Figure 1.
Induction of ER stress transcriptionally activates genes of the AP-1 complex in HepG2 cells.
Relative mRNA expression of A) GRP78/BIP, B) CHOP, C) CFOS, D) FRA-1, E) CJUN, and F) JUND in HepG2 cells treated with tunicamycin (Tm), homocysteine (Hcy) or thapsigargin (Tg) for 6 hours. Mean (n = 6) ± SD. * p<0.05 vs vehicle-treated control cells.
Figure 2.
Induction of ER stress in mice activates the hepatic AP-1 complex.
Relative hepatic mRNA expression of Grp78/Bip, Chop, cFos, Fra-1, cJun, and JunD in mice treated with tunicamycin (Tm) at doses of A) 2 mg/kg for 6 hours, B) 2 mg/kg for 72 hours, or C) 0.5 mg/kg over 5 days. Hepatic protein expression of total and phosphorylated CFOS and CJUN in mice treated with Tm at doses of D) 2 mg/kg for 6 hours, E) 2 mg/kg for 72 hours, or F) 0.5 mg/kg over 5 days. Quantitative PCR shown as mean (n = 6) ± SD. * p<0.05 vs vehicle-treated. Representative Western blot of pooled samples, n = 2–3.
Figure 3.
Prolonged low-grade ER stress promotes hepatocyte injury and apoptosis.
Markers of liver injury, apoptosis, and cellular proliferation in mice treated with a cumulative dose of 0.5/kg tunicamycin over 5 days. A) Representative H&E, TUNEL, and Ki67 staining of liver sections. B) Plasma ALT level (IU/L). Mean (n = 6) ± SD, *p<0.05.
Figure 4.
ER stress-induced activation of CFOS and FRA-1 is mediated by ERK1/2 signaling.
HepG2 cells pretreated with MEK1 inhibitor (PD) or vehicle followed by treatment with tunicamycin (Tm) or vehicle (control) for 6 hours. A) Representative Western blot of total and phosphorylated ERK, JNK, CFOS, and CJUN. Relative mRNA expression of B) GRP78/BIP, C) CHOP, D) CFOS, E) FRA-1, F) CJUN, and G) JUND. Mean (n = 6) ± SD. * p<0.05.
Figure 5.
Effects of ERK- and JNK-inhibition on tunicamycin-induced cytotoxicity and cellular proliferation.
Cytoxicity as measured by LDH release (A,C) and cellular proliferation as measured by BrdU incorporation (B,D) in HepG2 cells pretreated with MEK1 inhibitor (PD184352) or JNK inhibitor (SP600125) followed by treatment with tunicamycin or vehicle (control) for 6 hours. Mean (n = 6) ± SD. *p<0.05.
Figure 6.
ER stress-induced activation of CJUN and JUND is mediated by JNK signaling.
HepG2 cells pretreated with JNK inhibitor (SP600125) or vehicle followed by treatment with tunicamycin or vehicle (control) for 6 hours. A) Representative Western blot of total and phosphorylated JNK, ERK, CJUN, and CFOS. Relative mRNA expression of B) GRP78/BIP, C) CHOP, D) CJUN, E) JUND, F) CFOS, and G) FRA-1. Mean (n = 6) ± SD. * p<0.05.
Figure 7.
ER stress-induced transcriptional activation of CJUN and JUND is mediated by JNK1 signaling.
Relative mRNA expression of A) GRP78/BIP, B) CHOP, C) CJUN, D) JUND, E) CFOS, and F) FRA-1 in HepG2 cells pretreated with JNK1 siRNA or control siRNA followed by treatment with tunicamycin or vehicle (control) for 6 hours. Mean (n = 6) ± SD. * p<0.05.