Docosahexaenoic acid induces proteasome-dependent degradation of beta-catenin, down-regulation of survivin and apoptosis in human colorectal cancer cells not expressing COX-2.
n-3 Polyunsaturated fatty acids have been shown to powerfully inhibit the growth of colon cancer cells, mainly acting as pro-apoptotic agents through inhibition of cycloxygenase-2 (COX-2) expression. Since dysregulation of beta-catenin expression is frequently found at early stage of colorectal carcinogenesis, we analyzed whether docosahexaenoic acid (DHA) may modify the expression of beta-catenin in colon cancer cells (SW480 and HCT116) over-expressing this protein, but lacking COX-2. Futhermore, we investigated if alterations in beta-catenin expression may be associated with apoptosis induction. Treatment of cells with increasing concentrations of DHA induced a dose- and time-dependent inhibition of beta-catenin protein expression which, however, was not accompanied by modifications in beta-catenin transcription. Conversely, the proteasomal inhibitors MG132 and lactacystin prevented DHA-induced beta-catenin decrease, suggesting that DHA may regulate the proteasomal degradation of beta-catenin. The reduced levels of beta-catenin were accompanied by decreased translocation of beta-catenin into the nucleus, where it acts as a transcription factor in concert with T-Cell Factor (TCF). DHA, at the same range of concentrations, was also able to induce apoptosis by a caspase-3-dependent mechanism and to cause a dose- and time-dependent decrease of survivin, an apoptosis inhibitor undetectable in normal tissues and expressed in colorectal cancer through TCF-beta-catenin stimulation. Several other proteins regulated by the TCF-beta-catenin pathway and involved in regulation of tumor growth were down-regulated by DHA, including peroxisome proliferator-activated receptor-delta, membrane type 1 (MT1)-matrix metalloproteinase (MMP), MMP-7 and vascular endothelial growth factor. The present study, thus, raises the possibility that DHA may exert pro-apoptotic and antitumoral effects through proteasomal regulation of beta-catenin levels and alterations in the expression of TCF-beta-catenin target genes.
Calviello
Gabriella
G
Institute of General Pathology, Institute of Human Anatomy, Catholic University, Rome, Italy. g.calviello@rm.unicatt.it
Resci
Federica
F
Serini
Simona
S
Piccioni
Elisabetta
E
Toesca
Amelia
A
Boninsegna
Alma
A
Monego
Giovanni
G
Ranelletti
Franco O
FO
Palozza
Paola
P
D017209:Apoptosis / Q000187:drug effects*; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000473:pathology; D051546:Cyclooxygenase 2 / Q000096:biosynthesis / Q000235:genetics*; D004281:Docosahexaenoic Acids / Q000494:pharmacology*; D045325:HCT116 Cells; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics*; D008869:Microtubule-Associated Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis* / Q000235:genetics; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis* / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000502:physiology*; D000077022:Survivin; D051176:beta Catenin / Q000378:metabolism*
C107489:BIRC5 protein, human; D051034:Inhibitor of Apoptosis Proteins; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D000077022:Survivin; D051176:beta Catenin; D004281:Docosahexaenoic Acids; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D046988:Proteasome Endopeptidase Complex