Sustained IL-6/STAT-3 signaling in cholangiocarcinoma cells due to SOCS-3 epigenetic silencing.
OBJECTIVE
Interleukin 6 (IL-6)-mediated signal transducers and activators of transcription 3 (STAT-3) phosphorylation (activation) is aberrantly sustained in cholangiocarcinoma cells resulting in enhanced myeloid cell leukemia 1 (Mcl-1) expression and resistance to apoptosis. Because suppressor of cytokine signaling 3 (SOCS) controls the IL-6/STAT-3 signaling pathway by a classic feedback loop, the aims of this study were to examine SOCS-3 regulation in human cholangiocarcinoma.


METHODS
SOCS-3 expression was assessed in human cholangiocarcinoma tissue and the Mz-ChA-1 and CCLP1 human cholangiocarcinoma cell lines.


RESULTS
An inverse correlation was observed between phospho-STAT-3 and SOCS-3 protein expression in cholangiocarcinoma. In those cancers failing to express SOCS-3, extensive methylation of the SOCS-3 promoter was demonstrated in tumor but not in paired nontumor tissue. Likewise, methylation of the socs-3 promoter was also identified in 2 cholangiocarcinoma cell lines. Treatment with a demethylating agent, 5-aza-2'-deoxycytidine (DAC), restored IL-6 induction of SOCS-3, terminated the phospho-STAT-3 response, and reduced cellular levels of Mcl-1. Enforced expression of SOCS-3 also reduced IL-6 induction of phospho-STAT-3 and Mcl-1. Either DAC treatment or enforced SOCS-3 expression sensitized the cells to TRAIL-mediated apoptosis.


CONCLUSIONS
SOCS-3 epigenetic silencing is responsible for sustained IL-6/STAT-3 signaling and enhanced Mcl-1 expression in cholangiocarcinoma.
Isomoto
Hajime
H
Miles & Shirley Fiterman Center for Digestive Diseases, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA.
Mott
Justin L
JL
Kobayashi
Shogo
S
Werneburg
Nathan W
NW
Bronk
Steve F
SF
Haan
Serge
S
Gores
Gregory J
GJ
D017209:Apoptosis / Q000502:physiology; D001650:Bile Duct Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D001653:Bile Ducts, Intrahepatic / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D018281:Cholangiocarcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018899:CpG Islands / Q000502:physiology; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics* / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D015850:Interleukin-6; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C106644:SOCS3 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014443:Tyrosine