analysis of p21WAF1/CIP1 promoter sequences in human, rat, and mouse.
- Examination of p21WAF1/CIP1 expression patterns in the gastrointestinal tract and colonic neoplasms.
Main Results:
- p21WAF1/CIP1 expression in human skin increased after DNA damage, consistent with p53 regulation.
- Conserved p53-binding sites in promoter regions suggest a mechanism for DNA damage-induced expression.
- In normal tissues, p21WAF1/CIP1 expression was compartmentalized in the gastrointestinal tract, correlating with proliferation.
- This compartmentalization was lost in colonic neoplasms, indicating a breakdown in regulation.
Conclusions:
- p21WAF1/CIP1 exhibits precise topological control in normal tissues, linked to cell proliferation.
- Disruption of p21WAF1/CIP1 compartmentalization may be a critical event in the development of colon cancer.
- p53-independent regulation of p21WAF1/CIP1 occurs in specific cell types and conditions.