Activation of Stat5 is frequently found in leukemias. To study the mechanism and role of Stat5 activation, we introduced a constitutively activated Stat5a mutant, cS5F, into murine bone marrow (BM) cells. BM transplantation with cS5F-transfected cells caused development of multilineage leukemias in lethally irradiated wild-type or nonirradiated Rag2(-/-) mice. The leukemic cells showed strongly enhanced levels of cS5F tetramers but unchanged cS5F dimer levels in a DNA binding assay. Moreover, Stat5a mutants engineered to form only dimers, but not tetramers, failed to induce leukemias. In addition, Stat5 tetramers were found to accumulate in excess compared to dimers in various human leukemias. These data suggest that Stat5 tetramers are associated with leukemogenesis.

contributed equally to this work TACC3 is a centrosomal/mitotic spindle-associated protein that is highly expressed in a cell cycle-dependent manner in hematopoietic lineage cells. During embryonic development, TACC3 is expressed in a variety of tissues in addition to the hematopoietic lineages. TACC3 de®ciency causes an embryonic lethality at mid-to late gestation involving several lineages of cells. Hematopoietic stem cells, while capable of terminal differentiation, are unable to be expanded in vitro or in vivo in reconstitution approaches. Although gross alterations in centrosome numbers and chromosomal segregation are not observed, TACC3 de®ciency is associated with a high rate of apoptosis and expression of the p53 target gene, p21 Waf1/Cip1 . Hematopoietic stem cell functions, as well as de®ciencies in other cell lineages, can be rescued by combining the TACC3 de®ciency with p53 de®ciency. The results support the concept that TACC3 is a critical component of the centrosome/ mitotic spindle apparatus and its absence triggers p53-mediated apoptosis.

Cadherins are Ca2+-dependent cell adhesion molecules that play an important role in tissue construction and morphogenesis in multicellular organisms. Over the last few years, reports have emerged in the literature describing the involvement of cadherins in tumor invasion and metastasis. Cadherins typically demonstrate up and down-regulation according to the biological needs of the tissue. Additionally, up-regulation of N-cadherin is thought to be important for tumor formation in early stages of tumor development. We studied N-cadherin in surgical specimens of patients with primary glioblastoma by microarray analysis and found that N-cadherin mRNA expression is up-regulated compared to normal brain. To study the effects of N-cadherin expression on invasion and metastasis in vitro and in vivo, we overexpressed N-cadherin in the rat C6 glioma cell line which normally has low levels of N-cadherin. We found that up-regulation of N-cadherin resulted in a slight decreased adhesion to type IV collagen, fibronectin, and laminin, but statistically significant decreased adhesion to type I collagen. Furthermore, increased expression of N-cadherin correlated with a dramatic decrease in invasive behavior in extracellular matrix invasion assays. We then proceeded to study these cell lines in vivo in a rat intracranial glioma model, and found that N-cadherin expression inversely correlated with invasion into surrounding tissues, irregular margins, and extracranial invasion. In summary, these data collectively demonstrate that N-cadherin levels are important in the malignant behavior of gliomas, and may serve as a prognostic indicator for patients with high-grade gliomas.

Purpose Ionizing radiation, an important component of glioma therapy, is critically dependent on tumor oxygenation. However, gliomas are notable for areas of necrosis and hypoxia, which foster radioresistance. We hypothesized that pharmacologic manipulation of the typically dysfunctional tumor vasculature would improve intratumoral oxygenation and, therefore, the anti-glioma efficacy of ionizing radiation. Methods and Materials Orthotopic U87 xenografts were treated with either continuous interferon-beta (IFN-β) or bevacizumab, alone, or in combination with cranial irradiation (RT). Tumor growth was assessed by quantitative bioluminescence imaging; tumor vasculature, with immunohistochemical staining; and tumor oxygenation, with hypoxyprobe staining. Results Both IFN-β and bevaziumab profoundly affected the tumor vasculature, albeit with different cellular phenotypes. IFN-β caused a doubling in the percent area of perivascular cell staining while bevacizumab caused a rapid decrease in the percent area of endothelial cell staining. However, both agents increased intratumoral oxygenation, although with bevacizumab the effect was transient, being lost by five days. Administration of IFN-β or bevacizumab prior to RT was significantly more effective than any of the three modalities as monotherapy or when RT was administered concomitantly with IFN-β or bevacizumab, or five days after bevacizumab. Conclusions Bevacizumab and continuous delivery of IFN-β each induced significant changes in glioma vascular physiology, improving intratumoral oxygenation and enhancing the anti-tumor activity of ionizing radiation. Further investigation into the use and timing of these and other agents that modify vascular phenotype, in combination with radiation, is warranted in order to optimize cytotoxic activity.