MAP3K8 kinase regulates myeloma growth by cell-autonomous and non-autonomous mechanisms involving myeloma-associated monocytes/macrophages.

Benefit from cytotoxic therapy in myeloma may be limited by the persistence of residual tumour cells within protective niches. We have previously shown that monocytes/macrophages acquire a proinflammatory transcriptional profile in the myeloma microenvironment. Here we report constitutive activation of MAP3K8 kinase-dependent pathways that regulate the magnitude and extent of inflammatory activity of monocytes/macrophages within myeloma niches. In myeloma tumour cells, MAP3K8 acts as mitogen-induced MAP3K in mitosis and is required for TNF-mediated ERK activation. Pharmacological MAP3K8 inhibition results in dose-dependent, tumour cell-autonomous apoptosis despite contact with primary stroma. MAP3K8 blockade may disrupt crucial macrophage-tumour cell interactions within myeloma niches.