MAP2K1 and MAP3K1 mutations in langerhans cell histiocytosis

Abstract

Langerhans cell histiocytosis (LCH) is now understood to be a neoplastic disease in which over 50% of cases have somatic activating mutations of BRAF. However, the extracellular signal-related (ERK) pathway is activated in all cases including those with wild type BRAF alleles. Here, we applied a targeted massively parallel sequencing panel to 30 LCH samples to test for the presence of additional genetic alterations that might cause ERK pathway activation. In 20 BRAF wild type samples, we found 3 somatic mutations in MAP2K1 (MEK1) including C121S and C121S/G128D in the kinase domain, and 56_61QKQKVG>R, an in-frame deletion in the N-terminal regulatory domain. All three variant proteins constitutively phosphorylated ERK in in vitro kinase assays. The C121S/G128D and 56_61QKQKVG>R variants were resistant to the mitogen-activated protein kinase kinase (MEK) inhibitor trametinib in vitro. Within the entire sample set, we found 3 specimens with mutations in MAP3K1 (MEKK1), including two truncation mutants, T779fs and T1481fs; T1481fs encoded an unstable and nonfunctional protein when expressed in vitro. T779fs was present in a specimen carrying BRAF V600E. The third variant was a single nucleotide substitution, E1286V, which was fully functional and is likely a germline polymorphism. These results indicate that LCH cells can harbor additional genetic alterations in the RAS-RAF-MEK pathway which, in the case of MAP2K1, may be responsible for ERK activation in a wild type BRAF setting. The resistance of some of these variants to trametinib may also have clinical implications for the combined use of RAF and MEK inhibitors in LCH.

Rosai–Dorfman Disease Harboring an Activating KRAS K117N Missense Mutation

“…In summary, here we present a case of RDD involving the salivary gland harboring an activating KRAS mutation, suggesting that at least a subset of RDD cases may be clonal processes, which is also consistent with the findings from other recently published work by other authors [31]. Further mutational studies on this rare histiocytic disease should be undertaken to better characterize its pathogenesis as well as open up potential avenues for therapy.…”

“…However, recent studies have highlighted the role of the RAS/RAF/ERK (MAPK) pathway in the pathogenesis of several histiocytic disorders, although few cases of RDD have been evaluated [5][6][7][8][9]31]. The RAS/RAF/ERK (MAPK) pathway is involved in various cellular functions including cellular proliferation, differentiation, and migration; mutation of genes involved in this pathway has been implicated in oncogenesis [32].…”

Revised classification of histiocytoses and neoplasms of the macrophage-dendritic cell lineages

“…Rare mutations in other MAPK pathway members including ARAF and MAP3K1 have also been reported. 39,40 Finally, mutations affecting other signaling pathway such as PIK3CA, PICK1, and PICK3R2 have also been described in LCH. 37,41 The presence of BRAF mutations has been investigated in nonLCHs.…”

Biological and clinical significance of somatic mutations in Langerhans cell histiocytosis and related histiocytic neoplastic disorders

“…Targeted sequencing studies identified MAP2K1 mutations in 15%-50% of cases with wild-type BRAF (Figure 2). 20,21 Another WES study of 3 LCH cases revealed 1 lesion with BRAF-V600E, 1 with a complex somatic activating mutation in ARAF, and 1 without MAPK gene mutations identified. As in our series, Nelson et al also described a very low overall rate of somatic mutations.…”

“…23 Recurrent loss-of-function mutations in MAP3K1, encoding MEKK1 (which primarily impacts JNK signaling but also interacts with MAPK pathway) that are not exclusive to BRAF have also been described in a targeted sequencing approach in 3/30 LCH cases, but were not detected in our WES study of 41 LCH lesions. 21 Larger series will be required to determine the frequency and functional significance of recurrent mutations in pathways outside of MAPK signaling. The role of acquired modifying mutations or development of subclonal populations also requires further investigation.…”