XPB, a subunit of TFIIH, is a target of the natural product triptolide

Abstract

Triptolide (1) is a structurally unique diterpene triepoxide isolated from a traditional Chinese medicinal plant with anti-inflammatory, immunosuppressive, contraceptive and antitumor activities. Its molecular mechanism of action, however, has remained largely elusive to date. We report that triptolide covalently binds to human XPB/ERCC3, a subunit of the transcription factor TFIIH, and inhibits its DNA-dependent ATPase activity, which leads to the inhibition of RNA Polymerase II mediated transcription and likely nucleotide excision repair. The identification of XPB as the target of triptolide accounts for the majority of the known biological activities of triptolide. These findings also suggest that triptolide can serve as a novel molecular probe for studying transcription and, potentially, as a new type of anticancer agents through inhibition of the ATPase activity of XPB.

Triptolide-induced Cell Death in Pancreatic Cancer Is Mediated by O-GlcNAc Modification of Transcription Factor Sp1

“…However, its mechanisms of action have remained elusive. Studies using non-physiological doses of 10 M have indicated that this compound inhibits the XPB subunit of RNA polymerase IIB and shuts down global transcription (36). However, for most cancer cells, the LD 50 for triptolide has been found to be 100 nmol/liter (37), at which XPB remains unaffected.…”

DNA damage-induced ATM- and Rad-3-related (ATR) kinase activation in non-replicating cells is regulated by the XPB subunit of transcription factor IIH (TFIIH)

“…In contrast, DRB specifically inhibits the CDK9 kinase activity of the positive transcription elongation factor P-TEFb, which normally phosphorylates RNA polymersase II and facilitates the transition of the polymerase from its initiated to its elongating state. Lastly, TPL forms a covalent complex with the XPB subunit of TFIIH, which inactivates the ATPase activity of the enzyme and prevents the initiation of transcription (55).…”

“…Triptolide forms a covalent complex with the XPB subunit of transcription factor IIH (TFIIH) (55), which inhibits the ATPase activity of XPB that is required for TFIIH to unwind DNA during the initiation of transcription so that previously loaded RNA polymerase II can synthesize mRNA. Thus, TPL acts in a different manner than that of ActD or DRB, which instead inhibit transcriptional elongation via intercalation into DNA and by preventing RNA polymerase II phosphorylation (54), respectively.…”

Triptolide Inhibits Histone Methyltransferase EZH2 and Modulates the Expression of Its Target Genes in Prostate Cancer Cells

“…In view of previous studies (Liu et al, 2009;Titov et al, 2011;Huang et al, 2012), we can not state certainly that EZH2 inhibition is the sole mechanism of action that results in cell growth inhibition; however, considering Triptolide for 24h. Total RNA was isolated and qRT-PCR was performed with specific primers for the indicated target genes that are either transcriptionally repressed (A) or activated (B) by EZH2.…”

“…Numerous studies suggested that the expression of EZH2 was modulated at the transcriptional, posttranscriptional and post-translational levels (Chang et al, 2012). Recent works reported that Triptolide bound to a subunit of the transcription factor TFIIH (XPB) and induced degradation of the subunit of RNA polymeraseII (Rpb1) (Titov et al, 2011;Wang et al, 2011), resulting in transcriptional inhibition. Future work is needed to elucidate whether these novel mechanisms contribute to the effect of Triptolide on EZH2 and to provide more details on how Triptolide downregulates the expression of EZH2.…”