Oncogenic K-Ras turns death receptors into metastasis-promoting receptors in human and mouse colorectal cancer cells.
OBJECTIVE
Death receptors expressed on tumor cells can prevent metastasis formation by inducing apoptosis, but they also can promote migration and invasion. The determinants of death receptor signaling output are poorly defined. Here we investigated the role of oncogenic K-Ras in determining death receptor function and metastatic potential.


METHODS
Isogenic human and mouse colorectal cancer cell lines differing only in the presence or absence of the K-Ras oncogene were tested in apoptosis and invasion assays using CD95 ligand and tumor necrois factor-related apoptosis-inducing ligand (TRAIL) as stimuli. Metastatic potential was assessed by intrasplenic injections of green fluorescent protein- or luciferase-expressing tumor cells, followed by intravital fluorescence microscopy or bioluminescence imaging, and confocal microscopy and immunohistochemistry. Ras-effector pathway control of CD95 output was assessed by an RNA-interference and inhibitor-based approach.


RESULTS
CD95 ligand and TRAIL stimulated invasion of colorectal tumor cells and liver metastases in a K-Ras-dependent fashion. Loss of mutant K-Ras switched CD95 and TRAIL receptors back into apoptosis mode and abrogated metastatic potential. Raf1 was essential for the switch in CD95 function, for tumor cell survival in the liver, and for K-Ras-driven formation of liver metastases. K-Ras and Raf1 suppressed Rho kinase (ROCK)/LIM kinase-mediated phosphorylation of the actin-severing protein cofilin. Overexpression of ROCK or LIM kinase allowed CD95L to induce apoptosis in K-Ras-proficient cells and prevented metastasis formation, whereas their suppression protected K-Ras-deficient cells against apoptosis.


CONCLUSIONS
Oncogenic K-Ras and its effector Raf1 convert death receptors into invasion-inducing receptors by suppressing the ROCK/LIM kinase pathway, and this is essential for K-Ras/Raf1-driven metastasis formation.
Hoogwater
Frederik J H
FJ
Department of Surgery, University Medical Center Utrecht, Utrecht, The Netherlands.
Nijkamp
Maarten W
MW
Smakman
Niels
N
Steller
Ernst J A
EJ
Emmink
Benjamin L
BL
Westendorp
B Florien
BF
Raats
Danielle A E
DA
Sprick
Martin R
MR
Schaefer
Uta
U
Van Houdt
Winan J
WJ
De Bruijn
Menno T
MT
Schackmann
Ron C J
RC
Derksen
Patrick W B
PW
Medema
Jan-Paul
JP
Walczak
Henning
H
Borel Rinkes
Inne H M
IH
Kranenburg
Onno
O
D000818:Animals; D017209:Apoptosis; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000473:pathology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D006801:Humans; D054461:Lim Kinases / Q000502:physiology; D008113:Liver Neoplasms / Q000556:secondary*; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf / Q000502:physiology; D016283:Proto-Oncogene Proteins p21(ras); D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000502:physiology*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000502:physiology*; D019014:fas Receptor / Q000502:physiology*; D018631:ras Proteins / Q000502:physiology*; D054460:rho-Associated Kinases / Q000502:physiology
C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; D019014:fas Receptor; D054461:Lim Kinases; D019908:Proto-Oncogene Proteins c-raf; D054460:rho-Associated Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D053181:Caspase 8; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins