Isomeric lipid signatures reveal compartmentalized fatty acid metabolism in cancer

The cellular energy and biomass demands of cancer drive a complex dynamic between uptake of extracellular FAs and their de novo synthesis. Given that oxidation of de novo synthesized FAs for energy would result in net-energy loss, there is an implication that FAs from these two sources must have distinct metabolic fates; however, hitherto, all FAs have been considered part of a common pool. To probe potential metabolic partitioning of cellular FAs, cancer cells were supplemented with stable isotope-labeled FAs. Structural analysis of the resulting glycerophospholipids revealed that labeled FAs from uptake were largely incorporated to canonical (sn-) positions on the glycerol backbone. Surprisingly, labeled FA uptake also disrupted canonical isomer patterns of the unlabeled lipidome and induced repartitioning of n-3 and n-6 PUFAs into glycerophospholipid classes. These structural changes support the existence of differences in the metabolic fates of FAs derived from uptake or de novo sources and demonstrate unique signaling and remodeling behaviors usually hidden from conventional lipidomics.     

Quantification and Proteomic Characterization of β-Hydroxybutyrylation Modification in the Hearts of AMPKα2 Knockout Mice

AMP-activated protein kinase alpha 2 (AMPKα2) regulates energy metabolism, protein synthesis, and glucolipid metabolism myocardial cells. Ketone bodies produced by fatty acid β-oxidation, especially β-hydroxybutyrate, are fatty energy–supplying substances for the heart, brain, and other organs during fasting and long-term exercise. They also regulate metabolic signaling for multiple cellular functions. Lysine β-hydroxybutyrylation (Kbhb) is a β-hydroxybutyrate–mediated protein posttranslational modification. Histone Kbhb has been identified in yeast, mouse, and human cells. However, whether AMPK regulates protein Kbhb is yet unclear. Hence, the present study explored the changes in proteomics and Kbhb modification omics in the hearts of AMPKα2 knockout mice using a comprehensive quantitative proteomic analysis. Based on mass spectrometry (LC-MS/MS) analysis, the number of 1181 Kbhb modified sites in 455 proteins were quantified between AMPKα2 knockout mice and wildtype mice; 244 Kbhb sites in 142 proteins decreased or increased after AMPKα2 knockout (fold change >1.5 or <1/1.5, p < 0.05). The regulation of Kbhb sites in 26 key enzymes of fatty acid degradation and tricarboxylic acid cycle was noted in AMPKα2 knockout mouse cardiomyocytes. These findings, for the first time, identified proteomic features and Kbhb modification of cardiomyocytes after AMPKα2 knockout, suggesting that AMPKα2 regulates energy metabolism by modifying protein Kbhb.     

DNA-PKcs is activated under nutrient starvation and activates Akt,MST1, FoxO3a,and NDR1

BackgroundPresence of unperfused regions containing cells under hypoxia and nutrient starvation; contributes to radioresistance in solid human tumors. We have previously reported that cultured cells; under nutrient starvation show resistance to ionizing radiation compare with cells under normal; condition, and that nutrient starvation increases ATM activity, which causes cellular resistance to; ionizing radiation (Murata et al., BBRC2018). For further investigation of molecular mechanisms; underlying radioresistance of cells under nutrient starvation, effects of nutrient starvation on activity; of DNA-PKcs have been investigated because both DNA-PKcs and ATM belong to the PIKK family; and are required for DNA DSBs repair. In addition to DNA-PKcs, effects of nutrient starvation on; activities of FoxO3a and its regulators Akt, MST1 and AMPK have been investigated because FoxO3a; mediates cellular responses to stress and is activated under nutrient starvation.MethodsA human glioblastoma cell line, T98G was used to examine the effects of nutrient starvation on activities and expression of DNA-PKcs, Akt, MST1, FoxO3a, NDR1, and AMPK. To elucidate; signal transduction pathways for FoxO3a activation under nutrient starvation, we examined effects of; specific inhibitors or siRNA for DNA-PKcs or Akt on activities and expression of MST1, FoxO3, NDR1, andAMPK.ResultsUnder nutrient starvation, phosphorylations of DNA-PKcs at Ser2056, Akt at Ser473, MST at Thr183, FoxO3a at Ser413, NDR1 at Ser281 and Thr282, and AMPK at Thr172 were increased, which suggests their activation. Nutrient starvation did not affect expression of DNA-PKcs, Akt, MST1, or NDR1, with decreased expression of FoxO3a and increased expression of AMPK. Inhibition; of DNA-PK suppressed phosphorylation of Akt under nutrient starvation. Inhibition of DNA-PK or; Akt suppressed phosphorylations of MST1, FoxO3a, and NDR1 under nutrient starvation, which; suggests DNA-PKcs and Akt activate MST1, FoxO3a, and NDR1. Inhibition of DNA-PK did not; suppress phosphorylation ofAMPK under nutrient starvation.ConclusionOur data suggest that DN-PKcs is activated under nutrient starvation and activates AktMST1, FoxO3a, and NDR1.     

1-Deoxysphinganine initiates adaptive responses to serine and glycine starvation in cancer cells via proteolysis of sphingosine kinase

Cancer cells may depend on exogenous serine, depletion of which results in slower growth and activation of adaptive metabolic changes. We previously demonstrated that serine and glycine (SG) deprivation causes loss of sphingosine kinase 1 (SK1) in cancer cells, thereby increasing the levels of its lipid substrate, sphingosine (Sph), which mediates several adaptive biological responses. However, the signaling molecules regulating SK1 and Sph levels in response to SG deprivation have yet to be defined. Here, we identify 1-deoxysphinganine (dSA), a noncanonical sphingoid base generated in the absence of serine from the alternative condensation of alanine and palmitoyl CoA by serine palmitoyl transferase, as a proximal mediator of SG deprivation in SK1 loss and Sph level elevation upon SG deprivation in cancer cells. SG starvation increased dSA levels in vitro and in vivo and in turn induced SK1 degradation through a serine palmitoyl transferase-dependent mechanism, thereby increasing Sph levels. Addition of exogenous dSA caused a moderate increase in intracellular reactive oxygen species, which in turn decreased pyruvate kinase PKM2 activity while increasing phosphoglycerate dehydrogenase levels, and thereby promoted serine synthesis. We further showed that increased dSA induces the adaptive cellular and metabolic functions in the response of cells to decreased availability of serine likely by increasing Sph levels. Thus, we conclude that dSA functions as an initial sensor of serine loss, SK1 functions as its direct target, and Sph functions as a downstream effector of cellular and metabolic adaptations. These studies define a previously unrecognized “physiological” nontoxic function for dSA.     

In-depth Profiling and Quantification of the Lysine Acetylome in Hepatocellular Carcinoma with a Trapped Ion Mobility Mass Spectrometer

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related death worldwide with limited therapeutic options. Comprehensive investigation of protein posttranslational modifications in HCC is still limited. Lysine acetylation is one of the most common types of posttranslational modification involved in many cellular processes and plays crucial roles in the regulation of cancer. In this study, we analyzed the proteome and K-acetylome in eight pairs of HCC tumors and normal adjacent tissues using a timsTOF Pro instrument. As a result, we identified 9219 K-acetylation sites in 2625 proteins, of which 1003 sites exhibited differential acetylation levels between tumors and normal adjacent tissues. Interestingly, many novel tumor-specific K-acetylation sites were characterized, for example, filamin A (K865), filamin B (K697), and cofilin (K19), suggesting altered activities of these cytoskeleton-modulating molecules, which may contribute to tumor metastasis. In addition, we observed an overall suppression of protein K-acetylation in HCC tumors, especially for enzymes from various metabolic pathways, for example, glycolysis, tricarboxylic acid cycle, and fatty acid metabolism. Moreover, the expression of deacetylase sirtuin 2 (SIRT2) was upregulated in HCC tumors, and its role of deacetylation in HCC cells was further explored by examining the impact of SIRT2 overexpression on the proteome and K-acetylome in Huh7 HCC cells. SIRT2 overexpression reduced K-acetylation of proteins involved in a wide range of cellular processes, including energy metabolism. Furthermore, cellular assays showed that overexpression of SIRT2 in HCC cells inhibited both glycolysis and oxidative phosphorylation. Taken together, our findings provide valuable information to better understand the roles of K-acetylation in HCC and to treat this disease by correcting the aberrant acetylation patterns.     

A cancer-specific anti-podocalyxin monoclonal antibody (60-mG2a-f) exerts antitumor effects in mouse xenograft models of pancreatic carcinoma

Overexpression of podocalyxin (PODXL) is associated with progression, metastasis, and poor outcomes in several cancers. PODXL also plays an important role in the development of normal tissues. For antibody-based therapy to target PODXL-expressing cancers using monoclonal antibodies (mAbs), cancer-specificity is necessary to reduce the risk of adverse effects to normal tissues. In this study, we developed an anti-PODXL cancer-specific mAb (CasMab), named as PcMab-60 (IgM, kappa) by immunizing mice with soluble PODXL, which is overexpressed in LN229 glioblastoma cells. The PcMab-60 reacted with the PODXL-overexpressing LN229 (LN229/PODXL) cells and MIA PaCa-2 pancreatic cancer cells in flow cytometry but did not react with normal vascular endothelial cells (VECs), whereas one of non-CasMabs, PcMab-47 showed high reactivity for not only LN229/PODXL and MIA PaCa-2 cells but also VECs, indicating that PcMab-60 is a CasMab. Next, we engineered PcMab-60 into a mouse IgG_2a-type mAb, named as 60-mG_2a, to add antibody-dependent cellular cytotoxicity (ADCC). We further developed a core fucose-deficient type of 60-mG_2a, named as 60-mG_2a-f, to augment its ADCC activity. In vivo analysis revealed that 60-mG_2a-f exerted antitumor activity in MIA PaCa-2 xenograft models at a dose of 100 μg/mouse/week administered three times. These results suggested that 60-mG_2a-f could be useful for antibody-based therapy against PODXL-expressing pancreatic cancers.     

Oligodendrocyte-derived transcellular signaling regulates axonal energy metabolism

The unique morphology and functionality of central nervous system (CNS) neurons necessitate specialized mechanisms to maintain energy metabolism throughout long axons and extensive terminals. Oligodendrocytes (OLs) enwrap CNS axons with myelin sheaths in a multilamellar fashion. Apart from their well-established function in action potential propagation, OLs also provide intercellular metabolic support to axons by transferring energy metabolites and delivering exosomes consisting of proteins, lipids, and RNAs. OL-derived metabolic support is crucial for the maintenance of axonal integrity; its dysfunction has emerged as an important player in neurological disorders that are associated with axonal energy deficits and degeneration. In this review, we discuss recent advances in how these transcellular signaling pathways maintain axonal energy metabolism in health and neurological disorders.     

Multiomic Metabolic Enrichment Network Analysis Reveals Metabolite–Protein Physical Interaction Subnetworks Altered in Cancer

Metabolism is recognized as an important driver of cancer progression and other complex diseases, but global metabolite profiling remains a challenge. Protein expression profiling is often a poor proxy since existing pathway enrichment models provide an incomplete mapping between the proteome and metabolism. To overcome these gaps, we introduce multiomic metabolic enrichment network analysis (MOMENTA), an integrative multiomic data analysis framework for more accurately deducing metabolic pathway changes from proteomics data alone in a gene set analysis context by leveraging protein interaction networks to extend annotated metabolic models. We apply MOMENTA to proteomic data from diverse cancer cell lines and human tumors to demonstrate its utility at revealing variation in metabolic pathway activity across cancer types, which we verify using independent metabolomics measurements. The novel metabolic networks we uncover in breast cancer and other tumors are linked to clinical outcomes, underscoring the pathophysiological relevance of the findings.     

Discovery Proteomics Analysis Determines That Driver Oncogenes Suppress Antiviral Defense Pathways Through Reduction in Interferon-β Autocrine Stimulation

Since the discovery of oncogenes, there has been tremendous interest to understand their mechanistic basis and to develop broadly actionable therapeutics. Some of the most frequently activated oncogenes driving diverse cancers are c-MYC, EGFR, HER2, AKT, KRAS, BRAF, and MEK. Using a reductionist approach, we explored how cellular proteomes are remodeled in isogenic cell lines engineered with or without these driver oncogenes. The most striking discovery for all oncogenic models was the systematic downregulation of scores of antiviral proteins regulated by type 1 interferon. These findings extended to cancer cell lines and patient-derived xenograft models of highly refractory pancreatic cancer and osteosarcoma driven by KRAS and MYC oncogenes. The oncogenes reduced basal expression of and autocrine stimulation by type 1 interferon causing remarkable convergence on common phenotypic and functional profiles. In particular, there was dramatically lower expression of dsRNA sensors including DDX58 (RIG-I) and OAS proteins, which resulted in attenuated functional responses when the oncogenic cells were treated with the dsRNA mimetic, polyI:C, and increased susceptibility to infection with an RNA virus shown using SARS-CoV-2. Our reductionist approach provides molecular and functional insights connected to immune evasion hallmarks in cancers and suggests therapeutic opportunities.     

A novel Golgi mannosidase inhibitor: Molecular design,synthesis, enzyme inhibition,and inhibition of spheroid formation

Effective chemotherapy for solid cancers is challenging due to a limitation in permeation that prevents anticancer drugs from reaching the center of the tumor, therefore unable to limit cancer cell growth. To circumvent this issue, we planned to apply the drugs directly at the center by first collapsing the outer structure. For this, we focused on cell–cell communication (CCC) between N-glycans and proteins at the tumor cell surface. Mature N-glycans establish CCC; however, CCC is hindered when numerous immature N-glycans are present at the cell surface. Inhibition of Golgi mannosidases (GMs) results in the transport of immature N-glycans to the cell surface. This can be employed to disrupt CCC. Here, we describe the molecular design and synthesis of an improved GM inhibitor with a non-sugar mimic scaffold that was screened from a compound library. The synthesized compounds were tested for enzyme inhibition ability and inhibition of spheroid formation using cell-based methods. Most of the compounds designed and synthesized exhibited GM inhibition at the cellular level. Of those, AR524 had higher inhibitory activity than a known GM inhibitor, kifunensine. Moreover, AR524 inhibited spheroid formation of human malignant cells at low concentration (10 µM), based on the disruption of CCC by GM inhibition.     

Glutamine-Fructose-6-Phosphate Transaminase 2 (GFPT2) Is Upregulated in Breast Epithelial–Mesenchymal Transition and Responds to Oxidative Stress

Breast cancer cells that have undergone partial epithelial–mesenchymal transition (EMT) are believed to be more invasive than cells that have completed EMT. To study metabolic reprogramming in different mesenchymal states, we analyzed protein expression following EMT in the breast epithelial cell model D492 with single-shot LFQ supported by a SILAC proteomics approach. The D492 EMT cell model contains three cell lines: the epithelial D492 cells, the mesenchymal D492M cells, and a partial mesenchymal, tumorigenic variant of D492 that overexpresses the oncogene HER2. The analysis classified the D492 and D492M cells as basal-like and D492HER2 as claudin-low. Comparative analysis of D492 and D492M to tumorigenic D492HER2 differentiated metabolic markers of migration from those of invasion. Glutamine-fructose-6-phosphate transaminase 2 (GFPT2) was one of the top dysregulated enzymes in D492HER2. Gene expression analysis of the cancer genome atlas showed that GFPT2 expression was a characteristic of claudin-low breast cancer. siRNA-mediated knockdown of GFPT2 influenced the EMT marker vimentin and both cell growth and invasion in vitro and was accompanied by lowered metabolic flux through the hexosamine biosynthesis pathway (HBP). Knockdown of GFPT2 decreased cystathionine and sulfide:quinone oxidoreductase (SQOR) in the transsulfuration pathway that regulates H₂S production and mitochondrial homeostasis. Moreover, GFPT2 was within the regulation network of insulin and EGF, and its expression was regulated by reduced glutathione (GSH) and suppressed by the oxidative stress regulator GSK3-β. Our results demonstrate that GFPT2 controls growth and invasion in the D492 EMT model, is a marker for oxidative stress, and associated with poor prognosis in claudin-low breast cancer.     

Synthesis,biological evaluation and anti-proliferative mechanism of fluorine-containing proguanil derivatives

Proguanil, a member of biguanide family, has excellent anti-proliferative activities. Fluorine-containing compounds have been demonstrated to have super biological activities including enhanced binding interactions, metabolic stability, and reduced toxicity. In this study, based on the intermediate derivatization methods, we synthesized 13 new fluorine-containing proguanil derivatives, and found that 7a,7d and 8e had much lower IC₅₀ than proguanil in 5 human cancerous cell lines. The results of clonogenic and scratch wound healing assays revealed that the inhibitory effects of derivatives 7a,7d and 8e on proliferation and migration of human cancer cell lines were much better than proguanil as well. Mechanistic study based on representative derivative 7a indicated that this compound up-regulates AMPK signal pathway and downregulates mTOR/4EBP1/p70S6K. In conclusion, these new fluorine-containing derivatives show potential for the development of cancer chemotherapeutic drugs.     

Genome-wide DNA methylation profiling of stomach cancer in the ethnic population of Mizoram,North East India

Stomach cancer is the fifth most common cancer in terms of prevalence and incidence and the fourth leading cause of mortality in men and women worldwide. It is well-established that aberrant DNA methylation in cells can lead to carcinogenesis. The primary objective of our study was to investigate the aberrant DNA methylation status of genes associated with stomach cancer with a particular reference to the ethnic population of Mizoram, North East India. The site-level analysis identified 2883 CpG sites differentially methylated, representing ～922 genes. Out of which 476 Differentially Methylated Positions (DMPs) were promoter-associated, 452 DMPs were hypermethylated, and 24 were hypomethylated. The region-level analysis identified 462 Differentially Methylated Regions (DMRs) corresponding to ～320 genes, of which ～281 genes were hypermethylated and ～40 genes were hypomethylated. TCGA analysis showed that some of the genes had been previously implicated in other cancers including stomach cancer. Five hypermethylated genes were selected as candidate genes for further investigations and they have shown to be novel and could serve as candidate hypermethylation biomarkers for stomach cancer in this particular ethnic group.     

Interactome Analysis of Human Phospholipase D and Phosphatidic Acid-Associated Protein Network

Mammalian phospholipase D (PLD) enzyme family consists of six members. Among them, PLD1/2/6 catalyzes phosphatidic acid (PA) production, while PLD3/4/5 has no catalytic activities. Deregulation of the PLD-PA lipid signaling has been associated with various human diseases including cancer. However, a comprehensive analysis of the regulators and effectors for this crucial lipid metabolic pathway has not been fully achieved. Using a proteomic approach, we defined the protein interaction network for the human PLD family of enzymes and PA and revealed diverse cellular signaling events involving them. Through it, we identified PJA2 as a novel E3 ubiquitin ligase for PLD1 involved in control of the PLD1-mediated mammalian target of rapamycin signaling. Additionally, we showed that PA interacted with and positively regulated sphingosine kinase 1. Taken together, our study not only generates a rich interactome resource for further characterizing the human PLD-PA lipid signaling but also connects this important metabolic pathway with numerous biological processes.     

A glance at the emerging diagnostic biomarkers in the most prevalent genitourinary cancers

Genitourinary cancers comprise of a heterogenous group of cancers of which renal cell carcinoma, urothelial bladder carcinoma, and prostate adenocarcinoma are the most commonly encountered subtypes. A lot of research is ongoing using various strategies for exploration of novel biomarkers for genitourinary cancers. These biomarkers would not reduce the need for invasive diagnostic techniques but also could be used for early and accurate diagnosis to improve the clinical management required for the disease. Moreover, selecting the appropriate treatment regimen for the responsive patients based on these biomarkers would reduce the treatment toxicity as well as cost. Biomarkers identified using various advanced techniques like next generation sequencing and proteomics, which have been classified as immunological biomarkers, tissue-specific biomarkers and liquid biomarkers. Immunological biomarkers include markers of immunological pathways such as CTLA4, PD-1/PDl-1, tissue biomarkers include tissue specific molecules such as PSA antigen and liquid biomarkers include biomarkers detectable in urine, circulating cells etc.The purpose of this review is to provide a brief introduction to the most prevalent genitourinary malignancies, including bladder, kidney, and prostate cancers along with a major focus on the novel diagnostic biomarkers and the importance of targeting them prior to genitourinary cancers treatment. Understanding these biomarkers and their potential in diagnosis of genitourinary cancer would not help in early and accurate diagnosis as mentioned above but may also lead towards a personalized approach for better diagnosis, prognosis and specified treatment approach for an individual.     

Comparison of autophagy inducibility in various tyrosine kinase inhibitors and their enhanced cytotoxicity via inhibition of autophagy in cancer cells in combined treatment with azithromycin

Tyrosine kinase inhibitors (TKIs) induce autophagy in many types of cancer cells. We previously reported that gefitinib (GEF) and imatinib (IMA) induce autophagy in epidermal growth factor receptor (EGFR) knock-out A549 and non-BCR-ABL-expressing leukemia cell lines, respectively. This evidence suggests that TKI-induced autophagy is independent of the original target molecules. The present study compared the autophagy-inducing abilities of various TKIs, regardless of their targets, by quantitative autophagy flux assay. We established stable clones expressing the GFP-LC3-mCherry-LC3ΔG plasmid in A549, PC-9, and CAL 27 cell lines and assessed autophagy inducibility by monitoring the fluorescent ratios of GFP-LC3 to mCherry-LC3ΔG using an IncuCyte live cell imaging system during exposure to TKIs viz; GEF, osimertinib (OSI), lapatinib (LAP), lenvatinib (LEN), sorafenib (SOR), IMA, dasatinib (DAS), and tivantinib (TIV). Among these TKIs, DAS, GEF, and SOR exhibited prominent autophagy induction in A549 and PC-9 cells. In CAL 27 cells, IMA, SOR, and LEN, but not GEF, TIV, or OSI, exhibited autophagy induction. In the presence of azithromycin (AZM), which showed an inhibitory effect on autophagy flux, TKIs with prominent autophagy inducibility exhibited enhanced cytotoxicity via non-apoptotic cell death relative to effects of TKI alone. Therefore, autophagy inducibility of TKIs differed in the context of cancer cells. However, once induced, they appeared to have cytoprotective functions. Thus, blocking TKI-induced autophagy with AZM may improve the therapeutic effect of TKIs in cancer cells.     

Passive Diffusion of Ciprofloxacin and its Metalloantibiotic: A Computational and Experimental study

Fluoroquinolones (FQ) are antibiotics widely used in clinical practise, but the development of bacterial resistance to these drugs is currently a critical public health problem. In this context, ternary copper complexes of FQ (CuFQPhen) have been studied as a potential alternative. In this study, we compared the passive diffusion across the lipid bilayer of one of the most used FQ, ciprofloxacin (Cpx), and its ternary copper complex, CuCpxPhen, that has shown previous promising results regarding antibacterial activity and membrane partition. A combination of spectroscopic studies and molecular dynamics simulations were used and two different model membranes tested: one composed of anionic phospholipids, and the other composed of zwitterionic phospholipids. The obtained results showed a significantly higher membrane permeabilization activity, larger partition, and a more favourable free energy landscape for the permeation of CuCpxPhen across the membrane, when compared to Cpx. Furthermore, the computational results indicated a more favourable translocation of CuCpxPhen across the anionic membrane, when compared to the zwitterionic one, suggesting a higher specificity towards the former. These findings are important to decipher the influx mechanism of CuFQPhen in bacterial cells, which is crucial for the ultimate use of CuFQPhen complexes as an alternative to FQ to tackle multidrug-resistant bacteria.     

Isolation,purification and characterization of naturally derived Crocetin beta-d-glucosyl ester from Crocus sativus L. against breast cancer and its binding chemistry with ER-alpha/HDAC2

Saffron plant (Crocus sativus L.) is being used as a source of saffron spice and medicine to cure or prevent different types of diseases including cancers. We report the isolation, characterization of bioactive small molecule ([crocetin (β-d-glucosyl) ester] from the leaf biowastes of saffron plant of Kashmir, India. MTTC assay and Bio-autography aided approach were used to assess anti-oxidant activity and anti-cancer properties of crocin (s) against DPPH free radical and breast cancer cell line respectively. Crocetin beta-d-glucosyl ester restrained proliferation of human breast adeno-carcinoma cell model (MCF-7) without significantly affecting normal cell line (L-6). Further studies involving molecular mechanics generalized born surface area and molecular docking showed that crocetin beta-d-glucosyl ester exhibits strong affinity for estrogen receptor alpha and histone deacetylase 2 (crucial receptors involved in breast cancer signalling) as evidenced by the negative docking score and binding free energy (BFE) values. Therefore, crocetin beta-d-glucosyl ester from Crocus sativus biowastes showed antiproliferative effect possibly by inhibiting estrogen receptor alpha and HDAC2 mediated signalling cascade.     

Geranylgeranoic acid,a bioactive and endogenous fatty acid in mammals: a review

Geranylgeranoic acid (GGA) was first reported in 1983 as one of the mevalonic acid metabolites, but its biological significance was not studied for a long time. Our research on the antitumor effects of retinoids led us to GGA, one of the acyclic retinoids that induce cell death in human hepatoma-derived cell lines. We were able to demonstrate the presence of endogenous GGA in various tissues of male rats, including the liver, testis, and cerebrum, by LC-MS/MS. Furthermore, the biosynthesis of GGA from mevalonic acid in mammals including humans was confirmed by isotopomer spectral analysis using ¹³C-labeled mevalonolactone and cultured hepatoma cells, and the involvement of hepatic monoamine oxidase B in the biosynthesis of GGA was also demonstrated. The biological activity of GGA was analyzed from the retinoid (differentiation induction) and nonretinoid (cell death induction) aspects, and in particular, the nonretinoid mechanism by which GGA induces cell death in hepatoma cells was found to involve pyroptosis via ER stress responses initiated by TLR4 signaling. In addition to these effects of GGA, we also describe the in vivo effects of GGA on reproduction. In this review, based mainly on our published papers, we have shown that hepatic monoamine oxidase B is involved in the biosynthesis of GGA and that GGA induces cell death in human hepatoma-derived cell lines by noncanonical pyroptosis, one of the mechanisms of sterile inflammatory cell death.