Novel interacting proteins identified by tandem affinity purification coupled to nano LC–MS/MS interact with ribosomal S6 protein kinase 4 (RSK4) and its variant protein (RSK4m)

Expression of RSK4 protein in non-small cell lung cancer tissues, adjacent tissues and its correlation with clinicopathological features

OBJECTIVE

To evaluate the expression of Ribosomal S6 kinase 4 (RSK4) protein in non-small cell lung cancer (NSCLC) tissues and adjacent non-tumor tissues, and to elucidate its correlation with clinicopathological features of NSCLC.

METHODS

We analyzed 100 NSCLC patients treated at the Second Affiliated Hospital of Zhejiang University School of Medicine from June 2020 to June 2022. Patient demographics and clinical data, including gender, age, history of diabetes, tumor location, degree of tumor differentiation, lymph node metastasis, and clinical stage, were collected. RSK4 protein expression was assessed in tissue samples via immunohistochemical staining.

RESULTS

RSK4 protein was positively expressed in 35.00% of cancerous tissues, significantly lower than the 69.00% observed in adjacent non-tumor tissues (P < 0.05). Patients with lower tumor differentiation, advanced Tumor Node Metastasis (TNM) stages, and lymph node metastases showed significantly reduced RSK4 expression compared to those with higher differentiation, earlier TNM stages, and no lymph node metastases (all P < 0.05). Cox regression analysis indicated that TNM stage, low differentiation, and lymph node metastases significantly influenced RSK4 expression (all P < 0.05). Survival analysis revealed a higher positive prognosis survival rate of 74.29% (26/35) among patients with positive RSK4 expression, versus 53.85% (35/65) in those with negative expression (P < 0.05). Spearman correlation analysis demonstrated a significant positive correlation of RSK4 expression with TNM stage, lymph node metastasis, and patient prognosis (all P < 0.05).

CONCLUSION

Positive RSK4 expression in NSCLC tissues is significantly correlated with advanced cancer stage, poor differentiation, and presence of lymph node metastasis, suggesting a potential tumor suppressor role for RSK4 in NSCLC. This association underscores its prognostic relevance in NSCLC patients.

Down-regulated TAB1 suppresses the replication of Coxsackievirus B5 via activating the NF-κB pathways through interaction with viral 3D polymerase

Coxsackievirus Group B type 5 (CVB5), an important pathogen of hand-foot-mouth disease, is also associated with neurological complications and poses a public health threat to young infants. Among the CVB5 proteins, the nonstructural protein 3D, known as the Enteroviral RNA-dependent RNA polymerase, is mainly involved in viral genome replication and transcription. In this study, we performed immunoprecipitation coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify host proteins that interacted with CVB5 3D polymerase. A total of 116 differentially expressed proteins were obtained. Gene Ontology analysis identified that the proteins were involved in cell development and cell adhesion, distributed in the desmosome and envelope, and participated in GTPase binding. Kyoto Encyclopedia of Genes and Genomes analysis further revealed they participated in nerve diseases, such as Parkinson disease. Among them, 35 proteins were significantly differentially expressed and the cellular protein TGF-BATA-activated kinase1 binding protein 1 (TAB1) was found to be specifically interacting with the 3D polymerase. 3D polymerase facilitated the entry of TAB1 into the nucleus and down-regulated TAB1 expression via the lysosomal pathway. In addition, TAB1 inhibited CVB5 replication via inducing inflammatory factors and activated the NF-κB pathway through IκBα phosphorylation. Moreover, the 90-96aa domain of TAB1 was an important structure for the function. Collectively, our findings demonstrate the mechanism by which cellular TAB1 inhibits the CVB5 replication via activation of the host innate immune response, providing a novel insight into the virus-host innate immunity.

Proteomics Investigation of the Impact of the Enterococcus faecalis Secretome on MCF-7 Tumor Cells

Breast cancer is the most prevalent form of cancer among women. The microenvironment of a cancer tumor is surrounded by various cells, including the microbiota. An imbalance between microbes and their host may contribute to the development and spread of breast cancer. Therefore, the objective of this study is to investigate the influence of Enterococcus faecalis on a breast cancer cell line (MCF-7) to mimic the luminal A subtype of breast cancer, using an untargeted proteomics approach to analyze the proteomic profiles of breast cancer cells after their treatment with E. faecalis in order to understand the microbiome and its role in the development of cancer. The breast cancer cell line MCF-7 was cultured and then treated with a 10% bacterial supernatant at two time points (24 h and 48 h) at 37 °C in a humidified incubator with 5% CO2. Proteins were then extracted and separated using two-dimensional difference (2D-DIGE) gel electrophoresis, and the statistically significant proteins (p-value < 0.05, fold change > 1.5) were identified via matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS). The protein fingerprints showed a differential protein expression pattern in the cells treated with E. faecalis for 24 and 48 h compared with the control. We found 58 statistically significant proteins changes in the MCF-7 breast cancer cells affected by E. faecalis. Kilin and transgelin were upregulated after 24 h of treatment and could be used as diagnostic and prognostic markers for breast cancer. In addition, another protein involved in the inhibition of cell proliferation was coiled-coil domain-containing protein 154. The protein markers identified in this study may serve as possible biomarkers for breast cancer progression. This promotes their future uses as important therapeutic goals in the treatment and diagnosis of cancer and increases our understanding of the breast microbiome and its role in the development of cancer.

Prominent roles of ribosomal S6 kinase 4 (RSK4) in cancer

RSK4 refers to one Ser/Thr protein kinase functioning downstream pertaining to the signaling channel of protein kinase (MAPK) stimulated by Ras/mitogen. RSK4 can regulate numerous substrates impacting cells' surviving state, growing processes and proliferating process. Thus, dysregulated RSK4 active state display a relationship to several carcinoma categories, covering breast carcinoma, esophageal squamous cell carcinoma, glioma, colorectal carcinoma, lung carcinoma, ovarian carcinoma, leukemia, endometrial carcinoma, and kidney carcinoma. Whether RSK4 is a tumor suppressor gene or one oncogene remains controversial. No specific inhibiting elements for RSK4 have been found. This review briefs the existing information regarding RSK4 activating process, the function and mechanism of RSK4 in different tumors, and the research progress and limitations of existing RSK inhibitors. RSK4 may be a potential target of molecular therapy medicine in the future.

CASK, APBA1, and STXBP1 collaborate during insulin secretion

Calcium/calmodulin-dependent serine protein kinase (CASK) knockdown reduces insulin vesicle docking to cell membranes. Here, we explored CASK interactions with other proteins during insulin secretion. Using co-immunoprecipitation, liquid chromatography-mass spectrometry and bioinformatic analysis, we identified that CASK, Adapter protein X11 alpha (APBA1), and Syntaxin binding protein 1 (STXBP1) formed tripartite complex during insulin secretion. CASK enhanced APBA1-STXBP1 interaction and mediated their traffic from cytoplasm to plasma membrane during insulin release. High fatty acid stimulation decreased insulin secretion along with CASK, APBA1, and STXBP1 expression; Cask overexpression enhanced CASK/APBA1/STXBP1 tripartite complex function, and may thereby rescue lipotoxicity-induced insulin-release defects. Collectively, our results illustrated the function of CASK in insulin granules exocytosis, which broadens the underlying mechanism of insulin secretion and highlights the clinical potential of CASK as a drug target of type 2 Diabetes Mellitus (T2DM).

Development and application of a HPLC-MS/MS method for quantitation of fucosylated chondroitin sulfate and fucoidan in sea cucumbers

Fucosylated chondroitin sulfate (FCS) and fucoidan (FUC) are two main bioactive polysaccharides in sea cucumbers. A novel method for quantitation of FCS and FUC was developed by detecting chondroitin disaccharide and fucose produced through acid hydrolysis using HPLC-MS/MS. The present method showed satisfactory performance for both saccharides. It was applied to assay sea cucumbers (Stichopus japonicus) reared in pond grow-out or bottom sowing, and the results were compared with those obtained by traditional HPLC method and 1,9-dimethylmethylene blue test, which could only provide the total sea cucumber polysaccharide (SCP) contents. No difference of total SCP content was observed between sea cucumbers reared through different ways, while a higher ratio of FCS to FUC of sea cucumbers of pond grow-out was revealed by the present method. Thus, this novel method is potential to quantify the two polysaccharides and could be a powerful tool for quality evaluation of sea cucumbers.

Decoding the full picture of Raf1 function based on its interacting proteins

Raf1 is a member of the Raf kinase family and regulates many fundamental cell processes, including proliferation, differentiation, apoptosis, motility, and metabolism. However, the functions of Raf1 have not been completely elucidated. To better understand Raf1 function, we investigated the proteins that interacted with Raf1. We identified 198 Raf1 interacting proteins and our data suggested that Raf1 may regulate cell processes through these interactions. These interaction partners were involved in all ten hallmarks of cancer, suggesting that Raf1 is involved in different aspects of carcinogenesis. In addition, we showed that Raf1 interacting proteins were enriched in six signaling pathways and many human diseases. The interaction partners identified in this study may represent oncological candidates for future investigations into Raf1 function. Our findings have provided an overview of Raf1 function from a systems biology perspective.