Podoplanin-mediated platelet activation promotes proliferation and invasion of colon cancer cells

Abstract Background: Recent studies have shown that podoplanin is highly expressed in many tumors, suggesting that podoplanin may be related to the invasion and metastasis of malignant tumors. A potential mechanism by which podoplanin promote tumor invasion and metastasis is podoplanin-mediated platelet aggregation and activation.Methods: The expression of podoplanin in colon cancer LOVO cell line and lung adenocarcinoma cell line A549 was detected by immunoblotting. The above cells were co-cultured with washed mouse platelets. The platelet aggregation meter was used to determine the platelet aggregation rate and observe the cell morphology. Immunofluorescence staining and immunoblotting were used to detect the expression of EMT-related factors and the phosphorylation level of Smad2/3 downstream of the TGF-β signal; and then the matrigel-coated transwell chamber invasion test was used to evaluate the invasion ability of tumor cells. Lentiviruses targeting human podoplanin shRNA were constructed to infect colon cancer LOVO cells to generate cell lines with stable podoplanin knockdown, and the above experiments were repeated. Results: The colon cancer LOVO cell line with positive podoplanin expression had platelet aggregation activity, and the platelet aggregation activity of colon cancer LOVO cell line disappeared when anti-podoplanin monoclonal antibody MS-140 was added. However, no podoplanin expression and platelet aggregation activity were detected in lung adenocarcinoma cell line A549. When colon cancer LOVO cell-platelet reactant supernatant was added to colon cancer LOVO cell culture, the morphology of colon cancer LOVO cells showed EMT characteristics. Immunoblot showed that E-cadherin was down-regulated in colon cancer LOVO cells, while Vimentin And N-cadherin expression are upregulated. However, in lung adenocarcinoma A549 cells, there were no changes in EMT morphology and EMT factors. Immunoblot and ELISA showed that colon cancer LOVO cells with positive expression of podoplanin released TGF-β after aggregating with platelets, activated the TGF-β/Smad2/3 signaling pathway, and induced EMT and increased invasiveness of colon cancer LOVO cells. Treating colon cancer LOVO cells with TGF-β antibodies and TGF-β receptor inhibitors, or using LOVO cell lines with podoplanin knockdown, and repeating the above experiments suggest that platelet aggregation activity disappears and tumor cells EMT are eliminated, and The ability to invade is reduced. Conclusions: Podoplanin-mediated platelet activation plays an important role in colon cancer invasion and metastasis; its possible mechanism is that colon cancer LOVO cells with positive podoplanin expression react with platelets, activate platelets to release TGF-β, and activate TGF-β / Smad2 / 3 Signaling pathway induces EMT in colon cancer LOVO cells and enhances tumor cell proliferation and invasiveness.