Butyrate sensitizes human colon cancer cells to TRAIL-mediated apoptosis.
BACKGROUND
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a novel member of the tumor necrosis factor family, induces apoptosis in TRAIL-sensitive tumors through the activation of the caspase pathway. Sodium butyrate (NaBT) induces differentiation and apoptosis in certain colorectal cancers; the molecular mechanisms for these effects have not been clearly defined. The purpose of our study was to determine whether NaBT sensitizes TRAIL-resistant human colon cancer cells to the effects of TRAIL.


METHODS
Human colon cancer cells (KM12C, KML4A, and KM20) that are resistant to TRAIL treatment alone were treated with TRAIL (100 ng/mL), NaBT (5 mmol/L), or a combination of these agents and harvested for total RNA and protein. Western blots were performed to assess intracellular expression of Flice-like inhibitory protein (FLIP), a caspase inhibitor. Percent-specific apoptosis, relative caspase-3 activity, and Annexin-V immunofluorescence were determined at 24 and 48 hours. Cell cycle--related gene expression was assessed by RNase protection.


RESULTS
Treatment with NaBT for 24 and 48 hours decreased FLIP protein expression in all cell lines. Furthermore, NaBT sensitized these resistant cancer cells to the effects of TRAIL with significant increases noted in cell death, caspase-3 activity, and Annexin-V staining compared with NaBT alone.


CONCLUSIONS
Our findings suggest that the reduction of FLIP protein levels by NaBT renders TRAIL-resistant human colon cancer cells sensitive to TRAIL-mediated apoptosis. The combination of TRAIL with agents (such as NaBT, which target proteins that prevent cell death) may provide a more effective and less toxic regimen for the treatment of resistant colon cancers.
Hernandez
A
A
Department of Surgery, The University of Texas Medical Branch, Galveston, TX 77555-0536, USA.
Thomas
R
R
Smith
F
F
Sandberg
J
J
Kim
S
S
Chung
D H
DH
Evers
B M
BM
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D002087:Butyrates / Q000494:pharmacology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003110:Colonic Neoplasms; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D053221:TNF-Related Apoptosis-Inducing Ligand; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D002087:Butyrates; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C493956:CDKN1A protein, human; C506386:CFLAR protein, human; D002352:Carrier Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases