Endoplasmic reticulum membrane protein complex (EMC) is required for plasma membrane targeting and signaling of palmitoylated RAS isoforms

• Ano de defesa: 2024
• Autor(a) principal: Carvalho Junior, Airton de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Cancer; Câncer; Modificações pós-traducionais; Post-translational modifications; Prenilação e palmitoilação; Prenylation and palmitoylation
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/17/17136/tde-22012025-152222/

RAS proteins are small GTPases that transmit proliferation signals from the plasma membrane to downstream effectors. Plasma membrane targeting of RAS isoforms (HRAS, NRAS, KRAS4A, KRAS4B) requires prenylation and subsequent CaaX processing in the endoplasmic reticulum (ER) membrane followed by KRAS4B direct delivery to the plasma membrane or HRAS, NRAS and KRAS4A palmitoylation in the Golgi before delivery by vesicular trafficking to the plasma membrane. The ER membrane protein complex (EMC) is a translocase for subclasses of C-terminal tail-anchored and multipass transmembrane proteins. Here, we report that overexpression of EMC genes is correlated with poor survival of patients across cancers. We show that knockdown (KD) of either EMC1 or EMC3 subunits was sufficient to suppress RAS-induced tumorigenesis in several tissues of Drosophila melanogaster. The KD of the core EMC subunits is also sufficient to impair MAPK pathway activation through RAS signaling and cell proliferation in non-transformed and RAS-driven human cancer cells. Disrupting EMC impaired the plasma membrane targeting of palmitoylated RAS isoforms affecting neither KRAS4B nor RIT (a non-lipidated small GTPase), nor the palmitoylated RhoB small GTPase or the single-pass EGFR and multipass CD9 receptors. CaaX processing of RAS is dependent on EMC by neither Rce1 and ICMT expression nor RAS prenylation in basal conditions. Instead, palmitoylation efficiency and kinetics of the anterograde trafficking of HRAS toward the cell membrane are impaired upon EMC KD. In addition, we demonstrate that EMC3 KD combined with inhibition of Farnesyl Diphosphate Synthase (FDPS) abolished NRAS farnesylation and sensitized NRAS-driven melanoma cells to death. Thus, our work establishes the EMC role in the palmitoylation and trafficking of palmitoylated RAS isoforms, which is crucial for their signaling from the plasma membrane. According to this, we propose that EMC functions as a sorting platform for palmitoylated RAS access to the secretory pathway and that inhibition of the EMC can be exploited in cancers driven by HRAS and NRAS.