Endothelial expression of TNF receptor-1 generates a proapoptotic signal inhibited by integrin α6ß1 in glioblastoma.

Activation of TNF receptor 1 (TNF-R1) can generate signals that promote either apoptosis or survival. In this study, we show that these signals can be determined by the character of the extracellular matrix in the tumor microenvironment. Specifically, through studies of glioblastoma, we showed that TNFα stimulation induced apoptosis of primary brain endothelial cells (EC) attached to collagen or fibronectin (which engage integrins α2ß1/α3ß1 and α5ß1, respectively), but did not induce apoptosis of ECs attached to laminin (which engages integrins α6ß1 and α3ß1). TNF-R1 expression was significantly higher in ECs in glioblastoma (GBM) tumors compared with ECs in normal brain specimens. TNFα was also expressed in GBM tumor-associated ECs, which was associated with longer patient survival. ECs plated on anti-integrin α2 or α3 antibody were susceptible to TNFα-induced apoptosis, whereas those plated on anti-integrin α6 antibody were not. Moreover, the ECs plated on laminin, but not collagen, expressed cellular FLICE inhibitory protein (cFLIP) and TNFα stimulation of laminin-attached cells in which cFLIP had been downregulated resulted in the induction of apoptosis. In contrast, attachment to laminin did not induce cFLIP expression in GBM tumor stem cells. Together, our findings indicate that the laminin receptor integrin α6ß1 promotes the survival of brain ECs by inhibiting prodeath signaling by TNF-R1, in part by inducing cFLIP expression.

Downregulation of FIP200 induces apoptosis of glioblastoma cells and microvascular endothelial cells by enhancing Pyk2 activity.

The expression of focal adhesion kinase family interacting protein of 200-kDa (FIP200) in normal brain is limited to some neurons and glial cells. On immunohistochemical analysis of biopsies of glioblastoma tumors, we detected FIP200 in the tumor cells, tumor-associated endothelial cells, and occasional glial cells. Human glioblastoma tumor cell lines and immortalized human astrocytes cultured in complete media also expressed FIP200 as did primary human brain microvessel endothelial cells (MvEC), which proliferate in culture and resemble reactive endothelial cells. Downregulation of endogenous expression of FIP200 using small interfering RNA resulted in induction of apoptosis in the human glioblastoma tumor cells, immortalized human astrocytes, and primary human brain MvEC. It has been shown by other investigators using cells from other tissues that FIP200 can interact directly with, and inhibit, proline-rich tyrosine kinase 2 (Pyk2) and focal adhesion kinase (FAK). In the human glioblastoma tumor cells, immortalized human astrocytes, and primary human brain MvEC, we found that downregulation of FIP200 increased the activity of Pyk2 without increasing its expression, but did not affect the activity or expression of FAK. Coimmunoprecipitation and colocalization studies indicated that the endogenous FIP200 was largely associated with Pyk2, rather than FAK, in the glioblastoma tumor cells and brain MvEC. Moreover, the pro-apoptotic effect of FIP200 downregulation was inhibited significantly by a TAT-Pyk2-fusion protein containing the Pyk2 autophosphorylation site in these cells. In summary, downregulation of endogenous FIP200 protein in glioblastoma tumor cells, astrocytes, and brain MvECs promotes apoptosis, most likely due to the removal of a direct interaction of FIP200 with Pyk2 that inhibits Pyk2 activation, suggesting that FIP200 expression may be required for the survival of all three cell types found in glioblastoma tumors.

p300- and Myc-mediated regulation of glioblastoma multiforme cell differentiation.

Tumorigenic potential of glioblastoma multiforme (GBM) cells is, in part, attributable to their undifferentiated (neural stem cell-like) phenotype. Astrocytic differentiation of GBM cells is associated with transcriptional induction of Glial Fibrillary Acidic Protein (GFAP) and repression of Nestin, whereas the reciprocal transcription program operates in undifferentiated GBM cells. The molecular mechanisms underlying the regulation of these transcription programs remain elusive. Here, we show that the transcriptional co-activator p300 was expressed in GBM tumors and cell lines and acted as an activator of the GFAP gene and a repressor of the Nestin gene. On the other hand, Myc (formerly known as c-Myc overrode these p300 functions by repressing the GFAP gene and inducing the Nestin gene in GBM cells. Moreover, RNAi-mediated inhibition of p300 expression significantly enhanced the invasion potential of GBM cells in vitro. Taken together, these data suggest that dedifferentiated/undifferentiated GBM cells are more invasive than differentiated GBM cells. Because invasion is a major cause of GBM morbidity, differentiation therapy may improve the clinical outcome.

Gene array analysis of a rat model of pulmonary arteriovenous malformations after superior cavopulmonary anastomosis.

OBJECTIVE: Pulmonary arteriovenous malformations commonly develop in children who have undergone a cavopulmonary anastomosis as part of the palliative sequence for single-ventricle physiology. METHODS: We developed a rat model of cavopulmonary anastomosis that results in pulmonary arteriovenous malformations that are angiographically and histologically similar to the human condition. We used this model to analyze the gene expression profile associated with pulmonary arteriovenous malformations developing after cavopulmonary anastomosis. RESULTS: Six Sprague-Dawley rats underwent right superior cavopulmonary anastomosis, allowing the left lung to serve as a control. Total RNA was isolated from each lung at death 8 months postoperatively and compared by using the Affymetrix Rat Microarray RAE230 2.0 GeneChip (Affymetrix, Santa Clara, Calif). One hundred thirty-seven genes demonstrated altered expression in the lungs after cavopulmonary anastomosis compared with that seen in the control lungs: 55 (40%) genes demonstrated increased expression, and 82 (60%) genes demonstrated decreased expression. Modulation of genes associated with angiogenesis and vascular remodeling was found, including angiopoietin-2, placental growth factor, several matrix metalloproteases, and several collagen subtypes. Genes with vasoactive properties, including endothelin 1 and endothelin receptor type B, demonstrated altered gene expression. Several members of the transforming growth factor beta superfamily signaling pathway also demonstrated altered expression. CONCLUSIONS: These changes in gene expression might have causative implications for pulmonary arteriovenous malformations that develop after cavopulmonary anastomosis.

GPR4 plays a critical role in endothelial cell function and mediates the effects of sphingosylphosphorylcholine.

Angiogenesis is critical for many physiological and pathological processes. We show here that the lipid sphingosylphosphorylcholine (SPC) induces angiogenesis in vivo and GPR4 is required for the biological effects of SPC on endothelial cells (EC). In human umbilical vein EC, down-regulation of GPR4 specifically inhibits SPC-, but not sphingosine-1-phosphate-, or vascular endothelial growth factor (VEGF)-induced tube formation. Re-introduction of GPR4 fully restores the activity of SPC. In microvascular EC, GPR4 plays a pivotal role in cell survival, growth, migration, and tube formation through both SPC-dependent and -independent pathways. The biological effects resulting from SPC/GPR4 interactions involve the activation of both phosphatidylinositol-3 kinase and Akt. Moreover, the effects of SPC on EC require SPC induced trans-phosphorylation and activation of the VEGF receptor 2. These results identify SPC and its receptor, GPR4, as critical regulators of the angiogenic potential of EC.

Biology of LPA in health and disease.

The functions of lysophosphatidic acid (LPA) can be broadly divided into two classes: (1) physiological and (2) pathological roles. The role of LPA in embryonic development can be seen as early as oocyte formation. It continues in postnatal homeostasis, through its ability to impart a level of protection from both stress and local injury, by regulating cellular proliferation, apoptosis, and the reorganization of cytoskeletal fibers. LPA may function as a double-edged sword. While it helps maintain homeostasis against stress and insult, it may also augment the development and spread of pathological processes, including cancers.