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Northern blotting confirmed previous results indicating that the mitogen-activated protein kinase (MAPK) phosphatase Pyst2-L was highly expressed in leukocytes obtained from acute myeloid leukemia (AML) patients. High levels of Pyst2-L mRNA were expressed in bone marrow (BM) and peripheral leukocytes from nine AML and acute lymphoblastic leukemia (ALL) patients. BM from healthy individuals expressed very low levels of Pyst2-L. Whereas high levels of Pyst2-L mRNA and protein were detected in several leukemia cell lines, Pyst2-L mRNA was detected neither in 33/34 samples of normal peripheral blood mononuclear cells (PBMC) nor in leukocyte fractions enriched with CD34 þ cells. Certain solid tumor and lymphoblastoid cell lines expressed high levels of Pyst2-L mRNA. In view of the association of Pyst2-L to MAPK signaling cascades, we tested if cell activation, a process involving MAPK signaling, influences Pyst2-L expression. Indeed, activation of T cells and endothelial cells increased Pyst2-L in these cells. Furthermore, TPA, a known MAPK activator, induces the expression of both Pyst2-L mRNA as well as the Pyst2-L protein in leukemia cells. This induction was partially inhibited by PD098059, an Mek1/2-specific inhibitor. Based on the results of this and previous studies, we hypothesize that the high levels of Pyst2-L detected in the active state of AML and ALL diseases and in other types of cancer reflect an altered MAPK signaling pathway in such malignant processes. This alteration may be the result of a failed attempt to counter the constitutive activation of MAPK in transformed cells or alternatively, may represent the activated state of such cells.

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Extravasation of cancer cells is a pivotal step in the formation of hematogenous metastasis. Extravasation is initiated by the loose adhesion of cancer cells to endothelial cells via an interaction between endothelial selectins and selectin ligands expressed by the tumor cells. The present study shows that the interaction between recombinant E-selectin (rE-selectin) and colorectal cancer (CRC) cells alters the gene expression profile of the cancer cells. A DNA microarry analysis indicated that E-selectin-mediated alterations were significantly more pronounced in the metastatic CRC variants SW620 and KM12SM than in the corresponding non-metastatic local SW480 and KM12C variants. The number of genes altered by E-selectin in the metastatic variants was about 10-fold higher than the number of genes altered in the corresponding local variants. Aiming to identify genes involved in CRC metastasis, we focused, by using a DNA microarry analysis, on genes that were altered by E-selectin in a similar fashion exclusively in both metastatic variants. This analysis indicated that E-selectin down regulated (at least by 1.6-folds) the expression of 7 genes in a similar fashion, in both metastatic cells. The DNA microarry analysis was validated by real time PCR or by RT-PCR. HMGB1 was among these genes. Confocal microscopy indicated that E-selectin down regulated the cellular expression of the HMGB1 protein and enhanced the release of HMGB1 into the culture medium. The released HMGB1 in turn, activated endothelial cells to express E-selectin. ' 2008 Wiley-Liss, Inc.Key words: colorectal carcinoma; metastasis; extravasation; E-selectin; selectin ligands; gene expression; HMGB1The initial step in the transendothelial migration (extravasation) of leukocytes involves an interaction of fucosylated selectin ligands expressed by the leukocytes with selectins expressed by endothelial cells. 1,2 It is not entirely clear if the extravasation strategy of cancer cells follows that of leukocytes. 3 A large body of data demonstrates, however, that the interaction of selectin ligandexpressing tumor cells with selectin-expressing endothelial cells is a crucial event in tumor progression. [4][5][6][7][8][9][10][11] Several studies demonstrated that the modulation of selectin-selectin ligand interactions by selectin ligand mimetics, 12,13 diversion of the biosynthesis of selectin ligands toward nonadhesive structures, 14 modification or inhibition of the carbohydrate moieties that participate in selectinselectin-ligand interactions, 15,16 or inhibition of E-selectin expression 17 affected tumor cell adhesion and metastasis. This provided additional support for the hypothesis that cancer cells employ the selectin-selectin ligand interaction in their progression towards increased malignancy. Indirect support for the involvement of the selectin-selectin ligand axis in tumor progression was provided by studies demonstrating a correlation between a high expression of selectin ligands [such as sialyl Lewis-a (sLe-a) and sialyl Lewis-x (sLe-x)] by epit...

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