Triple-negative breast cancer (TNBC) is among the most aggressive forms of breast cancer with limited therapeutic options. TAK1 is implicated in aggressive behavior of TNBC, while means are not fully understood. Here, we report that pharmacological blockade of TAK1 signaling hampered ribosome biogenesis (RBG) by reducing expression of RBG regulators such as RRS1, while not changing expression of ribosomal core proteins. Notably, TAK1 blockade upregulated expression of p53 target genes in cell lines carrying wild type (wt) TP53 but not in p53-mutant cells, suggesting involvement of ribosomal stress in the response. Accordingly, p53 activation by blockade of TAK1 was prevented by depletion of ribosomal protein RPL11. Further, siRNA-mediated depletion of TAK1 or RELA resulted in RPL11-dependent activation of p53 signaling. Knockdown of RRS1 was sufficient to disrupt nucleolar structures and resulted in activation of p53. TCGA data showed that TNBCs express high levels of RBG regulators, and elevated RRS1 levels correlate with unfavorable prognosis. Cytotoxicity data showed that TNBC cell lines are more sensitive to TAK1 inhibitor compared to luminal and HER2 + cell lines. These results show that TAK1 regulates p53 activation by controlling RBG factors, and the TAK1ribosome axis is a potential therapeutic target in TNBC. Breast cancer (BC) is the second leading cause of cancer-related death in women 1. This heterogeneous disease includes multiple subtypes with distinct genetic, pathological and clinical features 2-4. Among BC subtypes, triple-negative breast cancers (TNBCs, ER/PR/HER2-negative) pose special challenges due to a lack of targeted therapy and overall poor prognosis 5 , underscoring a pressing need for better therapeutic options. Recent studies, including from our group, have implicated TGF-beta-activated kinase-1 (TAK1) in cancer progression and metastasis of breast, lung and colon cancers 6-12. TAK1 kinase, encoded by the MAP kinase kinase kinase gene (MAP3K7), mediates signaling by transforming growth factor beta (TGF-β) and pro-inflammatory cytokines 13-15. TAK1 activation involves E3-ubiquitin ligases cIAP1 and cIAP2 (cellular inhibitors of apoptosis, cIAPs), which mediate addition of K(lysine)-63-linked ubiquitin chains to RIP kinase and other signaling proteins 16. Activated TAK1 phosphorylates Ser/Thr residues in target proteins such as IKKα/CHUK, IKKβ/IKBKB and MKK3/6, leading to stimulation of MAPK (p38, ERK, JNK) and NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) signaling pathways 17. TAK1 protects cells from death-inducing agents by regulating cIAPs and cFLIP, a caspase-8 inhibitor 18,19 , and may also contribute to tumor resistance to radiation and chemotherapy 20,21. Preclinical studies with TNBC models have implicated TAK1 in tumor angiogenesis and metastases to the lungs and bone 11,22. Evidence also supports targeting TAK1 in treating colon and pancreatic cancers 9,12. Several pharmacological TAK1 inhibitors (TAK1-i) have been developed 23-25. The most potent TAK1...