The putative tumor metastasis suppressor nm23H1 was originally identified in murine melanomas by subtraction cloning. It displays nucleoside diphosphate kinase activity and regulates cellular events, including growth and development. Recently nm23H1 has been reported to also act as a GTPase-activating protein of the Ras-related GTPase Rad. We attempted to determine whether nm23H1 also regulates Rho-family GTPases. Although we were unable to detect a direct association between nm23H1 and Rho-family GTPases, nm23H1 was shown to be associated with a Rac1-specific nucleotide exchange factor, Tiam1, by interaction with its amino-terminal region in extracts from the cells expressing exogenous Tiam1 and from native tissue. Overexpression of nm23H1 inhibited the Tiam1-induced production of GTP-bound Rac1 and activation of c-Jun kinase. On the other hand, forced overexpression of the wild type, but not the kinase-inactivated mutant of nm23H1, converted the GDP-bound forms of Rac1, Cdc42, and RhoA to their GTP-bound forms in vitro by its nucleoside diphosphate kinase activity, but nm23H1 alone apparently did not produce the GTP-bound form of these GTPases in vivo . These results suggest that nm23H1 negatively regulates Tiam1 and inhibits Rac1 activation in vivo . Moreover, adhesion-stimulated membrane ruffles of Rat1 fibroblasts were reduced by overexpression of nm23H1. Based on these observations, we concluded that we had identified a function of nm23H1 as a regulator of Rac1 and that it may be related to the effect of nm23H1 as a tumor metastasis suppressor.

Prognostic impact of CD73 and A2A adenosine receptor expression in non-small-cell lung cancer Prognostic impact of CD73 and A2A adenosine receptor expression in non-small-cell lung cancer

The erythropoietin‐producing hepatocellular (EPH)A2 receptor, tyrosine kinase, is overexpressed and phosphorylated in several types of human tumors and has been associated with malignant transformation. A recent report, however, indicated that stimulation of the EPHA2 receptor ligand, ephrinA1 (EFNA1), inhibits the growth of EPHA2‐expressing breast cancer. The authors examined the expression of EPHA2 and EFNA1 using semiquantitative reverse transcription‐polymerase chain reaction (RT‐PCR) in four gastric cancer cell lines and 49 primary gastric cancer samples, as well as in normal gastric tissue. EPHA2 was more highly expressed in tumor tissue than in normal tissue in 27 cases (55%). EFNA1 was overexpressed in tumor tissue in 28 cases (57%). No significant correlation was detected between the expression levels and histologic features such as tumor size, age, vessel invasion, or lymph node involvement. However, EPHA2 overexpression was more prominent in macroscopic type 3 and 4 tumors than in type 1 or 2 advanced gastric cancer. The authors observed EPHA2 expression in three of the four gastric cancer cell lines (AGS, KATO3, and MKN74) that were examined. In one cell line, TMK1, EPHA2 expression was barely detectable using northern blotting, RT‐PCR, and western blotting. In contrast, EFNA1 was detected in all cell lines. In the gastric cancer cell lines that endogenously expressed EPHA2, stimulation with ephrinA1‐Fc led to decreased EPHA2 protein expression and increased EPHA2 phosphorylation. Finally, the growth of EPHA2‐expressing cells was inhibited by repetitive stimulation with soluble ephrinA1‐Fc. Taken together, these findings suggest that EPHA2 and EFNA1 expression may influence the behavior of human gastric cancer. (Cancer Sci 2005; 96: 42–48)

The identification of cancer biomarkers is critical for target‐linked cancer therapy. The overall level of phosphatidylcholine (PC) is elevated in colorectal cancer (CRC). To investigate which species of PC is overexpressed in colorectal cancer, an imaging mass spectrometry was performed using a panel of non‐neoplastic mucosal and CRC tissues. In the present study, we identified a novel biomarker, PC(16:0/16:1), in CRC using imaging mass spectrometry. Specifically, elevated levels of PC(16:0/16:1) expression were observed in the more advanced stage of CRC. Our data further showed that PC(16:0/16:1) was specifically localized in the cancer region when examined using imaging mass spectrometry. Notably, because the ratio of PC(16:0/16:1) to lyso‐PC(16:0) was higher in CRC, we postulated that lyso‐PC acyltransferase (LPCAT) activity is elevated in CRC. In an in vitro analysis, we showed that LPCAT4 is involved in the deregulation of PC(16:0/16:1) in CRC. In an immunohistochemical analysis, LPCAT4 was shown to be overexpressed in CRC. These data indicate the potential usefulness of PC(16:0/16:1) for the clinical diagnosis of CRC and implicate LPCAT4 in the elevated expression of PC(16:0/16:1) in CRC.

Clinical significance of PD-L1 and PD-L2 copy number gains in non-small-cell lung cancer Clinical significance of PD-L1 and PD-L2 copy number gains in non-small-cell lung cancer

Eph tyrosine kinase receptors and their membrane‐bound ligands, ephrins, are presumed to regulate cell–cell interactions. The major consequence of bidirectional activation of Eph receptors and ephrin ligands is cell repulsion. In this study, we discovered that Xenopus Dishevelled (Xdsh) forms a complex with Eph receptors and ephrin‐B ligands and mediates the cell repulsion induced by Eph and ephrin. In vitro re‐aggregation assays with Xenopus animal cap explants revealed that co‐expression of a dominant‐negative mutant of Xdsh affected the sorting of cells expressing EphB2 and those expressing ephrin‐B1. Co‐expression of Xdsh induced the activation of RhoA and Rho kinase in the EphB2‐overexpressed cells and in the cells expressing EphB2‐stimulated ephrin‐B1. Therefore, Xdsh mediates both forward and reverse signaling of EphB2 and ephrin‐B1, leading to the activation of RhoA and its effector protein Rho kinase. The inhibition of RhoA activity in animal caps significantly prevents the EphB2‐ and ephrin‐B1‐mediated cell sorting. We propose that Xdsh, which is expressed in various tissues, is involved in EphB and ephrin‐B signaling related to regulation of cell repulsion via modification of RhoA activity.