title: A 6-Base Pair in Frame Germline Deletion in Exon 7 Of RET Leads to Increased RET Phosphorylation, ERK Activation, and MEN2A.
abstract: BACKGROUND
  Multiple endocrine neoplasia type 2 (MEN2) is usually caused by missense mutations in the proto-oncogene, RET.
  
  
  OBJECTIVE
  This study aimed to determine the mutation underlying MEN2A in a female patient diagnosed with bilateral pheochromocytoma at age 31 years and with medullary thyroid carcinoma (MTC) 6 years later.
  
  
  METHODS
  Leukocyte DNA was used for exome and Sanger sequencing. Wild-type (WT) RET and mutants were expressed in HEK293 cells. Activation of MAPK/ERK and PI3K/AKT was analyzed by Western blotting and luciferase assay. The effect of RET mutants on cell proliferation was tested in a colony forming assay.
  
  
  RESULTS
  Exome sequencing revealed a 6-nucleotide/2-amino acid in-frame deletion in exon 7 of RET (c.1512_1517delGGAGGG, p.505_506del). In vitro expression showed that phosphorylation of the crucial tyrosine 905 was much stronger in the p.505_506del RET mutant compared with WT RET, indicating ligand-independent autophosphorylation. Furthermore, the p.505_506del RET mutant induced a strong activation of the MAPK/ERK pathway and the PI3K/AKT pathway. Consequently, the p.505_506del RET mutant cells increased HEK293 colony formation 4-fold compared with WT RET.
  
  
  CONCLUSIONS
  The finding of bilateral pheochromocytoma and MTC in our patient was highly suspicious of a RET mutation. Exome sequencing revealed a 6-base-pair deletion in exon 7 of RET, an exon not yet associated with MEN2. Increased ligand-independent phosphorylation of the p.505_506del RET mutant, increased activation of downstream pathways, and stimulation of cell proliferation demonstrated the pathogenic nature of the mutation. We therefore recommend screening the whole sequence of RET in MTC and pheochromocytoma patients with red flags for a genetic cause.
authors.affiliation: Department of Endocrinology and Metabolism (S.L., C.K., D.Z., D.F., L.C.M.), Institute of Cell Biology (Cancer Research) Faculty of Medicine (L.K.-H.), Department of Hematology (C.K.), Department of Nuclear Medicine (T.D.P.), and Institute of Pathology (K.W.S.), University of Duisburg-Essen, 45141 Essen, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Latteyer
authors.affiliation: Department of Endocrinology and Metabolism (S.L., C.K., D.Z., D.F., L.C.M.), Institute of Cell Biology (Cancer Research) Faculty of Medicine (L.K.-H.), Department of Hematology (C.K.), Department of Nuclear Medicine (T.D.P.), and Institute of Pathology (K.W.S.), University of Duisburg-Essen, 45141 Essen, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Klein-Hitpass
authors.affiliation: Department of Endocrinology and Metabolism (S.L., C.K., D.Z., D.F., L.C.M.), Institute of Cell Biology (Cancer Research) Faculty of Medicine (L.K.-H.), Department of Hematology (C.K.), Department of Nuclear Medicine (T.D.P.), and Institute of Pathology (K.W.S.), University of Duisburg-Essen, 45141 Essen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Khandanpour
authors.affiliation: Department of Endocrinology and Metabolism (S.L., C.K., D.Z., D.F., L.C.M.), Institute of Cell Biology (Cancer Research) Faculty of Medicine (L.K.-H.), Department of Hematology (C.K.), Department of Nuclear Medicine (T.D.P.), and Institute of Pathology (K.W.S.), University of Duisburg-Essen, 45141 Essen, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Zwanziger
authors.affiliation: Department of Endocrinology and Metabolism (S.L., C.K., D.Z., D.F., L.C.M.), Institute of Cell Biology (Cancer Research) Faculty of Medicine (L.K.-H.), Department of Hematology (C.K.), Department of Nuclear Medicine (T.D.P.), and Institute of Pathology (K.W.S.), University of Duisburg-Essen, 45141 Essen, Germany.
authors.forename: T D
authors.initials: TD
authors.lastname: Poeppel
authors.affiliation: Department of Endocrinology and Metabolism (S.L., C.K., D.Z., D.F., L.C.M.), Institute of Cell Biology (Cancer Research) Faculty of Medicine (L.K.-H.), Department of Hematology (C.K.), Department of Nuclear Medicine (T.D.P.), and Institute of Pathology (K.W.S.), University of Duisburg-Essen, 45141 Essen, Germany.
authors.forename: K W
authors.initials: KW
authors.lastname: Schmid
authors.affiliation: Department of Endocrinology and Metabolism (S.L., C.K., D.Z., D.F., L.C.M.), Institute of Cell Biology (Cancer Research) Faculty of Medicine (L.K.-H.), Department of Hematology (C.K.), Department of Nuclear Medicine (T.D.P.), and Institute of Pathology (K.W.S.), University of Duisburg-Essen, 45141 Essen, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Führer
authors.affiliation: Department of Endocrinology and Metabolism (S.L., C.K., D.Z., D.F., L.C.M.), Institute of Cell Biology (Cancer Research) Faculty of Medicine (L.K.-H.), Department of Hematology (C.K.), Department of Nuclear Medicine (T.D.P.), and Institute of Pathology (K.W.S.), University of Duisburg-Essen, 45141 Essen, Germany.
authors.forename: L C
authors.initials: LC
authors.lastname: Moeller
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000235:genetics / Q000473:pathology; D000328:Adult; D020029:Base Pairing / Q000235:genetics*; D018278:Carcinoma, Neuroendocrine / Q000235:genetics; D004789:Enzyme Activation; D005091:Exons / Q000235:genetics; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005260:Female; D018095:Germ-Line Mutation; D057809:HEK293 Cells; D006801:Humans; D018813:Multiple Endocrine Neoplasia Type 2a / Q000235:genetics*; D020125:Mutation, Missense; D010673:Pheochromocytoma / Q000235:genetics / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D000090063:Proto-Oncogene Mas; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion / Q000235:genetics*; D013964:Thyroid Neoplasms / Q000235:genetics
chemical_list: D048049:Extracellular Signal-Regulated MAP Kinases; D019869:Phosphatidylinositol 3-Kinases; D000090063:Proto-Oncogene Mas; D051096:Proto-Oncogene Proteins c-ret; C000715470:MAS1 protein, human