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Angiosarcomas are a rare group of tumours which have poor prognosis and limited treatment options. The development of new therapies has been hampered by a lack of good preclinical models. Here, we describe the development of an autochthonous mouse model of angiosarcoma driven by loss of p53 in VE-cadherin-expressing endothelial cells. Using Cdh5-Cre to drive recombination in adult endothelial cells, mice developed angiosarcomas with 100% penetrance upon homozygous deletion of Trp53 with a median lifespan of 325 days. In contrast, expression of the R172H mutant p53 resulted in formation of thymic lymphomas with a more rapid onset (median lifespan 151 days). We also used Pdgfrb-Cre-expressing mice, allowing us to target predominantly pericytes, as these have been reported as the cell of origin for a number of soft tissue sarcomas. Pdgfrb-Cre also results in low levels of recombination in venous blood endothelial cells in multiple tissues during development. Upon deletion of Trp53 in Pdgfrb-Cre-expressing mice (Pdgfrb-Cre, Trp53fl/fl mice), 65% developed lymphomas and 21% developed pleomorphic undifferentiated soft tissue sarcomas. None developed angiosarcomas. In contrast, 75% of Pdgfrb-Cre, Trp53R172H/R172H mice developed angiosarcomas, with 60% of these mice also developing lymphomas. The median lifespan of the Pdgfrb-Cre, Trp53R172H/R172H mice was 151 days. Re-implantation of angiosarcoma tumour fragments from Cdh5-Cre, Trp53fl/fl mice provided a more consistent and rapid model of angiosarcoma than the two spontaneous models. The ability to passage tumour fragments through the mouse provides a novel model which is amenable to preclinical studies and will help the development of potential new therapies for angiosarcoma., Editor's choice: Deletion of p53, rather than mutation, in endothelial cells leads to reliable angiosarcoma generation, which, along with establishment of a transplantation model, provides a novel approach for testing potential new therapeutics.

Kindler Syndrome (KS) is an autosomal recessive skin disorder characterized by skin blistering and photosensitivity. KS is caused by loss of function mutations in FERMT1, which encodes Kindlin‐1. Kindlin‐1 is a FERM domain containing adaptor protein that is found predominantly at cell‐extracellular matrix adhesions where it binds to integrin β subunits and is required for efficient integrin activation. Using keratinocytes derived from a patient with KS, into which wild type Kindlin‐1 (Kin1WT) has been expressed, we show that Kindlin‐1 binds to cyclin‐dependent kinase (CDK)1 and CDK2. CDK1 and CDK2 are key regulators of cell cycle progression, however, cell cycle analysis showed only small differences between the KS and KS‐Kin1WT keratinocytes. In contrast, G2/M cell cycle arrest in response to oxidative stress induced by hydrogen peroxide (H2O2) was enhanced in KS keratinocytes but not KS‐Kin1WT cells, following inhibition of CDK activity. Furthermore, KS keratinocytes were more sensitive to DNA damage in response to H2O2 and this was exacerbated by treatment with the CDK inhibitor roscovitine. Thus, in Kindlin‐1 deficient keratinocytes, CDK activity can further regulate oxidative damage induced cell cycle arrest and DNA damage. This provides further insight into the key pathways that control sensitivity to oxidative stress in KS patients.

Methylation of DNA at carbon 5 of cytosine is essential for mammalian development and implicated in transcriptional repression of genes and transposons. New patterns of DNA methylation characteristic of lineage-committed cells are established at the exit from pluripotency by de novo DNA methyltransferases enzymes, DNMT3A and DNMT3B, which are regulated by developmental signalling and require access to chromatin-organised DNA. Whether or not the capacity for de novo DNA methylation of developmentally regulated loci is preserved in differentiated somatic cells and can occur in the absence of exogenous signals is currently unknown. Here we demonstrate that fibroblasts derived from chromatin remodelling ATPase LSH (HELLS)-null mouse embryos, which lack DNA methylation from centromeric repeats, transposons and a number of gene promoters, are capable of re-establishing DNA methylation and silencing of miss-regulated genes upon re-expression of LSH. We also show that the ability of LSH to bind ATP and the cellular concentration of DNMT3B are critical for cell-autonomous de novo DNA methylation in somatic cells. These data suggest the existence of cellular memory that persists in differentiated cells through many cell generations and changes in transcriptional state.