EGFR-mutant lung adenocarcinomas (LUADs) that are vulnerable to the EGFR antagonist osimertinib (Osi) eventually relapse, owing in part to the emergence of drug-tolerant persister (DTP) cells that arise through epigenetic mechanisms. Intratumoral DTP cells can herald a worse clinical outcome, but the way in which DTP cells influence LUAD progression remains unclear. Osi-resistant (OR) cells exhibit typical DTP cell features, including a propensity to undergo senescence and epithelial-mesenchymal transition (EMT), which can activate heightened secretory states. Therefore, we postulated that OR cells influence LUAD progression through paracrine mechanisms. To test this hypothesis, we utilized congenic pairs of EGFR-mutant LUAD cell lines in which drug-naive (DN) cells were rendered OR by chronic exposure to escalating doses of Osi. Cocultured in vitro or coinjected into mice, paracrine signals from OR cells enhanced the growth and metastatic properties of DN cells. EMT and senescence activated nonoverlapping secretomes, and OR cells governed DN cells by undergoing EMT but not senescence. Mechanistically, Osi rapidly increased TGF-β2 levels to initiate EMT, which triggered a Golgi remodeling process that accelerated the biogenesis and anterograde trafficking of secretory vesicles. The protumorigenic activity of OR cells was diminished by depletion of EMT-dependent secreted proteins or the EMT-activating transcription factor ZEB1. These findings identify paracrine mechanisms by which OR cells drive LUAD progression.

Quiescin sulfhydryl oxidase 1 (QSOX1) is a disulfide bond-forming enzyme with both disulfide isomerase and oxidoreductase activities. It plays an important role in protein folding, stability, and secretion. Growing evidence demonstrates that QSOX1 is upregulated in multiple cancer types and influences key behaviors of cancer cells, including proliferation, migration, invasion, and metastasis. Elevated QSOX1 expression is also associated with tumor malignancy and disease relapse. However, the molecular mechanisms by which QSOX1 drives cancer progression remain incompletely understood. In this review, we summarize current knowledge of QSOX1 expression and regulation in cancer, discuss its functional roles, and highlight key unanswered questions to warrant further investigation.