PTEN and Hypoxia Regulate Tissue Factor Expression and Plasma Coagulation by Glioblastoma

Abstract

We have previously proposed that intravascular thrombosis and subsequent vasoocclusion contribute to the development of pseudopalisading necrosis, a pathologic hallmark that distinguishes glioblastoma (WHO grade 4) from lower grade astrocytomas. To better understand the potential prothrombotic mechanisms underlying the formation of these structures that drive tumor angiogenesis, we investigated tissue factor (TF), a potent procoagulant protein known to be overexpressed in astrocytomas. We hypothesized that PTEN loss and tumor hypoxia, which characterize glioblastoma but not lower grade astrocytomas, could up-regulate TF expression and cause intravascular thrombotic occlusion. We examined the effect of PTEN restoration and hypoxia on TF expression and plasma coagulation using a human glioma cell line containing an inducible wt-PTEN cDNA. Cell exposure to hypoxia (1% O 2 ) markedly increased TF expression, whereas restoration of wt-PTEN caused decreased cellular TF. The latter effect was at least partially dependent on PTEN's protein phosphatase activity. Hypoxic cells accelerated plasma clotting in tilt tube assays and this effect was prevented by both inhibitory antibodies to TF and plasma lacking factor VII, implicating TF-dependent mechanisms. To further examine the genetic events leading to TF upregulation during progression of astrocytomas, we investigated its expression in a series of human astrocytes sequentially infected with E6/E7/human telomerase, Ras, and Akt. Cells transformed with Akt showed the greatest incremental increase in hypoxia-induced TF expression and secretion. Together, our results show that PTEN loss and hypoxia up-regulate TF expression and promote plasma clotting by glioma cells, suggesting that these mechanisms may underlie intravascular thrombosis and pseudopalisading necrosis in glioblastoma. (Cancer Res 2005; 65(4): 1406-13)

Modulation of the oncogene-dependent tissue factor expression by kinase suppressor of ras 1

“…Our observations presented here could suggest that the lower risk of coagulopathy associated with Herceptin treatment may be due (at least in part) to downregulation of TF in cancer cells. It should be kept in mind, however, that TF is regulated not only by oncogenes but also by a multiplicity of other factors, including differentiation pathways [10], cell-cell inderactions [9] and tumour microenvironment [8]. Therefore, the impact of herceptin on the procoagulant events in vivo requires further evaluation.…”

“…Since, the TF promoter also contains functional sites for other transcription factors, including SP1 and Egr-1, other pathways may also be involved downstream of EGFR [26]. In this regard, the available experimental evidence suggests that TF can be regulated by the PI3K/Akt pathway following the loss of the tumour suppressor gene PTEN, especially in glioma [8]. It is unclear whether KSR1 contributes to TF regulation by these MAPK-unrelated modules.…”

“…The cancer related increase in TF levels is attributed to the regulatory influences of oncogenic signalling pathways [6,7], which may be coupled with the modulating role of the tumour microenvironment [8][9][10]. Activated K-ras and members of the ErbB family, such as epidermal growth factor receptor (EGFR) and EGFRvIII all upregulate TF on the surface of cancer cells [10][11][12] and trigger the release of TF-containing microvesicles into the circulation of tumour bearing mice [7,10].…”

MDM2 Regulates Hypoxic Hypoxia-inducible Factor 1α Stability in an E3 Ligase, Proteasome, and PTEN-Phosphatidylinositol 3-Kinase-AKT-dependent Manner

“…p53 Ϫ/Ϫ and p53 Ϫ/Ϫ MDM2 Ϫ/Ϫ MEFs were a kind gift from Dr. Inder Verma. Glioblastoma cell lines derived from U87MG containing inducible mutant PTEN, 23.24GE (lipid phosphatase inactive because of a G129E mutation) and 23.44GR (both lipid and protein phosphatase inactive because of a G129R mutation) were cultured as previously described (37,38). In these cell lines, PTEN was induced using 0.5 mol/liter muristerone.…”

Cerebral Ischemia Promotes Rich Pseudopalisading Necrosis in the Rat C6 Glioblastoma Model

“…20) The following hypothesis has been proposed to account for the presence of necrogenesis with pseudopalisading in glioblastoma. 3,17) Vascular occlusion and intravascular thrombosis lead to tissue hypoxia in the perivascular region. The tumor cells then become hypoxic and undergo apoptosis or necrosis, eventually leaving a central necrotic zone.…”