The CUL5 ubiquitin ligase complex mediates resistance to CDK9 and MCL1 inhibitors in lung cancer cells

Elife. 2019 Jul 11;8:e44288. doi: 10.7554/eLife.44288.


Overexpression of anti-apoptotic proteins MCL1 and Bcl-xL are frequently observed in many cancers. Inhibitors targeting MCL1 are in clinical development, however numerous cancer models are intrinsically resistant to this approach. To discover mechanisms underlying resistance to MCL1 inhibition, we performed multiple flow-cytometry based genome-wide CRISPR screens interrogating two drugs that directly (MCL1i) or indirectly (CDK9i) target MCL1. Remarkably, both screens identified three components (CUL5, RNF7 and UBE2F) of a cullin-RING ubiquitin ligase complex (CRL5) that resensitized cells to MCL1 inhibition. We find that levels of the BH3-only pro-apoptotic proteins Bim and Noxa are proteasomally regulated by the CRL5 complex. Accumulation of Noxa caused by depletion of CRL5 components was responsible for re-sensitization to CDK9 inhibitor, but not MCL1 inhibitor. Discovery of a novel role of CRL5 in apoptosis and resistance to multiple types of anticancer agents suggests the potential to improve combination treatments.

Keywords: CDK9 inhibitor; CUL5-RNF7-UBE2F ubiquitin ligase complex; MCL1 inhibitor; bim; cancer biology; cell biology; genome-wide CRISPRi screens; human; noxa.

Publication types

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

MeSH terms

  • Antineoplastic Agents / pharmacology
  • Apoptosis / drug effects
  • Bcl-2-Like Protein 11 / genetics
  • Cell Line, Tumor
  • Cullin Proteins / genetics*
  • Cyclin-Dependent Kinase 9 / antagonists & inhibitors
  • Cyclin-Dependent Kinase 9 / genetics*
  • Drug Resistance, Neoplasm / genetics
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Lung Neoplasms / drug therapy*
  • Lung Neoplasms / genetics
  • Lung Neoplasms / pathology
  • Myeloid Cell Leukemia Sequence 1 Protein / antagonists & inhibitors
  • Myeloid Cell Leukemia Sequence 1 Protein / genetics*
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Ubiquitin-Protein Ligase Complexes / genetics
  • Ubiquitin-Protein Ligases / genetics


  • Antineoplastic Agents
  • BCL2 protein, human
  • Bcl-2-Like Protein 11
  • CUL5 protein, human
  • Cullin Proteins
  • MCL1 protein, human
  • Myeloid Cell Leukemia Sequence 1 Protein
  • PMAIP1 protein, human
  • Proto-Oncogene Proteins c-bcl-2
  • Ubiquitin-Protein Ligase Complexes
  • RNF7 protein, human
  • Ubiquitin-Protein Ligases
  • CDK9 protein, human
  • Cyclin-Dependent Kinase 9