Glioblastoma multiforme is the most common and lethal primary malignant brain tumor. Although considerable progress has been made in technical proficiencies of surgical and radiation treatment for brain tumor patients, the impact of these advances on clinical outcome has been disappointing, with median survival time not exceeding 15 months. Over the last 30 years, no significant increase in survival of patients suffering from this disease has been achieved. A fundamental source of the management challenge presented in glioma patients is the insidious propensity of tumor invasion into distant brain tissue. Invasive tumor cells escape surgical removal and geographically dodge lethal radiation exposure and chemotherapy. Recent improved understanding of biochemical and molecular determinants of glioma cell invasion provide valuable insight into the underlying biological features of the disease, as well as illuminating possible new therapeutic targets. These findings are moving forward to translational research and clinical trials as novel antiglioma therapies.

Eph receptor tyrosine kinases are involved in nervous system development. Eph ligands, termed ephrins, are transmembrane proteins that bind to Eph receptors, the mutual activation of which causes repulsive effects in reciprocally contacting cells. Previously, we showed that overexpression of EphB2 in glioma cells increases cell invasion. Here, expression profiles of ephrin-B family members were determined in four glioma cell lines and in invading glioblastoma cells collected by laser capture microdissection. Ephrin-B3 mRNA was upregulated in migrating cells of four of four glioma cell lines (1.3-to 1.7-fold) and in invading tumor cells of eight of eight biopsy specimens (1.2-to 10.0-fold). Forced expression of ephrin-B3 in low expressor cell lines (U87, T98G) stimulated cell migration and invasion in vitro and ex vivo, concomitant with tyrosine phosphorylation of ephrin-B3. In high expressor cell lines (U251, SNB19), ephrin-B3 colocalized with Rac1 to lamellipodia of motile wild-type cells. Cells transfected with ephrin-B3 small interfering RNA (siRNA) showed significant morphologic change and decreased invasion in vitro and ex vivo. Depletion of endogenous ephrin-B3 expression abrogated the increase of migration and invasion induced by EphB2/Fc, indicating increased invasion is dependent on ephrin-B3 activation. Furthermore, using a Rac1-GTP pulldown assay, we showed that ephrin-B3 is associated with Rac1 activation. Reduction of Rac1 by siRNA negated the increased invasion by addition of EphB2/Fc. In human glioma specimens, ephrin-B3 expression and phosphorylation correlated with increasing tumor grade. Immunohistochemistry revealed robust staining for phosphorylated ephrin-B and ephrin-B3 in invading glioblastoma cells. These data show that ephrin-B3 expression and signaling through Rac1 are critically important to glioma invasion. (Cancer Res 2006; 66(17): 8492-500)

Telomere shortening is a trigger of cellular senescence. Biliary epithelial cells in damaged small bile ducts in primary biliary cirrhosis (PBC) show senescent features such as the expression of senescence-associated ␤-galactosidase and the increased expression of p16 INK4a and p21 WAF1/Cip1 . We investigated whether the telomere shortening is involved in the pathogenesis of biliary cellular senescence in PBC. We analyzed the telomere length of biliary epithelial cells using quantitative fluorescence in situ hybridization in livers taken from the patients with PBC (n ‫؍‬ 13) and control livers (n ‫؍‬ 13). We also assessed immunohistochemically the prevalence of DNA damage and the expression of p16 INK4a and p21 WAF1/Cip1 . The study showed a significant decrease in telomere length in biliary epithelial cells in the damaged small bile ducts and bile ductules in PBC compared with normal-looking bile ducts and bile ductules in PBC, chronic viral hepatitis, and normal livers (P < 0.01). ␥H2AX-DNA-damage-foci were detected in biliary epithelial cells in damaged small bile ducts and bile ductules in PBC but were absent in biliary epithelial cells in chronic viral hepatitis and normal livers. The expression of p16 INK4a and p21 WAF1/Cip1 was increased corresponding to telomere shortening and ␥H2AX-DNA-damage-foci in the damaged small bile ducts in PBC. R ecent progress in the field of hepatology disclosed that cellular senescence is involved in the pathophysiology of various chronic liver diseases 1-7 and hepatocarcinogenesis. 8,9 Cellular senescence is defined as a condition in which a cell no longer has the ability to proliferate. Senescent cells are irreversibly arrested at the G1 phase of the cell cycle and do not respond to various external stimuli but remain metabolically active. Senescent cells display several characteristics, including histological changes in vitro and in vivo, 10,11 shortened telomeres, increased expression of p16 INK4 and p21 WAF1/CIP1 , and increased activity of senescence-associated ␤-galactosidase. 12 Cellular senescence can be triggered by multiple mechanisms, including telomere shortening, the epigenetic derepression of the INK4a/ARF locus, and DNA damage. 13 The telomeres at the ends of chromosomes are composed of terminal DNA sequence repeats and telomerebinding proteins. 14 These structures have an essential role in the maintenance of chromosomal stability by capping the chromosomes and protecting them from end-to-end fusion. Telomere repeat sequences are subjected to shortening with each cell division because of their incomplete replication during DNA synthesis. 15 The loss of telomere repeat sequences has been proposed as a possible mechanism of cellular senescence. 14,16 Conversely, in germ cells, most established cell lines, and more than 85% of malignant cells, the length of the telomeres is maintained or increased through the action of telomerase. 17

Background: Glioblastoma multiforme (GBM) is the most common primary intracranial tumor and despite recent advances in treatment regimens, prognosis for affected patients remains poor. Active cell migration and invasion of GBM cells ultimately lead to ubiquitous tumor recurrence and patient death.