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.

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 (OSp-value = 0.736, EFSp-value = 0.75) nor across anatomical sites (OSp-value = 0.068, EFSp-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.

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.