Direct Contact with Platelets Induces Podoplanin Expression and Invasion in Human Oral Squamous Cell Carcinoma Cells

Oral squamous cell carcinoma (OSCC) is mostly diagnosed at an advanced stage, with local and/or distal metastasis. Thus, locoregional and/or local control of the primary tumor is crucial for a better prognosis in patients with OSCC. Platelets have long been considered major players in cancer metastasis. Traditional antiplatelet agents, such as aspirin, are thought to be potential chemotherapeutics, but they need to be used with caution because of the increased bleeding risk. Podoplanin (PDPN)-expressing cancer cells can activate platelets and promote OSCC metastasis. However, the reciprocal effect of platelets on PDPN expression in OSCC has not been investigated. In this study, we found that direct contact with platelets upregulated PDPN and integrin β1 at the protein level and promoted invasiveness of human OSCC Ca9.22 cells that express low levels of PDPN. In another human OSCC HSC3 cell line that express PDPN at an abundant level, silencing of the PDPN gene reduced cell invasiveness. Analysis of the public database further supported the co-expression of PDPN and integrin β1 and their increased expression in metastatic tissues compared to normal and tumor tissues of the oral cavity. Taken together, these data suggest that PDPN is a potential target to regulate platelet-tumor interaction and metastasis for OSCC treatment, which can overcome the limitations of traditional antiplatelet drugs.

Thymoquinone Suppresses Migration of Human Renal Carcinoma Caki-1 Cells through Inhibition of the PGE 2 -Mediated Activation of the EP2 Receptor Pathway

Renal cell carcinoma (RCC) is likely to metastasize to other organs, and is often resistant to conventional chemotherapies. Thymoquinone (TQ), a phytochemical derived from the seeds of Nigella sativa, has been shown to inhibit migration and metastasis in various cancers. In this study, we assessed the effect of TQ on the migratory activity of human RCC Caki-1 cells. We found that treatment with TQ reduced the proteolytic activity of matrix metalloproteinase-9 (MMP-9) in Caki-1 cells. TQ significantly repressed prostaglandin E2(PGE2) production, its EP2 receptor expression as well as the activation of Akt and p38, the wellknown upstream signal proteins of MMP-9. In addition, treatment with butaprost, a PGE2 agonist, also induced MMP-9 activity and migration/invasion in Caki-1 cells. Moreover, pharmacological inhibitors of PI3K/Akt and p38 remarkably attenuated butaprostinduced Caki-1 cell migration and invasion, implying that activation of PI3K/Akt and p38 is a bridge between the PGE2-EP2 axis and MMP-9-dependent migration and invasion. Taken together, these data suggest that TQ is a promising anti-metastatic drug to treat advanced and metastatic RCC.