SLFN12 is a ribonuclease that functions as a pro-apoptotic protein activated through estrogen-dependent and drug-induced pathways 1. Primary function: SLFN12 possesses intrinsic RNase activity that is significantly enhanced upon binding to phosphodiesterase 3A (PDE3A) 1. Mechanism: E2 and small molecule "velcrins" (including anagrelide, DNMDP, and nauclefine) stabilize the PDE3A-SLFN12 heterotetramer complex in the cytosol, promoting dephosphorylation and activating SLFN12's rRNA ribonuclease activity, which blocks protein translation and triggers apoptosis 2. This pathway operates particularly in tissues with high E2 concentration, with potential relevance to placental remodeling 1. Disease relevance: SLFN12 overexpression sensitizes triple-negative breast cancer cells to chemotherapy and radiotherapy by reducing CHK1/CHK2 phosphorylation, reducing DNA damage checkpoint activation 3. SLFN12 expression correlates with improved survival in triple-negative breast cancer 3. Clinical significance: SLFN12 may serve as a biomarker to predict and customize radiotherapy and chemotherapy responses 3. Recent clinical trials of PDE3A-SLFN12 complex inducers have encountered dose-limiting thrombocytopenia due to high PDE3A expression in platelets 4. Additionally, SLFN12 regulates human enterocyte differentiation through interactions with SERPB12 and deubiquitylases 5.