Download Aberrant JAK/STAT signaling confer epigenetic silencing of NR4A3

Aberrant JAK/STAT signaling confer epigenetic silencing of
NR4A3 and is associated with poor prognosis in gastric cancer
Speaker: Liang-Yu Chang
Adviser: Michael W.Y. Chan
Date : 2010/05/28
Abstract:
Gastric cancer is the 2nd leading cause of cancer worldwide. One of the major risk factors is
infection of H. pylori, particularly the CagA-positive H. pylori. Previous studies demonstrated that
infection of CagA-positive H. pylori induced activation of JAK/STAT3 signaling pathway. However,
the role of aberrant activation of this signaling pathway is unclear. Epigenetic alteration frequently
occurred in human cancer and is considered as hallmark of caner. However, how this alteration
occurred is not fully understood. We hypothesized that aberrant activation of JAK/STAT signaling
may lead to epigenetic silencing of STAT3 target genes in gastric cancer.
In this study, we transfected a constitutively activated mouse STAT3 mutant (Stat3c) into
MKN28 gastric cancer cell line in which the JAK/STAT signaling pathway is not active. Stat3c
stable transfectant MKN28/STATc-16(S16) showing hyper-phosphorylation of STAT3 showed
increased cell proliferation as compared to vector control MKN28/C-9(C9). To identify STAT3
target genes that are epigenetically silenced in S16 cells, expression microarray (Agilent 44K
oligonucleotide microarray) coupled with bioinformatic analysis were performed. Our result
showed that there are 18 downregulated genes with a STAT3 binding site around the promoter CpG
island.
Among the 18 STAT3 targets, NR4A3 and LOXL4 showed increased promoter methylation and
demethylation treatment restored expression of these 2 genes in S16 cells. These phenomena may
be partially related to the up-regulation of DNMT1 in S16 cells. We further investigated the
promoter methylation of these two genes in 48 primary gastric cancer samples using quantitative
MSP. Our results showed that methylation of LOXL4 correlate with that of NR4A3 in a sub-set of
gastric cancer showing high methylation level of this gene. Interestingly, there is a trend that the
degree of NR4A3 methylation correlated with STAT3 nuclear translocation in a sub-set of samples.
Importantly, high methylation of NR4A3 is significantly associated with poor prognosis of the
cancer patients. However, such correlation was not observed in LOXL4 thus suggestion that
methylation of LOXL4 may be associated with early gastric carcinogenesis. In conclusion, our
result demonstrated that aberrant JAK/STAT3 signaling may lead to epigenetic silencing of its
target genes in gastric cancer. Methylation of NR4A3 may be able to predict survival in gastric
cancer. In the future, the role of STAT3 in the initiation of methylation and the functional role of
NR4A3 and LOXL4 in gastric carcinogenesis would be investigated.