Cyclosporine A Causes Gingival Overgrowth by Promoting Entry into the S Phase at the G1/S Cell Cycle Checkpoint in Gingival Fibroblasts Exposed to Lipopolysaccharide.

OBJECTIVES: Cyclosporine A promotes gingival fibrosis by enhancing the proliferation of gingival fibroblasts, leading to gingival overgrowth. The population of gingival fibroblasts is regulated by cell cycle machinery, which balances cell growth and inhibition. Cells that detect DNA damage pause at the G1/S checkpoint to repair the damage instead of progressing to the S phase. Previous studies have linked drug-induced gingival overgrowth to the response of fibroblasts to lipopolysaccharide (LPS) and cyclosporine A. This research investigates the effects of cyclosporine A on the G1/S checkpoint and its mediators in LPS-treated gingival fibroblasts to clarify the mechanisms behind cyclosporine-A-induced gingival overgrowth. METHODS: Semi-confluent human gingival fibroblasts were treated with LPS or cyclosporine A in DMEM. Cell proliferation was evaluated by counting the total number of cells. The distribution of the cell cycle phases was analyzed using flow cytometry. Additionally, the expression levels of mRNAs and proteins related to cell cycle regulators were quantified by reverse-transcription quantitative PCR and Western blotting, respectively. RESULTS: Cyclosporine A treatment significantly enhanced cell proliferation and the G1-S cell cycle transition. It increased the mRNA levels of CDC25A and CYCLIN D while decreasing those of RB1, SMAD3, and SMAD4. Additionally, it upregulated the protein levels of CDC25A, CYCLIN D, CDK4, CDK6, and pRB and downregulated the protein levels of SMAD3 and SMAD4. CONCLUSIONS: Gingival overgrowth induced by cyclosporine A could be attributed to these alterations.