In response to stress, cells attenuate global protein synthesis but permit efficient translation of mRNAs encoding heat-shock proteins (HSPs). Although decades have passed since the first description ...of the heat-shock response, how cells achieve translational control of HSP synthesis remains enigmatic. Here we report an unexpected role for mitochondrial ribosomal protein L18 (MRPL18) in the mammalian cytosolic stress response. MRPL18 bears a downstream CUG start codon and generates a cytosolic isoform in a stress-dependent manner. Cytosolic MRPL18 incorporates into the 80S ribosome and facilitates ribosome engagement on mRNAs selected for translation during stress. MRPL18 knockdown has minimal effects on mitochondrial function but substantially dampens cytosolic HSP expression at the level of translation. Our results uncover a hitherto-uncharacterized stress-adaptation mechanism in mammalian cells, which involves formation of a 'hybrid' ribosome responsible for translational regulation during the cytosolic stress response.
Protein misfolding is a common event in living cells. Molecular chaperones not only assist protein folding; they also facilitate the degradation of misfolded polypeptides. When the intracellular ...degradative capacity is exceeded, juxtanuclear aggresomes are formed to sequester misfolded proteins. Despite the well-established role of chaperones in both protein folding and degradation, how chaperones regulate the aggregation process remains controversial. Here we investigate the molecular mechanisms underlying aggresome formation in mammalian cells. Analysis of the chaperone requirements for the fate of misfolded proteins reveals an unexpected role of heat shock protein 70 (Hsp70) in promoting aggresome formation. This proaggregation function of Hsp70 relies on the interaction with the cochaperone ubiquitin ligase carboxyl terminal of Hsp70/Hsp90 interacting protein (CHIP). Disrupting Hsp70-CHIP interaction prevents the aggresome formation, whereas a dominant-negative CHIP mutant sensitizes the aggregation of misfolded protein. This accelerated aggresome formation also relies on the stress-induced cochaperone Bcl2-associated athanogene 3. Our results indicate that a hierarchy of cochaperone interaction controls different aspects of the intracellular protein triage decision, extending the function of Hsp70 from folding and degradation to aggregation.
CircRNAs play an important role in various physiological and pathological biological processes. Despite their widespread involvement, the function of circRNAs in intermittent hypoxia (IH) remain ...incompletely understood. This study aims to clarify the molecular mechanism of it in IH. Differentially expressed circRNAs were identified by transcriptome sequencing analysis in intermittent hypoxia (IH) model. GO and KEGG enrichment analys were performed on the identified differentially expressed circRNAs. The circular characteristics of hsa_circ_0081065 in human umbilical vein endothelial cells (HUVECs) were detected by RT-qPCR. The sublocalization of hsa_circ_0081065 was examined by FISH. The effect of hsa_circ_0081065 on endothelial to mesenchymal transition (EndMT) was estimated by detecting the expression of EndMT related markers. Various techniques, including RNA-pull down, RIP, EMSA, dual-luciferase reporter assay and immunofluorescence staining were used to investigate the relationship among hsa_circ_0081065, miR-665 and HIF-1α. A total of 13,304 circRNAs were identified in HUVECs treatment with IH, among which 73 were differentially expressed, including 24 upregulated circRNAs and 49 downregulated circRNAs. Notably, hsa_circ_0081065 demonstrated a significantly upregulation. Hsa_circ_0081065 exhibited the circular characteristics of circRNA and was predominantly localized in the cytoplasm. Knockdown of hsa_circ_0081065 inhibited EndMT. Mechanically, we demonstrated that hsa_circ_0081065 acts as a sponge for miR-665 to up-regulate HIF-1α and exacerbate HIF-1α nuclear translocation in HUVECs. We have demonstrated that hsa_circ_0081065 is significantly upregulated in HUVECs treated with IH. Our findings indicate that hsa_circ_0081065 exacerbates IH-induced EndMT through the regulation of the miR-665/HIF-1α signal axis and facilitating HIF-1α nuclear translocation. These results provide a theoretical basis for considering of EndMT as a potential therapeutic target for OSAHS intervention.
Tilapia (
) is a freshwater fish which is farmed worldwide. Improving the muscle quality of fish has become a major goal while maintaining a sustainable aquaculture system. This research attempts to ...assess the effect of 0% (FB0), 40%(FB40), 50%(FB50), 60%(FB60) and 70% (FB70) faba bean on the texture parameter, histological analysis, proximate, amino acids, and fatty acids composition in tilapia fed 90 days. The results showed that hardness, chewiness, and shear force of tilapia muscle fed FB60, and FB70 were considerably more in comparison to fish fed FB0 at 90 days (
< 0.05). Tilapia fed faba beans had higher muscle fiber density, wider spaces between muscle fibers and smaller fiber diameter, with the greatest difference in tilapia fed FB60. The total protein content in tilapia fed FB40 was considerably more in comparison to in fish fed FB70 (
< 0.05), where the total protein content in muscle first increased and then reduced with increasing dietary faba bean level. The muscle ∑TAA, ∑EAA, valine, tyrosine, cysteine, aspartic acid, methionine, isoleucine, glutamic acid, leucine, arginine, and serine, contents in tilapia fed FB60 were much more in contrast to in fish fed FB0 (
< 0.05), which initially increased and then reduced with increasing dietary faba bean level. The muscle ∑PUFA content in tilapia fed dietary faba beans was greater compared with fish fed FB0, whereas the ∑SFA contents in tilapia fed FB50 and FB60 were lower in contrast to in fish fed FB0. In summary, dietary faba beans can improve muscle texture, muscle fibers, amino acids content and fatty acids content in tilapia. The research's results make a contribution to the improved knowledge of the association among muscle quality in tilapia and dietary faba beans.
The outbreak of coronavirus disease (COVID-19) has brought great challenges to the world. The objectives of this study were to describe the baseline characteristics and changes of biomarkers of these ...COVID-19 patients and identify predictive value of the above markers for patient death. Using patient death as the observational endpoints, clinical data of inpatients in a special ward for COVID-19 in Wuhan, China were retrospectively collected. Univariate and multivariate Cox regression analyses were used to evaluate prognostic value of baseline characteristics and laboratory data changes. This study included clinical data of 75 patients. Age, c-reactive protein (CRP) and interleukin-6 levels were independent predictors of patient death. Survivors were characterized as having declining neutrophil counts,
d
-dimer, N-terminal pronatriuretic peptide, troponin I (TnI) and c-reactive protein levels, while counts of lymphocyte gradually came back. Non-survivors were characterized with increasing white blood cell counts (WBC) and neutrophil counts. Changes of WBC, TnI and interleukin-6 were also independently associated with patient death. Older age, baseline CRP and IL-6 levels may be used as meaningful predictors to identify patients with poor prognosis. Changes of biomarkers should be closely monitored in the management of patients with COVID-19, while constantly increasing levels of WBC, TnI and interleukin-6 in the disease course also predict patient death.
Background/Aims: We aimed to evaluate the distribution of abnormal liver-related biomarkers in patients with coronavirus disease (COVID-19) and explore the prognostic value of elevated liver enzymes ...and abnormal liver synthetic capacity with regards to patient mortality.
Patients and Methods: This retrospective observational study included 80 laboratory-confirmed COVID-19 cases. Data were collected from the electronic medical record system by a trained team of physicians. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TB), albumin, and prealbumin levels at admission and on day 7 after admission were collected. The primary outcome of the current study was patient mortality.
Results: Abnormal ALT, AST, TB, albumin, and prealbumin levels were observed in 11 (13.8%), 15 (18.8%), 5 (6.3%), 22 (27.5%), and 31 (38.8%) patients, respectively. Male gender correlated with elevated ALT and AST levels (p = 0.027 and 0.036, respectively). Higher levels of AST and lower levels of albumin and prealbumin were associated with patient mortality (p = 0.009, 0.002, and 0.003, respectively). Multivariate Cox regression analysis identified patient age (p = 0.013, HR 1.108) and prealbumin levels (p = 0.015, HR 0.986) as independent predictors for patient mortality. However, changes in liver-related biomarkers were not associated with poor outcome in multivariate analysis (p > 0.05).
Conclusions: Abnormalities in albumin and prealbumin levels are common among COVID-19 patients and hypoprealbuminemia independently predicts adverse outcome and should be carefully considered in clinical practice. Moreover, changes in liver-related biomarkers is not a salient feature of COVID-19.
The journey of a newly synthesized polypeptide starts in the peptidyltransferase center of the ribosome, from where it traverses the exit tunnel. The interior of the ribosome exit tunnel is neither ...straight nor smooth. How the ribosome dynamics in vivo is influenced by the exit tunnel is poorly understood. Genome-wide ribosome profiling in mammalian cells reveals elevated ribosome density at the start codon and surprisingly the downstream 5th codon position as well. We found that the highly focused ribosomal pausing shortly after initiation is attributed to the geometry of the exit tunnel, as deletion of the loop region from ribosome protein L4 diminishes translational pausing at the 5th codon position. Unexpectedly, the ribosome variant undergoes translational abandonment shortly after initiation, suggesting that there exists an obligatory step between initiation and elongation commitment. We propose that the post-initiation pausing of ribosomes represents an inherent signature of the translation machinery to ensure productive translation.
The most abundant mRNA post-transcriptional modification is
N
6
-methyladenosine (m
6
A) that has broad roles in RNA biology
1
-
5
. In mammalian cells, the asymmetric distribution of m
6
A along ...mRNAs leaves relatively less methylation in the 5′ untranslated region (5′UTR) compared to other regions
6
,
7
. However, whether and how 5′UTR methylation is regulated is poorly understood. Despite the crucial role of the 5′UTR in translation initiation, very little is known whether m
6
A modification influences mRNA translation. Here we show that in response to heat shock stress, m
6
A is preferentially deposited to the 5′UTR of newly transcribed mRNAs. We found that the dynamic 5′UTR methylation is a result of stress-induced nuclear localization of YTHDF2, a well characterized m
6
A “reader”. Upon heat shock stress, the nuclear YTHDF2 preserves 5′UTR methylation of stress-induced transcripts by limiting the m
6
A “eraser” FTO from demethylation. Remarkably, the increased 5′UTR methylation in the form of m
6
A promotes cap-independent translation initiation, providing a mechanism for selective mRNA translation under heat shock stress. Using Hsp70 mRNA as an example, we demonstrate that a single site m
6
A modification in the 5′UTR enables translation initiation independent of the 5′ end m
7
G cap. The elucidation of the dynamic feature of 5′UTR methylation and its critical role in cap-independent translation not only expands the breadth of physiological roles of m
6
A, but also uncovers a previously unappreciated translational control mechanism in heat shock response.
Balanced protein synthesis and degradation are crucial for proper cellular function. Protein synthesis is tightly coupled to energy status and nutrient levels by the mammalian target of rapamycin ...complex 1 (mTORC1). Quality of newly synthesized polypeptides is maintained by the molecular chaperone and ubiquitin-proteasome systems. Little is known about how cells integrate information about the quantity and quality of translational products simultaneously. We demonstrate that cells distinguish moderate reductions in protein quality from severe protein misfolding using molecular chaperones to differentially regulate mTORC1 signaling. Moderate reduction of chaperone availability enhances mTORC1 signaling, whereas stress-induced complete depletion of chaperoning capacity suppresses mTORC1 signaling. Molecular chaperones regulate mTORC1 assembly in coordination with nutrient availability. This mechanism enables mTORC1 to rapidly detect and respond to environmental cues while also sensing intracellular protein misfolding. The tight linkage between protein quality and quantity control provides a plausible mechanism coupling protein misfolding with metabolic dyshomeostasis.
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