Tumor suppressive properties of PTPRK. (A) Restoration of PTPRK expression suppressed the cellular proliferation rate. The graph shows the proliferation rates of GFP-sorted PTPRK-transduced, and mock vector-transduced NKYS and KHYG cells. The cell proliferation rate was determined according to the degree of absorbance in the MTS assay. The absorbance of triplicate wells was plotted against the number of days after seeding. (B) The restoration of PTPRK expression suppressed anchorage-independent growth. (Left) Anchorage-independent colony formation in GFP-sorted PTPRK-transduced, and mock vector-transduced cells in 1.2% methylcellulose. (Right) Bar charts showing the number of colonies formed in 5 randomly selected microscopic fields after 5 days. (C) The restoration of PTPRK expression increased the percentages of NKTCL cells undergoing apoptosis. (Left) Representative graphical results of the flow cytometry analyses of GFP-sorted PTPRK-transduced, and mock vector-transduced NKTCL cells stained with Cy5-conjugated Annexin-V and 7-AAD. (Right) The quantitative differences in the percentages of PTPRK-transduced and mock vector-transduced NKYS cells are shown. For (A-C), each assay was repeated 3 times. The bars indicate the mean ± SE. (D) Reconstituted PTPRK expression increased the proportion of NKYS cells undergoing G0/G1 cell-cycle arrest. (Left) Representative graphical results of GFP-sorted PTPRK-transduced, and mock vector-transduced NKYS cells in different phases of the cell cycle, as determined by flow cytometry after propidium iodide staining. The peaks corresponding to the different phases of the cell cycle are indicated on the DNA histograms. The percentages of cells in the G0/G1, S, and G2/M phases are indicated next to each graph. (Right) The quantitative differences in the percentages of PTPRK-transduced and mock vector-transduced NKYS cells in different phases of the cell cycle. (E) The restoration of PTPRK expression triggered caspase-mediated apoptosis of NKYS cells. Western blots show cleaved caspase-9, caspase-3, and poly[ADP-ribose] polymerase (PARP) in GFP-sorted PTPRK-transduced, and mock vector-transduced NKYS cells. β-Actin was used as a loading control.