RIPK1 and breast cancer: Phosphorylation of RIPK1 at S320/321 was dependent on the TAK1-p38α-MK2 kinase cascade because inhibition of either TAK1 or p38α, which block TNF-induced MK2 phosphorylation and activation (Figures 3A–3C), or inhibition of MK2 itself, abolished the appearance of P-S321 in primary MEFs and BMDMs, and of P-S320 in human breast cancer MDA-MB-468 cells (Figures 3A–3C).