scholarly journals The chemotherapeutic agent CX-5461 irreversibly blocks RNA polymerase I initiation and promoter release to cause nucleolar disruption, DNA damage and cell inviability

NAR Cancer ◽  
2020 ◽  
Vol 2 (4) ◽  
Author(s):  
Jean-Clément Mars ◽  
Michel G Tremblay ◽  
Mélissa Valere ◽  
Dany S Sibai ◽  
Marianne Sabourin-Felix ◽  
...  
Keyword(s):  
Dna Damage ◽  
Rna Polymerase ◽  
Ribosomal Rna ◽  
Transcription Initiation ◽  
Ribosome Biogenesis ◽  
Chemotherapeutic Agent ◽  
Rna Polymerase I ◽  
Initiation Complex ◽  
Promoter Recruitment ◽  
Polymerase I

Abstract In the search for drugs to effectively treat cancer, the last 10 years have seen a resurgence of interest in targeting ribosome biogenesis. CX-5461 is a potential inhibitor of ribosomal RNA synthesis that is now showing promise in phase I trials as a chemotherapeutic agent for a range of malignancies. Here, we show that CX-5461 irreversibly inhibits ribosomal RNA transcription by arresting RNA polymerase I (RPI/Pol1/PolR1) in a transcription initiation complex. CX-5461 does not achieve this by preventing formation of the pre-initiation complex nor does it affect the promoter recruitment of the SL1 TBP complex or the HMGB-box upstream binding factor (UBF/UBTF). CX-5461 also does not prevent the subsequent recruitment of the initiation-competent RPI–Rrn3 complex. Rather, CX-5461 blocks promoter release of RPI–Rrn3, which remains irreversibly locked in the pre-initiation complex even after extensive drug removal. Unexpectedly, this results in an unproductive mode of RPI recruitment that correlates with the onset of nucleolar stress, inhibition of DNA replication, genome-wide DNA damage and cellular senescence. Our data demonstrate that the cytotoxicity of CX-5461 is at least in part the result of an irreversible inhibition of RPI transcription initiation and hence are of direct relevance to the design of improved strategies of chemotherapy.

scholarly journals Che-1/AATF binds to RNA polymerase I machinery and sustains ribosomal RNA gene transcription

2020 ◽  
Vol 48 (11) ◽  
pp. 5891-5906 ◽  
Author(s):  
Cristina Sorino ◽  
Valeria Catena ◽  
Tiziana Bruno ◽  
Francesca De Nicola ◽  
Stefano Scalera ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Rna Polymerase ◽  
Ribosomal Rna ◽  
Ribosome Biogenesis ◽  
Cellular Proliferation ◽  
Rna Polymerase I ◽  
Rrna Synthesis ◽  
Rrna Gene ◽  
Response To Stress ◽  
Polymerase I

Abstract Originally identified as an RNA polymerase II interactor, Che-1/AATF (Che-1) has now been recognized as a multifunctional protein involved in cell-cycle regulation and cancer progression, as well as apoptosis inhibition and response to stress. This protein displays a peculiar nucleolar localization and it has recently been implicated in pre-rRNA processing and ribosome biogenesis. Here, we report the identification of a novel function of Che-1 in the regulation of ribosomal RNA (rRNA) synthesis, in both cancer and normal cells. We demonstrate that Che-1 interacts with RNA polymerase I and nucleolar upstream binding factor (UBF) and promotes RNA polymerase I-dependent transcription. Furthermore, this protein binds to the rRNA gene (rDNA) promoter and modulates its epigenetic state by contrasting the recruitment of HDAC1. Che-1 downregulation affects RNA polymerase I and UBF recruitment on rDNA and leads to reducing rDNA promoter activity and 47S pre-rRNA production. Interestingly, Che-1 depletion induces abnormal nucleolar morphology associated with re-distribution of nucleolar proteins. Finally, we show that upon DNA damage Che-1 re-localizes from rDNA to TP53 gene promoter to induce cell-cycle arrest. This previously uncharacterized function of Che-1 confirms the important role of this protein in the regulation of ribosome biogenesis, cellular proliferation and response to stress.

scholarly journals Ribosomal RNA Transcription Regulation in Breast Cancer

Genes ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 502
Author(s):  
Cecelia M. Harold ◽  
Amber F. Buhagiar ◽  
Yan Cheng ◽  
Susan J. Baserga
Keyword(s):  
Breast Cancer ◽  
Rna Polymerase ◽  
Ribosomal Rna ◽  
Ribosome Biogenesis ◽  
Rna Polymerase I ◽  
Cancer Therapies ◽  
Rdna Transcription ◽  
Global Protein Synthesis ◽  
Novel Drugs ◽  
Polymerase I

Ribosome biogenesis is a complex process that is responsible for the formation of ribosomes and ultimately global protein synthesis. The first step in this process is the synthesis of the ribosomal RNA in the nucleolus, transcribed by RNA Polymerase I. Historically, abnormal nucleolar structure is indicative of poor cancer prognoses. In recent years, it has been shown that ribosome biogenesis, and rDNA transcription in particular, is dysregulated in cancer cells. Coupled with advancements in screening technology that allowed for the discovery of novel drugs targeting RNA Polymerase I, this transcriptional machinery is an increasingly viable target for cancer therapies. In this review, we discuss ribosome biogenesis in breast cancer and the different cellular pathways involved. Moreover, we discuss current therapeutics that have been found to affect rDNA transcription and more novel drugs that target rDNA transcription machinery as a promising avenue for breast cancer treatment.

scholarly journals Formation of the transcription initiation complex on mammalian rDNA.

1986 ◽  
Vol 6 (10) ◽  
pp. 3418-3427 ◽  
Author(s):  
H Kato ◽  
M Nagamine ◽  
R Kominami ◽  
M Muramatsu
Keyword(s):  
Rna Polymerase ◽  
Transcription Initiation ◽  
Short Pulse ◽  
Rna Polymerase I ◽  
Rrna Gene ◽  
Preinitiation Complex ◽  
Initiation Complex ◽  
Transcription Initiation Complex ◽  
Polymerase I

Steps for the formation of transcription initiation complex on the human rRNA gene (rDNA) in vitro were analyzed with partially purified transcription factors and RNA polymerase I. The reaction requires at least two factors besides RNA polymerase I for maximal efficiency. Preincubation and short-pulse analyses of the accurate transcripts revealed the following steps. First, the species-dependent factor, designated TFID, bound to the rDNA template, forming a preinitiation complex (PIC-1) which was resistant to a moderate concentration (0.015 to 0.02%) of Sarkosyl. Other factors, designated TFIA and RNA polymerase I, were then added to convert it to the final preinitiation complex PIC-3. This complex incorporated the first two nucleoside triphosphates of the starting site to complete the initiation complex (IC), which was resistant to a high concentration (0.2%) of Sarkosyl. Binding of TFID was rate limiting in the overall initiation reaction in vitro. Together with the kinetics of incorporation, the results are interpreted to mean that TFID, one bound, remains complexed with rDNA together with TFIA as the PIC-2 for many rounds of transcription by RNA polymerase I. Thus, the formation of PIC-2 may be a prerequisite for the stable opening of rDNA for transcription in vivo.

Formation of the transcription initiation complex on mammalian rDNA

1986 ◽  
Vol 6 (10) ◽  
pp. 3418-3427
Author(s):  
H Kato ◽  
M Nagamine ◽  
R Kominami ◽  
M Muramatsu
Keyword(s):  
Rna Polymerase ◽  
Transcription Initiation ◽  
Short Pulse ◽  
Rna Polymerase I ◽  
Rrna Gene ◽  
Preinitiation Complex ◽  
Initiation Complex ◽  
Transcription Initiation Complex ◽  
Polymerase I

Steps for the formation of transcription initiation complex on the human rRNA gene (rDNA) in vitro were analyzed with partially purified transcription factors and RNA polymerase I. The reaction requires at least two factors besides RNA polymerase I for maximal efficiency. Preincubation and short-pulse analyses of the accurate transcripts revealed the following steps. First, the species-dependent factor, designated TFID, bound to the rDNA template, forming a preinitiation complex (PIC-1) which was resistant to a moderate concentration (0.015 to 0.02%) of Sarkosyl. Other factors, designated TFIA and RNA polymerase I, were then added to convert it to the final preinitiation complex PIC-3. This complex incorporated the first two nucleoside triphosphates of the starting site to complete the initiation complex (IC), which was resistant to a high concentration (0.2%) of Sarkosyl. Binding of TFID was rate limiting in the overall initiation reaction in vitro. Together with the kinetics of incorporation, the results are interpreted to mean that TFID, one bound, remains complexed with rDNA together with TFIA as the PIC-2 for many rounds of transcription by RNA polymerase I. Thus, the formation of PIC-2 may be a prerequisite for the stable opening of rDNA for transcription in vivo.

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