CHOP and AP-1 cooperatively mediate PUMA expression during lipoapoptosis.
Endoplasmic reticulum (ER) stress-mediated apoptosis is a key feature of hepatocyte cytotoxicity by saturated free fatty acids (FFA). This lipoapoptosis is dependent, in part, on the transcriptional upregulation of the BH3-only protein PUMA (p53 upregulated modulator of apoptosis). Although the activator protein (AP)-1 complex facilitates PUMA expression by saturated FFA, the transcription factor CAAT/enhancer binding homologous protein (CHOP) is also induced by ER stress and promotes apoptosis. To integrate the role of these two transcription factors in ER stress-induced apoptosis, we examined the relative contribution of CHOP and AP-1 in mediating PUMA induction by saturated FFA. Our results demonstrate that short-hairpin RNA-targeted knockdown of CHOP attenuates palmitate-induced apoptosis in Huh-7 cells. Loss of CHOP induction also reduced the increase in PUMA mRNA and protein levels as well as Bax activation by palmitate. No functional CHOP binding sites were identified in the PUMA promoter sequence. Rather, we observed that CHOP physically interacts with the AP-1 complex protein c-Jun upon palmitate treatment, and a CHOP:phosphorylated c-Jun heteromeric complex binds to the AP-1 consensus binding sequence within the PUMA promoter region. Finally, loss of function studies suggest that both transcription factors are necessary for maximal PUMA induction. Collectively, these data suggest that CHOP and AP-1 cooperatively mediate PUMA induction during hepatocyte lipoapoptosis.
Cazanave
Sophie C
SC
Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
Elmi
Nafisa A
NA
Akazawa
Yuko
Y
Bronk
Steven F
SF
Mott
Justin L
JL
Gores
Gregory J
GJ
D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005234:Fatty Liver / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D022781:Hepatocytes / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D019301:Oleic Acid / Q000378:metabolism*; D019308:Palmitic Acid / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D015854:Up-Regulation; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; C438378:BBC3 protein, human; C497249:DDIT3 protein, human; D011518:Proto-Oncogene Proteins; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D051028:bcl-2-Associated X Protein; D051742:Transcription Factor CHOP; D019301:Oleic Acid; D019308:Palmitic Acid