Journal Article

Inhibition of the de novo pyrimidine biosynthesis pathway limits ribosomal RNA transcription causing nucleolar stress in glioblastoma cells

Venkateswaran, Niranjan, Kilgore, Jessica A., Kanji, Suman, Burma, Sandeep, Lafita-Navarro, M. Carmen, Buszczak, Michael, Conacci-Sorrell, Maralice, Barnes, Spencer, Han, Jungsoo, Williams, Noelle S.

2020

Overview

Glioblastoma is the most common and aggressive type of cancer in the brain; its poor prognosis is often marked by reoccurrence due to resistance to the chemotherapeutic agent temozolomide, which is triggered by an increase in the expression of DNA repair enzymes such as MGMT. The poor prognosis and limited therapeutic options led to studies targeted at understanding specific vulnerabilities of glioblastoma cells. Metabolic adaptations leading to increased synthesis of nucleotides by de novo biosynthesis pathways are emerging as key alterations driving glioblastoma growth. In this study, we show that enzymes necessary for the de novo biosynthesis of pyrimidines, DHODH and UMPS, are elevated in high grade gliomas and in glioblastoma cell lines. We demonstrate that DHODH’s activity is necessary to maintain ribosomal DNA transcription (rDNA). Pharmacological inhibition of DHODH with the specific inhibitors brequinar or ML390 effectively depleted the pool of pyrimidines in glioblastoma cells grown in vitro and in vivo and impaired rDNA transcription, leading to nucleolar stress. Nucleolar stress was visualized by the aberrant redistribution of the transcription factor UBF and the nucleolar organizer nucleophosmin 1 (NPM1), as well as the stabilization of the transcription factor p53. Moreover, DHODH inhibition decreased the proliferation of glioblastoma cells, including temozolomide-resistant cells. Importantly, the addition of exogenous uridine, which reconstitutes the cellular pool of pyrimidine by the salvage pathway, to the culture media recovered the impaired rDNA transcription, nucleolar morphology, p53 levels, and proliferation of glioblastoma cells caused by the DHODH inhibitors. Our in vivo data indicate that while inhibition of DHODH caused a dramatic reduction in pyrimidines in tumor cells, it did not affect the overall pyrimidine levels in normal brain and liver tissues, suggesting that pyrimidine production by the salvage pathway may play an important role in maintaining these nucleotides in normal cells. Our study demonstrates that glioblastoma cells heavily rely on the de novo pyrimidine biosynthesis pathway to generate ribosomal RNA (rRNA) and thus, we identified an approach to inhibit ribosome production and consequently the proliferation of glioblastoma cells through the specific inhibition of the de novo pyrimidine biosynthesis pathway.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Animals / Antineoplastic Agents - pharmacology / Antineoplastic Agents - therapeutic use / Biology and Life Sciences / Biosynthesis / Biphenyl Compounds - pharmacology / Biphenyl Compounds - therapeutic use / Brain cancer / Brain Neoplasms - drug therapy / Brain Neoplasms - pathology / Brain tumors / Breast cancer / Cancer / Cancer cells / Cancer genetics / Cancer research / Cancer therapies / Cell growth / Cell Line, Tumor / Cell Nucleolus - drug effects / Cell Nucleolus - metabolism / Cell proliferation / Cell size / Deoxyribonucleic acid / Dihydroorotate Dehydrogenase / DNA / Drug Screening Assays, Antitumor / Enzymes / Female / Fibroblasts / Genetic aspects / Genetic transcription / Genomes / Glioblastoma / Glioblastoma - drug therapy / Glioblastoma - pathology / Glioblastoma cells / Glioblastoma multiforme / Glioblastomas / Humans / Kinases / Leukemia / Malignancy / Medical prognosis / Medicine and Health Sciences / Mice / Multienzyme Complexes - antagonists & inhibitors / Multienzyme Complexes - metabolism / Myc protein / Nucleoli / Nucleophosmin / Oncology, Experimental / Orotate Phosphoribosyltransferase - antagonists & inhibitors / Orotate Phosphoribosyltransferase - metabolism / Orotidine-5'-Phosphate Decarboxylase - antagonists & inhibitors / Orotidine-5'-Phosphate Decarboxylase - metabolism / Oxidoreductases Acting on CH-CH Group Donors - antagonists & inhibitors / Oxidoreductases Acting on CH-CH Group Donors - metabolism / Patients / Phosphorylation / Physical Sciences / Physiological aspects / Protein synthesis / Proteins / Pyrimidines / Pyrimidines - biosynthesis / Radiation therapy / Research and Analysis Methods / Ribosomal RNA / Ribosomes - drug effects / Ribosomes - metabolism / RNA polymerase / RNA, Ribosomal - biosynthesis / rRNA / Stress, Physiological - drug effects / Transcription (Genetics) / Transcription, Genetic - drug effects / Tumor Suppressor Protein p53 - metabolism / Tumors / Xenograft Model Antitumor Assays