Spermatid perinuclear RNA-binding protein promotes UBR5-mediated proteolysis of Dicer to accelerate triple-negative breast cancer progression.

Triple-negative breast cancer (TNBC) is the most lethal subtype of breast cancer with no targeted therapy. Spermatid perinuclear RNA binding protein (STRBP), a poorly characterized RNA-binding protein (RBP), has an essential role in normal spermatogenesis and sperm function, but whether and how its dysregulation contributing to cancer progression has not yet been explored. Here, we report that STRBP functions as a novel oncogene to drive TNBC progression. STRBP expression was upregulated in TNBC tissues and correlated with poor disease prognosis. Functionally, STRBP promoted TNBC cell proliferation, migration, and invasion in vitro, and enhanced xenograft tumor growth and lung colonization in mice. Mechanistically, STRBP interacted with Dicer, a core component of the microRNA biogenesis machinery, and promoted its proteasomal degradation through enhancing its interaction with E3 ubiquitin ligase UBR5. MicroRNA-sequencing analysis identified miR-200a-3p as a downstream effector of STRBP, which was regulated by Dicer and affected epithelial-mesenchymal transition. Importantly, the impaired malignant phenotypes of TNBC cells caused by STRBP depletion were largely rescued by knockdown of Dicer, and these effects were compromised by transfection of miR-200a-3p mimics. Collectively, these findings revealed a previously unrecognized oncogenic role of STRBP in TNBC progression and identified STRBP as a promising target against TNBC.