title: Inhibition of C-terminal binding protein attenuates transcription factor 4 signaling to selectively target colon cancer stem cells.
abstract: Selective targeting of cancer stem cells (CSCs), implicated in tumor relapse, holds great promise in the treatment of colorectal cancer. Overexpression of C-terminal binding protein (CtBP), an NADH dependent transcriptional regulator, is often observed in colon cancer. Of note, TCF-4 signaling is also up-regulated in colonic CSCs. We hypothesized that CtBP, whose dehydrogenase activity is amenable to pharmacological inhibition by 4-methylthio-2-oxobutyric acid (MTOB), positively regulates TCF-4 signaling, leading to CSC growth and self-renewal. CSCs demonstrated significant upregulation of CtBP1 and CtBP2 levels (mRNA and protein) and activity partly due to increased NADH/NAD ratio, as well as increased TCF/LEF transcriptional activity, compared to respective controls. Depletion of CtBP2 inhibited, while its overexpression enhanced, CSC growth (1° spheroids) and self-renewal (2°/3° spheroids). Similarly, MTOB caused a robust inhibition of spheroid growth and self-renewal in a dose dependent manner. MTOB displayed significantly greater selectivity for growth inhibition in the spheroids, at least in part through induction of apoptosis, compared to monolayer controls. Moreover, MTOB inhibited basal as well as induced (by GSK-3β inhibitor) TCF/LEF activity while suppressing mRNA and protein levels of several β-catenin target genes (CD44, Snail, C-MYC and LGR5). Lastly, CtBP physically interacted with TCF-4, and this interaction was significantly inhibited in the presence of MTOB. The above findings point to a novel role of CtBPs in the promotion of CSC growth and self-renewal through direct regulation of TCF/LEF transcription. Moreover, small molecular inhibition of its function can selectively target CSCs, presenting a novel approach for treatment of colorectal cancer focused on targeting of CSCs.
authors.affiliation: a Hunter Holmes McGuire VA Medical Center ; Richmond , VA USA.
authors.forename: Jagrut
authors.initials: J
authors.lastname: Patel
authors.forename: Somesh
authors.initials: S
authors.lastname: Baranwal
authors.forename: Ian M
authors.initials: IM
authors.lastname: Love
authors.forename: Nirmita J
authors.initials: NJ
authors.lastname: Patel
authors.forename: Steven R
authors.initials: SR
authors.lastname: Grossman
authors.forename: Bhaumik B
authors.initials: BB
authors.lastname: Patel
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis / Q000235:genetics; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D014411:Neoplastic Stem Cells / Q000473:pathology*; D011485:Protein Binding / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D000073940:Transcription Factor 4; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000235:genetics
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C532096:TCF4 protein, human; D000073940:Transcription Factor 4; D014157:Transcription Factors; D051176:beta Catenin; D000429:Alcohol Oxidoreductases; C096794:C-terminal binding protein
keywords: 1°, primary; 2°, secondary; 3°, tertiary; C-terminal binding protein; CSC, cancer stem cell; CtBP, c-terminal binding protein; TCF-4; TCF-4, transcription factor 4; apoptosis; cancer stem cells; β-catenin