Triptolide is an inhibitor of RNA polymerase I and II–dependent transcription leading predominantly to down-regulation of short-lived mRNA

Abstract

Triptolide, a natural product extracted from the Chinese plant Tripterygium wilfordii, possesses antitumor properties. Despite numerous reports showing the proapoptotic capacity and the inhibition of NF-κB-mediated transcription by triptolide, the identity of its cellular target is still unknown. To clarify its mechanism of action, we further investigated the effect of triptolide on RNA synthesis in the human non-small cell lung cancer cell line A549. Triptolide inhibited both total RNA and mRNA de novo synthesis, with the primary action being on the latter pool. We used 44K human pan-genomic DNA microarrays and identified the genes primarily affected by a short treatment with triptolide. Among the modulated genes, up to 98% are down-regulated, encompassing a large array of oncogenes including transcription factors and cell cycle regulators. We next observed that triptolide induced a rapid depletion of RPB1, the RNA polymerase II main subunit that is considered a hallmark of a transcription elongation blockage. However, we also show that triptolide does not directly interact with the RNA polymerase II complex nor does it damage DNA. We thus conclude that triptolide is an original pharmacologic inhibitor of RNA polymerase activity, affecting indirectly the transcription machinery, leading to a rapid depletion of short-lived mRNA, including transcription factors, cell cycle regulators such as CDC25A, and the oncogenes MYC and Src. Overall, the data shed light on the effect of triptolide on transcription, along with its novel potential applications in cancers, including acute myeloid leukemia, which is in part driven by the aforementioned oncogenic factors. [Mol Cancer Ther 2009;8(10):2780-90]

Targeting RNA Polymerase I with an Oral Small Molecule CX-5461 Inhibits Ribosomal RNA Synthesis and Solid Tumor Growth

“…3C) cells to 300 nmol/L CX-5461 (that resulted in 63% and 55% reductions in pre-rRNA, respectively), an equal number of Pol II-transcribed genes were significantly upregulated as were downregulated. These changes in Pol II transcription were most likely secondary to the inhibition of Pol I by CX-5461, as an inhibition of Pol II transcription results in a distribution significantly skewed to the negative (16). To further illustrate selectivity of CX-5461 for Pol I versus Pol II transcription, we compared it with another drug (actinomycin D) known to inhibit Pol I transcription.…”

Natural Product Triptolide Mediates Cancer Cell Death by Triggering CDK7-Dependent Degradation of RNA Polymerase II

“…Triptolide possesses multiple apparently unrelated activities, including anti-inflammatory, immunosuppressive, antifertility, anticystogenesis, and anticancer activities (1), which seem to suggest multiple molecular mechanisms involved in those activities. Moreover, according to a comparative analysis using the NCI-60 internal database, the GI 50 profile of triptolide is significantly different from those of 118 reference anticancer compounds (2), suggesting that triptolide could have anticancer mechanisms and molecular targets potentially distinct from those of other anticancer agents. Consistent with its various activities, triptolide has been revealed to interact with several cellular proteins, including polycystin-2 (PC-2), disintegrin and metalloprotease 10 (ADAM10), dCTP pyrophosphatase 1 (DCTPP1), and XPB (1).…”

“…Triptolide inhibits RNA polymerase II (RNAPII)-dependent transcription, showing a distinct mode of action from those of other known transcriptional inhibitors, including 5,6-dichloro-1-b-D-ribofuranosylbenz-imidazole (DRB) and flavopiridol (CDK9 inhibitors), actinomycin D (a DNA binder), and a-amanitin (an RNAPII inhibitor; refs. [2][3][4][5]. Triptolide is thus considered to be a new type of transcriptional inhibitors (4).…”

“…Treatment with triptolide at low concentrations and/or short exposure largely inhibits the transcription of short-lived mRNA, and possibly as a compensatory response, increases the transcription of some other genes such as p53. In contrast, its high concentrations and persistent exposure could reduce 80% mRNA transcription (2). Two factors, XPB inhibition and RNAPII degradation induced by triptolide, have been proposed to be responsible for its transcriptional inhibition (1,6).…”

Molecular and Celluar Mechanism Studies on Anticancer Effects of Chinese Medicines

“…In endometrial and ovarian cancer cells, triptolide has been reported to have the anti-growth activity via targeting some specific genes, such as LRAP, CDH4, SFRP1 and so on . Besides, some studies indicate that triptolide could act as the inhibitor of RNA polymerase I and II-dependent transcription promoting some short-lived mRNA, for example cell cycle regulator CDC25A (Vispé et al, 2009). Celastrol is another main component isolated from radix tripterygii wilfordii, which has been reported to have the anti-cancer effect in cancer cell lines including leukemia , glioma ) and so on.…”