RACK1 Silencing Induces Cell Apoptosis and Inhibits Cell Proliferation in Hepatocellular Carcinoma MHCC97-H Cells

Decoding the Role of O-GlcNAcylation in Hepatocellular Carcinoma

Post-translational modifications (PTMs) influence protein functionality by modulating protein stability, localization, and interactions with other molecules, thereby controlling various cellular processes. Common PTMs include phosphorylation, acetylation, ubiquitination, glycosylation, SUMOylation, methylation, sulfation, and nitrosylation. Among these modifications, O-GlcNAcylation has been shown to play a critical role in cancer development and progression, especially in hepatocellular carcinoma (HCC). This review outlines the role of O-GlcNAcylation in the development and progression of HCC. Moreover, we delve into the underlying mechanisms of O-GlcNAcylation in HCC and highlight compounds that target O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) to improve treatment outcomes. Understanding the role of O-GlcNAcylation in HCC will offer insights into potential therapeutic strategies targeting OGT and OGA, which could improve treatment for patients with HCC.

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.

Identification and Functional Analysis of BmNPV-Interacting Proteins From Bombyx mori (Lepidoptera) Larval Midgut Based on Subcellular Protein Levels

Bombyx mori nucleopolyhedrovirus (BmNPV) is a major pathogen causing severe economic loss. However, the molecular mechanism of silkworm resistance to BmNPV and the interactions of this virus with the host during infection remain largely unclear. To explore the virus-binding proteins of silkworms, the midgut subcellular component proteins that may interact with BmNPV were analyzed in vitro based on one- and two-dimensional electrophoresis and far-western blotting combined with mass spectrometry (MS). A total of 24 proteins were determined to be specifically bound to budded viruses (BVs) in two subcellular fractions (mitochondria and microsomes). These proteins were involved in viral transportation, energy metabolism, apoptosis and viral propagation, and they responded to BmNPV infection with different expression profiles in different resistant strains. In particular, almost all the identified proteins were downregulated in the A35 strain following BmNPV infection. Interestingly, there were no virus-binding proteins identified in the cytosolic fraction of the silkworm midgut. Two candidate proteins, RACK1 and VDAC2, interacted with BVs, as determined with far-western blotting and reverse far-western blotting. We speculated that the proteins interacting with the virus could either enhance or inhibit the infection of the virus. The data provide comprehensive useful information for further research on the interaction of the host with BmNPV.

Overexpression of RACK1 Predicts Poor Prognosis in Melanoma

Melanoma is a highly malignant skin cancer with limited treatment options, the mechanism of the occurrence and development of melanoma is still unclear till now. Receptor for activated C kinase 1 (RACK1) is a scaffolding protein that mediates multiple signaling pathways; it interconnects distinct signaling pathways to control essential cellular processes. RACK1 was reported as an oncogene in human tumorigenesis, but little is known about its role in melanoma. This study aimed to investigate the expression of RACK1 in patients with melanoma and to reveal its possible functions in melanoma cells. The expression profiles of RACK1 detected in tumor tissues from melanoma patients showed that RACK1 was higher in tumor tissues, and its expression level was well associated with the clinical progression of melanoma (TNM stage, P=0.009). Furthermore, RNA interfering (RNAi) knockdown of RACK1 could efficiently suppress the proliferation, migration and invasion of A375 and A875 cells and promote their apoptosis. Taken together, these results suggest that RACK1 may be a poor prognostic factor in human melanoma, and it may be a new therapeutic target for melanoma treatment.

Role of RACK1 on cell proliferation, adhesion, and bortezomib-induced apoptosis in multiple myeloma

Receptor for activated C kinase 1 (RACK1), a scaffold protein, plays a crucial role in the progression of various cancers. However, the biological function and underlying mechanism of RACK1 in multiple myeloma (MM) cells remain unclear. The present study aimed to explore the function of RACK1 on the cell proliferation, adhesion, and bortezomib-induced apoptosis in MM. We found that RACK1 was significantly overexpressed in myeloma cell lines and primary myeloma cells compared with normal bone marrow plasma cells. Moreover, immunofluorescence revealed that RACK1 was primarily expressed in the cytoplasm of MM cells. Knockdown of RACK1 impaired growth of MM cells, blocked entry into the S-phase of the cell cycle, and resulted in reduced cell adhesion rates. More importantly, knockdown of RACK1 decreased the proliferation of MM cells by activating P-P38 and P-ERK in the MAPK/ERK signaling pathway. We also found that altered expression of RACK1 is associated with bortezomib-mediated MM cell apoptosis. In summary, these results may provide a possible target for therapy in MM.

Inhibition of CD9 expression reduces the metastatic capacity of human hepatocellular carcinoma cell line MHCC97-H

Metastasis is a characteristic of malignant tumors and may be a fatal clinical factor for many patients with cancer. Hepatocellular carcinoma (HCC) cells are highly metastatic; the mechanism of metastasis is complicated and may be influenced by a number of factors. Membrane proteins may block receptors or inhibit important enzymes, thus inhibiting tumor progression, and may be potential therapeutic targets for tumor prognosis and treatment. The present study aimed to use proteomics to analyze the dynamic changes of membrane proteins in HCC cells, to improve our understanding of membrane protein functions and to clarify the important components of the mechanisms of HCC metastasis. The present study used the highly metastatic MHCC97-H and the lowly metastatic MHCC97-L HCC cell lines, and the isobaric tags for relative and absolute quantitation (iTRAQ) approach was used for high-throughput screening of metastasis-related membrane proteins. A total of 22 membrane proteins were identified as differentially expressed between the MHCC97-H and MHCC97-L cell lines; these results were verified by reverse transcription-quantitative polymerase chain reaction and western blotting. A number of the identified proteins were revealed to be related to tumor metastasis, including the tetraspan in transmembrane protein CD9. CD9 was demonstrated to be highly expressed in MHCC97-H cells compared with MHCC97-L cells. The functional role of CD9 was characterized by inhibiting its expression using a small interfering RNAs, which demonstrated that reduced CD9 expression inhibited cell migration and metastasis, as determined by wound-healing and invasion assays. Results from the present study demonstrated that CD9 was highly expressed in the highly metastatic HCC cells and promoted HCC cell migration. This protein may be a novel target for regulating the invasive phenotype in HCC.

High MRPS23 expression contributes to hepatocellular carcinoma proliferation and indicates poor survival outcomes

Hepatocellular carcinoma is one of the most prevalent neoplasms and the leading cause of cancer-related mortality worldwide. Mitochondrial ribosomal protein S23 is encoded by a nuclear gene and participates in mitochondrial protein translation. Mitochondrial ribosomal protein S23 overexpression has been found in many types of cancer. In this study, we explored mitochondrial ribosomal protein S23 expression in primary hepatocellular carcinoma tissues compared with matched adjacent non-tumoral liver tissues using mitochondrial ribosomal protein S23 messenger RNA and protein levels collected from public databases and clinical samples. Immunohistochemistry was performed to analyze the relationship between mitochondrial ribosomal protein S23 and various clinicopathological features. The results indicated that mitochondrial ribosomal protein S23 was significantly overexpressed in hepatocellular carcinoma. High mitochondrial ribosomal protein S23 expression was correlated with the tumor size and tumor–metastasis–node stage. Moreover, patients with high mitochondrial ribosomal protein S23 expression levels presented poorer survival rates. Mitochondrial ribosomal protein S23 was an independent prognostic factor for survival, especially at the early stage of hepatocellular carcinoma. In addition, the downregulation of mitochondrial ribosomal protein S23 decreased the proliferation of hepatocellular carcinoma in vitro and in vivo. In conclusion, we verified for the first time that mitochondrial ribosomal protein S23 expression was upregulated in hepatocellular carcinoma. High mitochondrial ribosomal protein S23 levels can predict poor clinical outcomes in hepatocellular carcinoma, and this protein plays a key role in tumor proliferation. Therefore, mitochondrial ribosomal protein S23 may be a potential therapeutic target for hepatocellular carcinoma.