GBMs undergo genetic lesions that affect the epigenomic machinery that controls histone modifications, DNA methylation and gene expression. One such target is the histone H3 variant, H3.3, which is incorporated into chromatin in a cell cycle independent manner and is associated with transcriptionally active and silent chromatin in somatic and embryonic cells. Histone chaperones that are involved in the recruitment of H3.3 to chromatin are DAXX (death-domain associated protein), ATRX (alpha-thalassemia /mental retardation X-linked syndrome protein) and HIRA (histone cell cycle regulator). We discovered a novel chromatin-associated function of the PTEN tumor suppressor that represses oncogene expression and tumor growth in patient-derived glioma xenografts, through association with the DAXX-H3.3 complex. Our data show that DAXX physically interacts with PTEN, and PTEN regulates H3.3 loading on chromatin by limiting DAXX interactions with this histone, and thereby controls expression of several tumor-promoting genes. Moreover, DAXX inhibition affects global H3.3 deposition and gene expression, specifically suppresses intracranial tumor growth and significantly improves the survival of PTEN-null glioma-bearing mice. These results demonstrate a synthetic growth defect that occurs due to loss of these two tumor suppressor genes.