title: Alternative genetic mechanisms of BRAF activation in Langerhans cell histiocytosis.
abstract: Langerhans cell histiocytosis (LCH) is characterized by inflammatory lesions containing pathologic CD207+dendritic cells with constitutively activated ERK. Mutually exclusive somatic mutations in MAPK pathway genes have been identified in ∼75% of LCH cases, including recurrent BRAF-V600E and MAP2K1 mutations. To elucidate mechanisms of ERK activation in the remaining 25% of patients, we performed whole-exome sequencing (WES, n = 6), targeted BRAF sequencing (n = 19), and/or whole-transcriptome sequencing (RNA-seq, n = 6) on 24 LCH patient samples lacking BRAF-V600E or MAP2K1 mutations. WES and BRAF sequencing identified in-frame BRAF deletions in the β3-αC loop in 6 lesions. RNA-seq revealed one case with an in-frame FAM73A-BRAF fusion lacking the BRAF autoinhibitory regulatory domain but retaining an intact kinase domain. High levels of phospho-ERK were detected in vitro in cells overexpressing either BRAF fusion or deletion constructs and ex vivo in CD207+cells from lesions. ERK activation was resistant to BRAF-V600E inhibition, but responsive to both a second-generation BRAF inhibitor and a MEK inhibitor. These results support an emerging model of universal ERK-activating genetic alterations driving pathogenesis in LCH. A personalized approach in which patient-specific alterations are identified may be necessary to maximize benefit from targeted therapies for patients with LCH.
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.|Division of Pediatric Hematology-Oncology, Department of Pediatrics.
authors.forename: Rikhia
authors.initials: R
authors.lastname: Chakraborty
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.|Division of Pediatric Hematology-Oncology, Department of Pediatrics.|Program in Translational Biology and Molecular Medicine.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Burke
authors.affiliation: Department of Molecular and Human Genetics.|Human Genome Sequencing Center, and.
authors.forename: Oliver A
authors.initials: OA
authors.lastname: Hampton
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.|Division of Pediatric Hematology-Oncology, Department of Pediatrics.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Zinn
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.|Program in Translational Biology and Molecular Medicine.
authors.forename: Karen Phaik Har
authors.initials: KP
authors.lastname: Lim
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.
authors.forename: Harshal
authors.initials: H
authors.lastname: Abhyankar
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.
authors.forename: Brooks
authors.initials: B
authors.lastname: Scull
authors.affiliation: Department of Pathology and Immunology, Baylor College of Medicine, Houston, TX; and.
authors.forename: Vijetha
authors.initials: V
authors.lastname: Kumar
authors.affiliation: Department of Molecular and Human Genetics.
authors.forename: Nipun
authors.initials: N
authors.lastname: Kakkar
authors.affiliation: Department of Molecular and Human Genetics.|Human Genome Sequencing Center, and.
authors.forename: David A
authors.initials: DA
authors.lastname: Wheeler
authors.affiliation: Division of Pediatric Hematology-Oncology, Department of Pediatrics.|Department of Pathology and Immunology, Baylor College of Medicine, Houston, TX; and.
authors.forename: Angshumoy
authors.initials: A
authors.lastname: Roy
authors.affiliation: Tisch Cancer Institute, Icahn School of Medicine, New York, NY.
authors.forename: Poulikos I
authors.initials: PI
authors.lastname: Poulikakos
authors.affiliation: Tisch Cancer Institute, Icahn School of Medicine, New York, NY.
authors.forename: Miriam
authors.initials: M
authors.lastname: Merad
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.|Division of Pediatric Hematology-Oncology, Department of Pediatrics.
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: McClain
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.|Division of Pediatric Hematology-Oncology, Department of Pediatrics.|Program in Translational Biology and Molecular Medicine.|Department of Molecular and Human Genetics.|Human Genome Sequencing Center, and.
authors.forename: D Williams
authors.initials: DW
authors.lastname: Parsons
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Houston, TX.|Division of Pediatric Hematology-Oncology, Department of Pediatrics.|Program in Translational Biology and Molecular Medicine.
authors.forename: Carl E
authors.initials: CE
authors.lastname: Allen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004789:Enzyme Activation / Q000235:genetics; D005260:Female; D006646:Histiocytosis, Langerhans-Cell / Q000201:enzymology / Q000235:genetics*; D006801:Humans; D007223:Infant; D008297:Male; D009154:Mutation; D015514:Oncogene Proteins, Fusion / Q000235:genetics* / Q000378:metabolism; D000072417:Protein Domains; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics* / Q000378:metabolism
chemical_list: D015514:Oncogene Proteins, Fusion; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf