Estrogen receptor fuels breast cancer growth through an RNA-tagging loop, study finds

Scientists have uncovered a previously hidden molecular circuit that helps estrogen receptor-positive breast cancer, the most common form of the disease, grow and spread. The pathway links the hormone-driven transcription machinery of the tumor cell to a chemical tag on messenger RNA called N6-methyladenosine, or m6A, and ultimately to a helicase protein that keeps cancer cells dividing. The work, published in the British Journal of Cancer by a team at Huazhong University of Science and Technology in Wuhan, identifies the RNA-binding protein HNRNPC as a central player and proposes it as a promising therapeutic target for a cancer subtype that still claims tens of thousands of lives each year.

Breast cancer overtook lung cancer as the most commonly diagnosed cancer in women worldwide in 2020, and roughly seventy percent of cases are hormone receptor-positive, meaning their growth is driven by estrogen signaling. While patients with localized tumors enjoy five-year survival rates above ninety percent, those with metastatic disease fall below thirty percent, largely because of chemotherapy tolerance and spread to distant organs. Understanding the epigenetic and post-transcriptional programs that fuel progression has therefore become one of the most urgent quests in cancer biology, and RNA methylation has emerged as a key frontier in that search.

The m6A mark is the most prevalent chemical modification found on both coding and non-coding RNAs. It is installed by writer proteins such as METTL3, METTL14 and WTAP, removed by erasers like FTO and ALKBH5, and interpreted by reader proteins that determine the fate of the tagged molecule. Readers are widely considered the decisive regulators of the system because they dictate whether a modified RNA is stabilized, degraded, or translated. In breast cancer, previous work has shown that the demethylase FTO strips m6A from the tumor suppressor BNIP3 and hastens its decay, while the writer METTL3 promotes expression of the proliferation-driving HBXIP. Yet the roles of many readers, and their relationship to the estrogen receptor, remained unmapped.

To find the most relevant readers, the team mined the TCGA-BRCA database and found that several, including CPSF6, HNRNPA2B1, HNRNPC, PRRC2A and TRMT112, were abnormally elevated in tumors. HNRNPC stood out. Its levels were higher in tumor tissue than in adjacent normal tissue in paired patient samples, it was upregulated in most breast cancer cell lines tested, including the estrogen receptor-positive lines MCF7 and T47D, and analysis of two independent clinical datasets, GSE4922 and GSE7378, showed that patients with high HNRNPC expression had significantly worse disease-free survival.

Functionally, the protein behaved like a classic oncogene. When the researchers silenced HNRNPC with small interfering RNAs, proliferation of MCF7 and T47D cells dropped sharply across CCK-8 growth assays, colony formation tests and EdU incorporation assays that measure DNA replication. Flow cytometry revealed a G1-to-S phase arrest in the depleted cells, while wound healing and Transwell experiments showed reduced migration and invasion. Conversely, restoring HNRNPC reversed these effects. The picture was consistent: HNRNPC is not a passive passenger but an active driver of malignant behavior in estrogen receptor-positive cells.

The next question was what HNRNPC actually binds. Using RNA immunoprecipitation followed by sequencing, the team mapped its binding sites across the transcriptome of both cell lines. The majority of peaks clustered in three-prime untranslated regions, and the dominant sequence motif was a run of continuous uracil bases, exactly what earlier structural studies had predicted for this protein. Pathway analysis of the bound RNAs pointed to cancer-relevant programs including PI3K-Akt, mTOR and cell cycle regulation. Within the resulting network, one hub gene emerged: DDX6, an ATP-dependent DEAD-box RNA helicase already known to act oncogenically in gastric and colorectal cancers, where it regulates transcripts such as HER2, FGFR2 and c-Myc.

The mechanism connecting HNRNPC to DDX6 is the study’s most technically striking finding. HNRNPC does not bind the m6A mark itself. Instead, methylating an adenosine weakens its pairing with an opposite uracil, loosening the local RNA structure so that HNRNPC can latch onto the exposed continuous uracil tract, a phenomenon known as an m6A switch. In the DDX6 three-prime UTR, the team identified such a poly-U region around nucleotide 5500, flanked by predicted m6A sites. RNA pull-down assays with wild-type and mutated DDX6 probes confirmed the direct interaction, and immunofluorescence combined with fluorescent in situ hybridization placed both the protein and the transcript in the nucleus, where the binding occurs. Crucially, when the researchers lowered global m6A levels by knocking down METTL3 or using the inhibitor SAH, the HNRNPC-DDX6 interaction weakened, while knocking down the erasers FTO or ALKBH5 strengthened DDX6 expression. The binding is therefore genuinely m6A-dependent.

What does that binding accomplish? RNA decay assays using actinomycin D showed that loss of HNRNPC destabilized DDX6 mRNA, whereas overexpression of HNRNPC preserved it. DDX6, in turn, proved to be a bona fide tumor promoter in breast cancer: silencing it reduced proliferation and caused G1-S arrest, and it lowered levels of the cell cycle proteins cyclin D1 and CDK6. Most persuasively, overexpressing DDX6 rescued the proliferation, cell cycle progression, migration and invasion defects caused by HNRNPC depletion, establishing DDX6 as a functional downstream target. When the team mutated the poly-U sequence in the DDX6 transcript, converting it to poly-C, the mutant RNA could no longer rescue the tumor-suppressive phenotype, sealing the argument that the oncogenic effect flows through the m6A-switch-mediated interaction.

Upstream, the team traced the origin of HNRNPC overexpression to the estrogen receptor alpha itself. Database mining with JASPAR and Cistrome predicted ERα binding sites in the HNRNPC promoter, correlation analysis of TCGA data showed a significant positive relationship between ESR1 and HNRNPC expression, and chromatin immunoprecipitation with an ERα antibody confirmed that the receptor physically occupies the HNRNPC promoter. The result sketches a complete axis: estrogen receptor alpha transcriptionally upregulates HNRNPC, which stabilizes DDX6 mRNA in an m6A-dependent manner, and DDX6 drives cell cycle progression, proliferation and metastasis.

Animal experiments lent in vivo weight to the model. In nude mice implanted subcutaneously with luciferase-labeled MCF7 cells, stable knockdown of HNRNPC markedly slowed tumor growth, reduced final tumor weight and lowered Ki-67 staining, a standard marker of proliferation. In a tail-vein metastasis model using T47D cells, HNRNPC depletion reduced metastatic colonization of the lungs and liver. The authors are candid about limitations: the m6A switch model rests partly on bioinformatic prediction and lacks direct molecular structural validation, and HNRNPC is also elevated in some estrogen receptor-negative cancers, implying that other mechanisms must exist to upregulate it there. Even so, the ERα/HNRNPC/DDX6 axis offers a fresh mechanistic explanation for how hormone signaling and RNA epigenetics conspire in breast cancer, and it points to HNRNPC, or the m6A-switch interaction it mediates, as an actionable vulnerability in a disease that still needs better options for patients with advanced, treatment-resistant tumors.

Subject of Research: An ERα/HNRNPC/DDX6 regulatory axis in m6A-mediated mRNA stabilization and estrogen receptor-positive breast cancer progression

Article Title: ERa-induced m6A reader HNRNPC maintains DDX6 mRNA stability to promote tumor progression in ER+BC

Article References: ERa-induced m6A reader HNRNPC maintains DDX6 mRNA stability to promote tumor progression in ER+BC. (n.d.). https://doi.org/10.1038/s41416-026-03506-x

Image Credits: AI Generated

DOI: 10.1038/s41416-026-03506-x

Keywords: breast cancer, m6A methylation, HNRNPC, DDX6, estrogen receptor alpha, RNA-binding proteins, mRNA stability, epigenetics, oncology, tumor progression, RNA biology, British Journal of Cancer