Senomorphic miR-3155b suppresses the senescence-associated secretory phenotype in therapy-induced senescence.

Senomorphic microRNAs (miRNAs) are a class of small regulatory RNAs that selectively suppress the senescence-associated secretory phenotype (SASP) without eliminating senescent cells, thereby offering a targeted approach to counteract the pro-tumorigenic consequences of therapy-induced senescence (TIS). Despite their therapeutic potential, senomorphic miRNAs in luminal breast cancer remain poorly characterized. Here, we performed small RNA sequencing to profile miRNA expression changes in a doxorubicin-induced TIS model using the luminal breast cancer line MCF7. We identified miR-3155b as a previously uncharacterized miRNA significantly downregulated during TIS. Functional studies revealed that miR-3155b overexpression suppressed the mRNA and protein levels of multiple SASP factors, including IL6, IL8 (CXCL8), MMP13, TNF, IL1B, and IFNB1, whereas its knockdown enhanced their expression. Critically, these effects occurred without affecting core senescence phenotypes such as proliferation arrest, SA-β-gal activity, or DNA damage foci formation. This senomorphic function was further confirmed in an ionizing radiation (IR)-induced TIS model and in T47D luminal breast cancer cells. miR-3155b was confirmed to target the