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Altered expression of cyclin D1 and cyclin-dependent kinase 4 in azoxymethane-induced mouse colon tumorigenesis
Q S Wang1, A Papanikolaou, C L Sabourin
1University of Connecticut School of Pharmacy, Department of Pharmaceutical Sciences, Storrs 06269-2091, USA.
Abstract:
Alterations in the expression of the cell cycle regulators, cyclin D1 and cyclin-dependent kinase 4 (Cdk4), have been implicated in malignancies of both humans and experimental animal models. We hypothesize that altered expression of cyclin D1 and Cdk4 may also be involved in mouse colon tumorigenesis induced by the chemical carcinogen, azoxymethane (AOM). In the present study, SWR/J mice were given AOM by i.p. injection at a dose of 10 mg/kg once a week for 8 weeks, and colonic tissue and tumors were isolated 18 weeks later. The expression and localization of cyclin D1 and Cdk4 were examined by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical analyses. Cyclin D1 and Cdk4 mRNA levels in tumor samples were increased 1.3-fold (P < 0.01) and 1.2-fold (P < 0.01), respectively, when compared with control mouse colon tissue. Control colon epithelium was uniformly negative for cyclin D1 immunoreactivity, whereas minimal Cdk4 nuclear staining was confined to the lower portion of the crypts within the control tissue. Both cyclin D1 and Cdk4 immunoreactive cells were markedly increased in preneoplastic lesions and in adenomas isolated from AOM-treated mice. Furthermore, some morphologically normal colon crypts from AOM-treated mice showed positive cyclin D1 immunoreactivity. These findings suggest that overexpression of cyclin D1 and Cdk4 occurs early in the AOM-induced mouse colon tumorigenesis and may contribute to tumor progression in this model.
Insights
Altered expression of cyclin D1 and cyclin-dependent kinase 4 (Cdk4) is linked to mouse colon tumor development. These cell cycle regulators are overexpressed early in azoxymethane-induced tumorigenesis, suggesting a role in tumor progression.
Area of Science:
- Oncology
- Molecular Biology
- Carcinogenesis
Background:
- Cell cycle regulators cyclin D1 and cyclin-dependent kinase 4 (Cdk4) are frequently altered in human cancers.
- Azoxymethane (AOM) is a chemical carcinogen used to induce colon tumors in experimental models.
- The role of cyclin D1 and Cdk4 in AOM-induced mouse colon tumorigenesis requires further investigation.
Purpose of the Study:
- To investigate the expression and localization of cyclin D1 and Cdk4 in AOM-induced mouse colon tumors.
- To determine if altered expression of these cell cycle regulators occurs early in the tumorigenesis process.
Main Methods:
- SWR/J mice were administered AOM weekly for 8 weeks.
- Colonic tissue and tumors were collected 18 weeks post-treatment.
- Reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry were used to analyze cyclin D1 and Cdk4 expression and localization.
Main Results:
- Cyclin D1 and Cdk4 mRNA levels were significantly increased (1.3-fold and 1.2-fold, respectively) in AOM-induced tumor samples compared to controls.
- Immunohistochemistry revealed increased cyclin D1 and Cdk4 immunoreactivity in preneoplastic lesions and adenomas.
- Positive cyclin D1 immunoreactivity was also observed in some morphologically normal colon crypts of AOM-treated mice.
Conclusions:
- Overexpression of cyclin D1 and Cdk4 occurs early in AOM-induced mouse colon tumorigenesis.
- These findings suggest that cyclin D1 and Cdk4 play a contributing role in the progression of colon tumors in this model.