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Updated: Jun 14, 2026
Experimental Analysis of Apoptotic Thymocyte Engulfment by Macrophages
Published on: May 24, 2019
The G1 cell cycle arrest of macrophages infected with Aggregatibacter actinomycetemcomitans
H Kasai1, K Nakashima, M Yokota
1Division of Infections and Molecular Biology, Department of Health Promotion, Kyushu Dental College, Kokurakita-ku, Kitakyushu, Japan.
Objectives:
Infection of murine macrophage cell line J774.1 with the periodontopathic bacterium Aggregatibacter actinomycetemcomitans induces apoptotic cell death. The infection induces cell cycle arrest in the G1 phase prior to the appearance of apoptotic cells. This study determined the involvement of various cell cycle-related signal molecules in A. actinomycetemcomitans-induced G1 cell cycle arrest.
Materials And Methods:
Cell cycle in J774.1 cells infected with A. actinomycetemcomitans was analyzed with a flow cytometer. Immunoblot analysis was also employed to determine the expression levels of intracellular signal molecules.
Results:
Flow cytometric analysis revealed that the percentage of cells in the G1 phase increased to 77.2% at 12 h after A. actinomycetemcomitans infection. Additionally, according to immunoblot analysis, expression levels of hyperphosphorylated forms of retinoblastoma protein (ppRb) declined in J774.1 cells following A. actinomycetemcomitans infection, whereas hypophosphorylated Rb (pRb) expression levels were elevated slightly. Expression levels of cyclin D1 and D2 in the cells decreased gradually postinfection; CDK2, CDK4, CDK6 and cyclin E levels were not changed. Furthermore, postinfection, p21(CIP1/WAF1) expression increased at 6 h, followed by a subsequent decrease.
Conclusion:
These findings suggest that cyclin D1 and D2 and p21(CIP1/WAF1) participate in G1 cell cycle arrest in A. actinomycetemcomitans-infected J774.1 cells.
Insights
Aggregatibacter actinomycetemcomitans infection causes G1 cell cycle arrest in macrophages. Cyclin D1, D2, and p21(CIP1/WAF1) are key molecules involved in this process.
Area of Science:
- Cell Biology
- Microbiology
- Immunology
Background:
- The periodontopathic bacterium Aggregatibacter actinomycetemcomitans is known to induce apoptotic cell death in macrophages.
- Infection with A. actinomycetemcomitans leads to cell cycle arrest in the G1 phase before apoptosis occurs.
Purpose of the Study:
- To investigate the role of specific cell cycle regulatory molecules in A. actinomycetemcomitans-induced G1 phase arrest in the J774.1 macrophage cell line.
Main Methods:
- J774.1 cells were infected with A. actinomycetemcomitans.
- Cell cycle progression was analyzed using flow cytometry.
- Expression levels of key intracellular signaling molecules were determined via immunoblot analysis.
Main Results:
- A. actinomycetemcomitans infection significantly increased the proportion of cells in G1 phase (77.2% at 12h).
- Retinoblastoma protein (Rb) phosphorylation decreased, while cyclin D1 and D2 levels diminished post-infection.
- Expression of p21(CIP1/WAF1) initially increased then decreased, while CDK2, CDK4, CDK6, and cyclin E levels remained unchanged.
Conclusions:
- Cyclin D1, cyclin D2, and p21(CIP1/WAF1) are implicated in mediating G1 cell cycle arrest during A. actinomycetemcomitans infection in J774.1 cells.
