Myo-differentiation reporter screen reveals NF-Y as an activator of PAX3-FOXO1 in rhabdomyosarcoma.

Recurrent chromosomal rearrangements found in rhabdomyosarcoma (RMS) produce the PAX3-FOXO1 fusion protein, which is an oncogenic driver and a dependency in this disease. One important function of PAX3-FOXO1 is to arrest myogenic differentiation, which is linked to the ability of RMS cells to gain an unlimited proliferation potential. Here, we developed a phenotypic screening strategy for identifying factors that collaborate with PAX3-FOXO1 to block myo-differentiation in RMS. Unlike most genes evaluated in our screen, we found that loss of any of the three subunits of the Nuclear Factor Y (NF-Y) complex leads to a myo-differentiation phenotype that resembles the effect of inactivating PAX3-FOXO1. While the transcriptomes of NF-Y- and PAX3-FOXO1-deficient RMS cells bear remarkable similarity to one another, we found that these two transcription factors occupy nonoverlapping sites along the genome: NF-Y preferentially occupies promoters, whereas PAX3-FOXO1 primarily binds to distal enhancers. By integrating multiple functional approaches, we map the PAX3 promoter as the point of intersection between these two regulators. We show that NF-Y occupies CCAAT motifs present upstream of PAX3 to function as a transcriptional activator of PAX3-FOXO1 expression in RMS. These findings reveal a critical upstream role of NF-Y in the oncogenic PAX3-FOXO1 pathway, highlighting how a broadly essential transcription factor can perform tumor-specific roles in governing cellular state.

The influence of the bolus-surface distance on the dose distribution in the build-up region.

AIM: The aim of the paper is to examine the relation between the increase of the photon dose in water in the region of electronic disequilibrium - so-called build-up region - and the distance of the bolus from the water surface for the applied parameters of X-ray beams. MATERIALS AND METHODS: PDD measurements were carried out using the plane-parallel ionization chamber Markus in the automatic water phantom IBA BluePhantom with OmniPro-Accept V7 (IBA Dosimetry GmbH, Schwarzenbruck, Germany). All measurements were performed for different field sizes and for 6 MV and 15 MV X-ray beams, respectively. A water-equivalent RW3 slab (Goettingen White Water) produced by PTW was used as a bolus. RESULTS: Placing a bolus in an irradiated field changes the shape of the PDD curve in the build-up region in comparison with the one obtained for an open field. All results has been inserted in tables and figures. CONCLUSION: The closer the bolus is to the water surface, the smaller the depth of the maximum dose in the phantom for all investigated fields and energies. The changes in the build-up region are important, even if the bolus does not touch the surface of the water phantom. The influence of the bolus can be ignored when the bolus-surface distance equals 25 cm for 6MV X-ray beams and 39 cm for 15 MV X-ray beams.