Signaling pathways for induction of platelet aggregation by SAS tongue cancer cells--a mechanism of hematogenous metastasis

Abstract

Background: Tongue cancer metastasis is mainly through blood stream and possibly associated with tumor cell-induced platelet aggregation (TCIPA).

Methods: Platelet aggregation was induced by different amounts of SAS tongue cancer cells with/without inhibitors and the latent period for induction of platelet aggregation was recorded. Gene expression was analyzed by reverse transcriptase-polymerase chain reaction.

Results: SAS cells (4 x 10(4) to 1 x 10(6) cells/ml) induced platelet aggregation in a cell density-dependent manner. The latent period for induction of platelet aggregation reduced from 11.3 min (2 x 10(5) cells/ml) to 0.9 min (5 x 10(5) cells/ml). The extent of platelet aggregation increased from 39% to 76% by 2 x 10(5) and 5 x 10(5) SAS cells. Pre-treatment of SAS cells with aspirin showed little effect on its induction of platelet aggregation. SAS cells expressed tissue factor (TF) mRNA and the SAS cells-induced TCIPA was inhibited by TF neutralization antibody (5-20 microg/ml), heparin (5-10 U/ml), Hirudin fragment 54-65 (50 microg/ml) and D-Phenylalanyl-L-prolyl-L-arginine chloromethyl ketone. But areca nut (AN, a betel quid component known to generate reactive oxygen species (ROS)) extract showed little effect on TF expression in SAS cells. Pre-treatment with U73122 and 2-aminoethoxydiphenylborate inhibited SAS-induced TCIPA. Interestingly, catalase suppressed SAS cells-induced TCIPA, whereas AN extract enhanced this event.

Conclusions: These results suggest that tongue cancer cells may induce TCIPA and enhance tumor metastasis. SAS-induced TCIPA is related to TF secretion, thrombin generation and associated with Phospholipase C-Inositol triphosphate signaling and ROS production. Betel quid chewing may potentially promote tongue cancer metastasis.