Slc38a4 expression shifts in murine metastatic breast cancer model

Researchers examining a murine model of metastatic triple-negative breast cancer tracked shifting expression levels of the system A amino acid transporter Slc38a4 from primary mammary tumors to lung metastases, published in Nature. SLC38A4, also known as SNAT4, contributes to nutrient uptake and metabolic regulation, but its specific role during the progression of triple-negative breast cancer remained unclear prior to this investigation. National Institutes of Health’s National Library of Medicine (NIH/NLM) that features 12.6 million articles archived in PMC, which announced in February that changes to its Article Dataset Distribution Services are now complete following the 2025 launch of a modernized PMC full-text search and subsequent additions of new search features throughout 2026.

To evaluate these expression shifts, the study utilized RNA-sequencing data from GSE150928 comparing primary mammary tumors and lung metastases. In the RNA-seq data, Slc38a4 was upregulated in lung metastases relative to primary tumors with a log fold change of 3.93. Further analysis assigned the gene to a protein-protein interaction cluster enriched specifically for amino acid transport and vesicle trafficking.

Quantitative Real-Time PCR Findings

Quantitative real-time PCR measurements confirmed the expression patterns across different stages of tumor progression in the animal model. Eighteen female BALB/c mice implanted with 4T1 triple-negative breast cancer cells were divided into groups comprising those with primary mammary tumors and those with lung metastases.

Quantitative real-time PCR confirmed higher Slc38a4 expression in lung metastases at 6.23 ± 0.48 compared to 1.00 ± 0.08 in primary tumors, with a statistically significant value of P < 0.0001. Conversely, expression dropped lower in invasive mammary tumors at 0.51 ± 0.05 versus 1.00 ± 0.08 in primary tumors, also registering at P < 0.0001.

MicroRNA Levels Fail to Explain Expression Patterns

The research also measured levels of mmu-miR-6948-3p, a predicted regulatory microRNA, to see if it drove the shifting expression patterns. However, levels of mmu-miR-6948-3p did not differ significantly between the groups, demonstrating that the dynamic expression pattern of Slc38a4 is not explained by changes in this microRNA.

Public human datasets including TCGA, MET500, and DepMap were examined alongside the animal model data. In human data, SLC38A4 mRNA was lower in breast tumors than in normal breast tissue, and DNA methylation showed no clear relationship with its expression.

Ultimately, Slc38a4 expression depends entirely on tissue context during triple-negative breast cancer progression. Additional functional studies are required to determine whether the observed increase of the transporter in the lung actively drives colonization or merely serves as an adaptive response to it.