<i>circFAM134B</i> is a key factor regulating reticulophagy-mediated ferroptosis in hepatocellular carcinoma

Ferroptosis is an important mode of regulated cell death (RCD). Its inhibition is closely related to therapeutic resistance and poor prognosis in hepatocellular carcinoma (HCC). Previous reports have demonstrated ferroptosis as a biological process highly dependent on selective autophagy, such as ferritinophagy, lipophagy, and clockophagy. Our study also revealed a role for ER-phagy-mediated ferroptosis in HCC cells treated with multi-targeted tyrosine kinase inhibitors (TKIs). In the current study, we found that the homologous circular RNA (circRNA) of the family with sequence similarity 134, member B (<i>FAM134B</i>), hsa_circ_0128505 (was abbreviated as <i>circFAM134B</i> in the present study), was identified to specifically target ER-phagy to promote lenvatinib (LV)-induced ferroptosis using reactive oxygen species (ROS), Fe²⁺, malondialdehyde (MDA), and western blot (WB) assays in HCC cells. RNA pull-down and mass spectrometry analyses suggested that <i>circFAM134B</i> and <i>FAM134B</i> mRNA were enriched with several common interacting proteins. Among them, poly (A) binding protein cytoplasmic 4 (PABPC4) was identified as the most enriched binding partner. It was proven to be a novel antagonist against the nonsense-mediated mRNA decay (NMD) mechanism. We then applied RNA immunoprecipitation (RIP), RNA pull-down, luciferase reporter, and NMD reporter gene assays to further explore the exact role and underlying mechanism of <i>circFAM134B-</i>PABPC4-FAM134B axis in HCC cells. <i>circFAM134B</i> was confirmed as a sponge that competitively interacted with PABPC4, thereby influencing <i>FAM134B</i> mRNA nonsense decay. Our results provide novel evidences and strategies for the comprehensive treatment of HCC.