Genetic signature of histiocytic sarcoma revealed by a sleeping beauty transposon genetic screen in mice.

Histiocytic sarcoma is a rare, aggressive neoplasm that responds poorly to therapy. Histiocytic sarcoma is thought to arise from macrophage precursor cells via genetic changes that are largely undefined. To improve our understanding of the etiology of histiocytic sarcoma we conducted a forward genetic screen in mice using the Sleeping Beauty transposon as a mutagen to identify genetic drivers of histiocytic sarcoma. Sleeping Beauty mutagenesis was targeted to myeloid lineage cells using the Lysozyme2 promoter. Mice with activated Sleeping Beauty mutagenesis had significantly shortened lifespan and the majority of these mice developed tumors resembling human histiocytic sarcoma. Analysis of transposon insertions identified 27 common insertion sites containing 28 candidate cancer genes. Several of these genes are known drivers of hematological neoplasms, like Raf1, Fli1, and Mitf, while others are well-known cancer genes, including Nf1, Myc, Jak2, and Pten. Importantly, several new potential drivers of histiocytic sarcoma were identified and could serve as targets for therapy for histiocytic sarcoma patients

Kaplan Meier Survival Curve showing decreased survival in triple transgenic experimental animals compared to double transgenic controls.

<p>Significance determined using Logrank test.</p

Kaplan Meier Survival Curve showing decreased survival in triple transgenic experimental animals compared to double transgenic controls.

<p>Significance determined using Logrank test.</p

Representative images of tumor tissue.

<p>A) Disseminated HS in pancreas, liver, and thoracic cavity. B) HS adhering to peritoneum. C) HS within the thoracic cavity.</p

Eight candidate cooperating genes in HS.

<p>Eight candidate cooperating genes in HS.</p

Stat5 is critical for the development and maintenance of myeloproliferative neoplasm initiated by Nf1 deficiency

Juvenile myelomonocytic leukemia is a rare myeloproliferative neoplasm characterized by hyperactive RAS signaling. Neurofibromin1 (encoded by the NF1 gene) is a negative regulator of RAS activation. Patients with neurofibromatosis type 1 harbor loss-of-function mutations in NF1 and have a 200- to 500-fold increased risk of juvenile myelomonocytic leukemia. Leukemia cells from patients with juvenile myelomonocytic leukemia display hypersensitivity to certain cytokines, such as granulocyte-macrophage colony-stimulating factor. The granulocyte-macrophage colony-stimulating factor receptor utilizes pre-associated JAK2 to initiate signals after ligand binding. JAK2 subsequently activates STAT5, among other downstream effectors. Although STAT5 is gaining recognition as an important mediator of growth factor signaling in myeloid leukemias, the contribution of STAT5 to the development of hyperactive RAS-initiated myeloproliferative disease has not been well described. In this study, we investigated the consequence of STAT5 attenuation via genetic and pharmacological approaches in Nf1-deficient murine models of juvenile myelomonocytic leukemia. We found that homozygous Stat5 deficiency extended the lifespan of Nf1-deficient mice and eliminated the development of myeloproliferative neoplasm associated with Nf1 gene loss. Likewise, we found that JAK inhibition with ruxolitinib attenuated myeloproliferative neoplasm in Nf1-deficient mice. Finally, we found that primary cells from a patient with KRAS-mutant juvenile myelomonocytic leukemia displayed reduced colony formation in response to JAK2 inhibition. Our findings establish a central role for STAT5 activation in the pathogenesis of juvenile myelomonocytic leukemia and suggest that targeting this pathway may be of clinical utility in these patients