Oncogenic mutations in IKK? function through global changes induced by K63-linked ubiquitination and result in autocrine stimulation.

ABSTRACT: Mutations at position K171 in the kinase activation loop of Inhibitor of ?B kinase beta (IKK?) occur in multiple myeloma, spleen marginal zone lymphoma and mantle cell lymphoma. Previously, we demonstrated that these result in constitutive kinase activation and stimulate Signal Transducer and Activator of Transcription 3 (STAT3). This work also identified K147 as a site of K63-linked regulatory ubiquitination required for activation of signaling pathways. We now present a more detailed analysis of ubiquitination sites together with a comprehensive examination of the signaling pathways activated by IKK? K171E mutants. Downstream activation of STAT3 is dependent upon the activity of: UBE2N, the E2 ubiquitin ligase involved in K63-linked ubiquitination; TAK1 (MAP3K7), or TGF? Activated Kinase, which forms a complex required for NF?B activation; JAK kinases, involved proximally in the phosphorylation of STAT transcription factors in response to inflammatory cytokines; and gp130, or IL-6 Receptor Subunit Beta which, upon binding IL-6 or other specific cytokines, undergoes homodimerization leading to activation of associated JAKs, resulting in STAT activation. We further demonstrate, using an IL-6-responsive cell line, that IKK? K171E mutants stimulate the release of IL-6 activity into conditioned media. These results show that IKK? K171E mutants trigger an autocrine loop in which IL-6 is secreted and binds to the IL-6 receptor complex gp130, resulting in JAK activation. Lastly, by examining the differential abundance of proteins associated with K63-only-ubiquitinated IKK? K171E, proteomic analysis demonstrates the global activation of proliferative responses. As cancers harboring K171-mutated IKK? are likely to also exhibit activated STAT3 and p44/42 MAPK (Erk1/2), this suggests the possibility of using MAPK (Erk1/2) and JAK inhibitors, or specific ubiquitination inhibitors. K63-linked ubiquitination occurs in other kinases at sites homologous to K147 in IKK?, including K578 in BRAF V600E, which serves as an oncogenic driver in melanoma and other cancers.

SUBMITTER: Meyer AN 

PROVIDER: S-EPMC6193727 | biostudies-other | 2018

REPOSITORIES: biostudies-other