Domain 5 of kininogen inhibits proliferation of human colon cancer cell line (HCT‐116) by interfering with G1/S in the cell cycle

Background: Domain 5 (D5) of kininogen inhibits endothelial cell adhesion, migration, proliferation and angiogenesis by inducing apoptosis and disrupting a signaling pathway initiated by binding to the urokinase receptor (uPAR). Objectives: Because tumor cells frequently overexpress uPAR, we hypothesized that D5 can directly inhibit proliferation of colon carcinoma cells. Methods and results: A recombinant fusion protein of D5 and glutathione S‐transferase (GST‐D5) but not GST at 280 nm inhibited proliferation of human colon carcinoma cells (HCT‐116) in vitro by 75–86%. We found that treatment with GST‐D5 did not affect the survival pathway, phosphatidylinositol 3‐kinase or the apoptotic pathway. In contrast, the G1/S phase transition of the cell cycle was downregulated as evidenced by an increase of cells in G0/G1 and a decrease in cells in S by flow cytometry. We found a decrease in serine phosphorylation of the retinoblastoma protein Rb (p107) after incubation with GST‐D5. Less E2F‐1 transcription factor and p107 were released and fewer cells overcame the G1/S growth restriction point. Expression levels of cyclins D1, A and E were reduced as measured by densiometric analysis of western blots. Cyclin‐dependent protein kinase activities were downregulated and p27, the cyclin‐dependent kinase inhibitor, was activated by GST‐D5. Conclusions: These findings indicate that D5 of high molecular weight kininogen interferes with the G1 to S phase transition, reducing the proliferation of human colon carcinoma cells.