Proteomic analysis reveals that MAEL, a component of nuage, interacts with stress granule proteins in cancer cells

MAEL in human cancers and implications in prognostication and predicting benefit from immunotherapy over VEGFR/mTOR inhibitors in clear cell renal cell carcinoma: a bioinformatic analysis

Maelstrom (MAEL), a novel cancer/testis-associated gene, may facilitate the initiation and progression of human malignancies, warranting comprehensive investigations. Single-cell and tissue-bulk transcriptomic data demonstrated higher MAEL expression in testis (spermatogonia/spermatocyte), kidney (proximal tubular cell), and brain (neuron/astrocyte), and corresponding cancers, including testicular germ cell tumor, glioma, papillary renal cell carcinoma, and clear cell renal cell carcinoma (ccRCC). Of these cancers, only in ccRCC did MAEL expression exhibit associations with both recurrence-free survival and overall survival. High MAEL expression was associated with an anti-inflammatory tumor immune microenvironment and VEGFR/mTOR activation in ccRCC tissues and high sensitivities to VEGFR/PI3K-AKT-mTOR inhibitors in ccRCC cell lines. Consistent with these, low rather than high MAEL expression indicated remarkable progression-free survival benefits from immune checkpoint inhibitor (ICI)-based immunotherapies over VEGFR/mTOR inhibitors in two large phase III trials (JAVELIN Renal 101 and CheckMate-025). MAEL is a biologically and clinically significant determinant with potential for prognostication after nephrectomy and patient selection for VEGFR/mTOR inhibitors and immunotherapy-based treatments.

The DNA binding high mobility group box protein family functionally binds RNA

Nucleic acid binding proteins regulate transcription, splicing, RNA stability, RNA localization, and translation, together tailoring gene expression in response to stimuli. Upon discovery, these proteins are typically classified as either DNA or RNA binding as defined by their in vivo functions; however, recent evidence suggests dual DNA and RNA binding by many of these proteins. High mobility group box (HMGB) proteins have a DNA binding HMGB domain, act as transcription factors and chromatin remodeling proteins, and are increasingly understood to interact with RNA as means to regulate gene expression. Herein, multiple layers of evidence that the HMGB family are dual DNA and RNA binding proteins is comprehensively reviewed. For example, HMGB proteins directly interact with RNA in vitro and in vivo, are localized to RNP granules involved in RNA processing, and their protein interactors are enriched in RNA binding proteins involved in RNA metabolism. Importantly, in cell-based systems, HMGB-RNA interactions facilitate protein-protein interactions, impact splicing outcomes, and modify HMGB protein genomic or cellular localization. Misregulation of these HMGB-RNA interactions are also likely involved in human disease. This review brings to light that as a family, HMGB proteins are likely to bind RNA which is essential to HMGB protein biology. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

MAEL facilitates metabolic reprogramming and breast cancer progression by promoting the degradation of citrate synthase and fumarate hydratase via chaperone-mediated autophagy

Metabolic reprogramming is a hallmark of cancer. Several studies have shown that inactivation of Krebs cycle enzymes, such as citrate synthase (CS) and fumarate hydratase (FH), facilitates aerobic glycolysis and cancer progression. MAEL has been shown to play an oncogenic role in bladder, liver, colon, and gastric cancers, but its role in breast cancer and metabolism is still unknown. Here, we demonstrated that MAEL promoted malignant behaviours and aerobic glycolysis in breast cancer cells. Mechanistically, MAEL interacted with CS/FH and HSAP8 via its MAEL domain and HMG domain, respectively, and then enhanced the binding affinity of CS/FH with HSPA8, facilitating the transport of CS/FH to the lysosome for degradation. MAEL-induced degradation of CS and FH could be suppressed by the lysosome inhibitors leupeptin and NH₄ Cl, but not by the macroautophagy inhibitor 3-MA or the proteasome inhibitor MG132. These results suggested that MAEL promoted the degradation of CS and FH via chaperone-mediated autophagy (CMA). Further studies showed that the expression of MAEL was significantly and negatively correlated with CS and FH in breast cancer. Moreover, overexpression of CS or/and FH could reverse the oncogenic effects of MAEL. Taken together, MAEL promotes a metabolic shift from oxidative phosphorylation to glycolysis by inducing CMA-dependent degradation of CS and FH, thereby promoting breast cancer progression. These findings have elucidated a novel molecular mechanism of MAEL in cancer.

Morphine suppresses the immune function of lung cancer by up-regulating MAEL expression

BACKGROUND

Patients with cancer rely on morphine for analgesia, while studies have indicated morphine can induce immunosuppression in cancer. Therefore, investigating the immunosuppressive roles and molecular mechanism of morphine on lung cancer progression is imperative.

METHODS

Lactate dehydrogenase (LDH) release assay was used to determine the cytotoxicity of morphine to lung cancer cells. The percentage of CD4⁺ and CD8⁺ T cells was detected by flow cytometry. In addition, Maelstrom (MAEL), Nrf2, and PTEN were determined by western blot and RT-qPCR. Immune factors programmed death-ligand 1 (PD-L1), transforming growth factor (TGF-β), interleukin (IL)-10, and IL-2 were determined by western blot and ELISA assay.

RESULTS

Morphine increased the levels of PD-L1, TGF-β, and IL-10, while decreased IL-2 level. Morphine enhanced MAEL expression in A549 cells and H460 cells. Morphine up-regulated Nrf2 and down-regulated PTEN, and morphine-induced MAEL up-regulation was reversed by PTEN. However, MAEL silencing inhibited the enhanced effects of morphine on cell viability and proliferation of A549 cells. Furthermore, morphine treatment reduced the LDH release and the percentage of CD8⁺ T cells, and increased the ratio of CD4⁺/CD8⁺ T cells and tumor weight. Meanwhile, MAEL silencing reversed the effects of morphine on immune factors (PD-L1, TGF-β, IL-10, and IL-2), the percentage of CD8⁺ T cells, and the ratio of CD4⁺/CD8⁺ T cells.

CONCLUSION

Morphine activated MAEL in lung cancer cells by Nrf2/PTEN pathway and regulated the immune factors, thereby promoting tumor immune escape.

The Caenorhabditis elegans TDRD5/7-like protein, LOTR-1, interacts with the helicase ZNFX-1 to balance epigenetic signals in the germline

LOTUS and Tudor domain containing proteins have critical roles in the germline. Proteins that contain these domains, such as Tejas/Tapas in Drosophila, help localize the Vasa helicase to the germ granules and facilitate piRNA-mediated transposon silencing. The homologous proteins in mammals, TDRD5 and TDRD7, are required during spermiogenesis. Until now, proteins containing both LOTUS and Tudor domains in Caenorhabditis elegans have remained elusive. Here we describe LOTR-1 (D1081.7), which derives its name from its LOTUS and Tudor domains. Interestingly, LOTR-1 docks next to P granules to colocalize with the broadly conserved Z-granule helicase, ZNFX-1. The Tudor domain of LOTR-1 is required for its Z-granule retention. Like znfx-1 mutants, lotr-1 mutants lose small RNAs from the 3’ ends of WAGO and mutator targets, reminiscent of the loss of piRNAs from the 3’ ends of piRNA precursor transcripts in mouse Tdrd5 mutants. Our work shows that LOTR-1 acts with ZNFX-1 to bring small RNA amplifying mechanisms towards the 3’ ends of its RNA templates.

Germ granules are protein and RNA complexes that are critical for maintaining an animal’s fertility. Central to the composition of germ granules are their small RNAs, which have the capacity to convey a memory of germline-licensed expression from one generation to the next. Here we describe and characterize a new germ-granule protein in C. elegans that we’ve named LOTR-1, after its LOTUS and Tudor domains. This combination of LOTUS and Tudor domains can be found in the mammalian proteins TDRD5 and TDRD7, which are required during spermatogenesis. During C. elegans embryogenesis, germ granules demix or partition into subgranules with refined functions. We show that LOTR-1 partitions with a specific class of subgranules called Z granules, interacting with a Z-granule helicase called ZNFX-1. Here, LOTR-1 functions with ZNFX-1 to position small RNA amplification from RNA templates, ensuring a memory of germline expression across generations. These findings may provide new insight into the function of TDRD5 and TDRD7 during human germline development.

SYNCRIP Modulates the Epithelial-Mesenchymal Transition in Hepatocytes and HCC Cells

Heterogeneous nuclear ribonucleoproteins (hnRNPs) control gene expression by acting at multiple levels and are often deregulated in epithelial tumors; however, their roles in the fine regulation of cellular reprogramming, specifically in epithelial–mesenchymal transition (EMT), remain largely unknown. Here, we focused on the hnRNP-Q (also known as SYNCRIP), showing by molecular analysis that in hepatocytes it acts as a “mesenchymal” gene, being induced by TGFβ and modulating the EMT. SYNCRIP silencing limits the induction of the mesenchymal program and maintains the epithelial phenotype. Notably, in HCC invasive cells, SYNCRIP knockdown induces a mesenchymal–epithelial transition (MET), negatively regulating their mesenchymal phenotype and significantly impairing their migratory capacity. In exploring possible molecular mechanisms underlying these observations, we identified a set of miRNAs (i.e., miR-181-a1-3p, miR-181-b1-3p, miR-122-5p, miR-200a-5p, and miR-let7g-5p), previously shown to exert pro- or anti-EMT activities, significantly impacted by SYNCRIP interference during EMT/MET dynamics and gathered insights, suggesting the possible involvement of this RNA binding protein in their transcriptional regulation.

Stress Granules Involved in Formation, Progression and Metastasis of Cancer: A Scoping Review

The assembly of stress granules (SGs) is a well-known cellular strategy for reducing stress-related damage and promoting cell survival. SGs have become important players in human health, in addition to their fundamental role in the stress response. The critical role of SGs in cancer cells in formation, progression, and metastasis makes sense. Recent researchers have found that several SG components play a role in tumorigenesis and cancer metastasis via tumor-associated signaling pathways and other mechanisms. Gene-ontology analysis revealed the role of these protein components in the structure of SGs. Involvement in the translation process, regulation of mRNA stability, and action in both the cytoplasm and nucleus are among the main features of SG proteins. The present scoping review aimed to consider all studies on the effect of SGs on cancer formation, proliferation, and metastasis and performed based on a six-stage methodology structure and the PRISMA guideline. A systematic search of seven databases for qualified articles was conducted before July 2021. Publications were screened, and quantitative and qualitative analysis was performed on the extracted data. Go analysis was performed on seventy-one SGs protein components. Remarkably G3BP1, TIA1, TIAR, and YB1 have the largest share among the proteins considered in the studies. Altogether, this scoping review tries to demonstrate and provide a comprehensive summary of the role of SGs in the formation, progression, and metastasis of cancer by reviewing all studies.

An intronic variant in the CELF4 gene is associated with risk for colorectal cancer

BACKGROUND

Germline predisposition variants associated with colorectal cancer (CRC) have been identified but all are not yet identified. We sought to identify the responsible predisposition germline variant in an extended high-risk CRC pedigree that exhibited evidence of linkage to the 18q12.2 region (TLOD = +2.81).

METHODS

DNA from two distantly related carriers of the hypothesized predisposition haplotype on 18q12.2 was sequenced to identify candidate variants. The candidate rare variants shared by the related sequenced subjects were screened in 3,094 CRC cases and 5x population-matched controls from UKBiobank to test for association. Further segregation of the variant was tested via Taqman assay in other sampled individuals in the pedigree.

RESULTS

Analysis of whole genome sequence data for the two related hypothesized predisposition haplotype carriers, restricted to the shared haplotype boundaries, identified multiple (n = 6) rare candidate non-coding variants that were tested for association with CRC risk in UKBiobank. A rare intronic variant ofCELF4 gene, rs568643870, was significantly associated with CRC (p = 0.004, OR = 5.0), and segregated with CRC in other members of the linked pedigree.

CONCLUSION

Evidence of segregation in a high-risk pedigree, case-control association in an external dataset, and identification of additional CRC-affected carriers in the linked pedigree support a role for a rareCELF4 intronic variant in CRC risk.

MAEL as a diagnostic marker for the early detection of esophageal squamous cell carcinoma

Background

Esophageal cancer is one of the most common malignancies among Iranians and is categorized as adenocarcinoma and squamous cell carcinoma. Various environmental and genetic factors are involved in this malignancy. Despite the recent advances in therapeutic modalities there is still a noticeable mortality rate among such patients which can be related to the late diagnosis. Regarding high ratio of esophageal squamous cell carcinoma (ESCC) in Iran, therefore it is required to assess molecular biology of ESCC to introduce novel diagnostic markers. In present study we assessed the role of Maelstrom (MAEL) cancer testis gene in biology of ESCC among Iranian patients.

Methods

Forty-five freshly normal and tumor tissues were enrolled to evaluate the levels of MAEL mRNA expression using Real time polymerase chain reaction.

Results

MAEL under and over expressions were observed in 12 (26.7%) and 9 (20%) of patients, respectively. MAEL fold changes were ranged between -4.33 to -1.87 (mean SD: -2.90± 0.24) and 1.92 to 7.72 (mean SD: 3.97± 0.69) in under and over expressed cases, respectively. There was a significant association between stage and MAEL expression in which majority of MAEL over expressed tumors (8/9, 88.9%) were in stage I/II (p<0.001). There was also a significant correlation between MAEL expression and depth of invasion in which tumor with T1/2 had higher levels of MAEL expression compared with T3/4 tumors (p=0.017). Moreover, there were significant correlations between MAEL expression, tumor size (p=0.028), and grade (p=0.003) among male patients.

Conclusions

Our data showed that the MAEL was mainly involved in primary stages of tumor progression and it has a declining expression levels toward the advanced stages and higher depth of tumor invasions. Therefore, MAEL can be efficiently introduced as an early detection marker among Iranian ESCC patients.

Prognostic value of aberrantly expressed methylation genes in human hepatocellular carcinoma

Objectives: To identify the prognostic value of aberrantly methylated differentially expressed genes (DEGs) in hepatocellular carcinoma (HCC) and to explore the underlying mechanisms of tumorigenesis.

Methods: Gene expression profiles (GSE65372 and GSE37988) were analyzed using GEO2R to obtain aberrantly methylated DEGs. Functional enrichment analysis of screened genes was performed by the Database for Annotation, Visualization, and Integrated Discovery (DAVID). Cytoscape software was used to analyze the PPI network and to select hub genes. Transcriptional and proteinic expression data of hub genes were obtained through UALCAN and the Human Protein Reference Database. Finally, we analyzed the prognostic value of hub genes with the Kaplan–Meier Plotter and MethSurv database.

Results: In total, 24 up-hypomethylated oncogenes and 37 down-hypermethylated tumor suppressor genes (TSGs) were identified, and 8 hub genes, including 4 up-hypomethylated oncogenes (CDC5L, MERTK, RHOA and YBX1) and 4 down-hypermethylated TSGs (BCR, DFFA, SCUBE2 and TP63), were selected by PPI. Higher expression of methylated CDC5L-cg05671347, MERTK-cg08279316, RHOA-cg05657651 and YBX1-cg16306148, and lower expression of methylated BCR-cg25410636, DFFA-cg20696875, SCUBE2-cg19000089 and TP63-cg06520450, were associated with better overall survival (OS) in HCC patients. Multivariate analysis also showed they were independent prognostic factors for OS of HCC patients.

Conclusions: In summary, different expression of methylated genes above mentioned were associated with better prognosis in HCC patients. Altering the methylation status of these genes may be a therapeutic target for HCC, but it should be further evaluated in clinical studies.

MAEL Cancer-Testis Antigen as a Diagnostic Marker in Primary Stages of Gastric Cancer with Helicobacter pylori Infection

PURPOSE

Gastric cancer (GC) is the third leading cause of cancer related deaths in the world. Cancer testis antigens (CTAs) are involved in tumor progression of various cancers. These markers have not any expression or minimally expression in normal tissues, highlighting them as efficient methods for molecular targeted therapy. In the present study, we assessed the role of MAEL as a CTA in biology of GC and risk of Helicobacter Pylori (H pylori) infection.

METHODS

Levels of MAEL mRNA expression in 80 GC tumor tissues were compared to their corresponding normal margins using the real-time polymerase chain reaction.

RESULTS

There was a significant correlation between MAEL expression and tumor stage (p = 0.050). There were also significant correlations between MAEL expression and tumor grade (p = 0.015) and depth of invasion (p = 0.030) among the H pylori negative cases.

CONCLUSIONS

MAEL is probably associated with aggressiveness of primary-stage tumors and can be introduced as an efficient marker for the early detection and also H pylori infected tumors in GC patients.

A novel antisense lncRNA NT5E promotes progression by modulating the expression of SYNCRIP and predicts a poor prognosis in pancreatic cancer

A novel antisense lncRNA NT5E was identified in a previous microarray that was clearly up‐regulated in pancreatic cancer (PC) tissues. However, its biological function remains unclear. Thus, we aimed to explore its function and clinical significance in PC. The lncNT5E expression was determined in PC specimens and cell lines. In vitro and in vivo studies detected the impact of lncNT5E depletion on PC cell proliferation, migration and invasion. Western blotting investigated the epithelial‐mesenchymal transition (EMT) markers. The interaction between lncNT5E and the promoter region of SYNCRIP was detected by dual‐luciferase reporter assay. The role of lncNT5E in modulating SYNCRIP was investigated in vitro. Our results showed that lncNT5E was significantly up‐regulated in PC tissues and cell lines and associated with poor prognosis. LncNT5E depletion inhibited PC cell proliferation, migration, invasion and EMT in vitro and caused tumorigenesis arrest in vivo. Furthermore, SYNCRIP knockdown had effects similar to those of lncNT5E depletion. A significant positive relationship was observed between lncNT5E and SYNCRIP. Moreover, the dual‐luciferase reporter assays indicated that lncNT5E depletion significantly inhibited SYNCRIP promoter activity. Importantly, the malignant phenotypes of lncNT5E depletion were rescued by overexpressing SYNCRIP. In conclusion, lncNT5E predicts poor prognosis and promotes PC progression by modulating SYNCRIP expression.

Novel FMRP interaction networks linked to cellular stress

Silencing of the fragile X mental retardation 1 (FMR1) gene and consequently lack of synthesis of FMR protein (FMRP) are associated with fragile X syndrome, which is one of the most prevalent inherited intellectual disabilities, with additional roles in increased viral infection, liver disease, and reduced cancer risk. FMRP plays critical roles in chromatin dynamics, RNA binding, mRNA transport, and mRNA translation. However, the underlying molecular mechanisms, including the (sub)cellular FMRP protein networks, remain elusive. Here, we employed affinity pull-down and quantitative LC-MS/MS analyses with FMRP. We identified known and novel candidate FMRP-binding proteins as well as protein complexes. FMRP interacted with 180 proteins, 28 of which interacted with its N terminus. Interaction with the C terminus of FMRP was observed for 102 proteins, and 48 proteins interacted with both termini. This FMRP interactome comprises known FMRP-binding proteins, including the ribosomal proteins FXR1P, NUFIP2, Caprin-1, and numerous novel FMRP candidate interacting proteins that localize to different subcellular compartments, including CARF, LARP1, LEO1, NOG2, G3BP1, NONO, NPM1, SKIP, SND1, SQSTM1, and TRIM28. Our data considerably expand the protein and RNA interaction networks of FMRP, which thereby suggest that, in addition to its known functions, FMRP participates in transcription, RNA metabolism, ribonucleoprotein stress granule formation, translation, DNA damage response, chromatin dynamics, cell cycle regulation, ribosome biogenesis, miRNA biogenesis, and mitochondrial organization. Thus, FMRP seems associated with multiple cellular processes both under normal and cell stress conditions in neuronal as well as non-neuronal cell types, as exemplified by its role in the formation of stress granules.

Mael is essential for cancer cell survival and tumorigenesis through protection of genetic integrity

Germ line-specific genes are activated in somatic cells during tumorigenesis, and are accordingly referred to as cancer germline genes. Such genes that act on piRNA (Piwi-interacting RNA) processing play an important role in the progression of cancer cells. Here, we show that the spermatogenic transposon silencer maelstrom (Mael), a piRNA-processing factor, is required for malignant transformation and survival of cancer cells. A specific Mael isoform was distinctively overexpressed in diverse human cancer cell lines and its depletion resulted in cancer-specific cell death, characterized by apoptosis and senescence, accompanied by an increase in reactive oxygen-species and DNA damage. These biochemical changes and death phenotypes induced by Mael depletion were dependent on ATM. Interestingly Mael was essential for Myc/Ras-induced transformation, and its overexpression inhibited Ras-induced senescence. In addition, Mael repressed retrotransposon activity in cancer cells. These results suggest that Mael depletion induces ATM-dependent DNA damage, consequently leading to cell death specifically in cancer cells. Moreover, Mael possesses oncogenic potential that can protect against genetic instability.

MAEL contributes to gastric cancer progression by promoting ILKAP degradation

The cancer-testis gene MAEL is involved in the development and progression of bladder, liver and colorectal cancers. However, its role in other cancers is unclear. By systematically analyzing transcriptomics and genomics data from various cancer databases, we identified that the MAEL gene is aberrantly elevated in gastric cancer (GC) tissues and that its expression is strongly negatively correlated with DNA methylation (Pearson's correlation coefficient = −0.675). Survival analysis revealed that MAEL expression may serve as a prognostic marker for GC patients (overall survival: hazard ratio [HR] = 1.54, p = 1.2E-4; first progression: HR = 1.51, p = 8.7E-4). In vitro and in vivo experiments demonstrated that silencing MAEL expression in the GC cell lines HGC-27 and AGS inhibits proliferation, colony formation, migration, invasion and growth of xenograft tumors, whereas MAEL overexpression exerts the opposite effects in the normal gastric cell line GES-1. Mechanistically, MAEL promotes the lysosome-dependent degradation of the protein phosphatase ILKAP, leading to increased phosphorylation of its substrates (p38, CHK1 and RSK2). Moreover, adenovirus-mediated ILKAP overexpression reversed the oncogenic effects of MAEL in vitro and in vivo. Taken together, these results indicate that MAEL exerts its oncogenic function by promoting ILKAP degradation in the GC.

Roles of cancer/testis antigens (CTAs) in breast cancer

Breast cancer is the most common cancer diagnosed and is the second leading cause of cancer death among women in the US. For breast cancer, early diagnosis and efficient therapy remains a significant clinical challenge. Therefore, it is necessary to identify novel tumor associated molecules to target for biomarker development and immunotherapy. In this regard, cancer testis antigens (CTAs) have emerged as a potential clinical biomarker targeting immunotherapy for various malignancies due to the nature of its characteristics. CTAs are a group of tumor associated antigens (TAAs) that display normal expression in immune-privileged organs, but display aberrant expression in several types of cancers, particularly in advanced cancers. Investigation of CTAs for the clinical management of breast malignancies indicates that these TAAs have potential roles as novel biomarkers, with increased specificity and sensitivity compared to those currently used in the clinic. Moreover, TAAs could be therapeutic targets for cancer immunotherapy. This review is an attempt to address the promising CTAs in breast cancer and their possible clinical implications as biomarkers and immunotherapeutic targets with particular focus on challenges and future interventions.

Tissue-specific Co-expression of Long Non-coding and Coding RNAs Associated with Breast Cancer

Inference of the biological roles of lncRNAs in breast cancer development remains a challenge. Here, we analyzed RNA-seq data in tumor and normal breast tissue samples from 18 breast cancer patients and 18 healthy controls and constructed a functional lncRNA-mRNA co-expression network. We revealed two distinctive co-expression patterns associated with breast cancer, reflecting different underlying regulatory mechanisms: (1) 516 pairs of lncRNA-mRNAs have differential co-expression pattern, in which the correlation between lncRNA and mRNA expression differs in tumor and normal breast tissue; (2) 291 pairs have dose-response co-expression pattern, in which the correlation is similar, but the expression level of lncRNA or mRNA differs in the two tissue types. We further validated our findings in TCGA dataset and annotated lncRNAs using TANRIC. One novel lncRNA, AC145110.1 on 8p12, was found differentially co-expressed with 127 mRNAs (including TOX4 and MAEL) in tumor and normal breast tissue and also highly correlated with breast cancer clinical outcomes. Functional enrichment and pathway analyses identified distinct biological functions for different patterns of co-expression regulations. Our data suggested that lncRNAs might be involved in breast tumorigenesis through the modulation of gene expression in multiple pathologic pathways.

Activation of ERK1/2 Ameliorates Liver Steatosis in Leptin Receptor-Deficient (db/db) Mice via Stimulating ATG7-Dependent Autophagy

Although numerous functions of extracellular signal-regulated kinase 1/2 (ERK1/2) are identified, a direct effect of ERK1/2 on liver steatosis has not been reported. Here, we show that ERK1/2 activity is compromised in livers of leptin receptor-deficient (db/db) mice. Adenovirus-mediated activation of mitogen-activated protein kinase kinase 1 (MEK1), the upstream regulator of ERK1/2, significantly ameliorated liver steatosis in db/db mice, increased expression of genes related to fatty acid β-oxidation and triglyceride (TG) export and increased serum β-hydroxybutyrate (3-HB) levels. Opposite effects were observed in adenovirus-mediated ERK1/2 knockdown C57/B6J wild-type mice. Furthermore, autophagy and autophagy-related protein 7 (ATG7) expression were decreased or increased by ERK1/2 knockdown or activation, respectively, in primary hepatocytes and liver. Blockade of autophagy by the autophagy inhibitor chloroquine or adenovirus-mediated ATG7 knockdown reversed the ameliorated liver steatosis in recombinant adenoviruses construct expressing rat constitutively active MEK1 Ad-CA MEK1 db/db mice, decreased expression of genes related to fatty acid β-oxidation and TG export, and decreased serum 3-HB levels. Finally, ERK1/2 regulated ATG7 expression in a p38-dependent pathway. Taken together, these results identify a novel beneficial role for ERK1/2 in liver steatosis via promoting ATG7-dependent autophagy, which provides new insights into the mechanisms underlying liver steatosis and important hints for targeting ERK1/2 in treating liver steatosis.

Specifying and protecting germ cell fate

Germ cells are the special cells in the body that undergo meiosis to generate gametes and subsequently entire new organisms after fertilization, a process that continues generation after generation. Recent studies have expanded our understanding of the factors and mechanisms that specify germ cell fate, including the partitioning of maternally supplied 'germ plasm', inheritance of epigenetic memory and expression of transcription factors crucial for primordial germ cell (PGC) development. Even after PGCs are specified, germline fate is labile and thus requires protective mechanisms, such as global transcriptional repression, chromatin state alteration and translation of only germline-appropriate transcripts. Findings from diverse species continue to provide insights into the shared and divergent needs of these special reproductive cells.