Overexpression of promyelocytic leukemia protein and alteration of PML nuclear bodies in early stage of hepatocarcinogenesis

Deciphering roles of TRIMs as promising targets in hepatocellular carcinoma: current advances and future directions

Tripartite motif (TRIM) family is assigned to RING-finger-containing ligases harboring the largest number of proteins in E3 ubiquitin ligating enzymes. E3 ubiquitin ligases target the specific substrate for proteasomal degradation via the ubiquitin-proteasome system (UPS), which seems to be a more effective and direct strategy for tumor therapy. Recent advances have demonstrated that TRIM genes associate with the occurrence and progression of hepatocellular carcinoma (HCC). TRIMs trigger or inhibit multiple biological activities like proliferation, apoptosis, metastasis, ferroptosis and autophagy in HCC dependent on its highly conserved yet diverse structures. Remarkably, autophagy is another proteolytic pathway for intracellular protein degradation and TRIM proteins may help to delineate the interaction between the two proteolytic systems. In depth research on the precise molecular mechanisms of TRIM family will allow for targeting TRIM in HCC treatment. We also highlight several potential directions warranted further development associated with TRIM family to provide bright insight into its translational values in hepatocellular carcinoma.

The interactions between PML nuclear bodies and small and medium size DNA viruses

Promyelocytic leukemia nuclear bodies (PM NBs), often referred to as membraneless organelles, are dynamic macromolecular protein complexes composed of a PML protein core and other transient or permanent components. PML NBs have been shown to play a role in a wide variety of cellular processes. This review describes in detail the diverse and complex interactions between small and medium size DNA viruses and PML NBs that have been described to date. The PML NB components that interact with small and medium size DNA viruses include PML protein isoforms, ATRX/Daxx, Sp100, Sp110, HP1, and p53, among others. Interaction between viruses and components of these NBs can result in different outcomes, such as influencing viral genome expression and/or replication or impacting IFN-mediated or apoptotic cell responses to viral infection. We discuss how PML NB components abrogate the ability of adenoviruses or Hepatitis B virus to transcribe and/or replicate their genomes and how papillomaviruses use PML NBs and their components to promote their propagation. Interactions between polyomaviruses and PML NBs that are poorly understood but nevertheless suggest that the NBs can serve as scaffolds for viral replication or assembly are also presented. Furthermore, complex interactions between the HBx protein of hepadnaviruses and several PML NBs-associated proteins are also described. Finally, current but scarce information regarding the interactions of VP3/apoptin of the avian anellovirus with PML NBs is provided. Despite the considerable number of studies that have investigated the functions of the PML NBs in the context of viral infection, gaps in our understanding of the fine interactions between viruses and the very dynamic PML NBs remain. The complexity of the bodies is undoubtedly a great challenge that needs to be further addressed.

TRIM proteins in hepatocellular carcinoma

The tripartite motif (TRIM) protein family is a highly conserved group of E3 ligases with 77 members known in the human, most of which consist of a RING-finger domain, one or two B-box domains, and a coiled-coil domain. Generally, TRIM proteins function as E3 ligases to facilitate specific proteasomal degradation of target proteins. In addition, E3 ligase independent functions of TRIM protein were also reported. In hepatocellular carcinoma, expressions of TRIM proteins are both regulated by genetic and epigenetic mechanisms. TRIM proteins regulate multiple biological activities and signaling cascades. And TRIM proteins influence hallmarks of HCC. This review systematically demonstrates the versatile roles of TRIM proteins in HCC and helps us better understand the molecular mechanism of the development and progression of HCC.

Hepatocytes Deficient in Nuclear Envelope Protein Lamina-associated Polypeptide 1 are an Ideal Mammalian System to Study Intranuclear Lipid Droplets

Lipid droplets (LDs) are generally considered to be synthesized in the ER and utilized in the cytoplasm. However, LDs have been observed inside nuclei in some cells, although recent research on nuclear LDs has focused on cultured cell lines. To better understand nuclear LDs that occur in vivo, here we examined LDs in primary hepatocytes from mice following depletion of the nuclear envelope protein lamina-associated polypeptide 1 (LAP1). Microscopic image analysis showed that LAP1-depleted hepatocytes contain frequent nuclear LDs, which differ from cytoplasmic LDs in their associated proteins. We found type 1 nucleoplasmic reticula, which are invaginations of the inner nuclear membrane, are often associated with nuclear LDs in these hepatocytes. Furthermore, in vivo depletion of the nuclear envelope proteins lamin A and C from mouse hepatocytes led to severely abnormal nuclear morphology, but significantly fewer nuclear LDs than were observed upon depletion of LAP1. In addition, we show both high-fat diet feeding and fasting of mice increased cytoplasmic lipids in LAP1-depleted hepatocytes but reduced nuclear LDs, demonstrating a relationship of LD formation with nutritional state. Finally, depletion of microsomal triglyceride transfer protein did not change the frequency of nuclear LDs in LAP1-depleted hepatocytes, suggesting that it is not required for the biogenesis of nuclear LDs in these cells. Together, these data show that LAP1-depleted hepatocytes represent an ideal mammalian system to investigate the biogenesis of nuclear LDs and their partitioning between the nucleus and cytoplasm in response to changes in nutritional state and cellular metabolism in vivo.

The translational values of TRIM family in pan-cancers: From functions and mechanisms to clinics

Cancer is the second leading cause of human death across the world. Tripartite motif (TRIM) family, with E3 ubiquitin ligase activities in majority of its members, is reported to be involved in multiple cellular processes and signaling pathways. TRIM proteins have critical effects in the regulation of biological behaviors of cancer cells. Here, we discussed the current understanding of the molecular mechanism of TRIM proteins regulation of cancer cells. We also comprehensively reviewed published studies on TRIM family members as oncogenes or tumor suppressors in the oncogenesis, development, and progression of a variety of types of human cancers. Finally, we highlighted that certain TRIM family members are potential molecular biomarkers for cancer diagnosis and prognosis, and potential therapeutic targets.

Polymorphisms in microRNA target sites modulate risk of lymphoblastic and myeloid leukemias and affect microRNA binding

BACKGROUND

MicroRNA dysregulation is a common event in leukemia. Polymorphisms in microRNA-binding sites (miRSNPs) in target genes may alter the strength of microRNA interaction with target transcripts thereby affecting protein levels. In this study we aimed at identifying miRSNPs associated with leukemia risk and assessing impact of these miRSNPs on miRNA binding to target transcripts.

METHODS

We analyzed with specialized algorithms the 3' untranslated regions of 137 leukemia-associated genes and identified 111 putative miRSNPs, of which 10 were chosen for further investigation. We genotyped patients with acute myeloid leukemia (AML, n = 87), chronic myeloid leukemia (CML, n = 140), childhood acute lymphoblastic leukemia (ALL, n = 101) and healthy controls (n = 471). Association between SNPs and leukemia risk was calculated by estimating odds ratios in the multivariate logistic regression analysis. For miRSNPs that were associated with leukemia risk we performed luciferase reporter assays to examine whether they influence miRNA binding.

RESULTS

Here we show that variant alleles of TLX1_rs2742038 and ETV6_rs1573613 were associated with increased risk of childhood ALL (OR (95% CI) = 3.97 (1.43-11.02) and 1.9 (1.16-3.11), respectively), while PML_rs9479 was associated with decreased ALL risk (OR = 0.55 (0.36-0.86). In adult myeloid leukemias we found significant associations between the variant allele of PML_rs9479 and decreased AML risk (OR = 0.61 (0.38-0.97), and between variant alleles of IRF8_ rs10514611 and ARHGAP26_rs187729 and increased CML risk (OR = 2.4 (1.12-5.15) and 1.63 (1.07-2.47), respectively). Moreover, we observed a significant trend for an increasing ALL and CML risk with the growing number of risk genotypes with OR = 13.91 (4.38-44.11) for carriers of ≥3 risk genotypes in ALL and OR = 4.9 (1.27-18.85) for carriers of 2 risk genotypes in CML. Luciferase reporter assays revealed that the C allele of ARHGAP26_rs187729 creates an illegitimate binding site for miR-18a-3p, while the A allele of PML_rs9479 enhances binding of miR-510-5p and the C allele of ETV6_rs1573613 weakens binding of miR-34c-5p and miR-449b-5p.

CONCLUSIONS

Our study implicates that microRNA-binding site polymorphisms modulate leukemia risk by interfering with the miRNA-mediated regulation. Our findings underscore the significance of variability in 3' untranslated regions in leukemia.

Promyelocytic leukaemia protein links DNA damage response and repair to hepatitis B virus-related hepatocarcinogenesis

DNA damage response and repair pathways are important barriers to carcinogenesis. Here, we show that promyelocytic leukaemia (PML, also known as TRIM19), involved in sensing DNA damage and executing homologous recombination repair, is down-regulated in non-tumour liver cells surrounding hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC). No PML mutation or deletion was found in HBV-infected liver or HCC cells. Immunohistochemical analysis of liver biopsies from patients with breast or liver cancer and HBV reactivation after chemotherapy revealed PML up-regulation and HBV exacerbation in normal liver tissue in response to DNA damage (functional PML), PML down-regulation in HCC peritumour cells associated with high HBsAg accumulation and low HBV replication activity (suppressive PML), and heterogeneous nuclear PML expression in HCC cells that lost HBV DNA and HBsAg and were non-reactive to DNA damage (dysregulated PML). Loss of PML in HBsAg-transgenic mice promoted chromosome breaks in liver cells and accelerated the accumulation of body and liver fat and the development of a liver steatosis-dysplasia-adenoma-carcinoma sequence in an inflammation-independent and male-predominant manner, compared to PML knock-out or HBsAg-transgenic mice during the same time period. These results indicate that PML deficiency facilitates genomic instability and promotes HBsAg-related hepatocarcinogenesis, which also involves androgen and lipid metabolism. These findings uncover a novel PML link between HBV-related tumourigenesis, DNA repair, and metabolism.

Defective DNA damage response and repair in liver cells expressing hepatitis B virus surface antigen

Hepatitis B virus (HBV) is implicated in liver cancer. The aim of this study was to find out whether HBV or its components [HBV surface antigen (HBsAg), HBV core protein (HBc), and HBV X protein (HBx)] could interfere with the host DNA damage response and repair pathway. The full HBV genome or individual HBV open-reading frame (ORF) was introduced into HepG2 cells to examine the effect on host genomic stability, DNA repair efficacy in response to double-strand DNA damage, and DNA damage-induced cell death. Responses to apoptosis induction in the HBV ORF-transfected HepG2 cells were also compared with those in HBV-positive and HBV-negative human hepatocellular carcinoma (HCC) cells. In the absence of HBV replication, accumulation of HBsAg in liver cells without other HBV proteins enhanced DNA repair protein and tumor suppressor promyelocytic leukemia (PML) degradation, which resulted in resistance to apoptosis induction and deficient double-strand DNA repair. However, HBsAg-positive cells exhibited increased cell death with exposure to the poly(ADP-ribose) polymerase inhibitor that blocks single-strand DNA repair. These results indicate that suppression of PML by HBsAg disrupts cellular mechanisms that respond to double-strand DNA damage for DNA repair or apoptosis induction, which may facilitate hepatocarcinogenesis and open up a synthetic lethality strategy for HBsAg-positive HCC treatment.

The role of PML in the nervous system

The promyeloctic leukemia protein PML is a tumor suppressor that was originally identified due to its involvement in the (15;17) translocation of acute promyelocytic leukemia. While the majority of early research has focused upon the role of PML in the pathogenesis of leukemia, more recent evidence has identified important roles for PML in tissues outside the hemopoietic system, including the central nervous system (CNS). Here, we review recent literature on the role of PML in the CNS, with particular focus on the processes of neurodevelopment and neurodegeneration, and propose new lines of investigation.