Klein, M. A. | bioRxiv Science

bioRxiv2023

Methionine aminopeptidase 2 and its autoproteolysis product have different binding sites on the ribosome

Excision of the initiator methionine is among the first co-translational processes that occur at the ribosome. While this crucial step in protein maturation is executed by two types of methionine aminopeptidases in eukaryotes (MAP1 and MAP2), additional roles in disease and translational regulation have drawn more attention to MAP2. Here, we report several cryo-EM structures of MAP2 at the 80S-ribosome. The MAP2 interaction is highly robust but can be perturbed by emerging nascent chains, which induce an adaptive tilting of the enzyme. In rotation, the MAP2-specific N-terminal extension engages in stabilizing interactions with the long rRNA expansion segment ES27L. Loss of this extension by autoproteolytic cleavage impedes the tunnel interaction, while promoting MAP2 to enter the ribosomal A-site, where it engages with crucial functional centers of translation. These findings reveal that proteolytic remodeling of MAP2 severely affects ribosome binding, and set the stage for targeted functional studies.

biochemistry↗

bioRxiv2021

DARPP-32 promotes ERBB3-mediated resistance to molecular targeted therapy in EGFR-mutated lung adenocarcinoma

While molecular targeted therapies have improved prognoses of advanced stage lung adenocarcinoma expressing oncogenic driver mutations, acquired therapeutic resistance continues to be a major problem. Epidermal growth factor receptor (EGFR) activating mutations are among the most common targetable genetic alterations in lung adenocarcinoma, and EGFR tyrosine kinase inhibitors (TKIs) are recommended first-line therapy for EGFR mutation positive cancer patients. Unfortunately, most patients develop resistance to EGFR TKIs and rapid disease progression occurs. A better mechanistic understanding of therapy refractory cancer progression is necessary to develop new therapeutic approaches to predict and prevent acquired resistance to EGFR TKIs. Here, we identify a new mechanism of ERBB3-mediated resistance to EGFR TKIs in human lung adenocarcinoma. Specifically, we show that dopamine and cyclic AMP-regulated phosphoprotein, Mr 32000 (DARPP-32) physically recruits ERBB3 to EGFR to mediate a switch from EGFR homodimers to EGFR:ERBB3 heterodimers to bypass EGFR TKI-mediated inhibition to potentiate ERBB3-dependent activation of oncogenic AKT and ERK signaling that drives therapy refractory tumor cell survival. In a cohort of paired tumor specimens derived from 30 lung adenocarcinoma patients before and after the development of EGFR TKI refractory disease progression, we reveal that DARPP-32 as well as kinase-activated EGFR and ERBB3 proteins are overexpressed upon acquired EGFR TKI resistance. In vivo studies suggest that ablation of DARPP-32 protein activity sensitizes gefitinib-resistant lung tumor xenografts to EGFR TKI treatment, while DARPP-32 overexpression increases gefitinib-refractory lung cancer progression in gefitinib-sensitive lung tumors orthotopically xenografted into mice. Taken together, our findings introduce a DARPP-32-mediated, ERBB3-dependent mechanism used by lung tumor cells to evade EGFR TKI-induced cell death, potentially paving the way for the development of new therapies to prevent or overcome therapy-refractory lung adenocarcinoma progression.

cancer biology↗