Activation of transcription factor AP-1 in response to thermal injury in rat small intestine and IEC-6 cells
Zhang et al. BMC Gastroenterology
Activation of transcription factor AP-1 in response to thermal injury in rat small intestine and IEC-6 cells
Yonghong Zhang 1
Hong Zhao 1
Tao Liu 1
Changrong Wan 2
Xiaoxi Liu 1 2
Zhimin Gao 1
Xiaolin Hou 1
Linshu Jiang 0 1
Fenghua Liu 0 1
0 Equal contributors
1 Beijing Key Laboratory for Dairy Cow Nutrition, Beijing University of Agriculture , No. 7, Beinong Road, Changping District, Beijing 102206 , P. R. China
2 TCVM Laboratory, College of Veterinary Medicine, China Agricultural University , Beijing 100193 , China
Background: Our previous studies indicated that heat stress can cause significant damage to the intestinal epithelium and induce differential expression of many genes in rat small intestine. The transcription factors AP-1 and NF-κB, which act as important mediators by binding to specific DNA sequences within gene promoters, regulate the transcription of genes associated with immune regulation, stress response and cell fate. Methods: To determine whether AP-1 and NF-κB are involved in hyperthermia-induced injury in rat small intestine and IEC-6 cells, we investigated their activity, and the expression of related proteins, by electrophoretic mobility shift assays and western blotting, respectively. Results: Heat stress resulted in severe damage to the epithelium of the small intestine. The cell morphology and viability were obviously altered when IEC-6 cell was exposed to hyperthermia. AP-1 was activated in the small intestine of heat-stressed rats, as was phosphorylation of the JNK signaling pathway. In IEC-6 cell line, AP-1 activation in groups exposed to 42 °C for 1 h, 2 h and 4 h was significantly increased. In contrast, NF-κB was not activated in both in vivo and in vitro models. Conclusion: These results reveal that AP-1 is likely to play an important role in regulating gene transcription in rat small intestine and IEC-6 cells during exposure to heat stress.
AP-1; NF-κB; Heat stress; Rat small intestine; IEC-6
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Background
As one important physical stimulus, ambient temperature
can evoke a series of drastic changes in biological function
[1] including gastrointestinal injury and dysfunction [2].
Our previous studies have shown that heat stress can
induce damage in the rat small intestine, along with
differential expression of many genes associated with immune
regulation and metabolism, and those encoding regulatory
peptides [3]. A number of growth-related molecules (such
as Gdf15, Gdf9, Ctgf, and Egfr) which are critical for
cellular survival, proliferation and migration, have also been
shown to be differentially expressed in response to
hyperthermia-induced damage [4].
Transcription factors, important mediators involved in
signal transduction, bind to specific DNA sequences
within gene promoters, and thus regulate transcriptional
activity. Both NF-κB and AP-1 are well known pleiotropic
transcription factors that independently and/or
complementarily regulate a large number of genes related to a
wide range of functions, including immune regulation,
proliferation, differentiation, and apoptosis [5, 6].
NF-κB is a ubiquitous transcription factor and a
member of a family of proteins that are important regulators
of a variety of responses. NF-κB exists as a dimer
predominantly composed of p50 and p65 subunits, although
it also contains other family members, such as RelB,
cRel, v-Rel and p52 [7]. The activity of NF-κB is regulated
by a family of IκB inhibitor proteins [8], which sequester
NF-κB in the cytoplasm. In response to various external
pathogenic stimuli, IκB is phosphorylated, ubiquitinated,
and subsequently degraded by a proteosome-dependent
pathway. Degradation of IκB allows NF-κB to translocate
into the nucleus, where it binds to specific promoter
elements and induces gene transcription.
AP-1 is a central switch to convert extracellular signals
into genetic responses and to determine cell
proliferation, differentiation, and apoptosis. AP-1 complex
consists of homodimers and heterodimers formed by a
group of transcription factors, including members of the
Jun, Fos, and ATF families [9]. Previous studies indicate
that the c-Jun/ATF-2 heterodimer is one of the main
components of expression pathways associated with
oncogenesis [9] and the extreme cellular stress of
ischemia and reperfusion [10]. JNK is one member of the
mitogen-activated protein kinase (MAPK) family, which
play crucial roles in many responses [11]. JNK was
initially described as a stress-induced protein kinase acting
to phosphorylate the NH2-terminus of the transcription
factor c-Jun; hence, this pathway is often referred to as
the stress-activated protein kinase (SAPK) pathway [12].
Multiple stresses increase JNK activity including UV,
rirradiation, cytotoxic drugs, ischemia and reactive oxygen
species. JNK phosphorylates several transcription factors
including c-Jun, ATF-2, and p53 [13], which in turn
regulate the expression of genes mediating cell proliferation,
differentiatio (...truncated)