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 (FKHR͞FOXO1, FKHRL1͞FOXO3a, and AFX͞FOXO4), 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.

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.

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Highlights d Phosphorylation of PTEN at tyrosine 240 (pY240) by FGFR2 mediates IR resistance d pY240-PTEN plays a critical role in DNA damage repair d pY240-PTEN associates with chromatin DNA through interaction with Ki-67 d Blocking pY240-PTEN using FGFR inhibitors sensitizes tumors to ionizing radiation