K27-linked ubiquitination of BRAF by ITCH engages cytokine response to maintain MEK-ERK signaling

Abstract

BRAF plays an indispensable role in activating the MEK/ERK pathway to drive tumorigenesis. Receptor tyrosine kinase and RAS-mediated BRAF activation have been extensively characterized, however, it remains undefined how BRAF function is fine-tuned by stimuli other than growth factors. Here, we report that in response to proinflammatory cytokines, BRAF is subjected to lysine 27-linked poly-ubiquitination in melanoma cells by the ITCH ubiquitin E3 ligase. Lysine 27-linked ubiquitination of BRAF recruits PP2A to antagonize the S365 phosphorylation and disrupts the inhibitory interaction with 14–3–3, leading to sustained BRAF activation and subsequent elevation of the MEK/ERK signaling. Physiologically, proinflammatory cytokines activate ITCH to maintain BRAF activity and to promote proliferation and invasion of melanoma cells, whereas the ubiquitination-deficient BRAF mutant displays compromised kinase activity and reduced tumorigenicity. Collectively, our study reveals a pivotal role for ITCH-mediated BRAF ubiquitination in coordinating the signals between cytokines and the MAPK pathway activation in melanoma cells.

Beyond K48 and K63: non-canonical protein ubiquitination

“…Apart from its canonical role as an activator of NF-κB signaling, TNFα induces and sustains activation of MEK/ERK oncogenic signaling [ 94 ], where BRAF, a member of the RAF family protein kinases, is one of the key players [ 95 ]. Upon activation by inflammatory cytokines, the ITCH HECT-type E3 ligase ubiquitinates BRAF with K27-linked chains to provide sustained BRAF activation and to promote proliferation and invasion of melanoma cells [ 96 ]. Thus, one can imagine that ITCH could be targeted with therapeutic agents to prevent tumorigenesis, especially since ITCH has also been identified as an E3 targeting TIEG1 for K27-linked ubiquitination [ 97 ].…”

The unicellular eukaryotic parasite Toxoplasma gondii hijacks the migration machinery of mononuclear phagocytes to promote its dissemination

“…Note that 14-3-3 regulates multiple signalling pathways by molecular sequestration in the cytosol (Hermeking, 2003). Because Ras-Raf-Mek-Erk MAPK signalling is central to hypermigration (Olafsson et al, 2020) and 14-3-3 proteins modulate this signalling axis (Rajalingam and Rudel, 2005;Yin et al, 2019), it is likely that the abundant concentration of 14-3-3 to the PV impacts on MAPK signalling. Additionally, because 14-3-3 has been shown to regulate GABA receptor function (Laffray et al, 2012), Tg14-3-3 may be involved in the regulation of GABAergic signalling in parasitised DCs.…”

Integrative Proteomic Analysis of Posttranslational Modification in The Inflammatory Response

“…MG132, which inhibits the degradation of ubiquitinated protein, has been widely used to study the molecular mechanism of inflammation [24][25][26]. However, MG132 could directly influence the ubiquitination of certain proteins or indirectly influence ubiquitination by inhibiting the inflammatory response of macrophages.…”