Sec61 complex/translocon: The role of an atypical ER Ca2+-leak channel in health and disease

SEC61G promotes colorectal cancer progression by regulating cytosolic Ca2+ concentration

BACKGROUND

Intracellular calcium (Ca2+) signaling regulates key cancer processes. Research findings suggest that the SEC61 complex, involved in protein translocation, contributes to calcium leakage from the endoplasmic reticulum. However, the mechanism by which SEC61 Translocon Subunit Gamma (SEC61G), a component of this complex, influences colorectal cancer (CRC) progression remains unclear.

METHODS

Bioinformatics analysis was performed using The Cancer Genome Atlas data sets to identify candidate genes on chromosome 7p, examine their association with DNA copy number amplification. In addition, SEC61G expression in CRC cells and tissues was validated using reverse-transcription quantitative polymerase chain reaction and immunohistochemistry. Moreover, in vitro and in vivo experiments were performed to investigate the effects of SEC61G overexpression and knockdown on CRC cell proliferation. Furthermore, publicly available single-cell RNA sequencing (scRNA-seq) and spatial transcriptome sequencing (ST-seq) data were used to validate the role of SEC61G in CRC.

RESULTS

SEC61G was significantly upregulated in CRC tissues and was correlated with poor prognosis in patients with CRC. SEC61G overexpression enhanced cell proliferation and activated the EGFR pathway, promoting cell cycle progression from the G1 to S phase. In addition, SEC61G overexpression increased cytosolic Ca2+ levels, which activated EGFR signaling via calmodulin. Moreover, analyses of scRNA-seq and ST-seq data confirmed that SEC61G expression was higher in tumor epithelial cells and that it was co-expressed with EGFR pathway-related genes.

CONCLUSIONS

SEC61G promotes CRC progression by regulating cytosolic Ca2+ concentration, EGFR activation, and cell cycle progression, highlighting its potential as a prognostic biomarker and therapeutic target in CRC.

Aminooxyacetic acid ameliorates alcohol-induced learning and memory deficits through BDNF-TrkB pathway and calcium homeostasis

Chronic alcohol-related brain damage (ARBD) is mainly manifested as learning and memory impairment and cognitive decline in the long term. Ca2+ plays a key role in learning and memory impairment. The increase of intracellular Ca2+ concentration can directly cause mitochondrial dysfunction, destroy normal physiological signal transduction, and accelerate the process of learning and memory decline. Aminooxyacetic acid (AOAA), a selective inhibitor of Cystathionineβ-synthase (CBS), has a good effect on a variety of diseases, including improving stroke and reducing the incidence of convulsions. However, its potential in maintaining learning and memory functions by regulating Ca2+ and mitochondrial functional status remains uncertain. In this study, chronic alcoholism rats and human neuroblastoma cells (SHSY-5Y) were used as the research objects to establish a chronic alcohol-related brain damage model. We aimed to elucidate the specific mechanisms by which AOAA protects learning and memory functions in alcohol-induced learning and memory impairment. Through Morris water maze test, LTP test, Western blot (WB), immunohistochemistry (IHC), mitochondrial observation under electron microscope, calcium ion concentration measurement and mitochondrial membrane potential measurement, it was found that AOAA could not only regulate the level of endoplasmic reticulum stress (ERS) caused by H2S elevation, but also maintain the role of valve of Sec61 channel on Ca2+ by restoring the level of BIP, a key indicator of ERS, significantly alleviate mitochondrial dysfunction caused by Ca2+ overload, and optimize learning and memory function. The mechanism may be closely related to the BDNF-TrkB pathway.

A natural gene on-off system confers field thermotolerance for grain quality and yield in rice

Rising global temperatures threaten crop grain quality and yield; however, how temperature regulates grain quality and how to achieve synergistic thermotolerance for both quality and yield remain unknown. Here, we identified a rice major locus, QT12, which negatively controls grain-quality field thermotolerance by disrupting endosperm storage substance homeostasis through over-activating unfolded protein response (UPR). Natural variations in QT12 and an NF-Y complex form a natural gene on-off system to modulate QT12 expression and thermotolerance. High temperatures weaken NF-YB9/NF-YC10 interactions with NF-YA8, releasing QT12 suppression and triggering quality deterioration. Low QT12 expression confers superior quality and increases elite rice yield up to 1.31-1.93 times under large-scale high-temperature trials. Two trait regulatory haplotypes (TRHs) from co-selected variations of the four genetically unlinked genes in NF-Ys-QT12 were identified for subspecies thermotolerance differentiation. Our work provides mechanistic insights into rice field thermotolerance and offers a proof-of-concept breeding strategy to break stress-growth and yield-quality trade-offs.

Skeletal and dental tissue mineralization: The potential role of the endoplasmic reticulum/Golgi complex and the endolysosomal and autophagic transport systems

This paper presents a review of the potential role of the endoplasmic reticulum/Golgi complex and intracellular vesicles in mediating events leading to or associated with vertebrate tissue mineralization. The possible importance of these organelles in this process is suggested by observations that calcium ions accumulate in the tubules and lacunae of the endoplasmic reticulum and Golgi. Similar levels of calcium ions (approaching millimolar) are present in vesicles derived from endosomes, lysosomes and autophagosomes. The cellular level of phosphate ions in these organelles is also high (millimolar). While the source of these ions for mineral formation has not been identified, there are sound reasons for considering that they may be liberated from mitochondria during the utilization of ATP for anabolic purposes, perhaps linked to matrix synthesis. Published studies indicate that calcium and phosphate ions or their clusters contained as cargo within the intracellular organelles noted above lead to formation of extracellular mineral. The mineral sequestered in mitochondria has been documented as an amorphous calcium phosphate. The ion-, ion cluster- or mineral-containing vesicles exit the cell in plasma membrane blebs, secretory lysosomes or possibly intraluminal vesicles. Such a cell-regulated process provides a means for the rapid transport of ions or mineral particles to the mineralization front of skeletal and dental tissues. Within the extracellular matrix, the ions or mineral may associate to form larger aggregates and potential mineral nuclei, and they may bind to collagen and other proteins. How cells of hard tissues perform their housekeeping and other biosynthetic functions while transporting the very large volumes of ions required for mineralization of the extracellular matrix is far from clear. Addressing this and related questions raised in this review suggests guidelines for further investigations of the intracellular processes promoting the mineralization of the skeletal and dental tissues.

Guilu Erxian glue reduces endoplasmic reticulum stress-mediated apoptosis and restores the balance of extracellular matrix synthesis and degradation in chondrocytes by inhibiting the ATF6/GRP78/CHOP signaling pathway

Knee Osteoarthritis (KOA) is characterized by phenotypic alterations, apoptosis, and the breakdown of the extracellular matrix (ECM) in the superficial articular cartilage cells. The inflammatory response activates the Endoplasmic Reticulum Stress (ERS) signaling pathway, which plays a critical role in the pathophysiology and progression of KOA. Chondrocytes stimulated by thapsigargin(TG)exhibit heightened ERS and significantly increase the expression of ERS-associated proteins. Key mediators of ERS-induced apoptosis include X-box-binding protein 1(XBP1), elevated levels of the protein transport protein Sec61 subunit (SEC61), and C/EBP homologous protein (CHOP). While the precise mechanism of action of Guilu Erxian Glue (GEG), a medication commonly used in the clinical treatment of KOA, remains to be fully elucidated, our research has shown that GEG mitigates the imbalance between ECM synthesis and degradation, as well as chondrocyte apoptosis resulting from ERS. This effect is likely achieved through the suppression of the Activating Transcription Factor 6 (ATF6)/Glucose-Regulatory Protein 78 (GRP78)/CHOP signaling pathway. In summary,our research results indicate that GEG can activate the ATF6/GRP78/CHOP signaling pathway to restore endoplasmic reticulum (ER) homeostasis in chondrocytes, thereby reducing chondrocyte apoptosis and ultimately promoting the balance between ECM synthesis and degradation.

Identification of novel endoplasmic reticulum-related genes and their association with immune cell infiltration in major depressive disorder

BACKGROUND

Several lines of evidence point to an interaction between genetic predisposition and environmental factors in the onset of major depressive disorder (MDD). This study is aimed to investigate the pathogenesis of MDD by identifying key biomarkers, associated immune infiltration using bioinformatic analysis and human postmortem sample.

METHODS

The Gene Expression Omnibus (GEO) database of GSE98793 was adopted to identify hub genes linked to endoplasmic reticulum (ER) stress-related genes (ERGs) in MDD. Another GEO database of GSE76826 was employed to validate the novel target associated with ERGs and immune infiltration in MDD. Moreover, human postmortem sample from MDD patients was utilized to confirm the differential expression analysis of hub genes.

RESULTS

We discovered 12 ER stress-related differentially expressed genes (ERDEGs). A LASSO Cox regression analysis helped construct a diagnostic model for these ERDEGs, incorporating immune infiltration analysis revealed that three hub genes (ERLIN1, SEC61B, and USP13) show the significant and consistent expression differences between the two groups. Western blot analysis of postmortem brain samples indicated notably higher expression levels of ERLIN1 and SEC61B in the MDD group, with USP13 also tending to increase compared to control group.

LIMITATIONS

The utilization of the MDD gene chip in this analysis was sourced from the GEO database, which possesses a restricted number of pertinent gene chip samples.

CONCLUSIONS

These findings indicate that ERDEGs especially including ERLIN1, SEC61B, and USP13 associated the infiltration of immune cells may be potential diagnostic indicators for MDD.

Disrupted Endoplasmic Reticulum Ca2+ Handling: A Harβinger of β-Cell Failure

The β-cell workload increases in the setting of insulin resistance and reduced β-cell mass, which occurs in type 2 and type 1 diabetes, respectively. The prolonged elevation of insulin production and secretion during the pathogenesis of diabetes results in β-cell ER stress. The depletion of β-cell Ca2+ER during ER stress activates the unfolded protein response, leading to β-cell dysfunction. Ca2+ER is involved in many pathways that are critical to β-cell function, such as protein processing, tuning organelle and cytosolic Ca2+ handling, and modulating lipid homeostasis. Mutations that promote β-cell ER stress and deplete Ca2+ER stores are associated with or cause diabetes (e.g., mutations in ryanodine receptors and insulin). Thus, improving β-cell Ca2+ER handling and reducing ER stress under diabetogenic conditions could preserve β-cell function and delay or prevent the onset of diabetes. This review focuses on how mechanisms that control β-cell Ca2+ER are perturbed during the pathogenesis of diabetes and contribute to β-cell failure.

The ubiquitin-proteasome pathway inhibitor TAK-243 has major effects on calcium handling in mammalian cells

The ubiquitin-proteasome pathway (UPP) is a major route for protein degradation and a key regulatory mechanism in mammalian cells. UPP inhibitors, including TAK-243, a first-in-class inhibitor of the E1 ubiquitin-activating enzyme, are currently being used and tested for treatment of a range of diseases, particularly cancer. Here, we reveal that TAK-243 has major effects on Ca2+ handling in a range of cultured mammalian cells (αT3, HeLa and SH-SY5Y). Effects were seen on agonist-induced Ca2+ mobilization, basal cytosolic Ca2+ levels, Ca2+ leak from the endoplasmic reticulum (ER), store-operated Ca2+ entry and mitochondrial Ca2+ uptake. These effects correlated with induction of ER stress, as measured by PERK activation / eIF2α phosphorylation, and most seemed to be underpinned by enhanced Ca2+ leak from the ER. Overall, these data indicate that TAK-243 reprograms the Ca2+-handling properties of mammalian cells and that these effects should be considered when UPP inhibitors are employed as therapeutic agents.

SEC61 translocon subunit gamma enhances low-dose cisplatin-induced cancer-stem cell properties of head and neck squamous cell carcinoma via enhancing Ca2+-mediated autophagy

Background/purpose

High SEC61 translocon subunit gamma (SEC61G) expression is associated with an unfavorable prognosis in patients with head and neck squamous cell carcinoma (HNSCC), but the underlying mechanisms remain poorly understood.

Materials and methods

HNSCC representative cell lines SCC15 and CAL27 were used to explore the regulation of SEC61G on Ca2+ leak from the endoplasmic reticulum (ER). Ca2+-activated autophagy was monitored by fluorescent labeling of autophagosomes and western blotting assays. CSC marker expression, sphere formation, colony formation, and transwell of invasion were detected to investigate the role of SEC61G in regulating cancer-stem cell (CSC) properties.

Results

Among the SEC61 complex genes, only SEC61G upregulation is consistently associated with unfavorable progression-free interval and disease-specific survival in patients with HNSCC. Low-dose cisplatin (CDDP) treatment induced SEC61G upregulation in SCC15 and CAL27 cells. SEC61G knockdown significantly impaired CDDP-induced Ca2+ from the ER and the phosphorylation of ERK1/2 and AMPK. CDDP-induced autophagy in HNSCC cells were hampered by SEC61G shRNA, in terms of impaired autophagosome formation, lowered LC3-II/GAPDH ratio and restored p62 expression. CDDP-induced CSC properties, including CSC marker expression, sphere formation, colony formation, and invasive capabilities could be suppressed by shSEC61G and chloroquine, a specific autophagy inhibitor.

Conclusion

Findings of this study revealed the contribution of SEC61G in promoting cisplatin-induced CSC properties of HNSCC cells via promoting Ca2+-mediated autophagy.

Kinetics of the thapsigargin-induced Ca2+ mobilisation: A quantitative analysis in the HEK-293 cell line

Thapsigargin (TG) inhibits the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) pump and, when applied acutely, it initiates a Ca2+ mobilisation that begins with the loss of Ca2+ from the endoplasmic reticulum (ER) and culminates with store-operated Ca2+ entry (SOCE) from the extracellular space. Using the popular model cell line HEK-293, we quantified TG-induced changes in cytosolic and ER Ca2+ levels using FURA-2 and the FRET-based ER Ca2+ sensor D1ER, respectively. Our analysis predicts an ER Ca2+ leak of 5–6 µM⋅s−1 for the typical basal ER Ca2+ level of 335–407 µM in HEK-293 cells. The resulting cytosolic Ca2+ transients reached peak amplitudes of 0.6–1.0 µM in the absence of external Ca2+ and were amplified by SOCE that amounted to 28–30 nM⋅s−1 in 1 mM external Ca2+. Additionally, cytosolic Ca2+ transients were shaped by a Ca2+ clearance of 10–13 nM⋅s−1. Using puromycin (PURO), which enhances the ER Ca2+ leak, we show that TG-induced cytosolic Ca2+ transients are directly related to ER Ca2+ levels and to the ER Ca2+ leak. A one-compartment model incorporating ER Ca2+ leak and cytosolic Ca2+ clearance accounted satisfactorily for the basic features of TG-induced Ca2+ transients and underpinned the rule that an increase in amplitude associated with shortening of TG-induced cytosolic Ca2+ transients most likely reflects an increase in ER Ca2+ leak.