Letteratura scientifica selezionata sul tema "RPC7α"

RNA polymerase III (Pol III) subunit RPC7α, which is encoded by POLR3G in humans, has been linked to both tumor growth and metastasis. Accordantly, high POLR3G expression is a negative prognostic factor in multiple cancer subtypes. To date, the mechanisms underlying POLR3G upregulation have remained poorly defined. We performed a large-scale genomic survey of mRNA and chromatin signatures to predict drivers of POLR3G expression in cancer. Our survey uncovers positive determinants of POLR3G expression, including a gene-internal super-enhancer bound with multiple transcription factors (TFs) that promote POLR3G expression, as well as negative determinants that include gene-internal DNA methylation, retinoic-acid induced differentiation, and MXD4-mediated disruption of POLR3G expression. We show that novel TFs identified in our survey, including ZNF131 and ZNF207, functionally enhance POLR3G expression, whereas MXD4 likely obstructs MYC-driven expression of POLR3G and other growth-related genes. Integration of chromatin architecture and gene regulatory signatures identifies additional factors, including histone demethylase KDM5B, as likely influencers of POLR3G gene activity. Taken together, our findings support a model in which POLR3G expression is determined with multiple factors and dynamic regulatory programs, expanding our understanding of the circuitry underlying POLR3G upregulation and downstream consequences in cancer.

Abstract A 1969 report that described biochemical and activity properties of the three eukaryotic RNA polymerases revealed Pol III as highly distinguishable, even before its transcripts were identified. Now known to be the most complex, Pol III contains several stably-associated subunits referred to as built-in transcription factors (BITFs) that enable highly efficient RNA synthesis by a unique termination-associated recycling process. In vertebrates, subunit RPC7(α/β) can be of two forms, encoded by POLR3G or POLR3GL, with differential activity. Here we review promoter-dependent transcription by Pol III as an evolutionary perspective of eukaryotic tRNA expression. Pol III also provides nonconventional functions reportedly by promoter-independent transcription, one of which is RNA synthesis from DNA 3′-ends during repair. Another is synthesis of 5′ppp-RNA signaling molecules from cytoplasmic viral DNA in a pathway of interferon activation that is dysfunctional in immunocompromised patients with mutations in Pol III subunits. These unconventional functions are also reviewed, including evidence that link them to the BITF subunits. We also review data on a fraction of the human Pol III transcriptome that evolved to include vault RNAs and snaRs with activities related to differentiation, and in innate immune and tumor surveillance. The Pol III of higher eukaryotes does considerably more than housekeeping.

RNA polymerase III composition is shaped by the mutually exclusive incorporation of two paralogous subunits, RPC7α and RPC7β, encoded by genes POLR3G and POLR3GL in vertebrates. The expression of POLR3G and POLR3GL is spatiotemporally regulated during development, and multiple reports point to RPC7α-enhanced Pol III activity patterns, indicating that Pol III identity may underly dynamic Pol III transcription patterns observed in higher eukaryotes. In cancer, upregulation of POLR3G, but not POLR3GL, is associated with poor survival outcomes among patients, suggesting differences between RPC7α and RPC7β further influence disease progression and may translate into future biomarkers and therapeutic strategies. Here, we outline our current understanding of Pol III identity and transcription and reexamine the distinct protein characteristics of Pol III subunits RPC7α and RPC7β. Drawing on both structural and genomic studies, we discuss differences between RPC7α and RPC7β and the potential mechanisms by which Pol III identity may establish differential activities during development and disease.

AbstractRNA polymerase III (Pol III) includes two alternate isoforms, defined by mutually exclusive incorporation of subunit POLR3G (RPC7α) or POLR3GL (RPC7β), in mammals. The contributions of POLR3G and POLR3GL to transcription potential has remained poorly defined. Here, we discover that loss of subunit POLR3G is accompanied by a restricted repertoire of genes transcribed by Pol III. Particularly sensitive is snaR-A, a small noncoding RNA implicated in cancer proliferation and metastasis. Analysis of Pol III isoform biases and downstream chromatin features identifies loss of POLR3G and snaR-A during differentiation, and conversely, re-establishment of POLR3G gene expression and SNAR-A gene features in cancer contexts. Our results support a model in which Pol III identity functions as an important transcriptional regulatory mechanism. Upregulation of POLR3G, which is driven by MYC, identifies a subgroup of patients with unfavorable survival outcomes in specific cancers, further implicating the POLR3G-enhanced transcription repertoire as a potential disease factor.

L'ARN polymérase (Pol) III transcrit des petits ARN non-codants qui sont essentiels pour la cellule. Chez la plupart des vertébrés, il existe deux isoformes de la Pol III selon l’incorporation de la sous-unité RPC7α ou RPC7β. Alors que RPC7β est ubiquitaire, RPC7α est exprimée dans les cellules souches embryonnaires et certaines cellules tumorales. En particulier, RPC7α est surexprimée dans des échantillons cliniques et des lignées cellulaires de cancer du sein triple négatif (CSTN). La suppression de RPC7α dans la lignée CSTN MDA-MB-231 inhibe la croissance tumorale et la formation de métastases dans un modèle murin de xénogreffe. Cependant, les mécanismes moléculaires par lesquels la Pol IIIα régule la tumorigenèse et les métastases sont encore inconnus. Dans cette thèse, je montre que la suppression de RPC7α dans les cellules MDA-MB-231 modifie l'expression de plusieurs ARN messagers dont certains impliqués dans la régulation du cancer et de l’expression des gènes. L’analyse de la localisation de RPC7α indique qu’en plus de son occupation de gènes Pol III, elle est également colocalisée sur des gènes codants avec la Pol II. Ces gènes sont parmi les plus exprimés dans les cellules MDA-MB-231 et sont impliqués dans des mécanismes importants pour les tumeurs et les métastases tels que la traduction et l’interaction des cellules avec la matrice extracellulaire. Contrairement à RPC7α, RPC7β est seulement localisée sur des gènes Pol III. Ainsi, ces résultats suggèrent que RPC7α agit avec la Pol II directement au niveau de gènes codants, peut-être pour favoriser leur expression, ce qui expliquerait son rôle important dans la croissance tumorale et la génération de métastases dans le CSTN
RNA polymerase (Pol) III transcribes small non coding RNAs that are essential for the cell. There are two Pol III isoforms containing either RPC7α or RPC7β subunit. RPC7β is ubiquitously expressed whereas RPC7α is only expressed in embryonic stem cells and some tumor cells. Particularly, RPC7α is overexpressed in triple negative breast cancer (TNBC) clinical samples and cell lines. RPC7α deletion in the TNBC cell line MDA-MB-231 reduces tumor growth and metastases formation in a xenograft mouse model. However, the molecular mechanisms by which Pol IIIα regulates tumorigenesis and metastasis are still unknown. In this thesis, I show that the suppression of RPC7α in MDA-MB-231 cells alters the expression of several messenger RNAs, some of which are involved in the regulation of cancer and gene expression. Analysis of RPC7α localization indicates that, in addition to occupying Pol III genes, RPC7α also colocalizes with Pol II on coding genes. These genes are among the most highly expressed in MDA-MB-231 cells and are involved in important mechanisms for tumors and metastasis such as translation and cell interaction with the extracellular matrix. Unlike RPC7α, RPC7β is only localized on Pol III genes. Thus, these results suggest that RPC7α acts directly with Pol II on coding genes, possibly to promote their expression, which would explain its important role in tumor growth and metastasis generation in TNBC