Tribble 3, a novel oxidized low-density lipoprotein-inducible gene, is induced via the activating transcription factor 4-C/EBP homologous protein pathway.
1. C/EBP homologueueueous protein (CHOP), an endoplasmic reticulum (ER) stress-inducible protein, has a critical role in regulation of the cell cycle and apoptosis by forming heterodimers with other C/EBP proteins. However, how CHOP function is regulated remains to be determined. The human homologue of Drosophila tribbles (TRIB3) is associated with CHOP and is upregulated by oxidized low-density lipoprotein (ox-LDL). The aim of the present study was to investigate the role of CHOP in ox-LDL-induced TRIB3 expression in macrophages. 2. Human monocyte-derived macrophages were treated with various concentrations of ox-LDL (0, 2.5, 5, 10, 25 and 50 microg/mL) or 2 microg/mL tunicamycin for 0, 4, 8, 16, 24 and 48 h or were transfected with CHOP or TRIB3 expression plasmid and TRIB3 targeting short interference RNA (siRNA). The expression of CHOP and activating transcription factor 4 (ATF4) mRNA in treated cells was detected by quantitative real-time polymerase chain reaction (PCR). 3. The expression of CHOP and ATF4 mRNA increased with increasing concentrations of ox-LDL and duration of time. The ox-LDL-induced expression of TRIB3 mRNA was upregulated later than the expression of CHOP and ATF4 mRNA. Overexpression of CHOP increased the mRNA expression of TRIB3, which was further increased in CHOP-overexpressing macrophages treated with ox-LDL. Overexpression of TRIB3 suppressed the expression of CHOP, whereas TRIB3 silencing increased CHOP expression following ox-LDL stimulation by a negative feedback mechanism. 4. In conclusion, the expression of ATF4 and CHOP is upregulated by ox-LDL in a dose- and time-dependent manner in naturally differentiated human macrophages. Oxidized LDL induces TRIB3 expression via an ATF4/CHOP-dependent ER stress pathway.
Shang
Yuan-Yuan
YY
Department of Cardiology, Key Laboratory of Cardiovascular Remodelling and Function Research, Chinese Ministry of Education and Chinese Ministry of Public Health, Qilu Hospital of Shandong University, Ji'nan, China.
Zhong
Ming
M
Zhang
Li-Ping
LP
Guo
Zhong-Xiu
ZX
Wang
Zhi-Hao
ZH
Zhang
Yun
Y
Deng
Jing-Ti
JT
Zhang
Wei
W
D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism* / Q000037:antagonists & inhibitors; D034741:RNA, Small Interfering / Q000494:pharmacology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014415:Tunicamycin / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects*
D018797:Cell Cycle Proteins; C497249:DDIT3 protein, human; D008077:Lipoproteins, LDL; D034741:RNA, Small Interfering; D012097:Repressor Proteins; C474831:TRIB3 protein, human; C099252:oxidized low density lipoprotein; D014415:Tunicamycin; D051701:Activating Transcription Factor 4; D051742:Transcription Factor CHOP; D017346:Protein Serine-Threonine Kinases