Nuclear upregulation of PI3K p110β correlates with increased rRNA transcription in endometrial cancer cells

Mazloumi Gavgani, F.; Karlsson, T.; Tangen, I. L.; Papdine Morovicz, A.; Smith Arnesen, V.; Turcu, D.; Krakstad, C.; Guillermet-Guibert, J.; Lewis, A. E.

doi:10.1101/2019.12.20.884122

bioRxiv · 10.1101/2019.12.20.884122

Nuclear upregulation of PI3K p110β correlates with increased rRNA transcription in endometrial cancer cells

Mazloumi Gavgani, F.·Karlsson, T.·Tangen, I. L.·Papdine Morovicz, A.·Smith Arnesen, V.·Turcu, D.·Krakstad, C.·Guillermet-Guibert, J.·Lewis, A. E.

View original source ↗Export metadata ↓

Abstract

Genes encoding for components of the phosphoinositide 3-kinase (PI3K) pathway are frequently mutated in cancer, including inactivating mutations of PTEN and activating mutations of PIK3CA, encoding the PI3K catalytic subunit p110. PIK3CB, encoding p110{beta}, is rarely mutated, but can contribute to tumourigenesis in some PTEN-deficient tumours. The underlying molecular mechanisms are however poorly understood. By analysing cell lines and annotated clinical samples, we have previously found that p110{beta} is highly expressed in endometrial cancer (EC) cell lines and that PIK3CB mRNA levels increase early in primary tumours correlating with lower survival. Selective inhibition of p110 and p110{beta} led to different effects on cell signalling and cell function, p110 activity being correlated to cell survival in PIK3CA mutant cells and p110{beta} with cell proliferation in PTEN-deficient cells. To understand the mechanisms governing the differential roles of these isoforms, we assessed their sub-cellular localisation. p110 was cytoplasmic whereas p110{beta} was both cytoplasmic and nuclear with increased levels in both compartments in cancer cells. Immunohistochemistry of p110{beta} in clinically annotated patient tumour sections revealed high nuclear/cytoplasmic staining ratio, which correlated significantly with higher grades. Consistently, the presence of high levels of p110{beta} in the nuclei of EC cells, correlated with high levels of its product phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) in the nucleus. Using immunofluorescence labelling, we observed both p110{beta} and PtdIns(3,4,5)P3 in the nucleoli of EC cell lines. The production of nucleolar PtdIns(3,4,5)P3 was dependent upon p110{beta} activity. EC cells with high levels of nuclear PtdIns(3,4,5)P3 and p110{beta} showed elevated nucleolar activity as assessed by the increase in 47S pre-rRNA transcriptional levels in a p110{beta}-dependent manner. Altogether, these results present a nucleolar role for the PI3K pathway that may contribute to tumour progression in endometrial cancer.

Source connections

Published article ↗

Explore related subjects

molecular biology Preprint

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Mazloumi Gavgani, F., Karlsson, T., Tangen, I. L., Papdine Morovicz, A., Smith Arnesen, V., Turcu, D., Krakstad, C., Guillermet-Guibert, J., Lewis, A. E.. 2019-12-20. Nuclear upregulation of PI3K p110β correlates with increased rRNA transcription in endometrial cancer cells. https://doi.org/10.1101/2019.12.20.884122

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Fatty Acid Synthase Binds Cellular mRNAs and its Depletion Reduces Translational Efficiency

Metabolic enzymes with non-canonical RNA binding activity have drawn a growing interest, due to their implications for basic biology and disease. Here we present the first endogenous RNA interactome of fatty acid synthase (FASN), an emerging oncological and virological target. Utilizing crosslinking-based approaches, we characterize the direct RNA association of FASN in two human cell lines, identifying over 6000 binding sites across over 3500 protein-coding genes, with a striking preference for the 5' UTR. We provide a functional cross-screen on the effects of FASN depletion on cellular translation. This integration with ribosome profiling indicated a preferential reduction in the translational efficiencies of FASN-associated mRNAs - an effect shown to be dependent on binding location and site number. Associated transcripts were enriched for morphogenic and cell division-related functions, as well as palmitoylated proteins. This correlative work primes further investigation of FASN as a regulator of translation of its target mRNAs.

molecular biology↗

bioRxiv2026

Genomic features and instability of linezolid resistance in vancomycin-resistant Enterococcus faecalis ST525

This study investigated the mechanisms of oxazolidinone resistance and genomic background in clinical ST525 Enterococcus faecalis isolates, a poorly characterized lineage reported in Brazilian hospitals as either vancomycin-resistant (VRE) or linezolid- and vancomycin-resistant (LVRE). Five LVREfs from intensive care unit patients (linezolid MICs, 8-32 mg/L; vancomycin MICs, >256 mg/L) carried only G2576T and G2505A (in three of four rrl copies) as known linezolid resistance determinants, despite variable linezolid MICs. During serial in vitro passages without antibiotic pressure, isolates with initial MICs of 8-16 mg/L exhibited progressive MIC reductions accompanied by reversion of mutant to wild-type rrl copies, whereas the isolate with an initial MIC of 32 mg/L maintained high-level resistance without reversion. Additional domain V substitutions emerged during MIC decline, while growth kinetics remained broadly similar. Whole-genome sequencing of a representative isolate (LVREfs L7) revealed a ~2.8-Mb chromosome enriched in mobile genetic elements (~8.6%), lacking a functional CRISPR-Cas system. A plasmid-borne prototype Tn1546 carrying vanA, devoid of internal insertion sequences, was found inserted into a Tn3-family transposase gene, a platform not typically associated with vanA mobilization. Together, these findings indicate that ST525 LVREfs, whose genomic features are consistent with long-term persistence in hospitals, may pose a challenge to routine susceptibility testing. A single mutational mechanism can yield variable linezolid MICs, and the ratio of mutated vs wild-type rrl copies can become heterogeneous in the absence of antibiotic pressure, without correlating directly with these values, contrary to the well-documented copy number-MIC correlation.

molecular biology↗

bioRxiv2026

Global repression of mesenchymal genes in epithelial cells by the histone demethylase LSD1

Epithelial-mesenchymal transition (EMT) is an essential process in development, tissue repair, and tumour metastasis, and is triggered by SNAI, ZEB and TWIST transcription factors, that recruit lysine-specific demethylase 1 (LSD1) to repress epithelial genes such as E-cadherin. In mesenchymal cells, LSD1 inhibition restores E-cadherin expression and reduces migration and invasion, consistent with LSD1 inhibition reverting EMT, and offering a therapeutic modality for EMT-associated disease. Recent data, however, suggest context-dependent roles for LSD1, as its inhibition in epithelial cells increases mesenchymal marker expression, potentially promoting EMT. To investigate this discrepancy, we mapped genome-wide binding of LSD1 in HCT116 epithelial cells and used rapid degron-mediated ablation of endogenous LSD1 to measure changes in nascent and steady-state transcription and chromatin accessibility. In epithelial cells, LSD1 binds constitutively-accessible, primed mesenchymal promoters. These are rapidly derepressed after LSD1 ablation, with activation of SNAI2 and ZEB1, which repress epithelial hallmarks such as E-cadherin. Re-introduction of LSD1 downregulates SNAI2 and ZEB1 but, surprisingly, further represses E-cadherin, indicating sustained loss of epithelial characteristics. Collectively, our results show that LSD1 maintains epithelial identity by repressing mesenchymal genes, questioning the therapeutic utility of LSD1 inhibition for EMT control.

molecular biology↗