title: Radiosensitization and downregulation of heterogeneous nuclear ribonucleoprotein K (hnRNP K) upon inhibition of mitogen/extracellular signal-regulated kinase (MEK) in malignant melanoma cells.
abstract: BACKGROUND
  Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is an important cofactor in the p53-mediated DNA damage response pathway upon ionizing radiation (IR) and exerts anti-apoptotic effects also independent of p53 pathway activation. Furthermore, hnRNP K is overexpressed in various neoplasms including malignant melanoma (MM). Here, we investigate the role of hnRNP K in the radioresistance of MM cells.
  
  
  RESULTS
  Our results show cytoplasmic expression of hnRNP K in human MM surgical specimens, but not in benign nevi, and a quick dose- and time-dependent upregulation in response to IR accompanied by cytoplasmic redistribution of the protein in the IPC-298 cellular tumor model carrying an activating NRAS mutation (p.Q61L). SiRNA-based knockdown of hnRNP K induced a delayed decline in γH2AX/53BP1-positive DNA repair foci upon IR. Pharmacological interference with MAPK signaling abrogated ERK phosphorylation, diminished cellular hnRNP K levels, impaired γH2AX/53BP1-foci repair and proliferative capability and increased apoptosis comparable to the observed hnRNP K knockdown phenotype in IPC-298 cells.
  
  
  CONCLUSIONS
  Our results indicate that pharmacological interference with MAPK signaling increases vulnerability of NRAS-mutant malignant melanoma cells to ionizing radiation along with downregulation of endogenous hnRNP K and point towards a possible use for combined MEK inhibition and localized radiation therapy of MM in the NRAS-mutant setting where BRAF inhibitors offer no clinical benefit.
authors.affiliation: Bundeswehr Institute of Radiobiology, 80937 Munich, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Eder
authors.affiliation: Bundeswehr Institute of Radiobiology, 80937 Munich, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Lamkowski
authors.affiliation: Bundeswehr Institute of Radiobiology, 80937 Munich, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Priller
authors.affiliation: Bundeswehr Institute of Radiobiology, 80937 Munich, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Port
authors.affiliation: Bundeswehr Institute of Radiobiology, 80937 Munich, Germany.|Gerhard-Domagk-Institute of Pathology, University Hospital Muenster, 48149 Muenster, Germany.
authors.forename: Konrad
authors.initials: K
authors.lastname: Steinestel
mesh_terms: D015153:Blotting, Western; D004260:DNA Repair; D015536:Down-Regulation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005260:Female; D005434:Flow Cytometry; D020558:GTP Phosphohydrolases / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D034641:Heterogeneous-Nuclear Ribonucleoprotein K / Q000378:metabolism*; D006801:Humans; D008545:Melanoma / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009154:Mutation; D034741:RNA, Small Interfering; D011836:Radiation Tolerance / Q000502:physiology*; D046888:Tissue Array Analysis; D014162:Transfection
chemical_list: D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D048049:Extracellular Signal-Regulated MAP Kinases; D020558:GTP Phosphohydrolases; C579846:NRAS protein, human
keywords: MEK inhibition; NRAS; melanoma; nRNP K; radiotherapy