Porphyromonas gingivalis gingipains cause G₁ arrest in osteoblastic/stromal cells

Introduction: The program for mammalian cell growth and division consists of four successive phases; G₁, S, G₂, and M. Porphyromonas gingivalis may manipulate the host cell cycle to benefit bacterial virulence expression, which likely causes the cell and tissue tropism observed in chronic periodontal infections. We examined P. gingivalis for its effects on cell-cycle modulation in mouse ST2 osteoblastic/stromal cells. Methods: Synchronized ST2 cells were infected with P. gingivalis ATCC33277 (wild-type, WT), gingipain-mutants [KDP136 (ΔrgpAΔrgpBΔkgp), KDP129 (ΔrgpAΔrgpB), and KDP133 (Δkgp)], and a fimbria-deficient mutant (KDP150) for 24 h, then the cell cycle was evaluated using flow cytometry. Cell-cycle-related molecule expression was examined with a microarray, as well as with quantitative real-time polymerase chain reaction and Western blotting assays. Results: Both the WT and KDP150 strains significantly inhibited cellular proliferation and arrested the cell cycle in the G ₀/G₁ phase, while the expression levels of the cell-cycle regulatory molecules cyclin D and cyclin E were also decreased. In contrast, KDP136 did not show any effects. G₁ arrest was also clearly induced by KDP129 and KDP133, with KDP129 being more effective. Conclusion: The present findings suggest that P. gingivalis gingipains reduce cyclin expression and cause early G₁ arrest, leading to the inhibition of cellular proliferation.