A Novel Neoplastic Fusion Transcript, RAD51AP1-DYRK4, Confers Sensitivity to the MEK Inhibitor Trametinib in Aggressive Breast Cancers

Clin Cancer Res. 2021 Feb 1;27(3):785-798. doi: 10.1158/1078-0432.CCR-20-2769. Epub 2020 Nov 10.


Purpose: Luminal B breast tumors are more aggressive estrogen receptor-positive (ER+) breast cancers characterized by aggressive clinical behavior and a high risk of metastatic dissemination. The underlying pathologic molecular events remain poorly understood with a paucity of actionable genetic drivers, which hinders the development of new treatment strategies.

Experimental design: We performed large-scale RNA sequencing analysis to identify chimerical transcripts preferentially expressed in luminal B breast cancer. The lead candidate was validated by reverse transcription PCR in breast cancer tissues. The effects of inducible ectopic expression or genetic silencing were assessed by phenotypic assays such as MTS, transwell, and transendothelial migration assays, and by clonogenic assays to assess MEK inhibitor sensitivity. Subcellular fractionation, Western blots, and immunoprecipitation were performed to characterize the protein products and elucidate the engaged mechanisms.

Results: Here we report a novel tumor-specific chimeric transcript RAD51AP1-DYRK4 preferentially expressed in luminal B tumors. Analysis of 200 ER+ breast tumors detected RAD51AP1-DYRK4 overexpression in 19 tumors (9.5%), which is markedly enriched in the luminal B tumors (17.5%). Ectopic expression of RAD51AP1-DYRK4, but not wild-type RAD51AP1, leads to marked activation of MEK/ERK signaling, and endows increased cell motility and transendothelial migration. More importantly, RAD51AP1-DYRK4 appears to endow increased sensitivity to the MEK inhibitor trametinib through attenuating compensatory activation of HER2/PI3K/AKT under MEK inhibition.

Conclusions: This discovery sheds light on a new area of molecular pathobiology of luminal B tumors and implies potential new therapeutic opportunities for more aggressive breast tumors overexpressing this fusion.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Breast / pathology
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology
  • Cell Line, Tumor
  • DNA-Binding Proteins / genetics*
  • Datasets as Topic
  • Drug Resistance, Neoplasm / genetics
  • Female
  • Gene Expression Regulation, Neoplastic
  • Gene Knockdown Techniques
  • Humans
  • MAP Kinase Signaling System / drug effects
  • MAP Kinase Signaling System / genetics
  • Mitogen-Activated Protein Kinase Kinases / metabolism
  • Oncogene Proteins, Fusion / genetics*
  • Protein Serine-Threonine Kinases / genetics*
  • Protein-Tyrosine Kinases / genetics*
  • Pyridones / pharmacology*
  • Pyridones / therapeutic use
  • Pyrimidinones / pharmacology*
  • Pyrimidinones / therapeutic use
  • RNA-Binding Proteins / genetics*
  • RNA-Seq


  • DNA-Binding Proteins
  • Oncogene Proteins, Fusion
  • Pyridones
  • Pyrimidinones
  • RAD51AP1 protein, human
  • RNA-Binding Proteins
  • trametinib
  • Dyrk kinase
  • Protein-Tyrosine Kinases
  • Protein Serine-Threonine Kinases
  • Mitogen-Activated Protein Kinase Kinases