Role of S1P₁ in barrier-enhancing signaling by APC. Subconfluent untransfected cells (control) or cells transfected with siRNA targeting the indicated genes were incubated for 3 hours with carrier control (▪) or 5nMAPC(□) followed by analysis of permeability (means ± SD, n = 8 with 4 independent transfections, P values are indicated).