First-hit SETBP1 mutations cause a myeloproliferative disorder with bone marrow fibrosis.

ABSTRACT: SETBP1 mutations are found in various clonal myeloid disorders. However, it is unclear whether they can initiate leukemia, because SETBP1 mutations typically appear as later events during oncogenesis. To answer this question, we generated a mouse model expressing mutated SETBP1 in hematopoietic tissue: this model showed profound alterations in the differentiation program of hematopoietic progenitors and developed a myeloid neoplasm with megakaryocytic dysplasia, splenomegaly, and bone marrow fibrosis, prompting us to investigate SETBP1 mutations in a cohort of 36 triple-negative primary myelofibrosis (TN-PMF) cases. We identified 2 distinct subgroups, one carrying SETBP1 mutations and the other completely devoid of somatic variants. Clinically, a striking difference in disease aggressiveness was noted, with patients with SETBP1 mutation showing a much worse clinical course. In contrast to myelodysplastic/myeloproliferative neoplasms, in which SETBP1 mutations are mostly found as a late clonal event, single-cell clonal hierarchy reconstruction in 3 patients with TN-PMF from our cohort revealed SETBP1 to be a very early event, suggesting that the phenotype of the different SETBP1+ disorders may be shaped by the opposite hierarchy of the same clonal SETBP1 variants.

Loss of Lkb1 cooperates with BrafV600E and ultraviolet radiation, increasing melanoma multiplicity and neural-like dedifferentiation.

The mechanisms that work alongside BRAFV600E oncogene in melanoma development, in addition to ultraviolet (UV) radiation (UVR), are of great interest. Analysis of human melanoma tumors [data from The Cancer Genome Atlas (TCGA)] revealed that 50% or more of the samples expressed no or low amounts of serine/threonine protein kinase STK11 (also known as LKB1) protein. Here, we report that, in a mouse model, concomitant neonatal BrafV600E activation and Lkb1 tumor suppressor ablation in melanocytes led to full melanoma development. A single postnatal dose of UVB radiation had no effect on melanoma onset in Lkb1-depleted mice compared with BrafV600E-irradiated mice, but increased tumor multiplicity. In concordance with these findings and previous reports, Lkb1-null irradiated mice exhibited deficient DNA damage repair (DDR). Histologically, tumors lacking Lkb1 were enriched in neural-like tumor morphology. Genetic profiling and gene set enrichment analyses of tumor sample mutated genes indicated that loss of Lkb1 promoted the selection of altered genes associated with neural differentiation processes. Thus, these results suggest that the loss of Lkb1 cooperates with BrafV600E and UVR, impairing the DDR and increasing melanoma multiplicity and neural-like dedifferentiation.