Histone 3.3 hotspot mutations in conventional osteosarcomas: a comprehensive clinical and molecular characterization of six H3F3A mutated cases

Background: Histone 3.3 (H3.3) hotspot mutations in bone tumors occur in the vast majority of giant cell tumors of bone (GCTBs; 96%), chondroblastomas (95%) and in a few cases of osteosarcomas. However, clinical presentation, histopathological features, and additional molecular characteristics of H3.3 mutant osteosarcomas are largely unknown. Methods: In this multicentre, retrospective study, a total of 106 conventional high-grade osteosarcomas, across all age groups were re-examined for hotspot mutations in the H3.3 coding genes H3F3A and H3F3B. H3.3 mutant osteosarcomas were re-evaluated in a multidisciplinary manner and analyzed for genome-wide DNA-methylation patterns and DNA copy number aberrations alongside H3.3 wild-type osteosarcomas and H3F3A G34W/L mutant GCTBs. Results: Six osteosarcomas (6/106) carried H3F3A hotspot mutations. No mutations were found in H3F3B. All patients with H3F3A mutant osteosarcoma were older than 30 years with a median age of 65 years. Copy number aberrations that are commonly encountered in high-grade osteosarcomas also occurred in H3F3A mutant osteosarcomas. Unlike a single osteosarcoma with a H3F3A K27M mutation, the DNA methylation profiles of H3F3A G34W/R mutant osteosarcomas were clearly different from H3.3 wild-type osteosarcomas, but more closely related to GCTBs. The most differentially methylated promoters between H3F3A G34W/R mutant and H3.3 wild-type osteosarcomas were in KLLN/PTEN (p < 0.00005) and HIST1H2BB (p < 0.0005). Conclusions: H3.3 mutations in osteosarcomas may occur in H3F3A at mutational hotspots. They are overall rare, but become more frequent in osteosarcoma patients older than 30 years. Osteosarcomas carrying H3F3A G34W/R mutations are associated with epigenetic dysregulation of KLLN/PTEN and HIST1H2BB

Hepatoma-derived growth factor-related protein 2 promotes DNA repair by homologous recombination

We have recently identified lens epithelium-derived growth factor (LEDGF/p75, also known as PSIP1) as a component of the homologous recombination DNA repair machinery. Through its Pro-Trp-Trp-Pro (PWWP) domain, LEDGF/p75 binds to histone marks associated with active transcription and promotes DNA end resection by recruiting DNA endonuclease retinoblastoma-binding protein 8 (RBBP8/CtIP) to broken DNA ends. Here we show that the structurally related PWWP domain-containing protein, hepatoma-derived growth factor-related protein 2 (HDGFRP2), serves a similar function in homologous recombination repair. Its depletion compromises the survival of human U2OS osteosarcoma and HeLa cervix carcinoma cells and impairs the DNA damage-induced phosphorylation of replication protein A2 (RPA2) and the recruitment of DNA endonuclease RBBP8/CtIP to DNA double strand breaks. In contrast to LEDGF/p75, HDGFRP2 binds preferentially to histone marks characteristic for transcriptionally silent chromatin. Accordingly, HDGFRP2 is found in complex with the heterochromatin-binding chromobox homologue 1 (CBX1) and Pogo transposable element with ZNF domain (POGZ). Supporting the functionality of this complex, POGZ-depleted cells show a similar defect in DNA damage-induced RPA2 phosphorylation as HDGFRP2-depleted cells. These data suggest that HDGFRP2, possibly in complex with POGZ, recruits homologous recombination repair machinery to damaged silent genes or to active genes silenced upon DNA damage

MOESM2 of Histone 3.3 hotspot mutations in conventional osteosarcomas: a comprehensive clinical and molecular characterization of six H3F3A mutated cases

Additional file 2: Figure S1. Radiological data of H3F3A mutant osteosarcomas. (A) Case 77896: anteroposterior and lateral radiograph of the left wrist. Arrows indicate toward the lesion with permeated growth pattern (moth-eaten) and periosteal reaction. (B) Case 84676: anteroposterior and lateral radiograph (upper panel) with arrows indicating a large soft tissue mass with prominent mineralization and corresponding sagittal T1- and fat-saturated proton-weighted MR image (lower panel) of the right knee. The tumor involves the adjacent epiphyses through the epiphyseal growth plate (arrow). (C) Case 94316: anteroposterior and lateral radiograph (upper panel) and corresponding sagittal T1-weighted MR image (lower panel left) of the right knee. The MR image shows the intact bone cortex in the cranial part of the lesion (white arrows), but cortical disruption with “wrap-around” sign in the caudal part of the lesion. Anteroposterior radiograph (lower panel right) shows the local recurrence in the soft tissue adjacent to the knee joint prosthesis. (D) Case 84712: anteroposterior and lateral radiograph (upper panel) and corresponding axial T1-weighted and sagittal fat-saturated proton-weighted MR image (lower panel) of the right knee. Arrows indicate periosteal reaction and cortical disruption. (E) Case 94314: anteroposterior radiograph (upper panel, left), coronal fat-saturated T1-weighted MR image after administration of gadolinium contrast agent (upper panel, right) and coronal T1-weighted MR image (lower panel, left) of the right hip. Thickened bone cortex (arrow-heads, hypointense fibrous structure) is wrapped by the lesion. Anteroposterior radiograph (lower panel, right) after hip joint replacement