New somatic BRAF splicing mutation in Langerhans cell histiocytosis

Abstract

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia with constitutive activation of the MAPKinase RAS-RAF-MEK-ERK cell signaling pathway. We analyzed 9 LCH cases without BRAF V600 and MAP2K1 mutations by whole exome sequencing. We identified a new somatic BRAF splicing mutation in 2 cases. Both cases were childhood single system (SS) LCH cases, with self-healing outcome of the bone lesions. This mutant consisted in a 9 base pair duplication (c.1511_1517 + 2 duplication), encoding for a predicted mutant protein with insertion of 3 amino acids (p.Arg506_Lys507insLeuLeuArg) in the N-terminal lobe of the kinase domain of BRAF. Transient expression of the c.1511_1517 + 2dup BRAF mutant in HEK293 cells enhanced MAPKinase pathway activation, and was not inhibited by vemurafenib but was inhibited by PLX8394, a second-generation BRAF inhibitor able to inhibit signaling of BRAF monomers and dimers. Future LCH molecular screening panel should include this new mutation to better define its prevalence in LCH and its restriction to autoregressive bone SS LCH.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-017-0690-z) contains supplementary material, which is available to authorized users.

Langerhans cell histiocytosis in adults: Advances in pathophysiology and treatment

“…The introduction of next-generation sequencing analyses, such as whole exome/genome sequencing and targeted sequencing, has revealed several BRAF mutations in addition to V600E, including V600D, 600DLAT in-flame insertion, germ line T599A mutation, deletions in the β3-αC loop of the kinase domain (485_490LNVTAP>F, NVTAP486del, and 486_491NVTAPT>K), and a splicing mutation at the end of exon 12 (R506_K507insLLR) (Figure 1). [20][21][22] The kinase activity of these mutations has not been fully evaluated, but they might function similarly to BRAF-V600E, resulting in constitutive activation of BRAF. Additionally, BRAF-G466R, a missense mutation in the kinase domain of BRAF, has been described in LCH, although its function is also unknown.…”

Extracellular signal‐regulated kinase activation of self‐healing Langerhans cell histiocytosis: A case report

“…4 Previous studies have also revealed the presence of abnormal splicing of BRAF or MAP2K1 mutations in BRAF V600E-negative LCH. 2,10 Thus, LCH is considered to be driven by the following pathogenic mechanisms: during the differentiation process of bone marrow stem cells to the monocyte and dendritic cell lineages, somatic mutations such as BRAF occur and constitutively activate the MAPK signaling pathways; consequently, the downstream ERK is activated, thereby resulting in neoplastic formation of Langerhans cell-like cells. 3,11 In the present case, immunostaining of the affected skin tissue also confirmed sustained p-ERK expression in LCH tumor cells.…”

“…Its clinical manifestations vary widely and range from spontaneously resolving symptoms with a favorable prognosis to apparent neoplastic proliferation with a poor prognosis. LCH tumor cells harbor somatic mutations in BRAF genes ( V600E ) as observed in melanoma; abnormalities in splicing of the genes and the activation of the mitogen‐activated protein kinase (MAPK) pathway is thought to be associated with the pathogenesis of LCH . The disease types and prognosis of LCH are determined by the differentiation stage of stem cells into myeloid dendritic cells that acquire the above‐described mutations .…”

“…LCH tumor cells harbor somatic mutations in BRAF genes (V600E) as observed in melanoma; abnormalities in splicing of the genes and the activation of the mitogen-activated protein kinase (MAPK) pathway is thought to be associated with the pathogenesis of LCH. 1,2 The disease types and prognosis of LCH are determined by the differentiation stage of stem cells into myeloid dendritic cells that acquire the above-described mutations. 3 Herein, we present a case of single-system and skin-limited LCH that spontaneously resolved in an infant.…”

Progress towards molecular-based management of childhood Langerhans cell histiocytosis

“…Recurrent mutations (mainly deletions) in exons 2 and 3 of the MAP2K1 gene, which encodes MEK1, the BRAF downstream protein in the MAPKinase pathway, was reported in 15-20% of LCH cases [27,28]. Also, small in-frame BRAF deletions or insertions localized to exon 12, which encodes for the small N-terminal lobe of the BRAF kinase domain, were reported in 5-10% of LCH cases [27,29]. Finally, single cases of mutations of other genes that transcribe MAPKinase pathway proteins have been reported, such as a FAM73A-BRAF fusion [27], a MAP3K1 mutation [28], and an ARAF mutation [30].…”