Critical roles for Rac GTPases in T-cell migration to and within lymph nodes.

Naive T cells continuously recirculate between secondary lymphoid tissue via the blood and lymphatic systems, a process that maximizes the chances of an encounter between a T cell and its cognate antigen. This recirculation depends on signals from chemokine receptors, integrins, and the sphingosine-1-phosphate receptor. The authors of previous studies in other cell types have shown that Rac GTPases transduce signals leading to cell migration and adhesion; however, their roles in T cells are unknown. By using both 3-dimensional intravital and in vitro approaches, we show that Rac1- and Rac2-deficient T cells have multiple defects in this recirculation process. Rac-deficient T cells home very inefficiently to lymph nodes and the white pulp of the spleen, show reduced interstitial migration within lymph node parenchyma, and are defective in egress from lymph nodes. These mutant T cells show defective chemokine-induced chemotaxis, chemokinesis, and adhesion to integrin ligands. They have reduced lateral motility on endothelial cells and transmigrate in-efficiently. These multiple defects stem from critical roles for Rac1 and Rac2 in transducing chemokine and sphingosine-1-phosphate receptor 1 signals leading to motility and adhesion.

A novel Rac-dependent checkpoint in B cell development controls entry into the splenic white pulp and cell survival.

Rac1 and Rac2 GTPases transduce signals from multiple receptors leading to cell migration, adhesion, proliferation, and survival. In the absence of Rac1 and Rac2, B cell development is arrested at an IgD- transitional B cell stage that we term transitional type 0 (T0). We show that T0 cells cannot enter the white pulp of the spleen until they mature into the T1 and T2 stages, and that this entry into the white pulp requires integrin and chemokine receptor signaling and is required for cell survival. In the absence of Rac1 and Rac2, transitional B cells are unable to migrate in response to chemokines and cannot enter the splenic white pulp. We propose that loss of Rac1 and Rac2 causes arrest at the T0 stage at least in part because transitional B cells need to migrate into the white pulp to receive survival signals. Finally, we show that in the absence of Syk, a kinase that transduces B cell antigen receptor signals required for positive selection, development is arrested at the same T0 stage, with transitional B cells excluded from the white pulp. Thus, these studies identify a novel developmental checkpoint that coincides with B cell positive selection.

Evaluation of the expression of transcriptional factor NF-kappaB induced by phytic acid in colon cancer cells.

Over the last years phytic acid, a hexaphosphorylated inositol (IP6) has attracted particular attention due to its anti-cancer activity, however, the molecular mechanisms of its action have not been elucidated, as yet. The aim of this study was to evaluate the influence of phytic acid on the expression of genes encoding p65 and p50 subunits of NF-kappaB and of its inhibitor IkappaBalpha in human colorectal cancer cell line Caco-2. A kinetic study of p65 and p50 subunits and IkappaBalpha mRNAs expression was performed on Caco-2 cells after treatment with 1, 2.5 and 5 mM IP6 for 1, 6, 12 and 24 h. Quantification of the genes expression was carried out using real time QRT-PCR technique. Treatment of cells with 5 mM IP6 resulted in a strong increase in IkappaBalpha expression at 6 h, 12 h and 24 h. The level of p65 transcript after 1 h was lower in the cells exposed to 1, 2.5, and 5 mM IP6 than in the control cells. The increase in transcriptional activity of p65 gene in response to 5 mM IP6 after 6 h and 12 h was observed. Cells treated for 24 h with 2.5 mM and 5 mM IP6 showed a significant decrease in expression of p65 gene. There were no quantitative changes in the p50 gene expression in the cells treated with IP6 compared to the control cells. High positive correlation between the expression of IkappaBalpha and p65 was detected. The results of this study suggest that IP6 primarily influences p65 and IkappaBalpha genes expression in colon cancer cells. Changes in transcriptional activities of IkappaBalpha and p65 depend on IP6 concentration and time of its action.