Pin1 inhibition leads to the down-regulation of erbB2. A. Immunofluorescence of BT474 or AU565 cells stained with anti-Pin1 (red), anti Her2 (green) and nuclear DAPI stain, and a merged image. Cells were analyzed with a Zeiss Confocal Microscope 3 days after transfection of either control or Pin1 siRNA. B, C Immunoblotting of Her2 in cells transfected with Pin1 siRNA or control siRNA (B), or dominant-negative Pin1 (S16A mutation) or control vector (C). Actin levels (lower panel) remained stable while Pin1 levels decreased in response to siRNA treatment (B, middle panel) or increased after DN Pin1 expression (C, middle panel). Her2 levels decreased both in response to Pin1 siRNA treatment (B, upper panel) and in response to expression of DN Pin1 (C, upper panel). Cells were transfected with either vector or the mutant, and lysates collected for immunoblotting 72 hrs later.