Role of Gas6 in Cancer-Induced Venous Thrombosis

Abstract 108

Venous thrombosis is the most common morbid complication related to cancer and its treatments. The onset of cancer has been shown to predispose patients to hemostatic disorders mainly because of the pro-thrombotic milieu generated by the cancer. Growth arrest specific 6 (gas6) is a vitamin K dependent secreted protein that is expressed by different cell types. Gas6 and its receptor Axl are overexpressed in different cancers. Gas6 null mice have been shown to be protected against life-threatening thrombosis. Because of the association of gas6 with cancer and thrombosis, the objective of the present study is to elucidate the role of gas6 in cancer-induced venous thrombosis. Thus, we hypothesize that the absence of gas6 in a mouse model of cancer would reduce venous thrombosis. Wild type (WT) and gas6 null (−/−) mice received an intravenous injection of M27 murine lung cancer cells. After 2 weeks, WT and gas6^−/− mice developed end stage cancer. Venous thrombosis was induced using 10% ferric chloride. Thrombus surface area was evaluated using ultrasonography, 30 minutes after ferric chloride application. We found that thrombi induced in mice with cancer were smaller than those induced in WT mice, by both ultrasound (p<0.05) and histologically (p<0.05). To elucidate the role of gas6 in cancer-induced thrombosis, we co-cultured murine endothelial cells, prepared from lungs of both WT and gas6^−/− mice, with M27 cells. RNA was extracted from endothelial cells and we used a whole genome microarray analysis to identify differential gene expression induced by cancer in the presence or absence of gas6. Microarray analysis revealed that 28 genes were differentially expressed in WT or gas6^−/− cells in the presence of cancer. Of interest, we found that thrombospondin 2 was downregulated by cancer cells in WT endothelial cells and even further decreased in gas6^−/− cells. We confirmed these results using real-time qPCR and western blot analysis (p<0.05). These results suggest the possibility that gas6, through the downregulation of thrombospondin 2, has a pathophysiologic role in cancer-induced thrombosis.