Mantle Cell Lymphoma Cells Express B7 Family Molecules and B7-H1 Expression Are up-Regulated After LPS Exposure Via MEK-Dependent and PI3K/Akt-Dependent Pathways In Mantle Cell Lymphoma Cells

Abstract 3114

Mantle cell lymphoma (MCL) is a distinct subtype of B-cell non-Hodgkin lymphomas characterized by a specific t(11;14) (q13;q32) translocation, causing over-expression of cyclin D1. Recent studies demonstrated that B7 family molecules were not only expressed on antigen presenting cells but also on various hematopoietic malignancies, solid tumors and infiltrating immune cells and may play important roles in tumor immunology. Many cytokines could upregulate the expression of B7 molecules, however, the molecular mechanism of regulating expressions of B7 molecules is still unknown. In this study, we analyzed B7 family molecule expression on cultured mantle cell lymphoma cells and primary MCL cells by RT-PCR. We confirmed that B7 family molecules were detected in mantle cell lymphoma cell lines SP53, Jeko-1 and Mino and primary MCL cells. We next used LPS to activate TLR4 signaling pathway.

Although B7 family molecules were detected in mantle cell lymphoma cells, only B7-H1 expression was greatly enhanced after LPS exposure. B7-H1 mRNA was constitutively expressed on MCL cells and was further up-regulated after LPS stimulation in dose and time dependent manners. Western blot also indicated that total and surface B7-H1 protein expression were up-regulated after stimulated by LPS. Flow cytometry demonstrated that surface B7-H1 protein expression were up-regulated after stimulated by LPS. When we knockdown TLR4, LPS stimulation did not up-regulate B7-H1 expression. To clarify the signaling pathways of LPS induced B7-H1 up-regulation in MCL cells, we incubated the SP53 and Jeko-1 cells with LPS after pretreatment with different signal transduction pathway inhibitors for 1h and detect the activity of each inhibitor. Pretreatment and coincubation of SP53 and Jeko-1 cells with the MEK1/2 inhibitor UO126 and PI3K/Akt inhibitor LY294002 strongly reduced LPS induced B7-H1 expression, indicating that the MEK1/2 and PI3K/Akt pathway are crucial for B7-H1 expression in MCL cells. We also tested whether JNK or p38, respectively, are involved in controlling the expression of B7-H1 in MCL cells. Blocking of JNK and p38 MAPK with specific inhibitors reduced B7-H1 mRNA expression, but B7-H1 protein expression was not obvious, which may be regulated after transcriptional factors. To confirm that LPS induced B7-H1 expression through a MEK and PI3K/Akt pathway pathways in MCL cells, we stimulated SP53 and Jeko-1 with LPS and analyzed the phosphorylation of ERK1/2, p38, and JNK at different time. ERK1/2, p38, and JNK phosphorylation were significantly up-regulated following LPS treatment. We confirmed that pretreatment of the cells with these specific inhibitors inhibited LPS-induced phosphorylation of ERK1/2, p38 MAPK, and JNK, respectively. In conclusion, our study demonstrated that mantle cell lymphoma cells express B7 family molecules. B7-H1 expression were up-regulated after LPS exposure via MEK-dependent and PI3K/Akt-dependent in mantle cell lymphoma cells.