bims-lymeca 2022-08-14 papers

Issue of 2022‒08‒14
six papers selected by
Harilaos Filippakis
University of New England

Bio Protoc. 2022 Jul 05. pii: e4453. [Epub ahead of print]12(13):

A Robust Nanoparticle-based Magnetic Separation Method for Intact Lysosomes.

The Son Le, Mari Takahashi, Shinya Maenosono.

Lysosome isolation is a preresiquite for identifying lysosomal protein composition by mass spectroscopic analysis, to reveal lysosome functions, and their involvement in some diseases. Magnetic nanoparticle-based fractionation has received great attention for lysosome isolation, owing to its high efficiency, purity, and preservation of lysosomal structures. Understanding the intracellular trafficking of magnetic probes is the key point of this technique, to determine the appropriate time for magnetic isolation of lysosomes, because this parameter changes depending on different cell lines used. The traditional magnetic probes, such as superparamagnetic iron oxide nanoparticles (SPIONs), require surface modification by fluorescent dyes to enable the investigation of their intracellular trafficking, which has some disadvantages, including the possible alternation of their bio-interaction, and the instability of fluorescence properties in the lysosomal environment. To overcome those limitations, we present a protocol that employs magnetic-plasmonic nanoparticles (MPNPs) to investigate intracellular trafficking using their intrinsic imaging capability, followed by quick lysosome isolation using a magnetic column. This protocol can be easily applied to isolate the intact lysosomes of any adherent cell lines. Graphical abstract.

Keywords: Endocytosis ; Endolysosomal pathway ; Intracellular trafficking ; Lysosomes ; Magnetic separation ; Nanoparticles ; Plasmonic imaging

DOI: https://doi.org/10.21769/BioProtoc.4453

Nat Commun. 2022 Aug 10. 13(1): 4685

mTORC1 controls Golgi architecture and vesicle secretion by phosphorylation of SCYL1.

Stéphanie Kaeser-Pebernard, Christine Vionnet, Muriel Mari, Devanarayanan Siva Sankar, Zehan Hu, Carole Roubaty, Esther Martínez-Martínez, Huiyuan Zhao, Miguel Spuch-Calvar, Alke Petri-Fink, Gregor Rainer, Florian Steinberg, Fulvio Reggiori, Jörn Dengjel.

The protein kinase mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth and proliferation, supporting anabolic reactions and inhibiting catabolic pathways like autophagy. Its hyperactivation is a frequent event in cancer promoting tumor cell proliferation. Several intracellular membrane-associated mTORC1 pools have been identified, linking its function to distinct subcellular localizations. Here, we characterize the N-terminal kinase-like protein SCYL1 as a Golgi-localized target through which mTORC1 controls organelle distribution and extracellular vesicle secretion in breast cancer cells. Under growth conditions, SCYL1 is phosphorylated by mTORC1 on Ser754, supporting Golgi localization. Upon mTORC1 inhibition, Ser754 dephosphorylation leads to SCYL1 displacement to endosomes. Peripheral, dephosphorylated SCYL1 causes Golgi enlargement, redistribution of early and late endosomes and increased extracellular vesicle release. Thus, the mTORC1-controlled phosphorylation status of SCYL1 is an important determinant regulating subcellular distribution and function of endolysosomal compartments. It may also explain the pathophysiology underlying human genetic diseases such as CALFAN syndrome, which is caused by loss-of-function of SCYL1.

DOI: https://doi.org/10.1038/s41467-022-32487-7

Cell Death Dis. 2022 Aug 06. 13(8): 687

ErbB2/Her2-dependent downregulation of a cell death-promoting protein BLNK in breast cancer cells is required for 3D breast tumor growth.

Xiaoyang Liu, Sandhya Chipurupalli, Peijia Jiang, Mahtab Tavasoli, Byong Hoon Yoo, Michael McPhee, Sina Mazinani, Giulio Francia, Robert S Kerbel, Kirill V Rosen.

A significant proportion of breast cancers are driven by ErbB2/Her2 oncoprotein that they overexpress. These malignancies are typically treated with various ErbB2-targeted drugs, but many such cancers develop resistance to these agents and become incurable. Conceivably, treatment of ErbB2-positive cancers could be facilitated by use of agents blocking oncogenic signaling mechanisms downstream of ErbB2. However, current understanding of these mechanisms is limited. The ability of solid tumor cells to resist anoikis, cell death triggered by cell detachment from the extracellular matrix (ECM), is thought to be critical for 3D tumor growth. In an effort to understand the mechanisms of ErbB2-driven breast cancer cell anoikis resistance we found that detachment of non-malignant breast epithelial cells from the ECM upregulates a cell death-promoting tumor suppressor adapter protein BLNK and that ErbB2 blocks this upregulation by reducing tumor cell levels of transcription factor IRF6. We further observed that trastuzumab, a therapeutic anti-ErbB2 antibody, upregulates BLNK in human trastuzumab-sensitive but not trastuzumab-resistant ErbB2-positive breast cancer cells. Moreover, we established that BLNK promotes anoikis by activating p38 MAP kinase and that ErbB2-dependent BLNK downregulation blocks breast cancer cell anoikis. In search for pharmacological approaches allowing to upregulate BLNK in tumor cells we found that clinically approved proteasome inhibitor bortezomib upregulates IRF6 and BLNK in human breast cancer cells and inhibits their 3D growth in a BLNK-dependent manner. In addition, we found that BLNK upregulation in human ErbB2-positive breast cancer cells blocks their ability to form tumors in mice. Furthermore, we used publicly available data on mRNA levels in multiple breast cancers to demonstrate that increased BLNK mRNA levels correlate with increased relapse-free survival in a cohort of approximately 400 patients with ErbB2-positive breast cancer. In summary, we discovered a novel mechanism of ErbB2-driven 3D breast tumor growth mediated by ErbB2-dependent BLNK downregulation.

DOI: https://doi.org/10.1038/s41419-022-05117-9

Semin Cancer Biol. 2022 Aug 05. pii: S1044-579X(22)00181-X. [Epub ahead of print]

Deregulated transcription factors and poor clinical outcomes in cancer patients.

Yiwei Li, Asfar S Azmi, Ramzi M Mohammad.

Transcription factors are a group of proteins, which possess DNA-binding domains, bind to DNA strands of promoters or enhancers, and initiate transcription of genes with cooperation of RNA polymerase and other co-factors. They play crucial roles in regulating transcription during embryogenesis and development. Their physiological status in different cell types is also important to maintain cellular homeostasis. Therefore, any deregulation of transcription factors will lead to the development of cancer cells and tumor progression. Based on their functions in cancer cells, transcription factors could be either oncogenic or tumor suppressive. Furthermore, transcription factors have been shown to modulate cancer stem cells, epithelial-mesenchymal transition (EMT) and drug response; therefore, measuring deregulated transcription factors is hypothesized to predict treatment outcomes of patients with cancers and targeting deregulated transcription factors could be an encouraging strategy for cancer therapy. Here, we summarize the current knowledge of major deregulated transcription factors and their effects on causing poor clinical outcome of patients with cancer. The information presented here will help to predict the prognosis and drug response and to design novel drugs and therapeutic strategies for the treatment of cancers by targeting deregulated transcription factors.

Keywords: EMT; Transcription factor; cancer stem cell; clinical outcome; drug resistance

DOI: https://doi.org/10.1016/j.semcancer.2022.08.001

EMBO J. 2022 Aug 08. e110596

Mechanical strain stimulates COPII-dependent secretory trafficking via Rac1.

Santosh Phuyal, Elena Djaerff, Anabel-Lise Le Roux, Martin J Baker, Daniela Fankhauser, Sayyed Jalil Mahdizadeh, Veronika Reiterer, Amirabbas Parizadeh, Edward Felder, Jennifer C Kahlhofer, David Teis, Marcelo G Kazanietz, Stephan Geley, Leif Eriksson, Pere Roca-Cusachs, Hesso Farhan.

Cells are constantly exposed to various chemical and physical stimuli. While much has been learned about the biochemical factors that regulate secretory trafficking from the endoplasmic reticulum (ER), much less is known about whether and how this trafficking is subject to regulation by mechanical signals. Here, we show that subjecting cells to mechanical strain both induces the formation of ER exit sites (ERES) and accelerates ER-to-Golgi trafficking. We found that cells with impaired ERES function were less capable of expanding their surface area when placed under mechanical stress and were more prone to develop plasma membrane defects when subjected to stretching. Thus, coupling of ERES function to mechanotransduction appears to confer resistance of cells to mechanical stress. Furthermore, we show that the coupling of mechanotransduction to ERES formation was mediated via a previously unappreciated ER-localized pool of the small GTPase Rac1. Mechanistically, we show that Rac1 interacts with the small GTPase Sar1 to drive budding of COPII carriers and stimulates ER-to-Golgi transport. This interaction therefore represents an unprecedented link between mechanical strain and export from the ER.

Keywords: COPII; endoplasmic reticulum; mechanobiology

DOI: https://doi.org/10.15252/embj.2022110596

Front Oncol. 2022 ;12 903874

AXL Promotes Metformin-Induced Apoptosis Through Mediation of Autophagy by Activating ROS-AMPK-ULK1 Signaling in Human Esophageal Adenocarcinoma.

Jun Hong, Selma Maacha, Nataliya Pidkovka, Andreia Bates, Safia N Salaria, Mary K Washington, Abbes Belkhiri.

AXL receptor tyrosine kinase promotes an invasive phenotype and chemotherapy resistance in esophageal adenocarcinoma (EAC). AXL has been implicated in the regulation of autophagy, but the underlying molecular mechanism remains poorly understood. Herein, we investigate the mechanistic role of AXL in autophagy as well as metformin-induced effects on the growth and survival of EAC. We demonstrate that AXL mediates autophagic flux through activation of AMPK-ULK1 signaling in a reactive oxygen species (ROS)-dependent mechanism by glucose starvation. AXL positively regulates basal cellular ROS levels without significantly affecting mitochondrial ROS production in EAC cells. Pharmacological inhibition of cellular ROS using Trolox abrogates glucose starvation-induced AMPK signaling and autophagy. We demonstrate that AXL expression is required for metformin-induced apoptosis in EAC cells in vitro. The apoptosis induction by metformin is markedly attenuated by inhibition of autophagy through genetic silencing of Beclin1 or ATG7 autophagy mediators, thereby confirming the requirement of intact autophagy for enhancing metformin-induced apoptosis in EAC cells. Our data indicate that metformin-induced autophagy displays a pro-apoptotic function in EAC cells. We show that the metformin-induced suppression of tumor growth in vivo is highly dependent on AXL expression in a tumor xenograft mouse model of EAC. We demonstrate that AXL promotes metformin-induced apoptosis through activation of autophagy in EAC. AXL may be a valuable biomarker to identify tumors that are sensitive to metformin. Therefore, AXL expression could inform the selection of patients for future clinical trials to evaluate the therapeutic efficacy of metformin in EAC.

Keywords: AMPK; ATG7; Barrett’s esophagus; Beclin1; autophagic flux; glucose starvation; proliferation; reactive oxygen species

DOI: https://doi.org/10.3389/fonc.2022.903874