Hepatic monoamine oxidase B is involved in endogenous geranylgeranoic acid synthesis in mammalian liver cells

Abstract

Geranylgeranoic acid (GGA) originally was identified in some animals and has been developed as an agent for preventing second primary hepatoma. We previously have also identified GGA as an acyclic diterpenoid in some medicinal herbs. Recently, we reported that in human hepatoma-derived HuH-7 cells, GGA is metabolically labeled from 13C-mevalonate. Several cell-free experiments have demonstrated that GGA is synthesized through geranylgeranial by oxygen-dependent oxidation of geranylgeraniol (GGOH), but the exact biochemical events giving rise to GGA in hepatoma cells remain unclear. Monoamine oxidase B (MOAB) has been suggested to be involved in GGOH oxidation. Here, using two human hepatoma cell lines, we investigated whether MAOB contributes to GGA biosynthesis. Using either HuH-7 cell lysates or recombinant human MAOB, we found that: 1) the MAO inhibitor tranylcypromine dose-dependently downregulates endogenous GGA levels in HuH-7 cells; and 2) siRNA-mediated MAOB silencing reduces intracellular GGA levels in HuH-7 and Hep3B cells. Unexpectedly, however, CRISPR/Cas9-generated MAOB-KO human hepatoma Hep3B cells had GGA levels similar to those in MAOB-WT cells. A sensitivity of GGA levels to siRNA-mediated MAOB downregulation was recovered when the MAOB-KO cells were transfected with a MAOB-expression plasmid, suggesting that MAOB is the enzyme primarily responsible for GGOH oxidation and that some other latent metabolic pathways may maintain endogenous GGA levels in the MAOB-KO hepatoma cells. Along with the previous findings, these results provide critical insights into the biological roles of human MAOB and provide evidence that hepatic MAOB is involved in endogenous GGA biosynthesis via GGOH oxidation. Geranylgeranoic acid (GGA) originally was identified in some animals and has been developed as an agent for preventing second primary hepatoma. We previously have also identified GGA as an acyclic diterpenoid in some medicinal herbs. Recently, we reported that in human hepatoma-derived HuH-7 cells, GGA is metabolically labeled from 13C-mevalonate. Several cell-free experiments have demonstrated that GGA is synthesized through geranylgeranial by oxygen-dependent oxidation of geranylgeraniol (GGOH), but the exact biochemical events giving rise to GGA in hepatoma cells remain unclear. Monoamine oxidase B (MOAB) has been suggested to be involved in GGOH oxidation. Here, using two human hepatoma cell lines, we investigated whether MAOB contributes to GGA biosynthesis. Using either HuH-7 cell lysates or recombinant human MAOB, we found that: 1) the MAO inhibitor tranylcypromine dose-dependently downregulates endogenous GGA levels in HuH-7 cells; and 2) siRNA-mediated MAOB silencing reduces intracellular GGA levels in HuH-7 and Hep3B cells. Unexpectedly, however, CRISPR/Cas9-generated MAOB-KO human hepatoma Hep3B cells had GGA levels similar to those in MAOB-WT cells. A sensitivity of GGA levels to siRNA-mediated MAOB downregulation was recovered when the MAOB-KO cells were transfected with a MAOB-expression plasmid, suggesting that MAOB is the enzyme primarily responsible for GGOH oxidation and that some other latent metabolic pathways may maintain endogenous GGA levels in the MAOB-KO hepatoma cells. Along with the previous findings, these results provide critical insights into the biological roles of human MAOB and provide evidence that hepatic MAOB is involved in endogenous GGA biosynthesis via GGOH oxidation. alcohol dehydrogenase cytochrome P450 farnesal farnesol farnesyl diphosphate geranial geranylgeranoic acid geranylgeranial geranylgeraniol geranylgeranyl diphosphate geranylgeranyl pyrophosphatase geraniol monoamine oxidase mevalonate prenylcysteine oxidase 1 tranylcypromine zaragozic acid A Geranylgeranoic acid (all-trans 3,7,11,15-tetramethyl-2,6,10,14-hexadecatetraenoic acid or GGA), first recognized as a mevalonate (MVA)-derived metabolite in cell-free homogenates of the bovine retina in 1983 (1Fliesler S.J. Schroepfer G.J. Metabolism of mevalonic acid in cell-free homogenates of bovine retinas. Formation of novel isoprenoid acids.J. Biol. Chem. 1983; 258: 15062-15070Abstract Full Text PDF PubMed Google Scholar) and then in a parasitic worm in 1993 (2Foster J.M. Pennock J.F. Marshall I. Rees H.H. Biosynthesis of isoprenoid compounds in Schistosoma mansoni.Mol. Biochem. Parasitol. 1993; 61: 275-284Crossref PubMed Scopus (21) Google Scholar), is a compound consisting of 4-isoprene units linked in a tail-to-head manner. GGA and its didehydro derivative were shown to be potent ligands for nuclear retinoid receptors (3Araki H. Shidoji Y. Yamada Y. Moriwaki H. Muto Y. Retinoid agonist activities of synthetic geranyl geranoic acid derivatives.Biochem. Biophys. Res. Commun. 1995; 209: 66-72Crossref PubMed Scopus (77) Google Scholar), so these isoprenoid compounds have been developed as preventive agents against second primary hepatoma (4Muto Y. Moriwaki H. Ninomiya M. Adachi S. Saito A. Takasaki K.T. Tanaka T. Tsurumi K. Okuno M. Tomita E. et al.Prevention of second primary tumors by an acyclic retinoid, polyprenoic acid, in patients with hepatocellular carcinoma. Hepatoma Prevention Study Group.N. Engl. J. Med. 1996; 334: 1561-1567Crossref PubMed Google Scholar, 5Muto Y. Moriwaki H. Saito A. Prevention of second primary tumors by an acyclic retinoid in patients with hepatocellular carcinoma.N. Engl. J. Med. 1999; 340: 1046-1047Crossref PubMed Scopus (240) Google Scholar). In the past, we reported that GGA is a natural compound present in some medicinal herbs (6Shidoji Y. Ogawa H. Natural occurrence of cancer-preventive geranylgeranoic acid in medicinal herbs.J. Lipid Res. 2004; 45: 1092-1103Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). Recently, we found that GGA is not only present in plant tissues but is also endogenously present in various organs of male Wistar rats. Its biosynthesis from MVA via farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP) is also confirmed in human hepatoma-derived cells (7Shidoji Y. Tabata Y. Unequivocal evidence for endogenous geranylgeranoic acid biosynthesized from mevalonate in mammalian cells.J. Lipid Res. 2019; 60: 579-593Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar). A previous study reported that GGPP added in rat liver homogenates is converted to geranylgeraniol (GGOH) by geranylgeranyl pyrophosphatase (GGPPase), which is most active at physiologic pH and highly specific for GGPP (8Bansal V.S. Vaidya S. Characterization of two distinct allyl pyrophosphatase activities from rat liver microsomes.Arch. Biochem. Biophys. 1994; 315: 393-399Crossref PubMed Scopus (57) Google Scholar). GGOH produced by GGPPase had been thought to be oxidized to geranylgeranial (GGal) by cytosolic alcohol dehydrogenase (ADH) in the presence of NAD+ (9Endo S. Matsunaga T. Ohta C. Soda M. Kanamori A. Kitade Y. Ohno S. Tajima K. El-Kabbani O. Hara A. Roles of rat and human aldo–keto reductases in metabolism of farnesol and geranylgeraniol.Chem. Biol. Interact. 2011; 191: 261-268Crossref PubMed Scopus (46) Google Scholar), and GGal had been supposed to be further oxidized to GGA by nonspecific aldehyde dehydrogenase (9Endo S. Matsunaga T. Ohta C. Soda M. Kanamori A. Kitade Y. Ohno S. Tajima K. El-Kabbani O. Hara A. Roles of rat and human aldo–keto reductases in metabolism of farnesol and geranylgeraniol.Chem. Biol. Interact. 2011; 191: 261-268Crossref PubMed Scopus (46) Google Scholar). Indeed, we have confirmed that the enzymatic conversion from GGal to GGA is highly dependent on exogenous NAD+ in rat liver homogenates (10Muraguchi T. Okamoto K. Mitake M. Ogawa H. Shidoji Y. Polished rice as natural of geranylgeranoic Biochem. 2011; PubMed Scopus Google Scholar) and human hepatoma-derived HuH-7 cell lysates M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar). we found that a enzyme in either rat liver or HuH-7 cells involved in the oxidation of GGOH to GGal not exogenous NAD+ in the cell-free (10Muraguchi T. Okamoto K. Mitake M. Ogawa H. Shidoji Y. Polished rice as natural of geranylgeranoic Biochem. 2011; PubMed Scopus Google Scholar, M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar). GGOH oxidation was in the from rat liver homogenates (10Muraguchi T. Okamoto K. Mitake M. Ogawa H. Shidoji Y. Polished rice as natural of geranylgeranoic Biochem. 2011; PubMed Scopus Google Scholar). that the enzyme was to tranylcypromine an inhibitor against monoamine M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar), we have that a of the MAO is involved in GGOH oxidation to GGal in the of GGA biosynthesis (10Muraguchi T. Okamoto K. Mitake M. Ogawa H. Shidoji Y. Polished rice as natural of geranylgeranoic Biochem. 2011; PubMed Scopus Google Scholar, M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar). We so have the of evidence for MAOB as a 1) HuH-7 cell or rat liver enzyme not the exogenous NAD+ to 2) in the is of GGOH into HuH-7 cell lysates as an enzyme and the recombinant human MAOB GGOH to GGal M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar). MAOB, a enzyme to the and in the C. K. of MAO Google Scholar). these oxidized by MAOB, is and as an in the of MAOB in the is to the to the produced T. J. of monoamine oxidase B in 2019; PubMed Scopus Google Scholar). In the of MAOB is in and J. J.M. M. J. monoamine oxidase in of by enzyme 1994; PubMed Scopus Google Scholar, S.J. S. in a of to Res. PubMed Scopus Google Scholar), and MAOB have been investigated as for these M. of monoamine oxidase and for the of Med. Chem. PubMed Scopus (46) Google Scholar, M. of monoamine oxidase in from to 2019; PubMed Scopus Google Scholar). In to the MAOB in the the of MAOB in the liver is not the levels of MAOB not only those in the but also human organs C. J. M. S. A. K. et of the human by of and Full Text Full Text PDF PubMed Scopus Google Scholar). the liver MAOB enzyme is to to the of the liver is a that contributes to and MAOB for H. and of the monoamine oxidase 2011; PubMed Scopus Google Scholar). In the of liver MAOB has not been we that GGOH is an endogenous of hepatic MAOB, as we a on the of hepatic using an MAO inhibitor and to and the MAOB enzyme we that hepatic MAOB is involved in the of the intracellular GGA in human hepatoma-derived cells. that MAOB is involved in GGA biosynthesis we of the MAOB using the in human hepatoma cells, the intracellular GGA of cells was the as that of the cells. when the MAOB-KO cells were with MAOB plasmid, MAOB siRNA-mediated downregulation of the endogenous GGA was In other when MAOB is in human the intracellular of GGA is dependent on MAOB that other MAOB in MAOB-KO cells involved in the intracellular GGA is also GGA and were by and GGOH was by farnesol geraniol and and for cell and were from and were from was from was from acid A an inhibitor of was from other those were of hepatoma-derived HuH-7 and Hep3B cells were with at in a of HuH-7 cells in a were and in for the was with 1 of the cells with of or with of of the cells were using a cell and the GGA was using as of on the endogenous GGA levels was using for for the MAOB, and prenylcysteine oxidase 1 were from of to the of specific HuH-7 cells or Hep3B cells were on at a of the of were transfected using a was from cells to the levels of were for an in and for of intracellular In HuH-7 cells were with MAOB for the cells were for in the GGOH or HuH-7 or Hep3B cells in a were transfected with 1 of MAOB and 1 of an with but HuH-7 cell were by on a and a of MAOB using the and MAOB using the were confirmed in these cells. cells in a were transfected with 1 of human MAOB an with of MAOB using the and MAOB using the were confirmed in cells. was from cell using the was to the was using on a levels were using the and in study in were from the cells with and the were by of were by and were with an or a sensitivity using an GGOH or were with of active in of at for was at for to aldehyde were a and in and by with a was at a of aldehyde was and in synthesized aldehyde was by its at with as a and further for as a for of or were at with the recombinant human MAOB in a of of was then by on and the was with of was through a to the of farnesal and geranial by for was using HuH-7 or Hep3B cells and the were in by the the cell were added to cell and on at and the was to a and to a were with of and through a to GGA was by the in previous study (7Shidoji Y. Tabata Y. Unequivocal evidence for endogenous geranylgeranoic acid biosynthesized from mevalonate in mammalian cells.J. Lipid Res. 2019; 60: 579-593Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar). to GGOH and GGal was by A and B was at a of as a from B to a from B to specific of the and and cell for compound in were the as the previous (7Shidoji Y. Tabata Y. Unequivocal evidence for endogenous geranylgeranoic acid biosynthesized from mevalonate in mammalian cells.J. Lipid Res. 2019; 60: 579-593Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar). were using a or with as with a as we confirmed whether an inhibitor of as a inhibitor of GGA biosynthesis in a cell that added in the the of endogenous GGA in HuH-7 cells in a with an of not only the endogenous GGA but also the conversion of added GGOH to GGA in HuH-7 cells the of endogenous GGA and exogenous GGA in HuH-7 cells, we a that some other as and cytochrome P450 involved in the biosynthesis of we of the MAOB in HuH-7 cells using MAOB MAOB levels in HuH-7 cells transfected with MAOB were the by a in endogenous GGA at shown in a in the intracellular GGA by the exogenous GGOH was by MAOB In MAOB the inhibitor of endogenous GGA the shown in to the (9Endo S. Matsunaga T. Ohta C. Soda M. Kanamori A. Kitade Y. Ohno S. Tajima K. El-Kabbani O. Hara A. Roles of rat and human aldo–keto reductases in metabolism of farnesol and geranylgeraniol.Chem. Biol. Interact. 2011; 191: 261-268Crossref PubMed Scopus (46) Google Scholar, M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar, prenylcysteine is a Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Lipid metabolism of Lipid Res. Full Text Full Text PDF PubMed Scopus Google Scholar), and that a of GGA we these and then the of endogenous GGA in the of or with the levels of endogenous GGA in HuH-7 cells were not in the and cells in the cells at which is in to the of the MAOB the of MAOB in cell was the MAOB was by the intracellular levels of endogenous GGA were against MAOB levels in these cells, a was endogenous GGA and MAOB levels the results so in the present study that the MAOB enzyme is involved in GGA we to whether recombinant human MAOB is to the oxidation of acyclic by the from to to the a MAOB had to but produced from and GGal from GGOH using of GGOH or as a was shown in a that GGOH to GGal and the of the recombinant human MAOB was to be for which is in the of those of rat hepatic (10Muraguchi T. Okamoto K. Mitake M. Ogawa H. Shidoji Y. Polished rice as natural of geranylgeranoic Biochem. 2011; PubMed Scopus Google Scholar) and human hepatoma GGOH oxidase M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar). also demonstrated that the was for which is an inhibitor that MAOB C. A. M. A. of as a for the of human monoamine oxidase B by specific Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, and of a monoamine oxidase B inhibitor from Med. Chem. PubMed Scopus (46) Google Scholar, Y. A. Monoamine oxidase from as for of PubMed Scopus Google Scholar). the of the recombinant was in the enzyme was to be for and for GGOH that the be for GGOH for the we were that MAOB is at involved in GGA biosynthesis in HuH-7 cells. the experiments so we to of endogenous GGA in human hepatoma cells by MAOB-KO cell using the MAOB-KO cells not be in HuH-7 cells by human hepatoma-derived cell which not in the was the MAOB is on the A of Hep3B was and MAOB at the and levels the endogenous GGA of the cells not at with the Hep3B cells the that a MAOB of the endogenous GGA in HuH-7 cells was to its we further experiments using the MAOB in and MAOB a in MAOB levels by a in the intracellular GGA also in the MAOB not further the MAOB that was in the cells a in endogenous GGA of suggesting that the MAOB of endogenous GGA was not to its in HuH-7 and Hep3B cells. to that a metabolic of GGA biosynthesis by other was in the cells, we further experiments using of some in that may GGal in and for other involved in GGA of not in endogenous GGA either in or to the MAOB is linked to metabolic of the intracellular of endogenous cells were by with the MAOB of the MAOB into the cells the MAOB in the cells to the of the cells in with the MAOB levels of the MAOB in cells with the MAOB the of the MAOB as as the endogenous GGA the of cells of which MAOB reduces intracellular GGA the cells were to the as cells by of the MAOB into the cells as in In the present we provide evidence that hepatic MAOB is involved in the biosynthesis of which is to of MAOB by either MAO inhibitor or MAOB endogenous GGA levels in human hepatoma cells. the of intracellular GGA was not in MAOB-KO cells with MAOB-WT cells. of the MAOB into cells the MAOB siRNA-mediated of endogenous suggesting that the MAOB is the enzyme primarily responsible for of the endogenous GGA in human hepatoma cells. in the we reported rat endogenous GGA is in the liver in human hepatoma-derived cells, its biosynthesis from MVA via and GGPP was confirmed by (7Shidoji Y. Tabata Y. Unequivocal evidence for endogenous geranylgeranoic acid biosynthesized from mevalonate in mammalian cells.J. Lipid Res. 2019; 60: 579-593Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar). at the of GGA GGA was synthesized as a preventive for second primary hepatoma with or which was in with results (4Muto Y. Moriwaki H. Ninomiya M. Adachi S. Saito A. Takasaki K.T. Tanaka T. Tsurumi K. Okuno M. Tomita E. et al.Prevention of second primary tumors by an acyclic retinoid, polyprenoic acid, in patients with hepatocellular carcinoma. Hepatoma Prevention Study Group.N. Engl. J. Med. 1996; 334: 1561-1567Crossref PubMed Google Scholar, 5Muto Y. Moriwaki H. Saito A. Prevention of second primary tumors by an acyclic retinoid in patients with hepatocellular carcinoma.N. Engl. J. Med. 1999; 340: 1046-1047Crossref PubMed Scopus (240) Google Scholar, K. O. Tanaka K. S. Moriwaki H. K. Y. K. K. et of hepatocellular a PubMed Scopus Google Scholar, K. K. Y. K. M. K. S. S. et of patients with hepatocellular with an acyclic retinoid, the of a PubMed Scopus Google Scholar). we reported the natural occurrence of GGA in medicinal herbs (6Shidoji Y. Ogawa H. Natural occurrence of cancer-preventive geranylgeranoic acid in medicinal herbs.J. Lipid Res. 2004; 45: 1092-1103Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). In we reported that endogenous GGA be metabolically labeled from via in the MVA in mammalian cells (7Shidoji Y. Tabata Y. Unequivocal evidence for endogenous geranylgeranoic acid biosynthesized from mevalonate in mammalian cells.J. Lipid Res. 2019; 60: 579-593Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar). GGPP was reported to be converted to GGOH by GGPPase in rat liver (8Bansal V.S. Vaidya S. Characterization of two distinct allyl pyrophosphatase activities from rat liver microsomes.Arch. Biochem. Biophys. 1994; 315: 393-399Crossref PubMed Scopus (57) Google Scholar). GGOH was first reported to be oxidized by (9Endo S. Matsunaga T. Ohta C. Soda M. Kanamori A. Kitade Y. Ohno S. Tajima K. El-Kabbani O. Hara A. Roles of rat and human aldo–keto reductases in metabolism of farnesol and geranylgeraniol.Chem. Biol. Interact. 2011; 191: 261-268Crossref PubMed Scopus (46) Google Scholar), we have of evidence for the that MAOB may the oxidation of GGOH to GGal (10Muraguchi T. Okamoto K. Mitake M. Ogawa H. Shidoji Y. Polished rice as natural of geranylgeranoic Biochem. 2011; PubMed Scopus Google Scholar, M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar). we that MAOB be involved in the oxidation of a acyclic is that a acyclic in has been identified as a inhibitor against MAOB C. A. M. A. of as a for the of human monoamine oxidase B by specific Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, and of a monoamine oxidase B inhibitor from Med. Chem. PubMed Scopus (46) Google Scholar, Y. A. Monoamine oxidase from as for of PubMed Scopus Google Scholar). that is into the of MAOB and is to the and these that the is as a these provide for the C. A. M. A. of as a for the of human monoamine oxidase B by specific Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, we that GGOH is so that a the of GGOH and the of the in the of MAOB is the which is a the of the and the of the in to a the of GGOH to be oxidized and converted to GGal by the C. A. M. A. of as a for the of human monoamine oxidase B by specific Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). We have previously reported that the recombinant oxidized GGOH to GGal and the was by an inhibitor of and the was with of HuH-7 cells as enzyme M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar). In we to that MAOB enzyme is involved in the oxidation from GGOH to GGal using cell We first to whether of the MAO inhibitor the GGA in a in the downregulation of the endogenous GGA in HuH-7 cells with an of the GGA was not by at and at the in the GGA we supposed that some of endogenous GGA was produced by other of the of was to be which is in the of the of for MAOB enzyme H. J. J. et specific 1 J. Med. Chem. PubMed Scopus (21) Google Scholar). is that a similar of the GGA from exogenous GGOH the results that involved in the oxidation of GGOH to GGal to the but we that the enzyme is in to MAOB, H. J. J. et specific 1 J. Med. Chem. PubMed Scopus (21) Google Scholar), O. In of cytochrome P450 in human liver by a potent and its Google Scholar), and O. In of cytochrome P450 in human liver by a potent and its Google Scholar). evidence that the MAOB is responsible for of the GGA in HuH-7 cells. In other MAOB siRNA-mediated downregulation an of not only the endogenous GGA but also the intracellular GGA levels by either or exogenous GGOH suggesting that the of the GGA was produced through a we that a of GGA in the cells the downregulation of the MAOB In the (9Endo S. Matsunaga T. Ohta C. Soda M. Kanamori A. Kitade Y. Ohno S. Tajima K. El-Kabbani O. Hara A. Roles of rat and human aldo–keto reductases in metabolism of farnesol and geranylgeraniol.Chem. Biol. Interact. 2011; 191: 261-268Crossref PubMed Scopus (46) Google Scholar, M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar, prenylcysteine is a Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Lipid metabolism of Lipid Res. Full Text Full Text PDF PubMed Scopus Google Scholar), other MAOB reported to be to GGal however, of these not the intracellular GGA that of the and the GGA we were to the downregulation of is linked to the of the GGA at present we the downregulation of the in the of MAOB the levels of endogenous GGA with the levels of the MAOB in cells We that MAOB is a enzyme responsible for biosynthesis of GGA in human hepatoma cells. Using we confirmed previous that recombinant human MAOB is active in GGOH to GGal M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar). In the present we provide evidence that MAOB the oxidation of acyclic by that is an in to was not oxidized to that recombinant human not GGOH M. Shidoji Y. oxidase involved in of geranylgeranoic acid in human hepatoma Res. PubMed Scopus (7) Google Scholar) and the of the recombinant enzyme was to be for GGOH for we that the recombinant and GGOH as a specific and the oxidation for other acyclic we have not to as for a we the MAOB in the hepatoma cell and to the intracellular but we to using the MAOB-KO Hep3B cells by the the and levels of the MAOB as the of endogenous GGA in cells was not which is with the of the endogenous GGA in HuH-7 cells. we and 1) Hep3B cells may endogenous GGA using other MAOB, which is from HuH-7 cells. 2) in the endogenous GGA in HuH-7 cells by MAOB may be to an the MAOB is other may be to for the of MAOB and may maintain the GGA in cells. the the first was MAOB the intracellular GGA in to the as in HuH-7 cells. cells not the of intracellular that other the MAOB of the MAOB in the present study to the second to the we the other and or the in cells, but we found in the GGA of the cells a for the GGA in the cells has not been but of the on the that a In the as to whether MAOB was for GGA biosynthesis to and whether MAOB or a is in GGA biosynthesis. these we of the MAOB into cells to cells. a cells in the intracellular GGA with either Hep3B cells or MAOB-KO cells, the MAOB siRNA-mediated of the MAOB intracellular GGA levels in the of the MAOB the cells from MAOB of endogenous GGA these we that a metabolic is a primary for the GGA in human hepatoma cells. was not to a enzyme in is to in the to GGA biosynthesis. enzyme in the MAOB-KO cells, the of a at the of endogenous GGA in the MAOB-KO cells that GGA is an metabolite that has a for cell other cell in cells. Indeed, we biological of GGA from its in cells; that with GGA and the in Y. S. Shidoji Y. with geranylgeranoic acid and in Scholar) and and of A or a for to a to Scholar). the in the Hep3B cell but to the MAOB in the HuH-7 cell for the MAOB, of is an HuH-7 and Hep3B cell MAOB to a of the and a Hep3B cell a A study on human hepatocellular by PubMed Scopus Google Scholar, S. C. by in the of hepatocellular J. Med. Scholar), in HuH-7 cells, derivative reported derivative may for the to the MAOB in HuH-7 cells. we a oxidation of GGOH may be the these two cell and the enzyme may in In we that MAOB is involved in GGA biosynthesis through oxidation of GGOH in human hepatoma cells. has been that MAOB is involved in the of in the and of A for PubMed Scopus Google Scholar), and in the is to in the of in its present study that hepatic MAOB has a metabolic that has not been reported so is in the biosynthesis of a active isoprenoid we with that hepatic MAOB is also a GGOH a in the of the MAOB with HuH-7 cells. also to for the of GGOH oxidation. with

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