Enhanced sensitivity to IGF-II signaling links loss of imprinting of IGF2 to increased cell proliferation and tumor risk.
Loss of imprinting (LOI) of the insulin-like growth factor-II gene (IGF2), leading to abnormal activation of the normally silent maternal allele, is a common human epigenetic population variant associated with a 5-fold increased frequency of colorectal neoplasia. Here, we show first that LOI leads specifically to increased expression of proliferation-related genes in mouse intestinal crypts. Surprisingly, LOI(+) mice also have enhanced sensitivity to IGF-II signaling, not simply increased IGF-II levels, because in vivo blockade with NVP-AEW541, a specific inhibitor of the IGF-II signaling receptor, showed reduction of proliferation-related gene expression to levels half that seen in LOI(-) mice. Signal transduction assays in microfluidic chips confirmed this enhanced sensitivity with marked augmentation of Akt/PKB signaling in LOI(+) cells at low doses of IGF-II, which was reduced in the presence of the inhibitor to levels below those found in LOI(-) cells, and was associated with increased expression of the IGF1 and insulin receptor genes. We exploited this increased IGF-II sensitivity to develop an in vivo chemopreventive strategy using the azoxymethane (AOM) mutagenesis model. LOI(+) mice treated with AOM showed a 60% increase in premalignant aberrant crypt foci (ACF) formation over LOI(-) mice. In vivo IGF-II blockade with NVP-AEW541 abrogated this effect, reducing ACF to a level 30% lower even than found in exposed LOI(-) mice. Thus, LOI increases cancer risk in a counterintuitive way, by increasing the sensitivity of the IGF-II signaling pathway itself, providing a previously undescribed epigenetic chemoprevention strategy in which cells with LOI are "IGF-II addicted" and undergo reduced tumorigenesis in the colon upon IGF-II pathway blockade.
Kaneda
Atsushi
A
Center for Epigenetics and Department of Medicine, Johns Hopkins University School of Medicine, 1064 Ross, 720 Rutland Avenue, Baltimore, MD 21205, USA.
Wang
Chiaochun J
CJ
Cheong
Raymond
R
Timp
Winston
W
Onyango
Patrick
P
Wen
Bo
B
Iacobuzio-Donahue
Christine A
CA
Ohlsson
Rolf
R
Andraos
Rita
R
Pearson
Mark A
MA
Sharov
Alexei A
AA
Longo
Dan L
DL
Ko
Minoru S H
MS
Levchenko
Andre
A
Feinberg
Andrew P
AP
D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology; D001397:Azoxymethane / Q000494:pharmacology; D049109:Cell Proliferation; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D018392:Genomic Imprinting; D007335:Insulin-Like Growth Factor II / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009369:Neoplasms / Q000235:genetics* / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D011743:Pyrimidines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D015398:Signal Transduction
D016588:Anticarcinogenic Agents; C501177:NVP-AEW541; D011743:Pyrimidines; D011758:Pyrroles; D007335:Insulin-Like Growth Factor II; D001397:Azoxymethane