Abstract P1-07-32: Activated thrombin activatable fibrinolysis inhibitor is a novel anti-metastatic factor in breast cancer

Abstract

Abstract Thrombin activatable fibrinolysis inhibitor (TAFI) is a plasma zymogen initially known for its role in attenuating fibrinolysis. Activated TAFI (TAFIa) is formed through proteolytic cleavage by thrombin, plasmin or, its most effective activator, thrombin in complex with the endothelial cofactor thrombomodulin (TM). TAFIa is a carboxypeptidase, which acts by cleaving carboxyl terminal lysine and arginine residues from protein and peptide substrates, including plasminogen binding sites on cell surface receptors. Carboxyl terminal lysine residues play a vital role in accelerating plasminogen activation to plasmin on the cell surface. Plasmin has many critical functions including cleaving components of the extracellular matrix (ECM), which enhances invasion and migration of cancer cells. In addition, plasmin can activate matrix metalloproteinases (MMPs), which also play a role in degrading the ECM. Furthermore, the expression of TM in tumours is inversely correlated to metastasis. Studies have shown that the anti-metastatic effects of TM result from its ability to bind thrombin. Given that the thrombin/TM complex is responsible for the activation of TAFI, the anti-metastatic effects of TM may be modulated by TAFIa. We therefore hypothesize that the activation of TAFI on the cell surface inhibits plasminogen activation and decreases breast cancer cell invasion and migration. Expression of TAFI and TM were assessed in breast cancer cells with varying degrees of metastatic potential. Although TAFI mRNA levels did not correlate with malignancy, TM mRNA levels were found to be inversely correlated with breast cancer cell malignancy. Moreover, cell invasion and migration of MDA-MB-231 and SUM149 cells were assessed upon treatment with potato tuber carboxypeptidase inhibitor (PTCI), which is a specific inhibitor of TAFIa. Inhibition of TAFIa resulted in a significant increase in cell invasion and migration of both cell lines. Cell invasion and migration of MDA-MB-231 and SUM149 cells were also assessed upon treatment with TM. Treatment with TM significantly decreased cell invasion and migration of both MDA-MB-231 and SUM149 cells. Additionally, experiments using a fluorogenic collagen substrate showed an increase in extracellular collagen cleavage after PTCI treatment, using both MDA-MB-231 and SUM149 cells. Furthermore, the ability of TAFIa to inhibit pericellular plasminogen activation was evaluated. Plasminogen activation was significantly decreased on the surface of MDA-MB-231 and SUM149 cells following treatment with various concentrations of TAFIa. Taken together, these results indicate a vital role for TAFIa in regulating pericellular plasminogen activation and ultimately ECM proteolysis. Enhancement of TAFI activation in the breast cancer tumour microenvironment may be a therapeutic strategy to inhibit invasion and prevent metastasis of breast cancer cells. Citation Format: Zainab A Bazzi, Deborah Rudy, Lisa A Porter, Dora Cavallo-Medved, Michael B Boffa. Activated thrombin activatable fibrinolysis inhibitor is a novel anti-metastatic factor in breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-07-32.