UBE2C Promotes Breast Cancer Proliferation via the AKT/mTOR Signaling Pathway

Breast cancer (BC) remains a leading cause of cancer-related mortality among women globally. Despite advancements in early diagnosis and treatment, the molecular mechanisms driving BC progression require deeper exploration. Recent studies highlight the role of ubiquitin-conjugating enzyme E2C (UBE2C) in tumorigenesis across multiple cancer types, but its specific contributions to BC pathogenesis remain understudied. This investigation elucidates the molecular mechanisms by which UBE2C influences BC proliferation, focusing on its regulation of the AKT/mTOR signaling pathway.

Data Acquisition and Identification of Differentially Expressed Genes

The study integrated datasets from the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) to identify BC-associated genes. Three GEO datasets (GSE21422, GSE45827, GSE70947) comprising 292 tumor and 164 normal samples were analyzed alongside TCGA data. Differential expression analysis with thresholds of |log2 fold change| > 2 and false discovery rate (FDR) < 0.05 revealed 151 differentially expressed genes (DEGs). Among these, 55 were upregulated and 96 downregulated in BC tissues. Venn diagram analysis demonstrated overlapping DEGs across datasets, narrowing the focus to genes consistently altered in BC progression.

Functional and Pathway Enrichment Analysis

Gene Ontology (GO) analysis categorized DEGs into biological processes (BP), molecular functions (MF), and cellular components (CC). Enriched BP terms included mitotic nuclear division, lipid storage, and nuclear division. For CC, DEGs clustered in lipid droplets, midbodies, and membrane rafts. MF analysis highlighted organic acid-binding and growth factor binding as significant. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis associated DEGs with PPAR signaling, regulation of lipolysis in adipocytes, and proximal tubule bicarbonate reclamation, suggesting metabolic reprogramming as a hallmark of BC.

Protein-Protein Interaction Network and Hub Gene Identification

A protein-protein interaction (PPI) network constructed using STRING and visualized in Cytoscape identified three hub genes: FOXM1, UBE2C, and CDKN3. These genes exhibited the highest connectivity scores, implicating their central roles in BC pathogenesis. Survival analysis via the Kaplan-Meier Plotter revealed that elevated UBE2C expression correlated with poorer relapse-free survival (RFS) in BC patients (hazard ratio [HR] = 1.83, P < 0.05), establishing its prognostic relevance.

Experimental Validation of UBE2C in BC Cells

To validate bioinformatics findings, UBE2C was silenced in MCF-7 and MDA-MB-231 BC cell lines using small interfering RNA (siRNA). Quantitative reverse transcription PCR (RT-qPCR) and Western blot confirmed significant reductions in UBE2C mRNA (MDA-MB-231: P < 0.001; MCF-7: P < 0.01) and protein levels (P < 0.05) post-knockdown. Functional assays demonstrated that UBE2C suppression markedly inhibited cell proliferation and invasion.

Proliferation Assays
Cell Counting Kit-8 (CCK-8) assays revealed time-dependent growth inhibition in UBE2C-silenced cells. At 72 hours, MDA-MB-231 proliferation decreased by 45% (P < 0.001), while MCF-7 cells showed a 38% reduction (P < 0.01) compared to controls.

Invasion Assays
Transwell assays with Matrigel-coated chambers demonstrated a 60% reduction in MDA-MB-231 invasiveness (P < 0.001) and a 52% decrease in MCF-7 cells (P < 0.01) following UBE2C knockdown, underscoring its role in metastatic potential.

Mechanistic Insights into UBE2C Regulation of AKT/mTOR Signaling

Western blot analysis explored UBE2C’s impact on key signaling pathways. UBE2C knockdown increased phosphorylated phosphatase and tensin homolog (p-PTEN) levels (P < 0.05), a tumor suppressor that inhibits AKT activation. Concurrently, phosphorylated AKT (p-AKT) and mTOR (p-mTOR) levels decreased (P < 0.05), indicating pathway inactivation. Hypoxia-inducible factor-1α (HIF-1α), a downstream target of mTOR linked to tumor angiogenesis and metastasis, was also downregulated (P < 0.05). These findings suggest UBE2C promotes BC progression by suppressing PTEN and activating AKT/mTOR signaling.

Discussion

UBE2C, a member of the ubiquitin-conjugating enzyme family, is implicated in cell cycle regulation via its role in ubiquitin-mediated proteolysis. Overexpression of UBE2C has been documented in gastric, lung, and ovarian cancers, where it drives proliferation and chemoresistance. This study extends these findings to BC, demonstrating that UBE2C silencing suppresses tumor growth and invasiveness by modulating PTEN/AKT/mTOR axis activity.

The AKT/mTOR pathway is a central regulator of cell survival, proliferation, and metabolism. PTEN, a negative regulator of this pathway, is frequently inactivated in cancers, leading to constitutive AKT activation. Here, UBE2C knockdown increased p-PTEN, suggesting UBE2C may destabilize PTEN or enhance its degradation. Subsequent reductions in p-AKT and p-mTOR highlight UBE2C’s role in pathway activation, while HIF-1α downregulation links UBE2C to hypoxic stress responses critical for tumor adaptation.

Notably, UBE2C expression varied between BC subtypes, with higher levels in aggressive MDA-MB-231 cells compared to less invasive MCF-7 cells. This aligns with clinical data associating UBE2C overexpression with advanced BC stages and poor prognosis. The study’s integration of bioinformatics and experimental approaches strengthens the conclusion that UBE2C is a viable therapeutic target.

Conclusion

This study establishes UBE2C as a key oncogene in BC, driving proliferation and invasion through AKT/mTOR pathway activation. By enhancing PTEN phosphorylation and inhibiting downstream oncogenic signals, UBE2C silencing presents a promising strategy for BC treatment. Future studies should validate these findings in vivo and explore UBE2C inhibitors in preclinical models.

doi.org/10.1097/CM9.0000000000001708

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