Glioblastoma cellular cross-talk converges on NF-κB to attenuate EGFR inhibitor sensitivity.

In glioblastoma (GBM), heterogeneous expression of amplified and mutated epidermal growth factor receptor (EGFR) presents a substantial challenge for the effective use of EGFR-directed therapeutics. Here we demonstrate that heterogeneous expression of the wild-type receptor and its constitutively active mutant form, EGFRvIII, limits sensitivity to these therapies through an interclonal communication mechanism mediated by interleukin-6 (IL-6) cytokine secreted from EGFRvIII-positive tumor cells. IL-6 activates a NF-κB signaling axis in a paracrine and autocrine manner, leading to bromodomain protein 4 (BRD4)-dependent expression of the prosurvival protein survivin (BIRC5) and attenuation of sensitivity to EGFR tyrosine kinase inhibitors (TKIs). NF-κB and survivin are coordinately up-regulated in GBM patient tumors, and functional inhibition of either protein or BRD4 in in vitro and in vivo models restores sensitivity to EGFR TKIs. These results provide a rationale for improving anti-EGFR therapeutic efficacy through pharmacological uncoupling of a convergence point of NF-κB-mediated survival that is leveraged by an interclonal circuitry mechanism established by intratumoral mutational heterogeneity.

PAX3-FOXO1 controls expression of the p57Kip2 cell-cycle regulator through degradation of EGR1.

The chimeric protein PAX3-FOXO1, resulting from a translocation between chromosomes 2 and 13, is the most common genetic aberration in the alveolar subtype of the human skeletal muscle tumor, rhabdomyosarcoma. To understand how PAX3-FOXO1 contributes to tumor development, we isolated and characterized muscle cells from transgenic mice expressing PAX3-FOXO1 under control of the PAX3 promoter. We demonstrate that these myoblasts are unable to complete myogenic differentiation because of an inability to up-regulate p57Kip2 transcription. This defect is caused by reduced levels of the EGR1 transcriptional activator resulting from a direct, destabilizing interaction with PAX3-FOXO1. Neither PAX3 nor FOXO1 share the ability to regulate p57Kip2 transcription. Thus, the breakage and fusion of the genes encoding these transcription factors creates a unique chimeric protein that controls a key cell-cycle and -differentiation regulator.

Author Correction: Longitudinal assessment of tumor development using cancer avatars derived from genetically engineered pluripotent stem cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Longitudinal assessment of tumor development using cancer avatars derived from genetically engineered pluripotent stem cells.

Many cellular models aimed at elucidating cancer biology do not recapitulate pathobiology including tumor heterogeneity, an inherent feature of cancer that underlies treatment resistance. Here we introduce a cancer modeling paradigm using genetically engineered human pluripotent stem cells (hiPSCs) that captures authentic cancer pathobiology. Orthotopic engraftment of the neural progenitor cells derived from hiPSCs that have been genome-edited to contain tumor-associated genetic driver mutations revealed by The Cancer Genome Atlas project for glioblastoma (GBM) results in formation of high-grade gliomas. Similar to patient-derived GBM, these models harbor inter-tumor heterogeneity resembling different GBM molecular subtypes, intra-tumor heterogeneity, and extrachromosomal DNA amplification. Re-engraftment of these primary tumor neurospheres generates secondary tumors with features characteristic of patient samples and present mutation-dependent patterns of tumor evolution. These cancer avatar models provide a platform for comprehensive longitudinal assessment of human tumor development as governed by molecular subtype mutations and lineage-restricted differentiation.

Inhibition of Nuclear PTEN Tyrosine Phosphorylation Enhances Glioma Radiation Sensitivity through Attenuated DNA Repair.

Ionizing radiation (IR) and chemotherapy are standard-of-care treatments for glioblastoma (GBM) patients and both result in DNA damage, however, the clinical efficacy is limited due to therapeutic resistance. We identified a mechanism of such resistance mediated by phosphorylation of PTEN on tyrosine 240 (pY240-PTEN) by FGFR2. pY240-PTEN is rapidly elevated and bound to chromatin through interaction with Ki-67 in response to IR treatment and facilitates the recruitment of RAD51 to promote DNA repair. Blocking Y240 phosphorylation confers radiation sensitivity to tumors and extends survival in GBM preclinical models. Y240F-Pten knockin mice showed radiation sensitivity. These results suggest that FGFR-mediated pY240-PTEN is a key mechanism of radiation resistance and is an actionable target for improving radiotherapy efficacy.

Publisher Correction: PTEN regulates glioblastoma oncogenesis through chromatin-associated complexes of DAXX and histone H3.3.

This corrects the article DOI: 10.1038/ncomms15223.

PTEN regulates glioblastoma oncogenesis through chromatin-associated complexes of DAXX and histone H3.3.

Glioblastoma (GBM) is the most lethal type of human brain cancer, where deletions and mutations in the tumour suppressor gene PTEN (phosphatase and tensin homolog) are frequent events and are associated with therapeutic resistance. Herein, we report a novel chromatin-associated function of PTEN in complex with the histone chaperone DAXX and the histone variant H3.3. We show that PTEN interacts with DAXX and, in turn PTEN directly regulates oncogene expression by modulating DAXX-H3.3 association on the chromatin, independently of PTEN enzymatic activity. Furthermore, DAXX inhibition specifically suppresses tumour growth and improves the survival of orthotopically engrafted mice implanted with human PTEN-deficient glioma samples, associated with global H3.3 genomic distribution changes leading to upregulation of tumour suppressor genes and downregulation of oncogenes. Moreover, DAXX expression anti-correlates with PTEN expression in GBM patient samples. Since loss of chromosome 10 and PTEN are common events in cancer, this synthetic growth defect mediated by DAXX suppression represents a therapeutic opportunity to inhibit tumorigenesis specifically in the context of PTEN deletion.

Guilt by association: PAX3-FOXO1 regulates gene expression through selective destabilization of the EGR1 transcription factor.

Human cancer cells frequently harbor chromosomal translocations that create chimeric fusion genes. The t(2;13) translocation is characteristic of the pediatric muscle tumor, alveolar rhabdomyosarcoma, and produces the chimeric transcription factor, PAX3-FOXO1, that contains the DNA binding elements of PAX3 and the transcriptional activation domain of FOXO1. Experiments designed to determine how PAX3-FOXO1 expression contributes to the development of muscle cell-derived tumors resulted in the discovery that the fusion protein misregulates gene expression and interrupts myogenic differentiation through a unique gain of function mechanism. These results yield new insight into how tumor-associated genetic alterations increase the likelihood of cancer formation and may lead to new therapeutic approaches.

Disruption of forkhead transcription factor (FOXO) family members in mice reveals their functional diversification.

Genetic analysis in Caenorhabditis elegans has uncovered essential roles for DAF-16 in longevity, metabolism, and reproduction. The mammalian orthologs of DAF-16, the closely-related FOXO subclass of forkhead transcription factors (FKHR/FOXO1, FKHRL1/FOXO3a, and AFX/FOXO4), also have important roles in cell cycle arrest, apoptosis and stress responses in vitro, but their in vivo physiological roles are largely unknown. To elucidate their role in normal development and physiology, we disrupted each of the Foxo genes in mice. Foxo1-null embryos died on embryonic day 10.5 as a consequence of incomplete vascular development. Foxo1-null embryonic and yolk sac vessels were not well developed at embryonic day 9.5, and Foxo1 expression was found in a variety of embryonic vessels, suggesting a crucial role of this transcription factor in vascular formation. On the other hand, both Foxo3a- and Foxo4-null mice were viable and grossly indistinguishable from their littermate controls, indicating dispensability of these two members of the Foxo transcription factor family for normal vascular development. Foxo3a-null females showed age-dependent infertility and had abnormal ovarian follicular development. In contrast, histological analyses of Foxo4-null mice did not identify any consistent abnormalities. These results demonstrate that the physiological roles of Foxo genes are functionally diverse in mammals.