Inhibition of the sarco/endoplasmic reticulum (ER) Ca2+-ATPase by thapsigargin analogs induces cell death via ER Ca2+ depletion and the unfolded protein response

Abstract

Calcium (Ca) is a fundamental regulator of cell signaling and function. Thapsigargin (Tg) blocks the sarco/endoplasmic reticulum (ER) Ca-ATPase (SERCA), disrupts Ca homeostasis, and causes cell death. However, the exact mechanisms whereby SERCA inhibition induces cell death are incompletely understood. Here, we report that low (0.1 μm) concentrations of Tg and Tg analogs with various long-chain substitutions at the O-8 position extensively inhibit SERCA1a-mediated Ca transport. We also found that, in both prostate and breast cancer cells, exposure to Tg or Tg analogs for 1 day caused extensive drainage of the ER Ca stores. This Ca depletion was followed by markedly reduced cell proliferation rates and morphological changes that developed over 2-4 days and culminated in cell death. Interestingly, these changes were not accompanied by bulk increases in cytosolic Ca levels. Moreover, knockdown of two key store-operated Ca entry (SOCE) components, Orai1 and STIM1, did not reduce Tg cytotoxicity, indicating that SOCE and Ca entry are not critical for Tg-induced cell death. However, we observed a correlation between the abilities of Tg and Tg analogs to deplete ER Ca stores and their detrimental effects on cell viability. Furthermore, caspase activation and cell death were associated with a sustained unfolded protein response. We conclude that ER Ca drainage and sustained unfolded protein response activation are key for initiation of apoptosis at low concentrations of Tg and Tg analogs, whereas high cytosolic Ca levels and SOCE are not required.

An inability to maintain the ribonucleoprotein genomic structure is responsible for host detection of negative-sense RNA viruses

“…This dynamic would generate a feed forward loop in which aberrant viral RNA by-products of replication lead to shutdown of translation, and the subsequent generation of more aberrant viral RNA ultimately resulting in viral clearance or the induction of cell death. To formally investigate how the antiviral pathways that target translation would impact IAV biology, we infected cells treated with increasing amounts of thapsigargin, a compound that induces the unfolded protein response (UPR) by inhibiting the function of calcium-dependent chaperones ( Figure 5E) (Sehgal et al, 2017). Consistent with our previous results, these data demonstrated that engagement of the UPR rapidly resulted in loss of NP and a corresponding induction of the host response (as measured by IFN and IFIT1).…”

Metabolic implications of organelle–mitochondria communication

“…FUNDC1 ablation also decreases the levels of the MAM maintenance protein PACS2 . Inhibition of ER Ca 2+ uptake by SERCA initiates UPR and eventually provokes apoptosis . PDK4 inhibition decreases Ca 2+ flux in C2C12 myoblasts .…”

The overlooked aspect of excitotoxicity: Glutamate‐independent excitotoxicity in traumatic brain injuries

“…In addition to the harmful effects of the intracellular release of calcium from the ER, the depletion of calcium itself from this organelle is detrimental (Sehgal et al., ). Sehgal et al.…”

“…Sehgal et al. () reported that calcium depletion from the ER caused the activation of a cellular pathway called the unfolded protein response (UPR). Among the many physiological functions of the ER, proper protein folding is one function that is impaired in this circumstance (Lin et al., ).…”

“…In addition to the harmful effects of the intracellular release of calcium from the ER, the depletion of calcium itself from this organelle is detrimental (Sehgal et al, 2017). Sehgal et al (2017) reported that calcium depletion from the ER caused the activation of a cellular pathway called the unfolded protein response (UPR). Among the many physiological functions of the ER, proper protein folding is one function that is impaired in this circumstance .…”