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Transcriptional analysis of the expression and prognostic value of lipid droplet-localized proteins in hepatocellular carcinoma

ABSTRACT: The accumulation of lipid droplets (LDs) in hepatocytes is the main pathogenesis in nonalcoholic fatty liver disease (NAFLD), which is also the key risk factor for the progression of hepatocellular carcinoma (HCC). LDs behaviors are demonstrated to be associated with HCC advancement, and are tightly regulated by a subset protein localized on the surface of LDs. However, the role of LDs-localized protein in HCC has been rarely investigated. This study is focused on the transcriptional dynamic and prognostic value of LDs-localized protein in HCC. Firstly, we summarized the known LDs-localized proteins, which are demonstrated by immunofluorescence according to previous studies. Next, by the use of GEPIA/UALCAN/The Human Protein Atlas databases, we screened the transcriptional change in tumor and normal liver tissues, and found that 13 LDs-localized proteins may involve in the progression of HCC. Then we verified the transcriptional changes of 13 LDs-localized proteins by the use of HCC samples. Moreover, based on the assays of fatty liver of mice and human NAFLD liver samples, we found that the hepatic steatosis mainly contributed to the transcriptional change of selected LDs-localized proteins, indicating the involvement of these LDs-localized proteins in the negative role of NAFLD in HCC progression. Finally, we focused on the role of PLIN3 in HCC, and revealed that NAFLD status significantly promoted PLIN3 transcription in HCC tissue. Functional studies revealed that PLIN3 knockdown significantly limited the migration and chemosensitivity of hepatoma cells, suggesting the positive role of PLIN3 in HCC progression. Our study not only revealed the transcriptional change and prognostic value of lipid droplet-localized proteins in HCC, but also built the correlation between HCC and hepatic steatosis.

ORGANISM(S): Mus musculus

PROVIDER: GSE223446 | GEO | 2023/04/16

REPOSITORIES: GEO

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Project description:Non-alcoholic fatty liver disease (NAFLD), defined as fatty infiltration in >5% of hepatocytes (steatosis) in the absence of excessive alcohol consumption, is emerging as a leading cause of liver disease worldwide (1). Subjects with NAFLD have an increased risk of progressing into non-alcoholic steatohepatitis (NASH) as well as developing type 2 diabetes, cardiovascular disease, and liver cancer (2-4). Thus, understanding the pathobiology of NAFLD is of high medical relevance for the efficient prevention and treatment of a range of complex metabolic diseases. In NAFLD, excess lipids accumulate within intrahepatocellular lipid droplets (LDs), which are composed of a neutral lipid core of mainly triacylglycerol (TAG) and cholesterol esters surrounded by a phospholipid monolayer that harbors specific proteins. Once thought to be only inert energy storage depots, hepatic LDs are increasingly recognized as organelles that orchestrate liver lipid partitioning but also play a critical role in protein quality control and storage, cell signaling, and viral replication (5). Notably, LDs are shown to dynamically interact with a variety of cellular organelles including the endoplasmic reticulum (ER), mitochondria, peroxisomes, and endosomes (6). Liver LD surface-associated proteins regulate the functional properties of LDs, and dietary fat content as well as liver metabolic status have been shown to dynamically influence the composition of hepatic LD proteins (7, 8). Consequently, exploring how LD-associated proteins affect hepatic metabolism is important for understanding the molecular pathophysiology of NAFLD. In the search for novel targets that regulate ectopic lipid accumulation in the context of nutritional stress and obesity, we identified serine/threonine protein kinase (STK)25, a member of the Ste20 kinase superfamily (9), as a hepatic LD-associated protein, which critically controls the development and progression of NAFLD (10-15). We found that STK25 knockdown attenuates lipid deposition in human hepatocytes and mouse liver by repressing lipid synthesis and enhancing β-oxidation and very-low-density lipoprotein (VLDL)-TAG secretion, with the reciprocal phenotype seen when STK25 protein is overexpressed (10-15). Notably, administration of hepatocyte-targeting GalNAc-conjugated Stk25 antisense oligonucleotide (ASO) in obese mice effectively ameliorates diet-induced hepatic steatosis as well as NASH features (i.e., liver inflammation, hepatocellular ballooning, and fibrosis), providing in vivo nonclinical proof-of-principle for the metabolic benefit of pharmacological STK25 inhibitors (15). Furthermore, we observed that STK25 levels in human liver biopsies correlate with the severity of NASH, and several common non-linked single nucleotide polymorphisms (SNPs) in the human STK25 gene are associated with altered liver fat content (12-14). Although these studies suggest a key role for STK25 in the control of liver LD dynamics, the mechanism-of-action of STK25 in regulation of hepatic lipid partitioning has remained elusive. To provide novel insights into biological function of STK25 in the liver under steatotic conditions, we here characterized the hepatic LD-associated phosphoproteome in Stk25 knockout mice and their wild-type littermates following high-fat diet feeding using non-biased approach by isobaric tagging for relative quantification. Of the 4,515 proteins and 982 phosphoproteins identified with a 1% false discovery rate, we report a total of 131 proteins and 69 phosphoproteins that were differentially represented in STK25-deficient livers. Most notably, a number of proteins involved in peroxisomal function, antioxidant defense, and ubiquitination-mediated proteolysis were coordinately regulated in the livers from high-fat-fed Stk25-/- mice compared with wild-type controls.

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Transcriptional analysis of the expression and prognostic value of lipid droplet-localized proteins in hepatocellular carcinoma

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