RACK1 is required for adipogenesis

Ribosome heterogeneity in development and disease

Traditionally viewed as a fixed and homogeneous machinery for protein synthesis, the ribosome is increasingly recognized for its heterogeneity, as indicated by emerging studies highlighting the functional relevance of specialized ribosomes. However, whether ribosome heterogeneity is merely an outcome limited to specific conditions or a pervasive cellular phenomenon remains unclear, and existing evidence on the extensive existence of ribosome heterogeneity is scant. Here, we leveraged existing proteomic data and employed ribosome ratio-omics (RibosomeR), which comprehensively analyzes ribosome protein stoichiometry across various biological samples exhibiting distinct functions, developmental stages, and pathological states. Using the 80S monosome proteomic data, RibosomeR analysis unveils significant ribosome heterogeneity across different tissues, including fat, spleen, liver, kidney, heart, and skeletal muscles. Furthermore, examination of testes at various stages of spermatogenesis reveals distinct RibosomeR signatures during tissue development. Analysis of the whole cell proteomic data finds that RibosomeR undergoes dynamic changes during in vitro neuronal maturation, indicating functional associations with specific molecular aspects of neurodevelopment. In pathological contexts, RibosomeR signatures in gastric tumors demonstrate functional links to pathways associated with tumorigenesis. Additionally, dynamic alterations in RibosomeR are observed in macrophages following immune challenges. Collectively, our investigation across a diverse array of biological samples underscores the presence of ribosome heterogeneity, while previous studies observed functional aspects of ribosome specialization, in cellular function, development, and disease. The RibosomeR barcode serves as a valuable tool for elucidating these complexities.

RACK1 facilitates breast cancer progression by competitively inhibiting the binding of β-catenin to PSMD2 and enhancing the stability of β-catenin

The receptor for activated C kinase 1 (RACK1) is a key scaffolding protein with multifunctional and multifaceted properties. By mediating protein-protein interactions, RACK1 integrates multiple intracellular signals involved in the regulation of various physiological and pathological processes. Dysregulation of RACK1 has been implicated in the initiation and progression of many tumors. However, the exact function of RACK1 in cancer cellular processes, especially in proliferation, remains controversial. Here, we show that RACK1 is required for breast cancer cell proliferation in vitro and tumor growth in vivo. This effect of RACK1 is associated with its ability to enhance β-catenin stability and activate the canonical WNT signaling pathway in breast cancer cells. We identified PSMD2, a key component of the proteasome, as a novel binding partner for RACK1 and β-catenin. Interestingly, although there is no interaction between RACK1 and β-catenin, RACK1 binds PSMD2 competitively with β-catenin. Moreover, RACK1 prevents ubiquitinated β-catenin from binding to PSMD2, thereby protecting β-catenin from proteasomal degradation. Collectively, our findings uncover a novel mechanism by which RACK1 increases β-catenin stability and promotes breast cancer proliferation.

Ribosome Heterogeneity in Development and Disease

The functional ribosome is composed of ∼80 ribosome proteins. With the intensity-based absolute quantification (iBAQ) value, we calculate the stoichiometry ratio of each ribosome protein. We analyze the ribosome ratio-omics (Ribosome R ), which reflects the holistic signature of ribosome composition, in various biological samples with distinct functions, developmental stages, and pathological outcomes. The Ribosome R reveals significant ribosome heterogeneity among different tissues of fat, spleen, liver, kidney, heart, and skeletal muscles. During tissue development, testes at various stages of spermatogenesis show distinct Ribosome R signatures. During in vitro neuronal maturation, the Ribosome R changes reveal functional association with certain molecular aspects of neurodevelopment. Regarding ribosome heterogeneity associated with pathological conditions, the Ribosome R signature of gastric tumors is functionally linked to pathways associated with tumorigenesis. Moreover, the Ribosome R undergoes dynamic changes in macrophages following immune challenges. Taken together, with the examination of a broad spectrum of biological samples, the Ribosome R barcode reveals ribosome heterogeneity and specialization in cell function, development, and disease.

One-Sentence Summary

Ratio-omics signature of ribosome deciphers functionally relevant heterogeneity in development and disease.

Myostatin Mutation Enhances Bovine Myogenic Differentiation through PI3K/AKT/mTOR Signalling via Removing DNA Methylation of RACK1

Myostatin (MSTN) is a negative regulator of skeletal muscle development and plays an important role in muscle development. Fluctuations in gene expression influenced by DNA methylation are critical for homeostatic responses in muscle. However, little is known about the mechanisms underlying this fluctuation regulation and myogenic differentiation of skeletal muscle. Here we report a genome-wide analysis of DNA methylation dynamics in bovine skeletal muscle myogenesis after myostatin editing. We show that, after myostatin editing, an increase in TETs (DNA demethylases) and a concomitant increase in the receptor for activated C kinase 1 (RACK1) control the myogenic development of skeletal muscle. Interestingly, enhancement of PI3K/AKT/mTOR signaling by RACK1 appears to be an essential driver of myogenic differentiation, as it was associated with an increase in myogenic differentiation marker factors (MyHC and MyoG) during muscle differentiation. Overall, our results suggest that loss of myostatin promotes the myogenic differentiation response in skeletal muscle by decreasing DNA methylation of RACK1.

Hepatic RACK1 deletion disturbs lipid and glucose homeostasis independently of insulin resistance

Receptor for activated C kinase 1 (RACK1) is a versatile protein involved in multiple biological processes. In a previous study by Zhao et al., hepatic RACK1 deletion in mice led to an inhibition of autophagy, blocked autophagy-dependent lipolysis, and caused steatosis. Using the same mouse model (RACK1hep-/-), we revealed new roles of RACK1 in maintaining bile acid homeostasis and hepatic glucose uptake, which further affected circulatory lipid and glucose levels. To be specific, even under hepatic steatosis, the plasma lipids were generally reduced in RACK1hep-/- mouse, which was due to the suppression of intestinal lipid absorption. Accordingly, a decrease in total bile acid level was found in RACK1hep-/- livers, gallbladders, and small intestine tissues, and specific decrease of 12-hydroxylated bile acids was detected by liquid chromatography-mass spectrometry. Consistently, reduced expression of CYP8B1 was found. A decrease in hepatic glycogen storage was also observed, which might be due to the inhibited glucose uptake by GLUT2 insufficiency. Interestingly, RACK1-KO-inducing hepatic steatosis did not raise insulin resistance (IR) nor IR-inducing factors like endoplasmic reticulum stress and inflammation. In summary, this study uncovers that hepatic RACK1 might be required in maintaining bile acid homeostasis and glucose uptake in hepatocytes. This study also provides an additional case of hepatic steatosis disassociation with insulin resistance.

GNA14's interaction with RACK1 inhibits hepatocellular carcinoma progression through reducing MAPK/JNK and PI3K/AKT signaling pathway

Gαq subfamily proteins play critical roles in many biological functions including cardiovascular development, angiogenesis, and tumorigenesis of melanoma. However, the understanding of G Protein Subunit Alpha 14 (GNA14) in diseases, especially in cancers is limited. Here, we revealed that GNA14 was significantly low expression in Human hepatocellular carcinoma (HCC) samples. Low GNA14 expression was correlated with aggressive clinicopathological features. Moreover, the overall survival (OS) and disease-free survival (DFS) of high GNA14 expression HCC patients were much better than low GNA14 expression group. Lentivirus-mediated GNA14 knockdown significantly promoted the growth of liver cancer in vitro and in vivo. However, opposing results were observed when GNA14 is upregulated. Mechanistically, We identified receptor for activated C kinase 1 (RACK1) as a binding partner of GNA14 by co-immunoprecipitation and mass spectrometry (MS). Glutathione-S-transferase (GST) pull-down assay further verified the direct interaction between GNA14 and RACK1. RNA-Seq and loss- and gain-of-function assays also confirmed that GNA14 reduced the activity of both MAPK/JNK and PI3K/AKT signaling pathways through RACK1. GNA14 synergized with U73122 (PLC inhibitor) to enhance this effect. Further studies suggested that GNA14 potentially competed with protein kinase C (PKC) to bind with RACK1, consequently reducing the stability of PKC. Moreover, we also showed that GNA14’supression of p-AKT protein level depended on sufficient RACK1 expression. In conclusion, we indicated a different role of GNA14, which acted as a suppressor inhibiting liver cancer progression through MAPK/JNK and PI3K/AKT signaling pathways. Due to this, GNA14 served as a potentially valuable prognostic biomarker for liver cancer.

Reactivation of the Epicardium at the Origin of Myocardial Fibro-Fatty Infiltration During the Atrial Cardiomyopathy

RATIONALE

Fibro-fatty infiltration of subepicardial layers of the atrial wall has been shown to contribute to the substrate of atrial fibrillation.

OBJECTIVE

Here, we examined if the epicardium that contains multipotent cells is involved in this remodeling process.

METHODS AND RESULTS

One hundred nine human surgical right atrial specimens were evaluated. There was a relatively greater extent of epicardial thickening and dense fibro-fatty infiltrates in atrial tissue sections from patients aged over 70 years who had mitral valve disease or atrial fibrillation when compared with patients aged less than 70 years with ischemic cardiomyopathy as indicated using logistic regression adjusted for age and gender. Cells coexpressing markers of epicardial progenitors and fibroblasts were detected in fibro-fatty infiltrates. Such epicardial remodeling was reproduced in an experimental model of atrial cardiomyopathy in rat and in Wilms tumor 1 (WT1)^CreERT2/+;ROSA-tdT^+/- mice. In the latter, genetic lineage tracing demonstrated the epicardial origin of fibroblasts within fibro-fatty infiltrates. A subpopulation of human adult epicardial-derived cells expressing PDGFR (platelet-derived growth factor receptor)-α were isolated and differentiated into myofibroblasts in the presence of Ang II (angiotensin II). Furthermore, single-cell RNA-sequencing analysis identified several clusters of adult epicardial-derived cells and revealed their specification from adipogenic to fibrogenic cells in the rat model of atrial cardiomyopathy.

CONCLUSIONS

Epicardium is reactivated during the formation of the atrial cardiomyopathy. Subsets of adult epicardial-derived cells, preprogrammed towards a specific cell fate, contribute to fibro-fatty infiltration of subepicardium of diseased atria. Our study reveals the biological basis for chronic atrial myocardial remodeling that paves the way of atrial fibrillation.

Quantitative Proteomic Analysis To Identify Differentially Expressed Proteins in Myocardium of Epilepsy Using iTRAQ Coupled with Nano-LC-MS/MS

Epilepsy is a difficult-to-manage neurological disease that can result in organ damage, such as cardiac injury, that contributes to sudden unexpected death in epilepsy (SUDEP). Although recurrent seizure-induced cardiac dysregulation has been reported, the underlying molecular mechanisms are unclear. We established an epileptic model with Sprague-Dawley rats by applying isobaric tags for a relative and absolute quantification (iTRAQ)-based proteomics approach to identify differentially expressed proteins in myocardial tissue. A total of seven proteins in the acute epilepsy group and 60 proteins in the chronic epilepsy group were identified as differentially expressed. Bioinformatics analysis suggested that the pathogenesis of cardiac injury in acute and chronic epilepsy may be due to different molecular mechanisms. Three proteins, a receptor for activated protein kinase C1 (RACK1), aldehyde dehydrogenase 6 family member A1 (ALDH6A1), and glycerol uptake/transporter 1 (Hhatl), were identified as playing crucial roles in cardiac injury during epilepsy and were successfully confirmed by Western blot and immunohistochemistry analysis. Our study not only provides a deeper understanding of the pathophysiological mechanisms of myocardial damage in epilepsy, but also suggests some potential novel therapeutic targets for preventing cardiac injury and reducing the incidence of sudden death due to heart failure.

E3 ubiquitin ligase DTX4 is required for adipogenic differentiation in 3T3-L1 preadipocytes cell line

Deltex4 (DTX4) is a member of the Deltex family of proteins. To date several lines of evidences suggest that Deltex family of proteins is closely linked to cell development and cell differentiation. However, little is known about the role of DTX4 in adipogenic differentiation. In this study, we assessed the impact of DTX4 on adipogenic differentiation in vitro, we found that DTX4 protein expression gradually increased during adipogenic differentiation of 3T3-L1 preadipocytes cell line. While DTX4 stable knockdown by recombinant shRNA lentivirus (sh-DTX4) notably reduced the number of lipid droplets and down-regulated the expression of adipogenic transcription factors C/EBPα and PPARγ and adipogenic markers gene FABP4 and Adipsin. Besides, cell numbers and incorporation of 5-Ethynyl-2'-deoxyuridine (EdU) into cells were significantly decreased during mitotic clonal expansion (MCE) in sh-DTX4 cells postinduction. Furthermore, compared to recombinant shRNA lentivirus control group (sh-CON), the mRNA levels of Wnt signaling genes such as Wnt6, Wnt10b and β-catenin, were obviously elevated in sh-DTX4 group at day 3 of postinduction. Taken together, our results indicate that DTX4 stable knockdown inhibits adipogenesis of 3T3-L1 cells through inhibiting C/EBPα and PPARγ, arresting mitotic clonal expansion and regulating Wnt signaling pathway.