Prohibitin 1 Acts As a Negative Regulator of Wingless/Integrated-Beta-Catenin Signaling in Murine Liver and Human Liver Cancer Cells

Prohibitions in the meta-inflammatory response: a review

Prohibitins are the central regulatory element of cellular homeostasis, especially by modulating the response at different levels: Nucleus, mitochondria and membranes. Their localization and interaction with various proteins, homons, transcription and nuclear factors, and mtDNA indicate the globality and complexity of their pleiotropic properties, which remain to be investigated. A more detailed deciphering of cellular metabolism in relation to prohibitins under normal conditions and in various metabolic diseases will allow us to understand the precise role of prohibitins in the signaling cascades of PI3K/Akt, Raf/MAP/ERK, STAT3, p53, and others and to fathom their mutual influence. A valuable research perspective is to investigate the role of prohibitins in the molecular and cellular interactions between the two major players in the pathogenesis of obesity-adipocytes and macrophages - that form the basis of the meta-inflammatory response. Investigating the subtle intercellular communication and molecular cascades triggered in these cells will allow us to propose new therapeutic strategies to eliminate persistent inflammation, taking into account novel molecular genetic approaches to activate/inactivate prohibitins.

Wnt/β-Catenin signaling pathway in hepatocellular carcinoma: pathogenic role and therapeutic target

Hepatocellular carcinoma (HCC) is the most common primary malignant liver tumor and one of the leading causes of cancer-related deaths worldwide. The Wnt/β-Catenin signaling pathway is a highly conserved pathway involved in several biological processes, including the improper regulation that leads to the tumorigenesis and progression of cancer. New studies have found that abnormal activation of the Wnt/β-Catenin signaling pathway is a major cause of HCC tumorigenesis, progression, and resistance to therapy. New perspectives and approaches to treating HCC will arise from understanding this pathway. This article offers a thorough analysis of the Wnt/β-Catenin signaling pathway's function and its therapeutic implications in HCC.

Hepatic prohibitin 1 and methionine adenosyltransferase α1 defend against primary and secondary liver cancer metastasis

BACKGROUND & AIMS

The liver is a common site of cancer metastasis, most commonly from colorectal cancer, and primary liver cancers that have metastasized are associated with poor outcomes. The underlying mechanisms by which the liver defends against these processes are largely unknown. Prohibitin 1 (PHB1) and methionine adenosyltransferase 1A (MAT1A) are highly expressed in the liver. They positively regulate each other and their deletion results in primary liver cancer. Here we investigated their roles in primary and secondary liver cancer metastasis.

METHODS

We identified common target genes of PHB1 and MAT1A using a metastasis array, and measured promoter activity and transcription factor binding using luciferase reporter assays and chromatin immunoprecipitation, respectively. We examined how PHB1 or MAT1A loss promotes liver cancer metastasis and whether their loss sensitizes to colorectal liver metastasis (CRLM).

RESULTS

Matrix metalloproteinase-7 (MMP-7) is a common target of MAT1A and PHB1 and its induction is responsible for increased migration and invasion when MAT1A or PHB1 is silenced. Mechanistically, PHB1 and MAT1A negatively regulate MMP7 promoter activity via an AP-1 site by repressing the MAFG-FOSB complex. Loss of MAT1A or PHB1 also increased MMP-7 in extracellular vesicles, which were internalized by colon and pancreatic cancer cells to enhance their oncogenicity. Low hepatic MAT1A or PHB1 expression sensitized to CRLM, but not if endogenous hepatic MMP-7 was knocked down first, which lowered CD4+ T cells while increasing CD8+ T cells in the tumor microenvironment. Hepatocytes co-cultured with colorectal cancer cells express less MAT1A/PHB1 but more MMP-7. Consistently, CRLM raised distant hepatocytes' MMP-7 expression in mice and humans.

CONCLUSION

We have identified a PHB1/MAT1A-MAFG/FOSB-MMP-7 axis that controls primary liver cancer metastasis and sensitization to CRLM.

IMPACT AND IMPLICATIONS

Primary and secondary liver cancer metastasis is associated with poor outcomes but whether the liver has underlying defense mechanism(s) against metastasis is unknown. Here we examined the hypothesis that hepatic prohibitin 1 (PHB1) and methionine adenosyltransferase 1A (MAT1A) cooperate to defend the liver against metastasis. Our studies found PHB1 and MAT1A form a complex that suppresses matrix metalloproteinase-7 (MMP-7) at the transcriptional level and loss of either PHB1 or MAT1A sensitizes the liver to metastasis via MMP-7 induction. Strategies that target the PHB1/MAT1A-MMP-7 axis may be a promising approach for the treatment of primary and secondary liver cancer metastasis.

Prohibitin 1 inhibits cell proliferation and induces apoptosis via the p53-mediated mitochondrial pathway in vitro

BACKGROUND

Prohibitin 1 (PHB1) has been identified as an antiproliferative protein that is highly conserved and ubiquitously expressed, and it participates in a variety of essential cellular functions, including apoptosis, cell cycle regulation, proliferation, and survival. Emerging evidence indicates that PHB1 may play an important role in the progression of hepatocellular carcinoma (HCC). However, the role of PHB1 in HCC is controversial.

AIM

To investigate the effects of PHB1 on the proliferation and apoptosis of human HCC cells and the relevant mechanisms in vitro.

METHODS

HCC patients and healthy individuals were enrolled in this study according to the inclusion and exclusion criteria; then, PHB1 levels in the sera and liver tissues of these participates were determined using ELISA, RT-PCR, and immunohistochemistry. Human HepG2 and SMMC-7721 cells were transfected with the pEGFP-PHB1 plasmid and PHB1-specific shRNA (shRNA-PHB1) for 24-72 h. Cell proliferation was analysed with an MTT assay. Cell cycle progression and apoptosis were analysed using flow cytometry (FACS). The mRNA and protein expression levels of the cell cycle-related molecules p21, Cyclin A2, Cyclin E1, and CDK2 and the cell apoptosis-related molecules cytochrome C (Cyt C), p53, Bcl-2, Bax, caspase 3, and caspase 9 were measured by real-time PCR and Western blot, respectively.

RESULTS

Decreased levels of PHB1 were found in the sera and liver tissues of HCC patients compared to those of healthy individuals, and decreased PHB1 was positively correlated with low differentiation, TNM stage III-IV, and alpha-fetoprotein ≥ 400 μg/L. Overexpression of PHB1 significantly inhibited human HCC cell proliferation in a time-dependent manner. FACS revealed that the overexpression of PHB1 arrested HCC cells in the G0/G1 phase of the cell cycle and induced apoptosis. The proportion of cells in the G0/G1 phase was significantly increased and the proportion of cells in the S phase was decreased in HepG2 cells that were transfected with pEGFP-PHB1 compared with untreated control and empty vector-transfected cells. The percentage of apoptotic HepG2 cells that were transfected with pEGFP-PHB1 was 15.41% ± 1.06%, which was significantly greater than that of apoptotic control cells (3.65% ± 0.85%, P < 0.01) and empty vector-transfected cells (4.21% ± 0.52%, P < 0.01). Similar results were obtained with SMMC-7721 cells. Furthermore, the mRNA and protein expression levels of p53, p21, Bax, caspase 3, and caspase 9 were increased while the mRNA and protein expression levels of Cyclin A2, Cyclin E1, CDK2, and Bcl-2 were decreased when PHB1 was overexpressed in human HCC cells. However, when PHB1 was upregulated in human HCC cells, Cyt C expression levels were increased in the cytosol and decreased in the mitochondria, which indicated that Cyt C had been released into the cytosol. Conversely, these effects were reversed when PHB1 was knocked down.

CONCLUSION

PHB1 inhibits human HCC cell viability by arresting the cell cycle and inducing cell apoptosis via activation of the p53-mediated mitochondrial pathway.

Subcellular distribution of prohibitin 1 in rat liver during liver regeneration and its cellular implication

BACKGROUND

The function of prohibitin 1 (Phb1) during liver regeneration (LR) remains relatively unexplored. Our previous research identified downregulation of Phb1 in rat liver mitochondria 24 h after 70% partial hepatectomy (PHx), as determined by subcellular proteomic analysis.

AIM

To investigate the potential role of Phb1 during LR.

METHODS

We examined changes in Phb1 mRNA and protein levels, subcellular distribution, and abundance in rat liver during LR following 70% PHx. We also evaluated mitochondrial changes and apoptosis using electron microscopy and flow cytometry. RNA-interference-mediated knockdown of Phb1 (PHBi) was performed in BRL-3A cells.

RESULTS

Compared with sham-operation control groups, Phb1 mRNA and protein levels in 70% PHx test groups were downregulated at 24 h, then upregulated at 72 and 168 h. Phb1 was mainly located in mitochondria, showed a reduced abundance at 24 h, significantly increased at 72 h, and almost recovered to normal at 168 h. Phb1 was also present in nuclei, with continuous increase in abundance observed 72 and 168 h after 70% PHx. The altered ultrastructure and reduced mass of mitochondria during LR had almost completely recovered to normal at 168 h. PHBi in BRL-3A cells resulted in increased S-phase entry, a higher number of apoptotic cells, and disruption of mitochondrial membrane potential.

CONCLUSION

Phb1 may contribute to maintaining mitochondrial stability and could play a role in regulating cell proliferation and apoptosis of rat liver cells during LR.

The function of prohibitins in mitochondria and the clinical potentials

Prohibitins (PHBs) are a class of highly evolutionarily conserved proteins that widely distribute in prokaryotes and eukaryotes. PHBs function in cell growth and proliferation or differentiation, regulating metabolism and signaling pathways. PHBs have different subcellular localization in eukaryotes, but they are mainly located in mitochondria. In the mitochondria, PHBs stabilize the structure of the mitochondrial membrane and regulate mitochondrial autophagy, mitochondrial dynamics, mitochondrial biogenesis and quality control, and mitochondrial unfolded protein response. PHBs has shown to be associated with many diseases, such as mitochondria diseases, cancers, infectious diseases, and so on. Some molecule targets of PHBs can interfere with the occurrence and development of diseases. Therefore, this review clarifies the functions of PHBs in mitochondria, and provides a summary of the potential values in clinics.

S-adenosylmethionine inhibits la ribonucleoprotein domain family member 1 in murine liver and human liver cancer cells

BACKGROUND AND AIMS

Methionine adenosyltransferase 1A (MAT1A) is responsible for S-adenosylmethionine (SAMe) biosynthesis in the liver. Mice lacking Mat1a have hepatic SAMe depletion and develop NASH and HCC spontaneously. Several kinases are activated in Mat1a knockout (KO) mice livers. However, characterizing the phospho-proteome and determining whether they contribute to liver pathology remain open for study. Our study aimed to provide this knowledge.

APPROACH AND RESULTS

We performed phospho-proteomics in Mat1a KO mice livers with and without SAMe treatment to identify SAMe-dependent changes that may contribute to liver pathology. Our studies used Mat1a KO mice at different ages treated with and without SAMe, cell lines, in vitro translation and kinase assays, and human liver specimens. We found that the most striking change was hyperphosphorylation and increased content of La-related protein 1 (LARP1), which, in the unphosphorylated form, negatively regulates translation of 5'-terminal oligopyrimidine (TOP)-containing mRNAs. Consistently, multiple TOP proteins are induced in KO livers. Translation of TOP mRNAs ribosomal protein S3 and ribosomal protein L18 was enhanced by LARP1 overexpression in liver cancer cells. We identified LARP1-T449 as a SAMe-sensitive phospho-site of cyclin-dependent kinase 2 (CDK2). Knocking down CDK2 lowered LARP1 phosphorylation and prevented LARP1-overexpression-mediated increase in translation. LARP1-T449 phosphorylation induced global translation, cell growth, migration, invasion, and expression of oncogenic TOP-ribosomal proteins in HCC cells. LARP1 expression is increased in human NASH and HCC.

CONCLUSIONS

Our results reveal a SAMe-sensitive mechanism of LARP1 phosphorylation that may be involved in the progression of NASH to HCC.

Nuclear partitioning of Prohibitin 1 inhibits Wnt/β-catenin-dependent intestinal tumorigenesis

The Wnt/β-catenin signaling pathway is aberrantly activated in the majority of colorectal cancer cases due to somatic mutations in the adenomatous polyposis coli (APC) gene. Prohibitin 1 (PHB1) serves pleiotropic cellular functions with dynamic subcellular trafficking facilitating signaling crosstalk between organelles. Nuclear-localized PHB1 is an important regulator of gene transcription. Using mice with inducible intestinal epithelial cell (IEC)-specific deletion of Phb1 (Phb1^iΔIEC) and mice with IEC-specific overexpression of Phb1 (Phb1Tg), we demonstrate that IEC-specific PHB1 combats intestinal tumorigenesis in the Apc^Min/+ mouse model by inhibiting Wnt/β-catenin signaling. Forced nuclear accumulation of PHB1 in human RKO or SW48 CRC cell lines increased AXIN1 expression and decreased cell viability. PHB1 deficiency in CRC cells decreased AXIN1 expression and increased β-catenin activation that was abolished by XAV939, a pharmacological AXIN stabilizer. These results define a role of PHB1 in inhibiting the Wnt/β-catenin pathway to influence the development of intestinal tumorigenesis. Induction of nuclear PHB1 trafficking provides a novel therapeutic option to influence AXIN1 expression and the β-catenin destruction complex in Wnt-driven intestinal tumorigenesis.

Prohibitin ligands: a growing armamentarium to tackle cancers, osteoporosis, inflammatory, cardiac and neurological diseases

Over the last three decades, the scaffold proteins prohibitins-1 and -2 (PHB1/2) have emerged as key signaling proteins regulating a myriad of signaling pathways in health and diseases. Small molecules targeting PHBs display promising effects against cancers, osteoporosis, inflammatory, cardiac and neurodegenerative diseases. This review provides an updated overview of the various classes of PHB ligands, with an emphasis on their mechanism of action and therapeutic potential. We also describe how these ligands have been used to explore PHB signaling in different physiological and pathological settings.

The Synthetic Small Molecule FL3 Combats Intestinal Tumorigenesis via Axin1-Mediated Inhibition of Wnt/β-Catenin Signaling

Colorectal cancer exhibits aberrant activation of Wnt/β-catenin signaling. Many inhibitors of the Wnt/β-catenin pathway have been tested for Wnt-dependent cancers including colorectal cancer, but are unsuccessful due to severe adverse reactions. FL3 is a synthetic derivative of natural products called flavaglines, which exhibit anti-inflammatory and cytoprotective properties in intestinal epithelial cells, but has not been previously tested in cell or preclinical models of intestinal tumorigenesis. In vitro studies suggest that flavaglines target prohibitin 1 (PHB1) as a ligand, but this has not been established in the intestine. PHB1 is a highly conserved protein with diverse functions that depend on its posttranslational modifications and subcellular localization. Here, we demonstrate that FL3 combats intestinal tumorigenesis in the azoxymethane-dextran sodium sulfate and Apc^Min/+ mouse models and in human colorectal cancer tumor organoids (tumoroids) by inhibiting Wnt/β-catenin signaling via induction of Axin1 expression. FL3 exhibited no change in cell viability in normal intestinal epithelial cells or human matched-normal colonoids. FL3 response was diminished in colorectal cancer cell lines and human colorectal cancer tumoroids harboring a mutation at S45 of β-catenin. PHB1 deficiency in mice or in human colorectal cancer tumoroids abolished FL3-induced expression of Axin1 and drove tumoroid death. In colorectal cancer cells, FL3 treatment blocked phosphorylation of PHB1 at Thr258, resulting in its nuclear translocation and binding to the Axin1 promoter. These results suggest that FL3 inhibits Wnt/β-catenin signaling via PHB1-dependent activation of Axin1. FL3, therefore, represents a novel compound that combats Wnt pathway-dependent cancers, such as colorectal cancer. SIGNIFICANCE: Targeting of PHB1 by FL3 provides a novel mechanism to combat Wnt-driven cancers, with limited intestinal toxicity. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/17/3519/F1.large.jpg.

Circ-IGF1R inhibits cell invasion and migration in non-small cell lung cancer

BACKGROUND

Circular RNA (circRNA) is a novel molecular marker and target candidate that is closely associated with tumor invasion and migration. The mechanism of action of hsa_circ_0005035 (circ-IGF1R) in non-small cell lung cancer remains unclear. In this study, we aimed to study the mechanism of action of circ-IGF1R in lung cancer.

METHODS

We screened circ-IGF1R, one of the most notable differential expressions, from the Gene Expression Omnibus database, GSE104854, for further research. The expression level of circ-IGF1R was examined using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) in five different lung cancer cell lines and 50 pairs of lung cancer and adjacent tissues. Wound-healing and Transwell assays were used for verifying the biological function of circ-IGF1R. The effect of overexpressing circ-IGF1R on the transcriptome of whole lung cancer cells was explored in lung cancer cell lines using RNA-seq.

RESULTS

The expression level of circ-IGF1R was notably lower in lung cancer tissues and lung cancer cell lines than in the adjacent normal tissues and cells (P < 0.0001). In addition, the expression level of circ-IGF1R was associated with larger tumors (T2/T3/T4) and lymph node metastasis (N1/ N2/N3) (P < 0.05). The overexpression of circ-IGF1R significantly inhibited the invasion and migration of the lung cancer cells. The potential network of circ-IGF1R-miR-1270-VANGL2 was preliminarily determined, and the expression patterns of miR-1270 and VANGL2 were verified in lung cancer cell lines.

CONCLUSION

Circ-IGF1R may inhibit lung cancer invasion and migration through a potential network of circ-IGF1R-miR-1270-VANGL2.

Prohibitin 1 in liver injury and cancer

Prohibitin 1 is an evolutionary conserved and ubiquitously expressed protein that exerts different biological functions depending on its subcellular localization. The role of prohibitin 1 in liver cancer is controversial as it can be pro- or anti-tumorigenic. However, most of the studies to date have described prohibitin 1 primarily as a tumor suppressor in the liver. Its deficiency sensitizes the liver to cholestatic liver injury, non-alcoholic fatty liver disease, inflammatory insults, and cancer. Liver-specific Phb1-knockout mice spontaneously develop hepatocellular carcinoma, Phb1 heterozygotes are more susceptible to develop cholangiocarcinoma, and the majority of human hepatocellular carcinomas and cholangiocarcinomas have reduced prohibitin 1 expression. Consistent with a tumor suppressive role in the liver, prohibitin 1 negatively regulates proliferation in hepatocytes and human hepatocellular carcinoma and cholangiocarcinoma cell lines, and multiple oncogenic signaling pathways are activated when prohibitin 1 is deficient. Although best known as a mitochondrial chaperone, prohibitin 1 can protect the liver by mitochondrial-independent mechanisms. This review summarizes what’s known about prohibitin 1’s role in liver pathology, with the focus on hepatoprotection and carcinogenesis.

Impact statement

This review summarizes the last decades of research on PHB1 in liver pathobiology. PHB1 is a key player for liver health as it is hepatoprotective and tumor suppressive. We highlight the importance of PHB1’s subcellular localization, post-translational modifications, and interacting proteins as major determinants of PHB1 cytoprotective function and anti-tumor activity in the liver.

Methionine adenosyltransferases in liver cancer

Methionine adenosyltransferases (MATs) are essential enzymes for life as they produce S-adenosylmethionine (SAMe), the biological methyl donor required for a plethora of reactions within the cell. Mammalian systems express two genes, MAT1A and MAT2A, which encode for MATα1 and MATα2, the catalytic subunits of the MAT isoenzymes, respectively. A third gene MAT2B, encodes a regulatory subunit known as MATβ which controls the activity of MATα2. MAT1A, which is mainly expressed in hepatocytes, maintains the differentiated state of these cells, whilst MAT2A and MAT2B are expressed in extrahepatic tissues as well as non-parenchymal cells of the liver (e.g., hepatic stellate and Kupffer cells). The biosynthesis of SAMe is impaired in patients with chronic liver disease and liver cancer due to decreased expression and inactivation of MATα1. A switch from MAT1A to MAT2A/MAT2B occurs in multiple liver diseases and during liver growth and dedifferentiation, but this change in the expression pattern of MATs results in reduced hepatic SAMe level. Decades of study have utilized the Mat1a-knockout (KO) mouse that spontaneously develops non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) to elucidate a variety of mechanisms by which MAT proteins dysregulation contributes to liver carcinogenesis. An increasing volume of work indicates that MATs have SAMe-independent functions, distinct interactomes and multiple subcellular localizations. Here we aim to provide an overview of MAT biology including genes, isoenzymes and their regulation to provide the context for understanding consequences of their dysregulation. We will highlight recent breakthroughs in the field and underscore the importance of MAT’s in liver tumorigenesis as well as their potential as targets for cancer therapy.