# Bioinformatics insights into TMPO-AS1–let-7b-5p–ESPL1/E2F8 regulatory axis in breast cancer

## TL;DR

This study explores how the ESPL1 gene is overexpressed in breast cancer and how it interacts with other molecules to drive tumor growth and poor patient outcomes.

## Contribution

The paper identifies a novel regulatory axis involving TMPO-AS1, let-7b-5p, and ESPL1/E2F8 in breast cancer progression.

## Key findings

- ESPL1 is significantly overexpressed in breast cancer tumors and is linked to worse survival outcomes.
- ESPL1 and E2F8 are upregulated in ER-negative and PR-negative breast cancer patients.
- TMPO-AS1 sponges let-7b-5p, leading to increased ESPL1 expression and tumor progression.

## Abstract

Breast cancer (BC) is the most frequently diagnosed malignancy in women, contributing to high morbidity and mortality rates. Dysregulation of Extra Spindle Pole Bodies Like 1 (ESPL1), a mitotic regulator essential for chromosomal segregation, is frequently upregulated in cancers. However, the mechanisms underlying ESPL1 overexpression and its prognostic relevance in BC remain unclear.

The study performed the data mining of The Cancer Genome Atlas (TCGA) using various web-based computational tools, including TIMER 2.0, UALCAN, FIREHOSE, TISIDB, GEPIA2, OncoDB, TCGA Portal, TCGAnalyzeR v1.0, bc-GenExMiner v5.0, TNMplot, and DriverDBv4 to compare ESPL1 expression in tumor vs. normal tissues across pan-cancer and BC subtypes. The Kaplan-Meier (KM) Plotter database was used to determine the association between ESPL1 expression and the survival outcomes of BC patients. miRNet, TACCO, and CancerMIRNome databases were used to analyze miRNAs correlated with ESPL1, while lncRNAs were analyzed using the Enrichr database. For experimental validation, ESPL1 expression level was analyzed in BC tumor and adjacent normal tissue collected from BC patients.

We found that ESPL1 gene was significantly overexpressed in tumors, metastatic tissues, and circulating tumor cells, with tumor samples showing an overall 4-fold increase in expression compared to adjacent normal tissue of BC patients. Furthermore, BC patients with high ESPL1 expression exhibited shorter overall survival (OS), disease-free survival (DFS), and relapse-free survival (RFS) compared to patients with low expression. Tumors from ER-negative and PR-negative BC patients exhibited elevated expression levels of both ESPL1 and the transcription factor E2F8. Moreover, increased levels of ESPL1 and E2F8 were positively correlated with lncRNA TMPO-AS1, while negatively correlated with hsa-let-7b-5p. Notably, the 3′ untranslated region (3′UTR) of ESPL1 showed strong binding sites for hsa-let-7b-5p. We also identified Hesperidin as a high affinity ESPL1 binders, suggesting novel therapeutic candidates targeting this oncogenic network.

Elucidating cancer’s regulatory mechanisms behind ESPL1 gene expression. The scheme (A) shows that the upregulated transcriptional factor E2F8 causes the expression of ESPL1 mRNA in BC when it binds to the gene’s promoter region. Overexpression of ESPL1 messes up normal mitotic functions, resulting in chromosomal instability, mitotic catastrophe, and, finally, aggressive tumor growth. The scheme (B) shows how mRNA and ncRNAs are controlled, focusing on hsa-let-7b-5p (miRNA) and TMPO-AS1 (lncRNA). The upregulation of TMPO-AS1 leads to the downregulation of hsa-let-7b-5p by sponge formation. This prevents let-7b from binding to the miRNA regulatory element (MRE) on the ESPL1 transcript, resulting in excessive expression of ESPL1 in breast invasive carcinoma.Diagram illustrating cancer progression mechanisms. Panel A shows E2F8 upregulation causing ESPL1 gene transcription, leading to ESPL1 mRNA overexpression. This results in chromosomal segregation disruption and mitotic catastrophe. Panel B depicts reduced hsa-let-7b-5p levels and increased TMPO-AS1 in breast cancer, where TMPO-AS1 sponges hsa-let-7b-5p, preventing it from binding to ESPL1. This promotes tumor growth and chemotherapy resistance. Visuals include representations of mRNA, miRNA, lncRNA, and sponge formations with highlighted tumor sites in breast diagrams.

Elucidating cancer’s regulatory mechanisms behind ESPL1 gene expression. The scheme (A) shows that the upregulated transcriptional factor E2F8 causes the expression of ESPL1 mRNA in BC when it binds to the gene’s promoter region. Overexpression of ESPL1 messes up normal mitotic functions, resulting in chromosomal instability, mitotic catastrophe, and, finally, aggressive tumor growth. The scheme (B) shows how mRNA and ncRNAs are controlled, focusing on hsa-let-7b-5p (miRNA) and TMPO-AS1 (lncRNA). The upregulation of TMPO-AS1 leads to the downregulation of hsa-let-7b-5p by sponge formation. This prevents let-7b from binding to the miRNA regulatory element (MRE) on the ESPL1 transcript, resulting in excessive expression of ESPL1 in breast invasive carcinoma.