Galectin-3 modulates MUC2 mucin expression in human colon cancer cells at the level of transcription via AP-1 activation.
OBJECTIVE
Galectin-3 and MUC2 intestinal mucin each have been correlated with the malignant behavior of colon cancer cells. Galectin-3 modulates expression of MUC2 protein, but the specific regulatory mechanisms are unknown. This study sought to determine how galectin-3 increases MUC2 expression.


METHODS
Galectin-3 levels in human colon cancer cells of high and low metastatic ability were manipulated via expression of galectin-3 complementary DNA in sense or antisense orientation. Galectin-3 and MUC2 protein expression were determined by Western analysis and immunocytochemistry. Transient transfections of promoter reporter constructs were used to monitor MUC2 transcription and AP-1 activity. Electrophoretic mobility shift assays, site-directed mutagenesis, and chromatin immunoprecipitation were used to monitor the participation of AP-1 in MUC2 transcription.


RESULTS
Alterations in galectin-3 levels correlated with both MUC2 protein expression and transcription. By using MUC2 promoter constructs of different lengths, galectin-3 responsiveness was found between 1500 and 2186 bp upstream of the translation start site, a region that contains 1 consensus AP-1 binding site. AP-1 activity paralleled MUC2 transcription in the different cell lines. Mutation in the AP-1 site markedly decreased MUC2 promoter activity, and MUC2 transcription was inhibited by cotransfection with a dominant-negative AP-1 vector. Electrophoretic mobility shift assays, co-immunoprecipitation, and chromatin immunoprecipitation analyses suggested an association between galectin-3, c-Jun, and Fra-1 in forming a complex at the AP-1 site on the MUC2 promoter.


CONCLUSIONS
Galectin-3 up-regulation of MUC2 transcription occurs at the level of transcription through AP-1 activation. This may have important implications for understanding the role of galectin-3 and MUC2 in colon cancer metastasis.
Song
Shumei
S
Department of Gastrointestinal Medicine and Nutrition, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030-4009, USA.
Byrd
James C
JC
Mazurek
Nachman
N
Liu
Kaifeng
K
Koo
Ja Seok
JS
Bresalier
Robert S
RS
D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D037502:Galectin 3 / Q000378:metabolism*; D017353:Gene Deletion; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D055262:Mucin-2; D009077:Mucins / Q000235:genetics*; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000502:physiology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D000099169:Fos-Related Antigen 1
D037502:Galectin 3; D055262:Mucin-2; D009077:Mucins; D009687:Nuclear Proteins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D018808:Transcription Factor AP-1; D000099169:Fos-Related Antigen 1; C524625:MUC2 protein, human