bims-lymeca 2022-08-28 papers

Issue of 2022‒08‒28
five papers selected by
Harilaos Filippakis
University of New England

Science. 2022 Aug 25. eabg6621

Lysosomal GPCR-like protein LYCHOS signals cholesterol sufficiency to mTORC1.

Lysosomes coordinate cellular metabolism and growth upon sensing of essential nutrients, including cholesterol. Through bioinformatic analysis of lysosomal proteomes, we identified LYsosomal CHOlesterol Signaling (LYCHOS, previously annotated as G-protein coupled receptor 155), a multidomain transmembrane protein that enables cholesterol-dependent activation of the master growth regulator, the protein kinase mechanistic Target of Rapamycin Complex 1 (mTORC1). Cholesterol bound to the N-terminal permease-like region of LYCHOS, and mutating this site impaired mTORC1 activation. At high cholesterol concentrations, LYCHOS bound to the GATOR1 complex, a GTPase-activating protein for the Rag guanosine triphosphatases, through a conserved cytoplasm-facing loop. By sequestering GATOR1, LYCHOS promotes cholesterol- and Rag-dependent recruitment of mTORC1 to lysosomes. Thus, LYCHOS functions in a lysosomal pathway for cholesterol sensing, and couples cholesterol concentrations to mTORC1-dependent anabolic signaling.

DOI: https://doi.org/10.1126/science.abg6621

Front Mol Biosci. 2022 ;9 930223

Metabolic adaption of cancer cells toward autophagy: Is there a role for ER-phagy?

Debora Gentile, Marianna Esposito, Paolo Grumati.

Autophagy is an evolutionary conserved catabolic pathway that uses a unique double-membrane vesicle, called autophagosome, to sequester cytosolic components, deliver them to lysosomes and recycle amino-acids. Essentially, autophagy acts as a cellular cleaning system that maintains metabolic balance under basal conditions and helps to ensure nutrient viability under stress conditions. It is also an important quality control mechanism that removes misfolded or aggregated proteins and mediates the turnover of damaged and obsolete organelles. In this regard, the idea that autophagy is a non-selective bulk process is outdated. It is now widely accepted that forms of selective autophagy are responsible for metabolic rewiring in response to cellular demand. Given its importance, autophagy plays an essential role during tumorigenesis as it sustains malignant cellular growth by acting as a coping-mechanisms for intracellular and environmental stress that occurs during malignant transformation. Cancer development is accompanied by the formation of a peculiar tumor microenvironment that is mainly characterized by hypoxia (oxygen < 2%) and low nutrient availability. Such conditions challenge cancer cells that must adapt their metabolism to survive. Here we review the regulation of autophagy and selective autophagy by hypoxia and the crosstalk with other stress response mechanisms, such as UPR. Finally, we discuss the emerging role of ER-phagy in sustaining cellular remodeling and quality control during stress conditions that drive tumorigenesis.

Keywords: ER stress; ER-phagy; UPR; autophagy; cancer; endoplasmic reticulum; hypoxia

DOI: https://doi.org/10.3389/fmolb.2022.930223

Cells. 2022 Aug 17. pii: 2562. [Epub ahead of print]11(16):

Modulating Chaperone-Mediated Autophagy and Its Clinical Applications in Cancer.

Virginie Hubert, Sebastian Weiss, Andrew Jackson Rees, Renate Kain.

Autophagy is a central mechanism for maintaining cellular homeostasis in health and disease as it provides the critical energy through the breakdown and recycling of cellular components and molecules within lysosomes. One of the three types of autophagy is chaperone-mediated autophagy (CMA), a degradation pathway selective for soluble cytosolic proteins that contain a targeting motif related to KFERQ in their amino acid sequence. This motif marks them as CMA substrate and is, in the initial step of CMA, recognised by the heat shock protein 70 (Hsc70). The protein complex is then targeted to the lysosomal membrane where the interaction with the splice variant A of the lysosomal-associated membrane protein-2 (LAMP-2A) results in its unfolding and translocation into the lysosome for degradation. Altered levels of CMA have been reported in a wide range of pathologies including many cancer types that upregulate CMA as part of the pro-tumorigenic phenotype, while in aging a decline is observed and associated with a decrease of LAMP-2 expression. The potential of altering CMA to modify a physiological or pathological process has been firmly established through genetic manipulation in animals and chemical interference with this pathway. However, its use for therapeutic purposes has remained limited. Compounds used to target and modify CMA have been applied successfully to gain a better understanding of its cellular mechanisms, but they are mostly not specific, also influence other autophagic pathways and are associated with high levels of toxicity. Here, we will focus on the molecular mechanisms involved in CMA regulation as well as on potential ways to intersect them, describe modulators successfully used, their mechanism of action and therapeutic potential. Furthermore, we will discuss the potential benefits and drawbacks of CMA modulation in diseases such as cancer.

Keywords: KFERQ; LAMP-2A; autophagy; cancer; chaperone; chaperone-mediated autophagy; lysosome; protein degradation

DOI: https://doi.org/10.3390/cells11162562

Int J Mol Sci. 2022 Aug 17. pii: 9255. [Epub ahead of print]23(16):

Targeting the Sphingolipid Rheostat in Gliomas.

Faris Zaibaq, Tyrone Dowdy, Mioara Larion.

Gliomas are highly aggressive cancer types that are in urgent need of novel drugs and targeted therapies. Treatment protocols have not improved in over a decade, and glioma patient survival remains among the worst of all cancer types. As a result, cancer metabolism research has served as an innovative approach to identifying novel glioma targets and improving our understanding of brain tumors. Recent research has uncovered a unique metabolic vulnerability in the sphingolipid pathways of gliomas that possess the IDH1 mutation. Sphingolipids are a family of lipid signaling molecules that play a variety of second messenger functions in cellular regulation. The two primary metabolites, sphingosine-1-phosphate (S1P) and ceramide, maintain a rheostat balance and play opposing roles in cell survival and proliferation. Altering the rheostat such that the pro-apoptotic signaling of the ceramides outweighs the pro-survival S1P signaling in glioma cells diminishes the hallmarks of cancer and enhances tumor cell death. Throughout this review, we discuss the sphingolipid pathway and identify the enzymes that can be most effectively targeted to alter the sphingolipid rheostat and enhance apoptosis in gliomas. We discuss each pathway's steps based on their site of occurrence in the organelles and postulate novel targets that can effectively exploit this vulnerability.

Keywords: brain tumors; ceramide; gliomas; isocitrate dehydrogenase 1 mutation; rheostat; sphingolipids; sphingosine-1-phosphate

DOI: https://doi.org/10.3390/ijms23169255

Molecules. 2022 Aug 14. pii: 5175. [Epub ahead of print]27(16):

Quantitative Proteomics Explore the Potential Targets and Action Mechanisms of Hydroxychloroquine.

Jingxiang Zhao, Zhiqiang Zhao, Wanting Hou, Yue Jiang, Guobin Liu, Xuelian Ren, Kun Liu, Hong Liu, Kaixian Chen, He Huang.

Hydroxychloroquine (HCQ) is an autophagy inhibitor that has been used for the treatment of many diseases, such as malaria, rheumatoid arthritis, systemic lupus erythematosus, and cancer. Despite the therapeutic advances in these diseases, the underlying mechanisms have not been well determined and hinder the rational use of this drug in the future. Here, we explored the possible mechanisms and identified the potential binding targets of HCQ by performing quantitative proteomics and thermal proteome profiling on MIA PaCa-2 cells. This study revealed that HCQ may exert its functions by targeting some autophagy-related proteins such as ribosyldihydronicotinamide dehydrogenase (NQO2) and transport protein Sec23A (SEC23A), or regulating the expression of galectin-8 (LGALS8), mitogen-activated protein kinase 8 (MAPK8), and so on. Furthermore, HCQ may prevent the progression of pancreatic cancer by regulating the expression of nesprin-2 (SYNE2), protein-S-isoprenylcysteine O-methyltransferase (ICMT), and cotranscriptional regulator FAM172A (FAM172A). Together, these findings not only identified potential binding targets for HCQ but also revealed the non-canonical mechanisms of HCQ that may contribute to pancreatic cancer treatment.

Keywords: hydroxychloroquine; quantitative proteomics; thermal proteome profiling

DOI: https://doi.org/10.3390/molecules27165175