Dependence of Human Colorectal Cells Lacking the FBW7 Tumor Suppressor on the Spindle Assembly Checkpoint.
FBW7 (F-box and WD repeat domain containing 7), also known as FBXW7 or hCDC4, is a tumor suppressor gene mutated in a broad spectrum of cancer cell types. As a component of the SCF E3 ubiquitin ligase, FBW7 is responsible for specifically recognizing phosphorylated substrates, many important for tumor progression, and targeting them for ubiquitin-mediated degradation. Although the role of FBW7 as a tumor suppressor is well established, less well studied is how FBW7-mutated cancer cells might be targeted for selective killing. To explore this further, we undertook a genome-wide RNAi screen using WT and FBW7 knockout colorectal cell lines and identified the spindle assembly checkpoint (SAC) protein BUBR1, as a candidate synthetic lethal target. We show here that asynchronous FBW7 knockout cells have increased levels of mitotic APC/C substrates and are sensitive to knockdown of not just BUBR1 but BUB1 and MPS1, other known SAC components, suggesting a dependence of these cells on the mitotic checkpoint. Consistent with this dependence, knockdown of BUBR1 in cells lacking FBW7 results in significant cell aneuploidy and increases in p53 levels. The FBW7 substrate cyclin E was necessary for the genetic interaction with BUBR1. In contrast, the establishment of this dependence on the SAC requires the deregulation of multiple substrates of FBW7. Our work suggests that FBW7 knockout cells are vulnerable in their dependence on the mitotic checkpoint and that this may be a good potential target to exploit in FBW7-mutated cancer cells.
Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Melanie L
ML
Bailey
Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Tejomayee
T
Singh
Donnelly Centre and Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E1, Canada.
Patricia
P
Mero
Donnelly Centre and Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E1, Canada.
Jason
J
Moffat
Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada hieter@msl.ubc.ca.
Philip
P
Hieter
D000782:Aneuploidy; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000378:metabolism; D044783:F-Box Proteins / Q000235:genetics / Q000502:physiology*; D000073979:F-Box-WD Repeat-Containing Protein 7; D055786:Gene Knockout Techniques; D016147:Genes, Tumor Suppressor; D006801:Humans; D059566:M Phase Cell Cycle Checkpoints; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology; D034622:RNA Interference; D008941:Spindle Apparatus / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000502:physiology*
D018797:Cell Cycle Proteins; D019927:Cyclin E; D044783:F-Box Proteins; D000073979:F-Box-WD Repeat-Containing Protein 7; C513273:FBXW7 protein, human; D044767:Ubiquitin-Protein Ligases; C584277:BUB1 protein, human; D017346:Protein Serine-Threonine Kinases
BUBR1; FBW7; RNAi; spindle assembly checkpoint; synthetic lethality