Biology subjects

Samali, A.

Publications and source records attributed to Samali, A..

5 recordsLinked to original sources

bioRxiv2025

PERK orchestrates MERCS formation and mitochondrial remodelling promoting physiological adaptations during adaptive UPR signalling

The transfer of information and metabolites between mitochondria and the ER is mediated by mitochondria-ER contact sites (MERCS), facilitating adaptations following changes in cellular homeostasis. MERCS are dynamic structures, essential for maintaining cellular homeostasis through modulation of calcium transfer, redox signalling, lipid transfer, autophagy and mitochondrial dynamics. Acute ER stress in myoblasts promoted myogenesis that required the PERK arm of the UPRER for increased MERCS assembly, mitochondrial turnover and function. Similarly, induction of acute UPRER during early development in C. elegans resulted in increased lifespan and healthspan. Adaptive UPRER signalling in myoblasts and C. elegans, increased MERCS assembly and activated autophagy, ultimately promoting mitochondrial remodelling. Adaptations were dependent on the developmental stage, as treatment of myotubes or adult C. elegans resulted in a maladaptive response. The results identify that PERK is required for increased mitochondrial ER communication in response to adaptive UPR signalling, promoting mitochondrial remodelling and improved physiological function. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=172 SRC="FIGDIR/small/633960v1_ufig1.gif" ALT="Figure 1"> View larger version (58K): org.highwire.dtl.DTLVardef@66c0f2org.highwire.dtl.DTLVardef@57814org.highwire.dtl.DTLVardef@10e87d5org.highwire.dtl.DTLVardef@f7b69e_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2020

Downregulation of miR-17-92 cluster by PERK fine-tunes unfolded protein response mediated apoptosis

An important event in the unfolded protein response (UPR) is the activation of the endoplasmic reticulum kinase PERK (EIF2AK3). The PERK signalling branch first mediates a prosurvival response, which switches into a proapoptotic response upon prolonged ER stress. However, the molecular mechanisms of PERK-mediated cell death are not well understood. Here we show that expression of the primary miR-17-92 transcript and mature miRNAs belonging to miR-17-92 cluster is decreased during UPR. We found that activity of miR-17-92 promoter reporter was reduced during UPR in a PERK-dependent manner. We show that activity of miR-17-92 promoter is repressed by ectopic expression of ATF4 and NRF2. The promoter deletion analysis and ChIP assays mapped the region responding to UPR-mediated repression to site in the proximal region of the miR-17-92 promoter. Hypericin-mediated photo-oxidative ER damage reduced the expression of miRNAs belonging to miR-17-92 cluster in wild-type but not in PERK-deficient cells. Importantly, ER stress-induced apoptosis was inhibited upon miR-17-92 overexpression in SH-SY5Y and H9c2 cells. Our results reveal a novel function for NRF2, where repression of miR-17-92 cluster by NRF2 plays an important role in ER stress-mediated apoptosis. The data presented here provides mechanistic details how sustained PERK signalling via NRF2 mediated repression of miR-17-92 cluster can potentiate cell death.

cell biology↗

bioRxiv2019

Development of a novel preclinical glioblastoma mouse model and therapeutic impact of IRE1 inhibition

Glioblastoma multiforme (GBM) is the most severe primary brain cancer. Despite an aggressive treatment comprising surgical resection and radio/chemotherapy patients survival post diagnosis remains short. A limitation for success in finding novel improved therapeutic options for such dismal disease partly lies in the lack of a relevant animal model that accurately recapitulates patient disease and standard of care. In the present study, we have developed a novel immunocompetent GBM model that includes tumor surgery and a radio/chemotherapy regimen resembling the Stupp protocol and we have used this model to test the impact of the pharmacological inhibition of the endoplasmic reticulum (ER) stress sensor IRE1, on treatment efficacy.

cancer biology↗

bioRxiv2019

Structural distortions induced by Kinase Inhibiting RNase Attenuator (KIRA) compounds prevent the formation of face-to-face dimers of Inositol Requiring Enzyme 1α

Inositol-Requiring Enzyme 1 (IRE1) is a transmembrane dual kinase/ribonuclease protein involved in propagation of the unfolded protein response (UPR). IRE1 is currently explored as a potential drug target due to growing evidence of its role in variety of disease conditions. Upon activation, IRE1 cleaves X-box Binding Protein 1 (XBP1) mRNA through its RNase domain. Small molecules targeting the kinase site are known to either increase or decrease RNase activity, but the allosteric relationship between the kinase and RNase domains of IRE1 is poorly understood. Subsets of IRE1 kinase inhibitors (known as \"KIRA\" compounds) bind to the ATP-binding site and allosterically impede the RNase activity. KIRA compounds are able to regulate the RNase activity by stabilizing monomeric form of IRE1.\n\nIn the present work, computational analysis, protein-protein and protein-ligand docking studies, and molecular dynamics simulations were applied to different IRE1 dimer systems to provide structural insights into the perturbation of IRE1 dimers by small molecules kinase inhibitors that regulate the RNase activity. By analyzing structural deviations, energetic components and number of hydrogen bonds in the interface region, we propose that the KIRA inhibitors act at an early stage of IRE1 activation by interfering with IRE1 face-to-face dimer formation, thus disabling the activation of the RNase domain. The work sheds light on the mechanism of action of KIRA compounds and may assist in development of further compounds in e.g. cancer therapeutics. The work also provides information on the sequence of events and protein-protein interactions initiating the unfolded protein response.\n\nNon-technical SummaryThe unfolded protein response is a protective feedback mechanism whereby cells regulate high levels of misfolded proteins in the endoplasmic reticulum. Due to its significance in cell survival, the UPR has become an interesting target in cancer therapy. A key pathway of the UPR is initiated by the activation of inositol requiring enzyme 1 (IRE1), which must first dimerise in order to mediate the stress signal. Different inhibitors have been proposed in order to block the UPR at the level of IRE1. We here unveil, through detailed computational studies, the mode of action of a set of IRE1 inhibitors targeting the kinase domain, which in turn helps us to further understand the mechanism of activation and progression of the UPR.

biochemistry↗

bioRxiv2019

Constitutive IRE1α signaling maintains glioblastoma cell differentiation

Endoplasmic Reticulum (ER) proteostasis control and the Unfolded Protein Response (UPRER) have been shown to contribute to tumor development and aggressiveness. As such, the UPRER sensor IRE1 (referred to as IRE1 hereafter) is a major regulator of glioblastoma (GBM) development and is an appealing therapeutic target. To document IRE1 suitability as an antineoplastic pharmacological target, we investigated how this protein contributed to GBM cell reprogramming, a property involved in treatment resistance and disease recurrence. Probing the IRE1 activity molecular signature on transcriptome datasets of human tumors, showed that high IRE1 activity correlated with low expression of the main GBM stemness transcription factors SOX2, SALL2, POU3F2 and OLIG2. Henceforth, this phenotype was pharmacologically and genetically recapitulated in immortalized and primary GBM cell lines as well as in mouse models. We demonstrated that constitutive activation of the IRE1/XBP1/miR148a signaling axis repressed the expression of SOX2 and led to maintenance of a differentiation phenotype in GBM cells. Our results describe a novel role for IRE1 signaling in maintaining differentiated tumor cell state and highlight opportunities of informed IRE1 modulation utility in GBM therapy.

cancer biology↗