A new study from Ben-Gurion University of the Negev (BGU) has uncovered a molecular switch that determines whether stressed human cells choose to survive or undergo programmed cell death, known as apoptosis. The findings, published in the journal Redox Biology, could lead to new ways of overcoming chemotherapy resistance in aggressive cancers. The research was led by Dr. Aeid Igbaria, along with co-lead authors Laila Abu Madegam and Noa Gavriel, and researcher Raifu Tolulope Adebisi, all from BGU's Department of Life Sciences. The endoplasmic reticulum (ER) is a vital part of the cell responsible for producing and folding proteins. When cells face stress, such as from disease or injury, the ER uses a process called ER-to-cytosol signaling (ERCYS) to reduce internal pressure. This involves moving certain proteins from the ER to the cytosol, where they can help the cell survive by blocking proteins that would otherwise trigger cell death. Cancer cells often misuse this pathway to avoid the effects of chemotherapy and other treatments. However, the exact molecular mechanism that controls when this pathway is active—and why it stops under extreme stress—has been unclear. Through experiments using various human cell lines, the BGU team discovered that this survival mechanism works within a specific range of stress levels, controlled by the cell's redox balance—the balance between oxidation and reduction reactions. Under moderate stress, two proteins called DNAJB12 and DNAJB14 remain stable due to chemical bonds called disulfide bridges. These proteins help the cell survive by moving protective proteins to the cytosol and breaking down proteins that promote cell death. This allows the cell to avoid apoptosis while the stress is still manageable. However, when stress becomes too severe, the cell's levels of glutathione, a key antioxidant, increase. This breaks the disulfide bonds, causing DNAJB12 and DNAJB14 to become unstable and be destroyed. Without these proteins, the cell loses its ability to protect itself. A protein called BIK, which normally resides in the ER and promotes cell death, becomes active and recruits other proteins called BAX and BAK. These proteins then form pores in the ER membrane, leading to irreversible cell death through apoptosis. "Our findings show that the cell's redox balance acts like a precise molecular scale," explained Igbaria. "Rather than passively breaking down, the cell actively monitors stress levels through the stability of these chemical bonds. Under moderate stress, it uses molecular chaperones to survive, but when the stress becomes too high, it dismantles these protectors to initiate cell death." Abu Madegam added, "Understanding how this switch works gives us a clear target for therapy. Since cancer cells rely on this pathway to resist chemotherapy, disrupting DNAJB12 and DNAJB14 or changing the ER's redox environment could remove their defenses and force them into apoptosis." The researchers also tested this process in models of heart muscle under conditions of low oxygen followed by reoxygenation. Their findings suggest that controlling this molecular switch could help protect heart tissue from severe cell death after events like heart attacks, opening up new treatment possibilities for cardiovascular diseases.