Endoplasmic reticulum (ER) stress occurs when the ER cannot properly fold all the proteins it receives, leading to the accumulation of misfolded and unfolded proteins and disruption of cellular homeostasis. In response, cells activate the unfolded protein response (UPR), which initially works to restore normal ER function but can drive apoptosis if the stress is too strong or persists for too long. ER stress and dysregulated UPR signaling are closely linked to many chronic diseases, including diabetes, neurodegeneration, and cancer.​

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ATF4, ATF6, and CHOP are key transcription factors that determine how cells respond during ER stress, making them widely used markers and functional readouts of UPR activation:

• ATF4 helps coordinate stress adaptation and, under prolonged stress, contributes to pro-apoptotic gene expression

• ATF6 promotes the expression of chaperones and quality-control factors that support protein folding

• CHOP is strongly induced during severe or chronic ER stress and is closely associated with the switch from protective to pro-apoptotic signaling.

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To provide a convenient and sensitive way to monitor these pathways, Signosis offers luciferase reporter stable cell lines for ER stress response element (ERSE)–driven signaling as well as specific ATF4, ATF6, and CHOP reporter stable cell lines. These models enable researchers to track ER stress and distinct UPR branches in live cells, supporting both basic mechanistic studies and higher-throughput screening applications.​​