IMP2 and IMP3 cooperate to promote the metastasis of triple-negative breast cancer through destabilization of progesterone receptor.

Triple-negative breast cancer (TNBC) is one of the most aggressive malignancies and is associated with high mortality rates due to the lack of effective therapeutic targets. In this study, we demonstrated that insulin-like growth factor-II mRNA-binding protein 2 and 3 (IMP2 and IMP3) are specifically overexpressed in TNBC and cooperate to promote cell migration and invasion. Downregulation of both IMP2 and IMP3 in TNBC cells was found to produce a synergistic effect in suppressing cell invasion and invadopodia formation, whereas overexpression of IMP2 and IMP3 in luminal subtype cells enhanced epithelial-mesenchymal transition and metastasis. We also showed that IMP2 and IMP3 are direct targets of microRNA-200a (miR-200a), which is downregulated in TNBC. Conversely, IMP2 and IMP3 suppressed the transcription of miR-200a by destabilizing progesterone receptor (PR) mRNA through recruitment of the CCR4-NOT transcription complex subunit 1 (CNOT1) complex. Together, our findings suggest that IMP2 and IMP3 partially determine the characteristic phenotype and synergistically promote the metastasis of TNBC by downregulating PR. The identified IMP2/3-miR-200a-PR axis represents a novel double-negative feedback loop and serves as a new potential therapeutic target for the treatment of TNBC.