Activation of ACLY by SEC63 deploys metabolic reprogramming to facilitate hepatocellular carcinoma metastasis upon endoplasmic reticulum stress

BACKGROUND

Tumor cells display augmented capability to maintain endoplasmic reticulum (ER) homeostasis and hijack ER stress pathway for malignant phenotypes under microenvironmental stimuli. Metabolic reprogramming is a well-known hallmark for tumor cells to provide specific adaptive traits to the microenvironmental alterations. However, it's unknown how tumor cells orchestrate metabolic reprogramming and tumor progression in response to ER stress. Herein, we aimed to explore the pivotal roles of SEC63-mediated metabolic remodeling in hepatocellular carcinoma (HCC) cell metastasis after ER stress.

METHODS

The expression levels of SEC63 in HCC tissues and adjacent non-cancerous tissues were determined by immunohistochemistry and western blot. The regulatory roles of SEC63 in HCC metastasis were investigated both in vitro and in vivo by RNA-sequencing, metabolites detection, immunofluorescence, and transwell migration/invasion analyses. GST pull-down, immunoprecipitation/mass spectrometry and in vivo ubiquitination/phosphorylation assay were conducted to elucidate the underlying molecular mechanisms.

RESULTS

We identified SEC63 as a new regulator of HCC cell metabolism. Upon ER stress, the phosphorylation of SEC63 at T537 by IRE1α pathway contributed to SEC63 activation. Then, the stability of ACLY was upregulated by SEC63 to increase the supply of acetyl-CoA and lipid biosynthesis, which are beneficial for improving ER capacity. Meanwhile, SEC63 also entered into nucleus for increasing nuclear acetyl-CoA production to upregulate unfolded protein response targets to improve ER homeostasis. Importantly, SEC63 coordinated with ACLY to epigenetically modulate expression of Snail1 in the nucleus. Consequently, SEC63 promoted HCC cell metastasis and these effects were reversed by ACLY inhibition. Clinically, SEC63 expression was significantly upregulated in HCC tissue specimens and was positively correlated with ACLY expression. Importantly, high expression of SEC63 predicted unfavorable prognosis of HCC patients.

CONCLUSIONS

Our findings revealed that SEC63-mediated metabolic reprogramming plays important roles in keeping ER homeostasis upon stimuli in HCC cells. Meanwhile, SEC63 coordinates with ACLY to upregulate the expression of Snail1, which further promotes HCC metastasis. Metastasis is crucial for helping cancer cells seek new settlements upon microenvironmental stimuli. Taken together, our findings highlight a cancer selective adaption to ER stress as well as reveal the potential roles of the IRE1α-SEC63-ACLY axis in HCC treatment.

A SEC61A1 variant is associated with autosomal dominant polycystic liver disease

BACKGROUND AND AIMS

Autosomal dominant polycystic liver and kidney disease is a spectrum of hereditary diseases, which display disturbed function of primary cilia leading to cyst formation. In autosomal dominant polycystic kidney disease a genetic cause can be determined in almost all cases. However, in isolated polycystic liver disease (PLD) about half of all cases remain genetically unsolved, suggesting more, so far unidentified genes to be implicated in this disease.

METHODS

Customized next-generation sequencing was used to identify the underlying pathogenesis in two related patients with PLD. A variant identified in SEC61A1 was further analysed in immortalized patients' urine sediment cells and in an epithelial cell model.

RESULTS

In both patients, a heterozygous missense change (c.706C>T/p.Arg236Cys) was found in SEC61A1, which encodes for a subunit of the translocation machinery of protein biosynthesis at the endoplasmic reticulum (ER). While kidney disease is absent in the proposita, her mother displays an atypical polycystic kidney phenotype with severe renal failure. In immortalized urine sediment cells, mutant SEC61A1 is expressed at reduced levels, resulting in decreased levels of polycystin-2 (PC2). In an epithelial cell culture model, we found the proteasomal degradation of mutant SEC61A1 to be increased, whereas its localization to the ER is not affected.

CONCLUSIONS

Our data expand the allelic and clinical spectrum for SEC61A1, adding PLD as a new and the major phenotypic trait in the family described. We further demonstrate that mutant SEC61A1 results in enhanced proteasomal degradation and impaired biosynthesis of PC2.

Deletion of kif3a in CK19 positive cells leads to primary cilia loss, biliary cell proliferation and cystic liver lesions in TAA-treated mice

BACKGROUND & AIMS

Loss of primary cilia in epithelial cells is known to cause cystic diseases of the liver and kidney. We have previously shown that during experimental and human cirrhosis that primary cilia were predominantly expressed on biliary cells in the ductular reaction. However, the role of primary cilia in the pathogenesis of the ductular reaction is not fully understood.

METHODS

Primary cilia were specifically removed in biliary epithelial cells (BECs) by the administration of tamoxifen to Kif3a^f/f;CK19^CreERT mice at week 2 of a 20-week course of TAA treatment. Biliary progenitor cells were isolated and grown as organoids from gallbladders. Cells and tissue were analysed using histology, immunohistochemistry and Western blot assays.

RESULTS

At the end of 20 weeks TAA administration, primary cilia loss in liver BECs resulted in multiple microscopic cystic lesions within an unaltered ductular reaction. These were not seen in control mice who did not receive TAA. There was no effect of biliary primary cilia loss on the development of cirrhosis. Increased cellular proliferation was seen within the cystic structures associated with a decrease in hepatocyte lobular proliferation. Loss of primary cilia within biliary organoids was initially associated with reduced cell passage survival but this inhibitory effect was diminished in later passages. ERK but not WNT signalling was enhanced in primary cilia loss-induced cystic lesions in vivo and its inhibition reduced the expansion of primary cilia deficient biliary progenitor cells in vitro.

CONCLUSIONS

TAA-treated kif3a BEC-specific knockout mice had an unaltered progression to cirrhosis, but developed cystic lesions that showed increased proliferation.

Deletion of Sox9 in the liver leads to hepatic cystogenesis in mice by transcriptionally downregulating Sec63

Hepatic cysts are found in heterogeneous disorders with different pathogeneses, of which simple hepatic cysts and polycystic liver diseases are two major types. The process of hepatic cytogenesis for these two diseases is caused by defects in remodelling of the ductal plate during biliary tract development, which is called ductal plate malformation. SOX9 is a transcription factor participating in the process of bile duct development, and thus, its dysregulation may play important roles in hepatic cystogenesis. SEC63 encodes an endoplasmic reticulum membrane protein that is mutated in human autosomal dominant polycystic liver disease. However, the transcriptional regulation of SEC63 is largely unknown. In the present study, a liver-specific Sox9 knockout (Sox9^LKO ) mouse was generated to investigate the roles and underlying mechanism of SOX9 in hepatic cystogenesis. We found that hepatic cysts began to be observed in Sox9^LKO mice at 6 months of age. The number and size of cysts increased with age in Sox9^LKO mice. In addition, the characteristics of hepatic cytogenesis, including the activation of proliferation, absence of primary cilium, and disorder of polarity in biliary epithelial cells, were detected in the livers of Sox9^LKO mice. RNAi silencing of SOX9 in human intrahepatic biliary epithelial cells (HIBEpic) resulted in increased proliferation and reduced formation of the primary cilium. Moreover, Sec63 was downregulated in primary biliary epithelial cells from Sox9^LKO mice and SEC63 in HIBEpic transfected with siSOX9. Chromatin immunoprecipitation assays and luciferase reporter assays further demonstrated that SOX9 transcriptionally regulated the expression of SEC63 in biliary epithelial cells. Importantly, the overexpression of SEC63 in HIBEpic partially reversed the effects of SOX9 depletion on the formation of primary cilia and cell proliferation. These findings highlight the biological significance of SOX9 in hepatic cytogenesis and elucidate a novel molecular mechanism underlying hepatic cytogenesis. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Genetics of polycystic liver diseases

PURPOSE OF REVIEW

This review provides an outline of the most recent insights and significant discoveries regarding the genetic mechanisms involved in polycystic liver disease.

RECENT FINDINGS

Polycystic liver disease includes a heterogeneous group of genetic disorders characterized by multiple hepatic cysts. Isolated liver cysts are caused by mutations in Protein Kinase C Substrate 80K-H (PRKCSH), SEC63, and LDL Receptor Related Protein 5 (LRP5), whereas Polycystic Kidney Disease (PKD)1, PKD2, and PKHD1 mutations cause kidney cysts often accompanied by liver cysts. Glucosidase II Alpha Subunit (GANAB) has been reported to cause both phenotypes. These mutations, together with the newly identified ones in SEC61B and Alpha-1,3-Glucosyltransferase (ALG8), can be found in ∼50% of patients with isolated polycystic liver disease. Somatic second hit-mutations are hypothesized as driving force leading to cystogenesis. Subsequently, loss of heterozygosity in the cystic tissue aggravates disease progression. All genetic mutations lead to reduced levels of functional polycystin-1. This ciliary protein is therefore considered to be the central factor in the development and severity of liver cysts.

SUMMARY

Recent advances of the genetic complexity leading to hepatic cystogenesis provide novel candidate genes and important mechanistic insights with polycystin-1 as a common denominator.

Wnt-β-catenin signalling in liver development, health and disease

The canonical Wnt-β-catenin pathway is a complex, evolutionarily conserved signalling mechanism that regulates fundamental physiological and pathological processes. Wnt-β-catenin signalling tightly controls embryogenesis, including hepatobiliary development, maturation and zonation. In the mature healthy liver, the Wnt-β-catenin pathway is mostly inactive but can become re-activated during cell renewal and/or regenerative processes, as well as in certain pathological conditions, diseases, pre-malignant conditions and cancer. In hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), the two most prevalent primary liver tumours in adults, Wnt-β-catenin signalling is frequently hyperactivated and promotes tumour growth and dissemination. A substantial proportion of liver tumours (mainly HCC and, to a lesser extent, CCA) have mutations in genes encoding key components of the Wnt-β-catenin signalling pathway. Likewise, hepatoblastoma, the most common paediatric liver cancer, is characterized by Wnt-β-catenin activation, mostly as a result of β-catenin mutations. In this Review, we discuss the most relevant molecular mechanisms of action and regulation of Wnt-β-catenin signalling in liver development and pathophysiology. Moreover, we highlight important preclinical and clinical studies and future directions in basic and clinical research.

Culture System of Bile Duct-Like Cystic Structures Derived from Human-Inducible Pluripotent Stem Cells

Inducible pluripotent stem (iPS) cells are multipotent stem cells that are produced by gene transfer of reprogramming factors to somatic cells. They are thought to be an important source of regenerative medicine because of their pluripotency and self-renewal ability. Although the liver has high regeneration ability, continuous death of hepatocytes due to chronic inflammation leads to liver cirrhosis and liver carcinoma. With regard to such serious liver diseases, liver transplantation is used as a complete cure, but there is a problem of donor shortage. Therefore, transplantation therapy using liver tissue generated from stem cells in vitro is expected.We are developing a system to induce the differentiation of cholangiocytes, one of important non-parenchymal cells in living liver tissue, from human iPS cells. Bile duct-like cystic structures can be induced by purifying human iPS cell-derived hepatoblasts expressing hepatic progenitor cell surface markers and inducing differentiation under appropriate culture conditions. These cells are considered to be useful in constructing a hepatic organoid that reproduces the liver structure of the living body.

Changes in the urinary extracellular vesicle proteome are associated with nephronophthisis-related ciliopathies

Nephronophthisis is one of the leading genetic causes of end-stage renal disease in childhood. Early diagnostics and prognostics for nephronophthisis are currently limited. We aimed to identify non-invasive protein biomarkers for nephronophthisis in urinary extracellular vesicles. Extracellular vesicles were isolated from urine of 12 patients with a nephronophthisis-related ciliopathy and 12 age- and gender-matched controls, followed by in-depth label-free LC-MS/MS proteomics analysis of gel fractionated extracellular vesicle proteins. Supervised cluster analysis of proteomic profiles separated patients from controls. We identified 156 differentially expressed proteins with fold change ≥4 in patients compared to controls (P < .05). Importantly, expression levels of discriminating proteins were correlated with chronic kidney disease stage, suggesting possible applications for urinary extracellular vesicle biomarkers in prognostics for nephronophthisis. Enrichment analysis of gene ontology terms revealed GO terms including signaling, actin cytoskeleton and endocytosis among the downregulated proteins in patients, whereas terms related to response to wounding and extracellular matrix organization were enriched among upregulated proteins. Our findings represent the first step towards a non-invasive diagnostic test for nephronophthisis. Further research is needed to determine specificity of the candidate biomarkers. In conclusion, proteomic profiles of urinary extracellular vesicles differentiate nephronophthisis-related ciliopathy patients from healthy controls. SIGNIFICANCE: Nephronophthisis is an important cause of end-stage renal disease in children and is associated with an average diagnostic delay of 3.5 years. This is the first study investigating candidate biomarkers for nephronophthisis using global proteomics analysis of urinary extracellular vesicles in patients with nephronophthisis compared to control individuals. We show that measuring protein markers in urinary extracellular vesicles is a promising approach for non-invasive early diagnostics of nephronophthisis.

CRISPR/Cascade 9-Mediated Genome Editing-Challenges and Opportunities

Clustered Regularly Interspaced Palindromic Repeats (CRISPR) and Cascade 9 (also known as Cas9, CRISPR associated protein 9) confer protection against invading viruses or plasmids. The CRISPR/Cascade 9 system constitutes one of the most powerful genome technologies available to researchers today. So far, this technology has enabled efficient genome editing and modification in several model organisms and has successfully been used in biomedicine and biomedical engineering. However, challenges for efficient and safe genetic manipulation in several organisms persist. Here, we review functional approaches and future challenges associated with the use of the CRISPR/Cascade 9 genome editing system and discuss opportunities, ethical issues and future directions within this field.