Trans-2-enoyl-CoA reductase limits Ca2+ accumulation in the endoplasmic reticulum by inhibiting the Ca2+ pump SERCA2b

Novel SERCA2 inhibitor Diphyllin displays anti-tumor effect in non-small cell lung cancer by promoting endoplasmic reticulum stress and mitochondrial dysfunction

Abnormal calcium signaling is associated with non-small cell lung cancer (NSCLC) malignant progression, poor survival and chemotherapy resistance. Targeting endoplasmic reticulum (ER) Ca2+ channels or pumps to block calcium uptake in the ER induces ER stress and concomitantly promotes mitochondrial calcium uptake, leading to mitochondrial dysfunction and ultimately inducing cell death. Here, we identified Diphyllin was a potential specific inhibitor of endoplasmic reticulum (ER) calcium-importing protein sarco/endoplasmic-reticulum Ca2+ ATPase 2 (SERCA2). In vitro and in vivo studies showed that Diphyllin increased NSCLC cell apoptosis, along with inhibition of cell proliferation and migration. Mechanistically, Diphyllin promoted ER stress by directly inhibiting SERCA2 activity and decreasing ER Ca2+ levels. At the same time, the accumulated Ca2+ in cytoplasm flowed into mitochondria to increase reactive oxygen species (ROS) and decrease mitochondrial membrane potential (MMP), leading to cytochrome C (Cyto C) release and mitochondrial dysfunction. In addition, we found that Diphyllin combined with cisplatin could have a synergistic anti-tumor effect in vitro and in vivo. Taken together, our results suggested that Diphyllin, as a potential novel inhibitor of SERCA2, exerts anti-tumor effects by blocking ER Ca2+ uptake and thereby promoting ER stress and mitochondrial dysfunction.

The A-kinase anchoring protein Yotiao decrease the ER calcium content by inhibiting the store operated calcium entry

The meticulous regulation of ER calcium (Ca2+) homeostasis is indispensable for the proper functioning of numerous cellular processes. Disrupted ER Ca2+ balance is implicated in diverse diseases, underscoring the need for a systematic exploration of its regulatory factors in cells. Our recent genomic-scale screen identified a scaffolding protein A-kinase anchoring protein 9 (AKAP9) as a regulator of ER Ca2+ levels, but the underlying molecular mechanisms remain elusive. Here, we reveal that Yotiao, the smallest splicing variant of AKAP9 decreased ER Ca2+ content in animal cells. Additional testing using a combination of Yotiao truncations, knock-out cells and pharmacological tools revealed that, Yotiao does not require most of its interactors, including type 1 inositol 1,4,5-trisphosphate receptors (IP3R1), protein kinase A (PKA), protein phosphatase 1 (PP1), adenylyl cyclase type 2 (AC2) and so on, to reduce ER Ca2+ levels. However, adenylyl cyclase type 9 (AC9), which is known to increases its cAMP generation upon interaction with Yotiao for the modulation of potassium channels, plays an essential role for Yotiao's ER-Ca2+-lowering effect. Mechanistically, Yotiao may work through AC9 to act on Orai1-C terminus and suppress store operated Ca2+ entry, resulting in reduced ER Ca2+ levels. These findings not only enhance our comprehension of the interplay between Yotiao and AC9 but also contribute to a more intricate understanding of the finely tuned mechanisms governing ER Ca2+ homeostasis.

A Msp1-containing complex removes orphaned proteins in the mitochondrial outer membrane of T. brucei

The AAA-ATPase Msp1 extracts mislocalised outer membrane proteins and thus contributes to mitochondrial proteostasis. Using pulldown experiments, we show that trypanosomal Msp1 localises to both glycosomes and the mitochondrial outer membrane, where it forms a complex with four outer membrane proteins. The trypanosome-specific pATOM36 mediates complex assembly of α-helically anchored mitochondrial outer membrane proteins such as protein translocase subunits. Inhibition of their assembly triggers a pathway that results in the proteasomal digestion of unassembled substrates. Using inducible single, double, and triple RNAi cell lines combined with proteomic analyses, we demonstrate that not only Msp1 but also the trypanosomal homolog of the AAA-ATPase VCP are implicated in this quality control pathway. Moreover, in the absence of VCP three out of the four Msp1-interacting mitochondrial proteins are required for efficient proteasomal digestion of pATOM36 substrates, suggesting they act in concert with Msp1. pATOM36 is a functional analog of the yeast mitochondrial import complex complex and possibly of human mitochondrial animal-specific carrier homolog 2, suggesting that similar mitochondrial quality control pathways linked to Msp1 might also exist in yeast and humans.

Very-long-chain fatty acids are crucial to neuronal polarity by providing sphingolipids to lipid rafts

Fatty acids have long been considered essential to brain development; however, the involvement of their synthesis in nervous system formation is unclear. We generate mice with knockout of GPSN2, an enzyme for synthesis of very-long-chain fatty acids (VLCFAs) and investigate the effects. Both GPSN2-/- and GPSN2+/- mice show abnormal neuronal networks as a result of impaired neuronal polarity determination. Lipidomics of GPSN2-/- embryos reveal that ceramide synthesis is specifically inhibited depending on FA length; namely, VLCFA-containing ceramide is reduced. We demonstrate that lipid rafts are highly enriched in growth cones and that GPSN2+/- neurons lose gangliosides in their membranes. Application of C24:0 ceramide, but not C16:0 ceramide or C24:0 phosphatidylcholine, to GPSN2+/- neurons rescues both neuronal polarity determination and lipid-raft density in the growth cone. Taken together, our results indicate that VLCFA synthesis contributes to physiological neuronal development in brain network formation, in particular neuronal polarity determination through the formation of lipid rafts.

Phillygenin ameliorates nonalcoholic fatty liver disease via TFEB-mediated lysosome biogenesis and lipophagy

BACKGROUND

Lipophagy is an autophagic process, which delivers the intracellular lipid droplets to the lysosomes for degradation. Recent studies revealed that the impairment of lysosomal biogenesis and autophagic flux led to dysregulation of lipophagy in hepatocytes, which exacerbated the development of nonalcoholic fatty liver disease (NAFLD). Therefore, agents restoring autophagic flux and lipophagy in hepatocytes may have therapeutic potential against this increasingly prevalent disease. Phillygenin (PHI), a lignin extracted from Forsythia suspense, exerts hepatoprotective and anti-inflammatory effects. However, the effect of PHI on NAFLD remains unknown.

PURPOSE

This study aimed to investigate the protective effect of PHI on NAFLD and elucidate the underlying mechanism.

METHODS

The effects of PHI were examined in palmitate (PA)-stimulated AML12 cells and primary hepatocytes, as well as in NAFLD mice induced by a high-fat diet (HFD). We also used transcription factor EB (TFEB) knockdown hepatocytes and hepatocyte-specific TFEB knockout (TFEB^Δhep) mice for mechanistic studies. In vivo and in vitro studies were performed using western blots, immunofluorescence techniques, and transmission electron microscopy.

RESULTS

Our results indicated that autophagic flux and lysosome biogenesis in PA-stimulated hepatocytes were impaired. PHI alleviated lipid deposition by increasing lysosomal biogenesis and autophagic flux. It also stimulated the release of endoplasmic reticulum Ca²⁺ to activate calcineurin, which regulated TFEB dephosphorylation and nuclear translocation, and promoted lysosomal biogenesis. In addition, PHI blocked the NLRP3 inflammasome pathway and improved hepatocyte inflammation in an autophagy-dependent manner. Consistent with the in vitro results, PHI improved hepatic steatosis and inflammation in HFD mice, but these beneficial effects were eliminated in hepatocyte-specific TFEB knockout mice.

CONCLUSION

Despite PHI has been reported to have anti-hepatic fibrosis effects, whether it has a hepatoprotective effects against NAFLD and the underlying molecular mechanism remain unclear. Herein, we found that PHI restored lipophagy and suppressed lipid accumulation and inflammation by regulating the Ca²⁺-calcineurin-TFEB axis in hepatocytes. Thus, PHI represents a therapeutic candidate for the treatment of NAFLD.

SERCA interacts with chitin synthase and participates in cuticular chitin biogenesis in Drosophila

The biogenesis of chitin, a major structural polysaccharide found in the cuticle and peritrophic matrix, is crucial for insect growth and development. Chitin synthase, a membrane-integral β-glycosyltransferase, has been identified as the core of the chitin biogenesis machinery. However, a yet unknown number of auxiliary proteins appear to assist in chitin biosynthesis, whose precise function remains elusive. Here, we identified a sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA), in the fruit fly Drosophila melanogaster, as a chitin biogenesis-associated protein. The physical interaction between DmSERCA and epidermal chitin synthase (Krotzkopf verkehrt, Kkv) was demonstrated and analyzed using split-ubiquitin membrane yeast two-hybrid, bimolecular fluorescent complementation, pull-down, and immunoprecipitation assays. The interaction involves N-terminal regions (aa 48-81 and aa 247-33) and C-terminal regions (aa 743-783 and aa 824-859) of DmSERCA and two N-terminal regions (aa 121-179 and aa 369-539) of Kkv, all of which are predicted be transmembrane helices. While tissue-specific knock-down of DmSERCA in the epidermis caused larval and pupal lethality, the knock-down of DmSERCA in wings resulted in smaller and crinkled wings, a significant decrease in chitin deposition, and the loss of chitin lamellar structure. Although DmSERCA is well-known for its role in muscular contraction, this study reveals a novel role in chitin synthesis, contributing to our knowledge on the machinery of chitin biogenesis.