Porphyromonas gingivalis, a host-adapted opportunistic pathogen, produces a serine phosphatase, SerB, known to affect virulence, invasion and persistence within the host cell. SerB induces actin filament rearrangement in epithelial cells, but the mechanistic basis of this is not fully understood. Here we investigated the effects of SerB on the actin depolymerizing host protein cofilin. P.gingivalis infection resulted in the dephosphorylation of cofilin in gingival epithelial cells. In contrast, a SerB-deficient mutant of P.gingivalis was unable to cause cofilin dephosphorylation. The involvement of cofilin in P.gingivalis invasion was determined by quantitative image analysis of epithelial cells in which cofilin had been knocked down or knocked in with various cofilin constructs. siRNA-silencing of cofilin led to a significant decrease in numbers of intracellular P.gingivalis marked by an absence of actin colocalization. Transfection with wild-type cofilin or constitutively active cofilin both increased numbers of intracellular bacteria, while constitutively inactive cofilin abrogated invasion. Expression of LIM kinase resulted in reduced P.gingivalis invasion, an effect that was reversed by expression of constitutively active cofilin. These results show that P.gingivalis SerB activity induces dephosphorylation of cofilin, and that active cofilin is required for optimal invasion into gingival epithelial cells.
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