Metastasis and tumor relapses are the primary causes of mortality in breast cancer. Using an orthotopic xenograft mouse model implanted with bioluminescent-labeled wild-type and mdig knockout (KO) triple-negative breast cancer (TNBC) MDA-MB-231 cells, along with transcriptomics and chromatin immunoprecipitation and sequencing (ChIP-seq), we uncovered key molecular insights into mdig-mediated regulation of metastasis in TNBC. Although mdig KO cells formed smaller primary tumors, they exhibited increased lung and liver metastasis in vivo and greater invasive potential of circulating tumor cells in vitro . Restoring mdig expression in mdig KO cells reduced metastatic spread, particularly to the liver. Bulk RNA sequencing revealed up-regulation of metastasis-promoting genes in mdig KO cells, including SPOCK1 , WNT5A , MAGEB2 , TGFBI , SNAI2 , VEGFA , and MAGED2 . ChIP-seq analysis showed a global increase in histone H3 lysine 9 trimethylation (H3K9me3) and H3K36me3. Integrative RNA-sequencing and ChIP-seq analyses further demonstrated that genes associated with epithelial–mesenchymal transition and metastasis, such as KDM5C , IQSEC2 , SMC1A , KLF8 , RRAGB , FAM120C , and MAGED2 , were highly enriched in genomic regions marked by dual H3K9me3 and H3K36me3. These regions appear to act as active enhancers through recruiting H3K4 monomethyl transferase SETD7 in mdig KO cells. Together, these findings establish mdig as a suppressor of TNBC metastasis and suggest that restoring mdig expression may help alleviate the metastatic burden in breast cancer by counteracting epigenetic changes that drive pro-metastatic gene expression.
Thakur et al. (Sun,) studied this question.