TAK1 signaling regulates p53 through a mechanism involving ribosomal stress.

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 TAK1-ribosome axis is a potential therapeutic target in TNBC.