Bile salt-induced apoptosis in human colon cancer cell lines involves the mitochondrial transmembrane potential but not the CD95 (Fas/Apo-1) receptor.
OBJECTIVE
Depending on their physico-chemical characteristics, bile acids can be potent inducers of apoptosis in colon cancer cells. This observation contrasts with bile acids being promoters of colorectal cancer carcinogenesis. Our recent observation of caspase activation in deoxycholate (DC)-treated colon cancer cell lines prompted us to analyze the mechanisms of bile acid-induced colon cancer cell death.


METHODS
CD95 expression was correlated to DC-induced cell death in four colon cancer cell lines. Mitochondrial transmembrane potential (MTP) was determined in whole cells as well as in isolated mitochondria.


RESULTS
On 2 of the 4 human colon cancer cell lines investigated, no CD95 was detected. These data were supported by a lack of CD95 mRNA in those cell lines that did not express CD95 on their surface. The apoptotic response to bile acids did not correlate with CD95 receptor expression on the respective cell lines. Therefore, we analyzed the MTP after the addition of toxic bile acids. MTP was destabilized early after the addition of deoxycholate to SW480 cells. These data were confirmed in isolated mitochondria, which showed strong swelling after the addition of DC. Accordingly, release of cytochrome-c from the mitochondrial intermembrane space into the cytosol, indicating dissipation of the MTP, and subsequent caspase-3 cleavage were detectable as early as 3 min after the addition of DC.


CONCLUSIONS
In contrast to hepatocytes and hepatic carcinoma cell lines, DC induces apoptosis in colon cancer cell lines via a CD95 receptor-independent mechanism. Direct induction of the mitochondrial permeability transition by toxic bile acids is suggested as the apoptosis-inducing mechanism in colon cancer cells.
Wachs
Frank-Peter
FP
Department of Internal Medicine I, University Hospital Regensburg, 93042 Regensburg, Germany.
Krieg
René C
RC
Rodrigues
Cecilia M P
CM
Messmann
Helmut
H
Kullmann
Frank
F
Knüchel-Clarke
Ruth
R
Schölmerich
Jürgen
J
Rogler
Gerhard
G
Schlottmann
Klaus
K
D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology*; D003840:Deoxycholic Acid / Q000494:pharmacology*; D005434:Flow Cytometry; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D019014:fas Receptor; D003840:Deoxycholic Acid