Overexpression-mediated activation of MET in the Golgi promotes HER3/ERBB3 phosphorylation

Abstract

Ligand-dependent oligomerization of receptor tyrosine kinases (RTKs) results in their activation through highly specific conformational changes in the extracellular and intracellular receptor domains. These conformational changes are unique for each RTK sub-family, limiting cross-activation between unrelated RTKs. The proto-oncogene MET receptor tyrosine kinase overcomes these structural constraints and phosphorylates unrelated RTKs in numerous cancer cell lines. The molecular basis for these interactions is unknown. We investigated the mechanism by which MET phosphorylates the human epidermal growth factor receptor-3 (HER3 or ERBB3), a catalytically impaired RTK whose phosphorylation by MET has been described as an essential component of drug resistance to inhibitors targeting EGFR and HER2. We find that in untransformed cells, HER3 is not phosphorylated by MET in response to ligand stimulation, but rather to increasing levels of MET expression, which results in MET activation in a ligand-independent manner. Phosphorylation of HER3 by its canonical dimerization partners, EGFR and HER2, is achieved by engaging an allosteric site on the HER3 kinase domain, but this site is not required when HER3 is phosphorylated by MET. We also observe that HER3 preferentially interacts with MET during its maturation along the secretory pathway, before MET is post-translationally processed by cleavage within its extracellular domain. This results in accumulation of phosphorylated HER3 in the Golgi apparatus. We further show that in addition to HER3, MET phosphorylates other RTKs in the Golgi, suggesting that this mechanism is not limited to HER3 phosphorylation. These data demonstrate a link between MET overexpression and its aberrant activation in the Golgi endomembranes and suggest that non-canonical interactions between MET and unrelated RTKs occur during maturation of receptors. Our study highlights a novel aspect of MET signaling in cancer that would not be accessible to inhibition by therapeutic antibodies.

N822K- or V560G-mutated KIT activation preferentially occurs in lipid rafts of the Golgi apparatus in leukemia cells

“…This requires palmitoylation of its cysteine residues for migration to the lipid rafts, where it can activate the TBK1-IRF3 pathway [51]. MET tyrosine kinase is activated and palmitoylated on its extracellular domain at the Golgi [69, 70], and lipid rafts contribute to receptor distribution and stability [70, 71]. These studies raise the interesting possibility that incorporation of KIT into the lipid rafts of the Golgi is involved in protein acylation.…”

Wrong place at the wrong time: how retrograde trafficking drives cancer metastasis through receptor mislocalization

“…ErbB3 is subject to significantly slower rates of endocytosis than EGF-bound EGFR due to the anti-internalization regions within the C-terminus, allowing for longer periods of receptor activation (when in a heterodimer) [71,112] . This delayed trafficking results in perinuclear accumulation, thereby allowing nuclear localization via retrotranslocation [113] . Once in the nucleus, ErbB3 presents in an activated, uncleaved format, capable of associating with the Cyclin D1 promoter to drive cell proliferation, similar to the mechanism seen in EGFR [54,56,114] .…”

Disruption of the HER3-PI3K-mTOR oncogenic signaling axis and PD-1 blockade as a multimodal precision immunotherapy in head and neck cancer

“…The crystal structure of CDX-3379 binding to HER3 has been solved, which revealed that it binds HER3 outside of the NRG-ligand binding domain and locks HER3 in its auto-inhibited configuration, making the HER3 incapable of binding ligand or dimerizing with other receptors 26,40 . These findings suggest that CDX-3379 may inhibit HER3 via two distinct primary mechanisms of action, liganddependent (i.e., NRG-driven HER3 activation) and ligandindependent (i.e., activation driven by high activity of EGFR, HER2, or multiple other tyrosine kinases 41 ). The Fc portion of CDX-3379 was engineered to enhance binding to the neonatal Fc receptor (FcRN) and thus enhancing its serum half-life in patients and target exposure.…”