Blood Journal
Leading the way in experimental and clinical research in hematology

RNAi screening uncovers Dhx9 as a modifier of ABT-737 resistance in an Eμ-myc/Bcl-2 mouse model

  1. John R. Mills1,
  2. Abba Malina1,
  3. Teresa Lee1,
  4. Domenic Di Paola1,
  5. Ola Larsson2,
  6. Cornelius Miething3,4,
  7. Frank Grosse5,
  8. Hengli Tang6,
  9. Maria Zannis-Hadjopoulos1,7,8,
  10. Scott W. Lowe3,4,9, and
  11. Jerry Pelletier1,7,8
  1. 1Department of Biochemistry McGill University, Montreal, Quebec, Canada;
  2. 2Department of Oncology-Pathology, Karolinska Institute, Stockholm, Sweden;
  3. 3Cold Spring Harbor Laboratories, Cold Spring Harbor, NY;
  4. 4Memorial Sloan-Kettering Cancer Center, New York, NY;
  5. 5Leibniz Institute for Age Research, Fritz Lipmann Institute, Jena, Germany;
  6. 6Department of Biological Science, Florida State University, Tallahassee, FL;
  7. 7Department of Oncology and
  8. 8The Rosalind and Morris Goodman Cancer Research Center, McGill University, Montreal, Quebec, Canada; and
  9. 9Howard Hughes Medical Institute, New York, NY

Key Points

  • A focused RNAi screen identifies Dhx9 as a regulator of ABT-737 sensitivity in Eµ-myc/Bcl-2 lymphomas.

  • Dhx9 suppression activates an apoptotic signal through the Chk1/p53 replicative stress pathway in Myc-driven cells.

Abstract

ABT-737 is a promising chemotherapeutic agent that promotes apoptosis by acting as a selective BH3 mimetic to neutralize Bcl-2–like family members. One shortcoming with its use is that Mcl-1, a member of the Bcl-2 family, is poorly inhibited by ABT-737 and thus is a major cause of resistance. We performed a short hairpin RNA (shRNA)-based drop-out screen to identify novel genes and pathways that could reverse resistance to ABT-737 treatment in Eµ-myc/Bcl-2 lymphoma cells engineered to rely on endogenous Mcl-1 for survival. Several drug-sensitive shRNAs were identified that were selectively depleted in the presence of ABT-737. Of these, 2 independent shRNAs targeting the RNA/DNA helicase Dhx9 were found to sensitize lymphomas to ABT-737 to an extent comparable to control Mcl-1 shRNAs. Although Dhx9 suppression sensitized both mouse and human cells to ABT-737 treatment, it did so without altering MCL-1 levels. Rather, loss of Dhx9 appeared to activate a p53-dependent apoptotic program, through aggravation of replicative stress, which was found to be both necessary and sufficient for the ABT-737–shDhx9 synthetic lethal relationship.

  • Submitted June 1, 2012.
  • Accepted February 12, 2013.
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