Aberrant activation of endoplasmic reticulum (ER) stress by extrinsic and intrinsic factors contributes to tumorigenesis and resistance to chemotherapies in various cancer types. Our previous studies have shown that the downregulation of PHLPP, a novel family of Ser/Thr protein phosphatases, promotes tumor initiation, and progression. Here we investigated the functional interaction between the ER stress and PHLPP expression in colon cancer. We found that induction of ER stress significantly decreased the expression of PHLPP proteins through a proteasome-dependent mechanism. Knockdown of PHLPP increased the phosphorylation of eIF2α as well as the expression of autophagy-associated genes downstream of the eIF2α/ATF4 signaling pathway. In addition, results from immunoprecipitation experiments showed that PHLPP interacted with eIF2α and this interaction was enhanced by ER stress. Functionally, knockdown of PHLPP improved cell survival under ER stress conditions, whereas overexpression of a degradation-resistant mutant PHLPP1 had the opposite effect. Taken together, our studies identified ER stress as a novel mechanism that triggers PHLPP downregulation; and PHLPP-loss promotes chemoresistance by upregulating the eIF2α/ATF4 signaling axis in colon cancer cells.
Mitochondria and endoplasmic reticulum (ER) contact sites (MERCs) are protein‐ and lipid‐enriched hubs that mediate interorganellar communication by contributing to the dynamic transfer of Ca2+, lipid, and other metabolites between these organelles. Defective MERCs are associated with cellular oxidative stress, neurodegenerative disease, and cardiac and skeletal muscle pathology via mechanisms that are poorly understood. We previously demonstrated that skeletal muscle‐specific knockdown (KD) of the mitochondrial fusion mediator optic atrophy 1 (OPA1) induced ER stress and correlated with an induction of Mitofusin‐2, a known MERC protein. In the present study, we tested the hypothesis that
- PAR ID:
- 10493274
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Cellular Physiology
- ISSN:
- 0021-9541
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Mitochondrial population maintenance in neurons is essential for neuron function and survival. Contact sites between mitochondria and the endoplasmic reticulum (ER) are poised to regulate mitochondrial homeostasis in neurons. These contact sites can facilitate transfer of calcium and lipids between the organelles and have been shown to regulate aspects of mitochondrial dynamics. Vesicle-associated membrane protein-associated protein B (VapB) is an ER membrane protein present at a subset of ER–mitochondrial contact sites. A proline-to-serine mutation in VapB at amino acid 56 (P56S) correlates with susceptibility to amyotrophic lateral sclerosis (ALS) type 8. Given the relationship between failed mitochondrial health and neurodegenerative disease, we investigated the function of VapB in mitochondrial population maintenance. We demonstrated that transgenic expression of VapBP56Sin zebrafish larvae (sex undetermined) increased mitochondrial biogenesis, causing increased mitochondrial population size in the axon terminal. Expression of wild-type VapB did not alter biogenesis but, instead, increased mitophagy in the axon terminal. Using genetic manipulations to independently increase mitochondrial biogenesis, we show that biogenesis is normally balanced by mitophagy to maintain a constant mitochondrial population size. VapBP56Stransgenics fail to increase mitophagy to compensate for the increase in mitochondrial biogenesis, suggesting an impaired mitophagic response. Finally, using a synthetic ER–mitochondrial tether, we show that VapB's function in mitochondrial turnover is likely independent of ER–mitochondrial tethering by contact sites. Our findings demonstrate that VapB can control mitochondrial turnover in the axon terminal, and this function is altered by the P56S ALS-linked mutation.
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Endoplasmic reticulum (ER) stress has been causatively linked to the onset of various pathologies. However, if and how inherent variations in the resulting unfolded protein response (UPR) affect the predisposition to ER stress-associated metabolic conditions remains to be established. By using genetically diverse deer mice (Peromyscus maniculatus) as a model, we show that the profile of tunicamycin-induced UPR in fibroblasts isolated at puberty varies between individuals and predicts deregulation of lipid metabolism and diet-induced hepatic steatosis later in life. Among the different UPR targets tested, CHOP more consistently predicted elevated plasma cholesterol and hepatic steatosis. Compared to baseline levels or inducibility, the maximal intensity of the UPR following stimulation best predicts the onset of pathology. Differences in the expression profile of the UPR recorded in cells from different populations of deer mice correlate with the varying response to ER stress in altitude adaptation. Our data suggest that the response to ER stress in cultured cells varies among individuals and its profile early in life may predict the onset of ER stress-associated disease in the elderly.more » « less
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k off≥2×103 s−1,k on≥7×106 M−1 s−1) and in multiple cell types. R‐CatchER captured spatiotemporal ER Ca2+dynamics in neurons and hotspots at dendritic branchpoints, enabled the first report of ER Ca2+oscillations mediated by calcium sensing receptors (CaSRs), and revealed ER Ca2+‐based functional cooperativity of CaSR. We elucidate the mechanism of R‐CatchER and propose a principle to rationally design genetically encoded Ca2+indicators with a single Ca2+‐binding site and fast kinetics by tuning rapid fluorescent‐protein dynamics and the electrostatic potential around the chromophore. The design principle is supported by the development of G‐CatchER2, an upgrade of our previous (G‐)CatchER with improved dynamic range. Our work may facilitate protein design, visualizing Ca2+dynamics, and drug discovery. -
Abstract Multi‐scale calcium (Ca2+) dynamics, exhibiting wide‐ranging temporal kinetics, constitutes a ubiquitous mode of signal transduction. We report a novel endoplasmic‐reticulum (ER)‐targeted Ca2+indicator, R‐CatchER, which showed superior kinetics in vitro (
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