Discovery and preliminary SAR of bisbenzylisoquinoline alkaloids as inducers of C/EBPα

A high throughput in vitro screen has been developed to identify substances that induce expression of C/EBPα in tumor cells. An extract of the fruit of Gyrocarpus jacquinii showed induction of C/EBPα activity that was attributed to the bisbenzylisoquinoline (BBIQ) alkaloid pheanthine (13) by dereplication analysis. The research project was broadened to assess the effect of other natural BBIQ structural types occurring outside the genus Gyrocarpus. Several of the 28 compounds assayed showed enhancement of C/EBPα induction in U937 cells. The results of this study should encourage future efforts toward obtaining and screening a larger set of both natural and synthetic analogs of this interesting group of alkaloids.     

Artemisinic acid is a regulator of adipocyte differentiation and C/EBP δ expression

Adipocyte dysfunction is associated with the development of obesity. In this study, artemisinic acid, which was isolated from Artemisia annua L., inhibited adipogenic differentiation of human adipose tissue-derived mesenchymal stem cells (hAMSCs) and its mechanism of action was determined. The mRNA levels of peroxidase proliferation-activated receptor (PPAR) γ and CCAAT/enhancer binding protein (C/EBP) α, late adipogenic factors, were reduced by artemisinic acid. Moreover, the mRNA levels of the PPAR γ target genes lipoprotein lipase, CD36, adipocyte protein, and liver X receptor were down-regulated by artemisinic acid. Artemisinic acid reduced expression of the C/EBP δ gene without impacting C/EBP β. In addition, attempts to elucidate a possible mechanism underlying the artemisinic acid-mediated effects revealed that reduced expression of the C/EBP δ gene was mediated by inhibiting Jun N-terminal kinase (JNK). Additionally, artemisinic acid also reduced the expression of the adipogenesis-associated genes glucose transporter-4 and vascular endothelial growth factor. In addition to the interference of artemisinic acid with adipogenesis, artemisinic acid significantly attenuated tumor necrosis factor-α-induced secretion of interleukin-6 by undifferentiated hAMSCs, thus influencing insulin resistance and the inflammatory state characterizing obesity. Taken together, these findings indicate that inhibiting adipogenic differentiation of hAMSCs by artemisinic acid occurs primarily through reduced expression of C/EBP δ, which is mediated by the inhibition of JNK and suggest that aremisinic acid may be used as a complementary treatment option for obesity associated with metabolic syndrome.     

The methylation of C/EBP β gene promoter and regulated by GATA-2 protein

Mammalian genomes are punctuated by DNA sequences containing an atypically high frequency of CpG sites (CpG islands; CGIs) that are associated with the majority of annotated gene promoters. Methylated C bases of CpG sites inhibit the expression of downstream genes. During the differentiation of 3T3-L1 preadipocytes, the CCAAT/enhancer-binding protein (C/EBP) β gene plays an important role. We studied the CpG island methylation status of the C/EBP β promoter and its relationship with the GATA-2 protein. We used computer analysis to determine that the C/EBP β promoter sequence is rich in CGIs, and observed that two of seven methylated C bases were demethylated during the preadipocyte differentiation using bisulfite sequencing PCR (BSP). This corresponded with the onset of notable C/EBP β gene expression. Immunofluorescence and molecular docking showed that the GATA-2 protein binds the C/EBP β promoter in front of the first demethylated CpG site. We also found that expression of GATA-2 and C/EBP β proteins is negatively correlated. These results indicate that the methylated C bases in the C/EBP β promoter relate to expression of the C/EBP β gene, and that its demethylation is linked with GATA-2 protein association.     

C/EBPα基因与肿瘤

C/EBPα基因是抑癌基因,有抑制增殖、促进分化和调节DNA损伤反应等作用。各种机制如对抗性的蛋白质-蛋白质相互作用、基因突变和翻译后修饰等导致C/EBPα转录抑制或活性丧失,可能诱发肿瘤。本文结合国内外研究现状,介绍C/EBPα基因的结构、功能及与肿瘤的诊断、治疗和预后的关系。