Summary Skeletal muscle differentiation requires a cascade of transcriptional events to control the spatial and temporal expression of muscle-specific genes. Until recently, muscle-specific transcription was primarily attributed to prototypic enhancer-binding factors while the role of core promoter recognition complexes in directing myogenesis remained unknown. Here, we report the development of a purified reconstituted system to analyze the properties of a TAF3/TRF3 complex in directing transcription initiation at the Myogenin promoter. Importantly, this new complex is required to replace the canonical TFIID to recapitulate MyoD-dependent activation of Myogenin. In vitro and cell-based assays identify a domain of TAF3 that mediates co-activator functions targeted by MyoD. Our findings also suggest changes to CRSP/Mediator in terminally differentiated myotubes. This switching of the core promoter recognition complex during myogenesis allows a more balanced division of labor between activators and TAF coactivators thus providing another strategy to accommodate cell-specific regulation during metazoan development.

Due to its molecular heterogeneity and infiltrative nature, glioblastoma multiforme (GBM) is notoriously resistant to traditional and experimental therapeutics. To overcome these hurdles, targeted agents have been combined with conventional therapy. We evaluated the preclinical potential of a novel, orally bioavailable PI3K/mTOR dual inhibitor (XL765) in in vitro and in vivo studies. In vivo serially passaged human GBM xenografts that are more genetically stable than GBM cell lines in culture were used for all experiments. Biochemical downstream changes were evaluated by immunoblot and cytotoxicity by colorimetric ATP-based assay. For in vivo experiments, human xenograft GBM 39 grown intracranially in nude mice was altered to express luciferase to monitor tumor burden by optical imaging. XL765 resulted in concentration-dependent decreases in cell viability in vitro. Cytotoxic doses resulted in specific inhibition of PI3K signaling. Combining XL765 with temozolomide (TMZ) resulted in additive toxicity in 4 of 5 xenografts. In vivo, XL765 administered by oral gavage resulted in greater than 12-fold reduction in median tumor bioluminescence compared with control (Mann-Whitney test p = 0.001) and improvement in median survival (logrank p = 0.05). TMZ alone showed a 30-fold decrease in median bioluminescence, but the combination XL765 + TMZ yielded a 140-fold reduction in median bioluminescence (Mann-Whitney test p = 0.05) with a trend toward improvement in median survival (logrank p = 0.09) compared with TMZ alone. XL765 shows activity as monotherapy and in combination with conventional therapeutics in a range of genetically diverse GBM xenografts.

Histone deacetylase (HDAC) inhibitors can radiosensitize cancer cells. Radiation is critical in high-risk neuroblastoma treatment, and combinations of HDAC inhibitor vorinostat and radiation are proposed for neuroblastoma trials. Therefore, we investigated radiosensitizing effects of vorinostat in neuroblastoma. Treatment of neuroblastoma cell lines decreased cell viability and resulted in additive effects with radiation. In a murine metastatic neuroblastoma in vivo model vorinostat and radiation combinations decreased tumor volumes compared to single modality. DNA repair enzyme Ku-86 was reduced in several neuroblastoma cells treated with vorinostat. Thus, vorinostat potentiates anti-neoplastic effects of radiation in neuroblastoma possibly due to down-regulation of DNA repair enzyme Ku-86.