Mis-splicing Drives Loss of Function of p53E224D Point Mutation.

Background: Tp53 is the most commonly mutated gene in cancer. Canonical Tp53 DNA damage response pathways are well characterized and classically thought to underlie the tumor suppressive effect of Tp53. Challenging this dogma, mouse models have revealed that p53 driven apoptosis and cell cycle arrest are dispensable for tumor suppression. Here, we investigated the inverse context of a p53 mutation predicted to drive expression of canonical targets, but is detected in human cancer. Methods: We established a novel mouse model with a single base pair mutation (GAG>GAC, p53E221D) in the DNA-Binding domain that has wild-type function in screening assays, but is paradoxically found in human cancer in Li-Fraumeni syndrome. Using mouse p53E221D and the analogous human p53E224D mutant, we evaluated expression, transcriptional activation, and tumor suppression in vitro and in vivo. Results: Expression of human p53E224D from cDNA translated to a fully functional p53 protein. However, p53E221D/E221D RNA transcribed from the endogenous locus is mis-spliced resulting in nonsense mediated decay. Moreover, fibroblasts derived from p53E221D/E221D mice do not express a detectable protein product. Mice homozygous for p53E221D exhibited increased tumor penetrance and decreased life expectancy compared to p53 WT animals. Conclusions: Mouse p53E221D and human p53E224D mutations lead to splice variation and a biologically relevant p53 loss of function in vitro and in vivo.

Radiation-Induced Phosphorylation of a Prion-Like Domain Regulates Transformation by FUS-CHOP.

Chromosomal translocations generate oncogenic fusion proteins in approximately one-third of sarcomas, but how these proteins promote tumorigenesis is not well understood. Interestingly, some translocation-driven cancers exhibit dramatic clinical responses to therapy, such as radiotherapy, although the precise mechanism has not been elucidated. Here we reveal a molecular mechanism by which the fusion oncoprotein FUS-CHOP promotes tumor maintenance that also explains the remarkable sensitivity of myxoid liposarcomas to radiation therapy. FUS-CHOP interacted with chromatin remodeling complexes to regulate sarcoma cell proliferation. One of these chromatin remodelers, SNF2H, colocalized with FUS-CHOP genome-wide at active enhancers. Following ionizing radiation, DNA damage response kinases phosphorylated the prion-like domain of FUS-CHOP to impede these protein-protein interactions, which are required for transformation. Therefore, the DNA damage response after irradiation disrupted oncogenic targeting of chromatin remodelers required for FUS-CHOP-driven sarcomagenesis. This mechanism of disruption links phosphorylation of the prion-like domain of an oncogenic fusion protein to DNA damage after ionizing radiation and reveals that a dependence on oncogenic chromatin remodeling underlies sensitivity to radiation therapy in myxoid liposarcoma. SIGNIFICANCE: Prion-like domains, which are frequently translocated in cancers as oncogenic fusion proteins that drive global epigenetic changes, confer sensitivity to radiation via disruption of oncogenic interactions.

Successful Treatment of Painful Cutaneous Vasculopathy With Rivaroxaban in a Patient With Systemic Lupus Erythematosus.

Novel oral anticoagulant (NOAC) medications have revolutionized hematology and cardiology. Recently, NOACs have demonstrated additional promise in dermatology. Specifically, rivaroxaban, a direct factor Xa inhibitor NOAC, has been shown to be successful in the treatment of livedoid vasculopathy. Herein, we describe a patient with systemic lupus erythematosus who presented with painful cutaneous vasculopathy, demonstrated on biopsy with occlusive microvascular fibrin thrombi without evidence of concurrent vasculitis. Interestingly, imaging and laboratory studies did not show evidence of hypercoagulability, arterial disease, or embolic disease. The patient’s vasculopathy and pain progressed despite antiplatelet therapy, often considered first-line in cases of microvascular occlusive disease. However, with rivaroxaban therapy, the patient experienced complete regression of her painful lesions, thereby supporting a further role for NOACs in cutaneous vasculopathy treatment. J Drugs Dermatol. 2020;19(5) doi:10.36849/JDD.2020.4684.

The Fusion Oncogene FUS-CHOP Drives Sarcomagenesis of High-Grade Spindle Cell Sarcomas in Mice.

Myxoid liposarcoma is a malignant soft tissue sarcoma characterized by a pathognomonic t(12;16)(q13;p11) translocation that produces a fusion oncoprotein, FUS-CHOP. This cancer is remarkably sensitive to radiotherapy and exhibits a unique pattern of extrapulmonary metastasis. Here, we report the generation and characterization of a spatially and temporally restricted mouse model of sarcoma driven by FUS-CHOP. Using different Cre drivers in the adipocyte lineage, we initiated in vivo tumorigenesis by expressing FUS-CHOP in Prrx1+ mesenchymal progenitor cells. In contrast, expression of FUS-CHOP in more differentiated cells does not form tumors in vivo, and early expression of the oncoprotein during embryogenesis is lethal. We also employ in vivo electroporation and CRISPR technology to rapidly generate spatially and temporally restricted mouse models of high-grade FUS-CHOP-driven sarcomas for preclinical studies.

CSF-1R-Dependent Lethal Hepatotoxicity When Agonistic CD40 Antibody Is Given before but Not after Chemotherapy.

Cancer immunotherapies are increasingly effective in the clinic, especially immune checkpoint blockade delivered to patients who have T cell-infiltrated tumors. Agonistic CD40 mAb promotes stromal degradation and, in combination with chemotherapy, drives T cell infiltration and de novo responses against tumors, rendering resistant tumors susceptible to current immunotherapies. Partnering anti-CD40 with different treatments is an attractive approach for the next phase of cancer immunotherapies, with a number of clinical trials using anti-CD40 combinations ongoing, but the optimal therapeutic regimens with anti-CD40 are not well understood. Pancreatic ductal adenocarcinoma (PDA) is classically resistant to immunotherapy and lacks baseline T cell infiltration. In this study, we used a tumor cell line derived from a genetically engineered mouse model of PDA to investigate alterations in the sequence of anti-CD40 and chemotherapy as an approach to enhance pharmacological delivery of chemotherapy. Unexpectedly, despite our previous studies showing anti-CD40 treatment after chemotherapy is safe in both mice and patients with PDA, we report in this article that anti-CD40 administration <3 d in advance of chemotherapy is lethal in more than half of treated C57BL/6 mice. Anti-CD40 treatment 2 or 3 d before chemotherapy resulted in significantly increased populations of both activated myeloid cells and macrophages and lethal hepatotoxicity. Liver damage was fully abrogated when macrophage activation was blocked using anti-CSF-1R mAb. These studies highlight the dual nature of CD40 in activating both macrophages and T cell responses, and the need for preclinical investigation of optimal anti-CD40 treatment regimens for safe design of clinical trials.