The G1 cell cycle arrest of macrophages infected with Aggregatibacter actinomycetemcomitans.
OBJECTIVE
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.


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.


CONCLUSIONS
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.
Kasai
H
H
Division of Infections and Molecular Biology, Department of Health Promotion, Kyushu Dental College, Kokurakita-ku, Kitakyushu, Japan.
Nakashima
K
K
Yokota
M
M
Nishihara
T
T
D016976:Aggregatibacter actinomycetemcomitans / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D019938:Cyclin D1 / Q000096:biosynthesis; D056742:Cyclin D2 / Q000096:biosynthesis; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis; D016193:G1 Phase / Q000502:physiology*; D008264:Macrophages / Q000378:metabolism / Q000382:microbiology*; D051379:Mice; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000378:metabolism
D056742:Cyclin D2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016160:Retinoblastoma Protein; D019938:Cyclin D1