Trychta, K. A. | bioRxiv Science

bioRxiv2022

Caffeine and MDMA (ecstasy) exacerbate ER stress triggered by hyperthermia

Drugs of abuse can cause local and systemic hyperthermia, a known trigger of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). Another trigger of ER stress and UPR is ER calcium depletion which causes ER exodosis, the secretion of ER resident proteins. Club drugs such as 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) can create hyperthermic conditions in the brain and cause toxicity that is affected by the environmental temperature and the presence of other drugs, such as caffeine. Here we examine the secretion of ER resident proteins and activation of the UPR under combined exposure to MDMA and caffeine in a cellular model of hyperthermia. We show that hyperthermia triggers the secretion of normally ER resident proteins and that this aberrant protein secretion is potentiated by the presence of MDMA, caffeine, or a combination of the two drugs. Hyperthermia activates the UPR but the addition of MDMA or caffeine does not alter canonical UPR gene expression despite the drug effects on ER exodosis of UPR-related proteins. One exception was increased BiP/Grp78 mRNA levels in MDMA-treated cells exposed to hyperthermia. These findings suggest that club drug use under hyperthermic conditions exacerbates disruption of ER proteostasis contributing to cellular toxicity. HighlightsO_LIER resident proteins are redistributed into the extracellular space in response to hyperthermia and caffeine and MDMA further enhance this secretion. C_LIO_LIStabilizing ER calcium and overexpressing KDEL receptors reduces ER resident protein secretion following hyperthermia. C_LIO_LIHyperthermia triggers a UPR response with MDMA augmenting BiP expression in hyperthermic conditions. C_LI

cell biology↗

bioRxiv2021

Computational modeling of C-terminal tails to predict the calcium-dependent secretion of ER resident proteins

The lumen of the endoplasmic reticulum (ER) has resident proteins that are critical to perform the various tasks of the ER such as protein maturation and lipid metabolism. These ER resident proteins typically have a carboxy-terminal ER retention sequence (ERS). The canonical ERS is Lys-Asp-Glu-Leu (KDEL) and when an ER resident protein moves from the ER to the Golgi, KDEL receptors (KDELRs) in the Golgi recognize the ERS and return the protein to the ER lumen. Depletion of ER calcium leads to the mass departure of ER resident proteins in a process termed exodosis, which is also regulated by KDELRs. Here, by combining computational prediction with machine learning-based models and experimental validation, we identify carboxy tail sequences of ER resident proteins divergent from the canonical "KDEL" ERS. Using molecular modeling and simulations, we demonstrated that two representative non-canonical ERS can stably bind to the KDELR. Collectively, we developed a method to predict whether a carboxy-terminal sequence acts as a putative ERS that would undergo secretion in response to ER calcium depletion and interact with the KDELRs. Identification of proteins that undergo exodosis will further our understanding of changes in ER proteostasis under physiological and pathological conditions where ER calcium is depleted.

cell biology↗