The HDAC1 target gene Prss1 gene negatively affects proliferation in human tumor cells. (A) Equal numbers (120,000) of untransfected, empty-vector-transfected (VecA and VecB), and Prss11-overexpressing (Prss11A, Prss11B, and Prss11C) U2OS cells were plated in triplicate on 10-cm dishes. Cell numbers were determined after 3 days by using a Casy cell counter. The insert shows mean values for three vector-transfected cell lines (U2OS+vec) and three Prss11-overexpressing cell lines (U2OS+Prss11). (B) Ki67 staining of the same cell lines as used for panel A. Ki67 was visualized by indirect fluorescence microscopy, and nuclear DNA was stained with DAPI. Data are presented as percentages of Ki67-positive cells per 100 counted cells. The insert shows mean values for Ki67-positive cells for cell lines transfected with empty-vector (U2OS+vec) and Prss11-overexpressing (U2OS+Prss11) cell lines.