Insulin alters the expression of components of the Wnt signaling pathway including TCF-4 in the intestinal cells.
BACKGROUND
Epidemiological and experimental evidence that support the correlation between Type 2 diabetes mellitus (T2D) and increased risks of colorectal cancer formation have led us to hypothesize the existence of molecular crosstalk between insulin and canonical Wnt signaling pathways. Insulin was shown to stimulate Wnt target gene expression, utilizing the effector of the Wnt signaling pathway. Whether insulin affects expression of components of Wnt pathway has not been extensively examined.


METHODS
cDNA microarray was utilized to assess the effect of insulin on gene expression profile in the rat intestinal non-cancer IEC-6 cell line, followed by real-time RT-PCR, Western blotting and reporter gene analyses in intestinal cancer and non-cancer cells.


RESULTS
Insulin was shown to alter the expression of a dozen of Wnt pathway related genes including TCF-4 (=TCF7L2) and frizzled- (Fzd-4). The stimulatory effect of insulin on TCF-4 expression was then confirmed by real-time RT-PCR, Western blotting and luciferase reporter analyses, while the activation on Fzd-4 was confirmed by real-time PCR.


CONCLUSIONS
Our observations suggest that insulin may crosstalk with the Wnt signaling pathway in a multi-level fashion, involving insulin regulation of the expression of Wnt target genes, a Wnt receptor, as well as mediators of the Wnt signaling pathway.
Sun
Jane
J
Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada; Division of Cell and Molecular Biology, University Health Network, Canada.
Wang
Dingyan
D
Jin
Tianru
T
D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D005786:Gene Expression Regulation / Q000187:drug effects; D019073:HT29 Cells / Q000502:physiology; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007422:Intestines / Q000187:drug effects / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D051381:Rats; D000073940:Transcription Factor 4; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D051153:Wnt Proteins / Q000187:drug effects / Q000235:genetics* / Q000502:physiology
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D017931:DNA Primers; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D007328:Insulin; C532096:TCF4 protein, human; C491192:Tcf4 protein, rat; D000073940:Transcription Factor 4; D014157:Transcription Factors; D051153:Wnt Proteins