bims-unfpre 2023-10-22 papers

Issue of 2023–10–22
five papers selected by
Susan Logue, University of Manitoba

Cell Metab. 2023 Oct 10. pii: S1550-4131(23)00368-6. [Epub ahead of print]

CD36 maintains lipid homeostasis via selective uptake of monounsaturated fatty acids during matrix detachment and tumor progression.

Alexander R Terry, Veronique Nogueira, Hyunsoo Rho, Gopalakrishnan Ramakrishnan, Jing Li, Soeun Kang, Koralege C Pathmasiri, Sameer Ahmed Bhat, Liping Jiang, Shafi Kuchay, Stephanie M Cologna, Nissim Hay.

A high-fat diet (HFD) promotes metastasis through increased uptake of saturated fatty acids (SFAs). The fatty acid transporter CD36 has been implicated in this process, but a detailed understanding of CD36 function is lacking. During matrix detachment, endoplasmic reticulum (ER) stress reduces SCD1 protein, resulting in increased lipid saturation. Subsequently, CD36 is induced in a p38- and AMPK-dependent manner to promote preferential uptake of monounsaturated fatty acids (MUFAs), thereby maintaining a balance between SFAs and MUFAs. In attached cells, CD36 palmitoylation is required for MUFA uptake and protection from palmitate-induced lipotoxicity. In breast cancer mouse models, CD36-deficiency induced ER stress while diminishing the pro-metastatic effect of HFD, and only a palmitoylation-proficient CD36 rescued this effect. Finally, AMPK-deficient tumors have reduced CD36 expression and are metastatically impaired, but ectopic CD36 expression restores their metastatic potential. Our results suggest that, rather than facilitating HFD-driven tumorigenesis, CD36 plays a supportive role by preventing SFA-induced lipotoxicity.

Keywords: CD36; cancer metabolism; fatty acids; matrix detachment; metastasis; palmitoylation

DOI: https://doi.org/10.1016/j.cmet.2023.09.012

Plant Cell Physiol. 2023 Oct 21. pii: pcad131. [Epub ahead of print]

Sterol Biosynthesis Contributes to Brefeldin-A-Induced Endoplasmic Reticulum Stress Resistance in Chlamydomonas reinhardtii.

Sujeong Je, Bae Young Choi, Eunbi Kim, Kyungyoon Kim, Yuree Lee, Yasuyo Yamaoka.

The endoplasmic reticulum (ER) stress response is an evolutionarily conserved mechanism in most eukaryotes. In this response, sterols in the phospholipid bilayer play a crucial role in controlling membrane fluidity and homeostasis. Despite the significance of both the ER stress response and sterols in maintaining ER homeostasis, their relationship remains poorly explored. Our investigation focused on Chlamydomonas strain CC-4533 and revealed that free sterol biosynthesis increased in response to ER stress, except in mutants of the ER stress sensor IRE1. Transcript analysis of Chlamydomonas experiencing ER stress unveiled the regulatory role of the IRE1/bZIP1 pathway in inducing the expression of ERG5, which encodes C-22 sterol desaturase. Through the isolation of three erg5 mutant alleles, we observed a defect in the synthesis of Chlamydomonas' sterol end products, ergosterol and 7-dehydroporiferasterol. Furthermore, these erg5 mutants also exhibited increased sensitivity to ER stress induced by brefeldin A (BFA, an inhibitor of ER-Golgi trafficking), whereas tunicamycin (Tm, an inhibitor of N-glycosylation) and dithiothreitol (DTT, an inhibitor of disulfide-bond formation) had no such effect. Intriguingly, the sterol biosynthesis inhibitors fenpropimorph (Fp) and fenhexamid (Fh), which impede steps upstream of the ERG5 enzyme in sterol biosynthesis, rescued BFA hypersensitivity in CC-4533 cells. Collectively, our findings support the conclusion that the accumulation of intermediates in the sterol biosynthetic pathway influences ER stress in a complex manner. This study highlights the significance and complexity of regulating sterol biosynthesis during the ER stress response in microalgae.

Keywords: Chlamydomonas; ER stress; ERG5; Sterols, UPR

DOI: https://doi.org/10.1093/pcp/pcad131

Mol Cell Biochem. 2023 Oct 18.

Novel functions of the ER-located Hsp40s DNAJB12 and DNAJB14 on proteins at the outer mitochondrial membrane under stress mediated by CCCP.

Pattarawut Sopha, Tirawit Meerod, Bunkuea Chantrathonkul, Nadgrita Phutubtim, Douglas M Cyr, Piyarat Govitrapong.

The endoplasmic reticulum (ER) membrane provides infrastructure for intracellular signaling, protein degradation, and communication among the ER lumen, cytosol, and nucleus via transmembrane and membrane-associated proteins. Failure to maintain homeostasis at the ER leads to deleterious conditions in humans, such as protein misfolding-related diseases and neurodegeneration. The ER transmembrane heat shock protein 40 (Hsp40) proteins, including DNAJB12 (JB12) and DNAJB14 (JB14), have been studied for their importance in multiple aspects of cellular events, including degradation of misfolded membrane proteins, proteasome-mediated control of proapoptotic Bcl-2 members, and assembly of multimeric ion channels. This study elucidates a novel facet of JB12 and JB14 in that their expression could be regulated in response to stress caused by the presence of ER stressors and the mitochondrial potential uncoupler CCCP. Furthermore, JB14 overexpression could affect the level of PTEN-induced kinase 1 (PINK1) expression under CCCP-mediated stress. Cells with genetic knockout (KO) of DNAJB12 and DNAJB14 exhibited an altered kinetic of phosphorylated Drp1 in response to the stress caused by CCCP treatment. Surprisingly, JB14-KO cells exhibited a prolonged stabilization of PINK1 during chronic exposure to CCCP. Cells depleted with JB12 or JB14 also revealed an increase in the mitochondrial count and branching. Hence, this study indicates the possible novel functions of JB12 and JB14 involving mitochondria in nonstress conditions and under stress caused by CCCP.

Keywords: ER stress; Hsp40; Intracellular communication; J-protein; Mitochondrial dynamics; Mitochondrial stress response

DOI: https://doi.org/10.1007/s11010-023-04866-1

JHEP Rep. 2023 Nov;5(11): 100879

Macrophage RIPK3 triggers inflammation and cell death via the XBP1-Foxo1 axis in liver ischaemia-reperfusion injury.

Xiaoye Qu, Tao Yang, Xiao Wang, Dongwei Xu, Yeping Yu, Jun Li, Longfeng Jiang, Qiang Xia, Douglas G Farmer, Bibo Ke.

Background & Aims: Receptor-interacting serine/threonine-protein kinase 3 (RIPK3) is a central player in triggering necroptotic cell death. However, whether macrophage RIPK3 may regulate NOD1-dependent inflammation and calcineurin/transient receptor potential cation channel subfamily M member 7 (TRPM7)-induced hepatocyte death in oxidative stress-induced liver inflammatory injury remains elusive.
Methods: A mouse model of hepatic ischaemia-reperfusion (IR) injury, the primary hepatocytes, and bone marrow-derived macrophages were used in the myeloid-specific RIPK3 knockout (RIPK3M-KO) and RIPK3-proficient (RIPK3FL/FL) mice.
Results: RIPK3M-KO diminished IR stress-induced liver damage with reduced serum alanine aminotransferase/aspartate aminotransferase levels, macrophage/neutrophil infiltration, and pro-inflammatory mediators compared with the RIPK3FL/FL controls. IR stress activated RIPK3, inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α), x-box binding protein 1 (XBP1), nucleotide-binding oligomerisation domain-containing protein 1 (NOD1), NF-κB, forkhead box O1 (Foxo1), calcineurin A, and TRPM7 in ischaemic livers. Conversely, RIPK3M-KO depressed IRE1α, XBP1, NOD1, calcineurin A, and TRPM7 activation with reduced serum tumour necrosis factor α (TNF-α) levels. Moreover, Foxo1M-KO alleviated IR-induced liver injury with reduced NOD1 and TRPM7 expression. Interestingly, chromatin immunoprecipitation coupled with massively parallel sequencing revealed that macrophage Foxo1 colocalised with XBP1 and activated its target gene Zc3h15 (zinc finger CCCH domain-containing protein 15). Activating macrophage XBP1 enhanced Zc3h15, NOD1, and NF-κB activity. However, disruption of macrophage Zc3h15 inhibited NOD1 and hepatocyte calcineurin/TRPM7 activation, with reduced reactive oxygen species production and lactate dehydrogenase release after macrophage/hepatocyte coculture. Furthermore, adoptive transfer of Zc3h15-expressing macrophages in RIPK3M-KO mice augmented IR-triggered liver inflammation and cell death.
Conclusions: Macrophage RIPK3 activates the IRE1α-XBP1 pathway and Foxo1 signalling in IR-stress livers. The XBP1-Foxo1 interaction is essential for modulating target gene Zc3h15 function, which is crucial for the control of NOD1 and calcineurin-mediated TRPM7 activation. XBP1 functions as a transcriptional coactivator of Foxo1 in regulating NOD1-driven liver inflammation and calcineurin/TRPM7-induced cell death. Our findings underscore a novel role of macrophage RIPK3 in stress-induced liver inflammation and cell death, implying the potential therapeutic targets in liver inflammatory diseases.
Impact and implications: Macrophage RIPK3 promotes NOD1-dependent inflammation and calcineurin/TRPM7-induced cell death cascade by triggering the XBP1-Foxo1 axis and its target gene Zc3h15, which is crucial for activating NOD1 and calcineurin/TRPM7 function, implying the potential therapeutic targets in stress-induced liver inflammatory injury.

Keywords: ER stress; Foxo1; IRE1α; Innate immunity; Liver inflammation; Necroptosis; Reactive oxygen species; XBP1

DOI: https://doi.org/10.1016/j.jhepr.2023.100879

Exp Dermatol. 2023 Oct 17.

Endoplasmic reticulum stress in skin aging induced by UVB.

Meiling Tai, Jieli Chen, Jiawen Chen, Xiaoyan Shen, Jiahui Ni.

Aging is a normal and complex biological process. Skin is located in the most superficial layer of the body, and its degree of aging directly reflects the aging level of the body. Endoplasmic reticulum stress refers to the aggregation of unfolded or misfolded proteins in the endoplasmic reticulum and the disruption of the calcium ion balance when cells are stimulated by external stimuli. Mild endoplasmic reticulum stress can cause a series of protective mechanisms, including the unfolded protein response, while sustained high intensity stimulation leads to endoplasmic reticulum stress and eventually apoptosis. Photoaging caused by ultraviolet radiation is an important stimulus in skin aging. Many studies have focused on oxidative stress, but increasing evidence shows that endoplasmic reticulum stress plays an important role in photoaging. This paper reviews the development and mechanism of endoplasmic reticulum stress (ERS) in skin photoaging, and provides research directions for targeting the ERS pathway to slow aging.

Keywords: endoplasmic reticulum stress; photoaging; skin aging

DOI: https://doi.org/10.1111/exd.14956