No abstract

Overexpression of zinc finger E-box binding homeobox transcription factor 1 (Zeb1) in cancer leads to epithelial-to-mesenchymal transition (EMT) and increased metastasis. As opposed to overexpression, we show that mutation of Zeb1 in mice causes a mesenchymal-epithelial transition in gene expression characterized by ectopic expression of epithelial genes such as E-cadherin and loss of expression of mesenchymal genes such as vimentin. In contrast to rapid proliferation in cancer cells where Zeb1 is overexpressed, this mesenchymal-epithelial transition in mutant mice is associated with diminished proliferation of progenitor cells at sites of developmental defects, including the forming palate, skeleton and CNS. Zeb1 dosage-dependent deregulation of epithelial and mesenchymal genes extends to mouse embryonic fibroblasts (MEFs), and mutant MEFs also display diminished replicative capacity in culture, leading to premature senescence. Replicative senescence in MEFs is classically triggered by products of the Ink4a (Cdkn2a) gene. However, this Ink4a pathway is not activated during senescence of Zeb1 mutant MEFs. Instead, there is ectopic expression of two other cell cycle inhibitory cyclin-dependent kinase inhibitors, p15Ink4b (Cdkn2b) and p21Cdkn1a (Cdkn1a). We demonstrate that this ectopic expression of p15Ink4b extends in vivo to sites of diminished progenitor cell proliferation and developmental defects in Zeb1-null mice.

SUMMARY Activation of the RB1 pathway triggers the cell-cycle arrest that mediates cell-cell contact inhibition. Accordingly, mutation of all three RB1 family members leads to loss of contact inhibition and outgrowth of fibroblasts into spheres where cell-cell contacts predominate. We present evidence that such outgrowth triggers reprogramming to generate cells with properties of cancer stem cells. Fibroblasts with only a single RB1 mutation remain contact inhibited; however, if this contact inhibition is bypassed by forcing the RB1−/− cells to form spheres in suspension, cells with properties of cancer stem cells are also generated. These cells not only form tumors in nude mice but also generate differentiated cells. We propose that contact inhibition imposed by the RB1 pathway performs an unexpected tumor suppressor function by preventing cell outgrowth into structures where cells with properties of cancer stem cells can be generated from differentiated somatic cells in advancing cancers.

Atk can be activated by two independent phosphorylation events. Growth factor-dependent phosphorylation of threonine 308 (Akt-308) by phosphatidylinositol 3-kinase-dependent PDK1 leads to activation of mammalian target of rapamycin (mTor) complex 1 (TORC1) and stimulation of protein synthesis. Phosphorylation on serine 473 (Akt-473) is catalyzed by mTor in a second complex (TORC2), and Akt-473 phosphorylates Foxo3a to inhibit apoptosis. Accumulation of both phosphorylated forms of Akt is frequent in cancer, and TORC2 activity is required for progression to prostate cancer with Pten mutation. Here, we link Akt-473 to the Rb1 pathway and show that mTor is overexpressed with loss of the Rb1 family pathway. This leads to constitutive Akt-473 and, in turn, phosphorylation of Foxo3a and resistance to cell adhesion-dependent apoptosis (anoikis). Additionally, Akt-473 accumulation blocks c-Raf activation, thereby preventing downstream Erk activation. This block cannot be overcome by constitutively active Ras, and it also prevents induction of the Arf tumor suppressor by Ras. These studies link inactivation of the Rb1 pathway, a hallmark of cancer, to accumulation of Akt-473, resistance to anoikis, and a block in c-Raf/Erk activation.

Abstract. Ovarian epithelial cancer is a significant cause of death among women, accounting for 5% of all female cancer-related fatalities. A lack of reliable detection methods and resistance to chemotherapy agents are considerable obstacles in the treatment of this cancer. Recently, high-level expression of the pituitary tumor transforming gene (PTTG) was found in a wide range of tumors, including ovarian cancers. Elevated PTTG levels were found to induce cellular transformation in vitro and tumor formation in nude mice. Therefore, we hypothesize a correlation exists between the levels of PTTG expression and tumorigenesis, and that downregulation of PTTG levels will result in the suppression of tumor growth. We used small interfering RNA (siRNA) to silence PTTG expression in human A2780 ovarian carcinoma cells and assessed the effect of PTTG silencing in tumor formation in vitro and in vivo. The siRNA directed against PTTG reduced its expression at both the mRNA and protein levels. A fifty percent reduction in cell proliferation was achieved in cells constitutively expressing PTTG siRNA compared to vector or control-siRNA transfected cells. Furthermore, colony formation in soft agar was reduced by 70% in PTTG siRNA stable cell lines. Using nude mice, we showed that animals injected with A2780 cells constitutively expressing PTTG-siRNA decreased the incidence of tumor development and tumor growth. Taken together, these results strongly suggest that PTTG may serve as an important molecular target for the discovery of new anticancer agents and treatment strategies.

Pediatric high-grade gliomas (HGG) are rare aggressive tumors that present a prognostic and therapeutic challenge. Diffuse midline glioma, H3K27M–mutant is a new entity introduced to HGG in the latest WHO classification. In this study we evaluated the presence of H3K27M mutation in 105 tumor samples histologically classified into low-grade gliomas (LGG) (n = 45), and HGG (n = 60). Samples were screened for the mutation in histone H3.3 and H3.1 variants to examine its prevalence, prognostic impact, and assess its potential clinical value in limited resource settings. H3K27M mutation was detected in 28 of 105 (26.7%) samples, and its distribution was significantly associated with midline locations (p-value < 0.0001) and HGG (p-value = 0.003). Overall and event- free survival (OS and EFS, respectively) of patients with mutant tumors did not differ significantly, neither according to histologic grade (OS p-value = 0.736, EFS p-value = 0.75) nor across anatomical sites (OS p-value = 0.068, EFS p-value = 0.153). Detection of H3K27M mutation in pediatric gliomas provides more precise risk stratification compared to traditional histopathological techniques. Hence, mutation detection should be pursued in all pediatric gliomas. Meanwhile, focusing on midline LGG can be an alternative in lower-middle-income countries to maximally optimize patients’ treatment options.

The pituitary tumor transforming gene (PTTG)/securin is an oncogene that is involved in cell cycle regulation and sister chromatid separation. PTTG is highly expressed in various tumors including ovarian tumors, suggesting that PTTG may play a role in ovarian tumorigenesis. Overexpression of PTTG resulted in induction of cellular transformation in vitro and tumor formation in nude mice. To ascertain PTTG function in ovarian tumorigenesis, we generated a transgenic mouse model of PTTG by cloning PTTG cDNA downstream of Mullerian inhibitory substance type II receptor gene promoter (MISIIR) in order to target the ovarian surface epithelium. By screening of transgenic animals, we identified five founders (four males and one female). Using the four male founders, we developed four transgenic lines. PTTG expression was increased in ovarian surface epithelium, ovarian granulosa cells, as well as in the pituitary gland. Transgenic females did not develop any visible ovarian tumors at 8-10 months of age; however, there was an overall increase in the corpus luteum mass in transgenic ovary, suggesting increased luteinization. These changes were associated with an increase in serum LH and testosterone levels. In addition, there was a generalized hypertrophy of the myometrium of MISIIR-PTTG transgenic uteri with cystic glandular and hyperplasia of the endometrium. Based on these results, we conclude that the overexpression of PTTG may be required to initiate precancerous conditions but is not sufficient to induce ovarian tumorigenesis and may require another partner to initiate cellular transformation.

Successful T cell immunotherapy for brain cancer requires that the T cells can access tumour tissues, but this has been difficult to achieve. Here we show that, in contrast to inflammatory brain diseases such as multiple sclerosis, where endothelial cells upregulate ICAM1 and VCAM1 to guide the extravasation of pro-inflammatory cells, cancer endothelium downregulates these molecules to evade immune recognition. By contrast, we found that cancer endothelium upregulates activated leukocyte cell adhesion molecule (ALCAM), which allowed us to overcome this immune-evasion mechanism by creating an ALCAM-restricted homing system (HS). We re-engineered the natural ligand of ALCAM, CD6, in a manner that triggers initial anchorage of T cells to ALCAM and conditionally mediates a secondary wave of adhesion by sensitizing T cells to low-level ICAM1 on the cancer endothelium, thereby creating the adhesion forces necessary to capture T cells from the bloodstream. Cytotoxic HS T cells robustly infiltrated brain cancers after intravenous injection and exhibited potent antitumour activity. We have therefore developed a molecule that targets the delivery of T cells to brain cancer.