Phosphatidic Acid Phosphatase, a Key Enzyme in the Regulation of Lipid Synthesis

PA 2The abbreviations used are: PA, phosphatidic acid; PAP, PA phosphatase; DAG, diacylglycerol; PE, phosphatidylethanolamine; PC, phosphatidylcholine; TAG, triacylglycerol; HAD, haloacid dehalogenase; PI, phosphatidylinositol; ER, endoplasmic reticulum; UASINO, inositol-responsive upstream activating sequence; CL, cardiolipin. phosphatase (PAP 3The acronym PAP (also known as PAP1) is used to designate PA phosphatase, the enzyme that is specific for PA and that requires Mg2+ for activity (3Carman G.M. Han G.-S. Trends Biochem. Sci... 2006; 31: 694-699Google Scholar). PAP is distinct from lipid phosphate phosphatase (previously known as PAP2), the enzyme that dephosphorylates PA and other lipid phosphates (e.g., lyso-PA, DAG pyrophosphate, sphingoid base phosphates, and isoprenoid phosphates) by a catalytic mechanism that does not require Mg2+ (3Carman G.M. Han G.-S. Trends Biochem. Sci... 2006; 31: 694-699Google Scholar). The molecular and biochemical differences between PAP and lipid phosphate phosphatase enzymes are discussed elsewhere (3Carman G.M. Han G.-S. Trends Biochem. Sci... 2006; 31: 694-699Google Scholar).; 3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4) catalyzes the Mg2+-dependent dephosphorylation of PA, yielding DAG and Pi (Fig. 1) (1Brindley D.N. Prog. Lipid Res... 1984; 23: 115-133Google Scholar, 2Nanjundan M. Possmayer F. Am. J. Physiol... 2003; 284: L1-L23Google Scholar, 3Carman G.M. Han G.-S. Trends Biochem. Sci... 2006; 31: 694-699Google Scholar). In de novo lipid synthesis, the DAG generated from the PAP reaction is utilized for the synthesis of the phospholipids PE and PC via the Kennedy pathway and for the synthesis of TAG (Fig. 1) (3Carman G.M. Han G.-S. Trends Biochem. Sci... 2006; 31: 694-699Google Scholar). The enzyme substrate PA is also used for phospholipid synthesis via CDP-DAG (Fig. 1) (1Brindley D.N. Prog. Lipid Res... 1984; 23: 115-133Google Scholar, 2Nanjundan M. Possmayer F. Am. J. Physiol... 2003; 284: L1-L23Google Scholar, 3Carman G.M. Han G.-S. Trends Biochem. Sci... 2006; 31: 694-699Google Scholar). In lipid signaling, PAP generates a pool of DAG used for protein kinase C activation, and by the nature of its reaction, it attenuates the signaling functions of PA (Fig. 1) (4Exton J.H. J. Biol. Chem... 1990; 265: 1-4Google Scholar, 5Exton J.H. Biochim. Biophys. Acta.. 1994; 1212: 26-42Google Scholar, 6Testerink C. Munnik T. Trends Plant Sci... 2005; 10: 368-375Google Scholar, 7Waggoner D.W. Xu J. Singh I. Jasinska R. Zhang Q.X. Brindley D.N. Biochim. Biophys. Acta.. 1999; 1439: 299-316Google Scholar, 8Sciorra V.A. Morris A.J. Biochim. Biophys. Acta.. 2002; 1582: 45-51Google Scholar). Thus, the regulation of PAP activity may govern the pathways by which phospholipids are synthesized and control the cellular contents of important signaling lipids. Recent genetic and biochemical studies in yeast and mammalian cells have revealed key roles that PAP plays in lipid metabolism and cell physiology. The PAP reaction was first characterized in animal tissues in 1957 by Kennedy and co-workers (9Smith S.W. Weiss S.B. Kennedy E.P. J. Biol. Chem... 1957; 228: 915-922Google Scholar). Subsequent studies during the last half of the 20th century implicated PAP as an important enzyme in lipid metabolism (1Brindley D.N. Prog. Lipid Res... 1984; 23: 115-133Google Scholar, 2Nanjundan M. Possmayer F. Am. J. Physiol... 2003; 284: L1-L23Google Scholar, 10Carman G.M. Biochim. Biophys. Acta.. 1997; 1348: 45-55Google Scholar). However, studies to establish the roles of PAP in lipid metabolism and cell physiology had been hampered by the lack of genetic and molecular information on the enzyme. In fact, a gene encoding PAP was discovered only recently in 2006 from the yeast Saccharomyces cerevisiae (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar). The yeast gene (PAH1; known previously as SMP2) was identified through a reverse genetic approach from amino acid sequence information derived from a purified preparation of the enzyme (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar). The heterologous expression of PAH1 in Escherichia coli has confirmed that its protein product is a PAP enzyme with enzymological properties essentially identical to those of enzymes purified from yeast (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 12Lin Y.-P. Carman G.M. J. Biol. Chem... 1989; 264: 8641-8645Google Scholar, 13Lin Y.-P. Carman G.M. J. Biol. Chem... 1990; 265: 166-170Google Scholar, 14Wu W.-I. Lin Y.-P. Wang E. Merrill Jr., A.H. Carman G.M. J. Biol. Chem... 1993; 268: 13830-13837Google Scholar). The yeast PAH1-encoded PAP is a 95-kDa monomeric protein that migrates upon SDS-PAGE as a 124-kDa protein (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar). Smaller molecular mass forms (e.g. 91 kDa) of PAP purified from yeast (12Lin Y.-P. Carman G.M. J. Biol. Chem... 1989; 264: 8641-8645Google Scholar) appear to be proteolytic products of the enzyme (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar). PAH1-encoded PAP is associated with the cytosolic and membrane fractions of the cell, and its association with membranes is peripheral in nature (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 12Lin Y.-P. Carman G.M. J. Biol. Chem... 1989; 264: 8641-8645Google Scholar). The enzyme is specific for PA and catalyzes its dephosphorylation reaction based on a DXDX(T/V) motif within a HAD-like domain (Fig. 2) (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 12Lin Y.-P. Carman G.M. J. Biol. Chem... 1989; 264: 8641-8645Google Scholar, 15Han G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar). The identification of the yeast PAP-encoding gene has led to the revelation that mammalian lipins (encoded by Lpin1, Lpin2, and Lpin3), which have homology to yeast PAH1-encoded PAP at the N terminus (referred to as the NLIP domain) and within its HAD-like domain (Fig. 2) (16Peterfy M. Phan J. Xu P. Reue K. Nat. Genet... 2001; 27: 121-124Google Scholar), are also PAP enzymes (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 17Donkor J. Sariahmetoglu M. Dewald J. Brindley D.N. Reue K. J. Biol. Chem... 2007; 282: 3450-3457Google Scholar). Lpin1 was first identified by Reue and co-workers (16Peterfy M. Phan J. Xu P. Reue K. Nat. Genet... 2001; 27: 121-124Google Scholar) through positional cloning as the mutated gene in the fatty liver dystrophy (fld) mouse. In addition, Reue and co-workers (16Peterfy M. Phan J. Xu P. Reue K. Nat. Genet... 2001; 27: 121-124Google Scholar, 18Phan J. Reue K. Cell Metab... 2005; 1: 73-83Google Scholar) had previously established that lipin 1 is a major fat-regulating protein in mice. Loss of lipin 1 prevents normal adipose tissue development, leading to lipodystrophy and insulin resistance, whereas its overexpression leads to obesity (16Peterfy M. Phan J. Xu P. Reue K. Nat. Genet... 2001; 27: 121-124Google Scholar, 18Phan J. Reue K. Cell Metab... 2005; 1: 73-83Google Scholar). Thus, the molecular function of lipin 1 as a PAP enzyme provides a mechanistic basis for why the absence or overexpression of lipin 1 in mice has a major effect on fat metabolism (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 16Peterfy M. Phan J. Xu P. Reue K. Nat. Genet... 2001; 27: 121-124Google Scholar, 18Phan J. Reue K. Cell Metab... 2005; 1: 73-83Google Scholar). The three lipins exhibit distinct but overlapping expression patterns in many tissues (17Donkor J. Sariahmetoglu M. Dewald J. Brindley D.N. Reue K. J. Biol. Chem... 2007; 282: 3450-3457Google Scholar). That mammalian lipins 1 and 2 complement the phenotypes (see below) exhibited by yeast pah1Δ mutant cells (19Grimsey N. Han G.-S. O'Hara L. Rochford J.J. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 29166-29174Google Scholar) indicates the evolutionarily conserved functions of PAP. Insights into the roles that PAP plays in lipid metabolism and cell physiology have been gained through studies using mutants defective in the enzyme (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 15Han G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar, 20Santos-Rosa H. Leung J. Grimsey N. Peak-Chew S. Siniossoglou S. EMBO J.. 2005; 24: 1931-1941Google Scholar, 21O'Hara L. Han G.-S. Peak-Chew S. Grimsey N. Carman G.M. Siniossoglou S. J. Biol. Chem... 2006; 281: 34537-34548Google Scholar). The yeast pah1Δ mutant contains elevated levels of PA and decreased levels of DAG and TAG (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 15Han G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar). In addition, the contents of the major phospholipids PC, PE, and PI, sterol esters, and fatty acids are affected by the pah1Δ mutation (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 15Han G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar), demonstrating that PAP plays a role in the regulation of overall lipid synthesis. The effects of the pah1Δ mutation on phospholipid composition are most pronounced in exponential phase, whereas the effects on the contents of TAG and other neutral lipids are most pronounced in stationary phase (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 15Han G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar). In fact, the loss of PAP activity in stationary phase cells results in a >90% decrease in TAG content (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar). This phenotype is reminiscent of the lipodystrophy phenotype observed in the fld mouse that lacks Lpin1-encoded PAP activity (16Peterfy M. Phan J. Xu P. Reue K. Nat. Genet... 2001; 27: 121-124Google Scholar, 17Donkor J. Sariahmetoglu M. Dewald J. Brindley D.N. Reue K. J. Biol. Chem... 2007; 282: 3450-3457Google Scholar, 22Nadra K. De Preux Charles A.-S. Medard J.-J. Hendriks W.T. Han G.-S. Gres S. Carman G.M. Saulnier-Blache J.-S. Verheijen M.H.G. Chrast R. Genes Dev... 2008; 22: 1647-1661Google Scholar). The pah1Δ mutation causes the aberrant expansion of the nuclear/ER membrane and the derepression of phospholipid synthesis genes that contain a UASINO in the promoters (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 15Han G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar, 20Santos-Rosa H. Leung J. Grimsey N. Peak-Chew S. Siniossoglou S. EMBO J.. 2005; 24: 1931-1941Google Scholar). The derepression of phospholipid synthesis genes is a consequence of elevated PA content at the nuclear/ER membrane (23Carman G.M. Henry S.A. J. Biol. Chem... 2007; 282: 37293-37297Google Scholar). Along with the Scs2 protein, PA binds Opi1 at the nuclear/ER membrane and prevents its translocation into the nucleus, where it functions to repress transcription of phospholipid synthesis genes (23Carman G.M. Henry S.A. J. Biol. Chem... 2007; 282: 37293-37297Google Scholar). The membrane expansion phenotype correlates with the increased expression of phospholipid synthesis genes (20Santos-Rosa H. Leung J. Grimsey N. Peak-Chew S. Siniossoglou S. EMBO J.. 2005; 24: 1931-1941Google Scholar). However, data indicate that an increase in phospholipid synthesis alone is not sufficient for nuclear/ER membrane expansion (21O'Hara L. Han G.-S. Peak-Chew S. Grimsey N. Carman G.M. Siniossoglou S. J. Biol. Chem... 2006; 281: 34537-34548Google Scholar), suggesting a specific role of PAP activity in the maintenance of nuclear/ER membrane structure. The effect of the pah1Δ mutation on membrane structure appears to be related to an increased level of PA as opposed to a decreased level of DAG. This hypothesis is supported by the recent identification of the DGK1 gene encoding a novel CTP-dependent DAG kinase whose function counteracts the PAH1-encoded PAP activity (Fig. 1) (24Han G.-S. O'Hara L. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 20433-20442Google Scholar, 25Han G.-S. O'Hara L. Siniossoglou S. Carman G.M. J. Biol. Chem... 2008; 283: 20443-20453Google Scholar). Overexpression of DGK1 causes the accumulation of PA and the expansion of the nuclear/ER membrane as shown in the pah1Δ mutant (24Han G.-S. O'Hara L. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 20433-20442Google Scholar). The introduction of the dgk1Δ mutation into the pah1Δ mutant causes a decrease in PA content without affecting DAG content and restores normal nuclear/ER membrane structure and expression of UASINO-containing phospholipid synthesis genes (24Han G.-S. O'Hara L. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 20433-20442Google Scholar). The phenotypes associated with the pah1Δ mutation, which also include slow growth, temperature sensitivity, and respiratory deficiency (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 20Santos-Rosa H. Leung J. Grimsey N. Peak-Chew S. Siniossoglou S. EMBO J.. 2005; 24: 1931-1941Google Scholar, 26Irie K. Takase M. Araki H. Oshima Y. Genet... 1993; Scholar), are to the loss of PAP activity and not to the loss of other function associated with the PAP protein G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar). PAP enzymes with a mutation in a conserved NLIP domain or conserved catalytic motif or to complement phenotypes by the pah1Δ mutation G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar). loss of PAP lipin 1) activity in the fld mouse causes loss of fat (16Peterfy M. Phan J. Xu P. Reue K. Nat. Genet... 2001; 27: 121-124Google Scholar). In addition, mice lipin 1 exhibit peripheral that is characterized by cell and and a in K. De Preux Charles A.-S. Medard J.-J. Hendriks W.T. Han G.-S. Gres S. Carman G.M. Saulnier-Blache J.-S. Verheijen M.H.G. Chrast R. Genes Dev... 2008; 22: 1647-1661Google Scholar, J. Biol. Chem... Scholar, J. Biol. Chem... 1989; 264: Scholar). effects are through the protein kinase pathway that is by elevated levels of PA to the loss of PAP activity K. De Preux Charles A.-S. Medard J.-J. Hendriks W.T. Han G.-S. Gres S. Carman G.M. Saulnier-Blache J.-S. Verheijen M.H.G. Chrast R. Genes Dev... 2008; 22: 1647-1661Google Scholar). the level and of lipin 1 a major on the and of M. Zhang Sariahmetoglu M. K. Reue K. Brindley D.N. J. Lipid Scholar). 1 appears to have cellular as a PAP enzyme for the synthesis of lipids and as a in the regulation of lipid metabolism gene expression Jr., Cell Metab... 2006; Scholar, M. Phan J. Reue K. J. Biol. Chem... 2005; Scholar, K. Zhang P. 2008; Scholar). of the mammalian PAP enzymes is at the level of transcription (19Grimsey N. Han G.-S. O'Hara L. Rochford J.J. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 29166-29174Google Scholar, M. Phan J. Reue K. J. Biol. Chem... 2005; Scholar, N. Phan J. Jr., Reue K. 2006; Scholar, S. S. 2007; Scholar, J. H. Reue K. J. Metab... 2007; Scholar, Sariahmetoglu M. J. M. Reue K. R. Brindley D.N. J. Lipid Res... 2008; Scholar, P. L. Brindley D.N. Reue K. J. Lipid Res... 2008; Scholar). Lpin1 expression is during (19Grimsey N. Han G.-S. O'Hara L. Rochford J.J. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 29166-29174Google Scholar, M. Phan J. Reue K. J. Biol. Chem... 2005; Scholar) and in cells that P. R. C. M. Wang J. C. S. J. Biol. Chem... 2007; 282: Scholar, R. H. M. S. J. Biol. Chem... 2007; 282: Scholar). The of Lpin1 during is by and regulation is by a within the Sariahmetoglu M. J. M. Reue K. R. Brindley D.N. J. Lipid Res... 2008; Scholar, P. L. Brindley D.N. Reue K. J. Lipid Res... 2008; Scholar). expression is during that lipins 1 and 2 have distinct and functions in (19Grimsey N. Han G.-S. O'Hara L. Rochford J.J. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 29166-29174Google Scholar). In addition, of Lpin1 to lipin 1 and that are to distinct functions in M. Phan J. Reue K. J. Biol. Chem... 2005; Scholar). with mammalian PAP, is known the regulation of the yeast enzyme. gene indicates that PAH1 expression is elevated in the stationary phase of growth, and M. which a with increased levels of TAG in stationary phase and with the increased of phospholipid synthesis genes G.M. Henry S.A. Prog. Lipid Res... 1999; Scholar). of the enzymological properties and biochemical regulation of PAP activity has been by the of the PAH1-encoded enzyme from S. cerevisiae (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 12Lin Y.-P. Carman G.M. J. Biol. Chem... 1989; 264: 8641-8645Google Scholar). activity is on Mg2+ and the at (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 12Lin Y.-P. Carman G.M. J. Biol. Chem... 1989; 264: 8641-8645Google Scholar). The function of is to a with the lipid substrate PA, a membrane for (12Lin Y.-P. Carman G.M. J. Biol. Chem... 1989; 264: 8641-8645Google Scholar, 13Lin Y.-P. Carman G.M. J. Biol. Chem... 1990; 265: 166-170Google Scholar, G.M. J. Biol. Chem... Scholar). The as a in which PA is a of substrate at the Y.-P. Carman G.M. J. Biol. Chem... 1990; 265: 166-170Google Scholar). PAP activity is on the (e.g. of and (e.g. of substrate on the of PA Y.-P. Carman G.M. J. Biol. Chem... 1990; 265: 166-170Google Scholar). This is of where PAP binds to the to its substrate and G.M. J. Biol. Chem... Scholar). PAP with in the absence of the enzyme with its substrate is Y.-P. Carman G.M. J. Biol. Chem... 1990; 265: 166-170Google Scholar). This is in the enzyme is associated with the cytosolic and membrane fractions of the cell (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar). PAP with the PA at the nuclear/ER membrane used for the synthesis of phospholipids and The of PAP activity on PA is (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 14Wu W.-I. Lin Y.-P. Wang E. Merrill Jr., A.H. Carman G.M. J. Biol. Chem... 1993; 268: 13830-13837Google Scholar), a role for the enzyme. The expression of the mammalian genes in cells has revealed that lipins 1 and and are PAP enzymes that are specific for PA and require Mg2+ for activity (17Donkor J. Sariahmetoglu M. Dewald J. Brindley D.N. Reue K. J. Biol. Chem... 2007; 282: 3450-3457Google Scholar). the yeast the mammalian PAP exhibit with to the of PA (17Donkor J. Sariahmetoglu M. Dewald J. Brindley D.N. Reue K. J. Biol. Chem... 2007; 282: 3450-3457Google Scholar). studies on the and biochemical properties of the mammalian PAP enzymes by yeast PAH1-encoded PAP activity is by the phospholipids PI, and W.-I. Carman G.M. Scholar), whereas the activity is by the sphingoid and W.-I. Lin Y.-P. Wang E. Merrill Jr., A.H. Carman G.M. J. Biol. Chem... 1993; 268: 13830-13837Google Scholar). sphingoid are of PAP that to the of PA from the enzyme. PI, and are of PAP activity W.-I. Carman G.M. Scholar). The major effect of the is to decrease the for the of PAP activity by and PI, whereas it causes an increase in the of W.-I. Carman G.M. Scholar). has effect on the of activation, but causes an increase in the for W.-I. Carman G.M. Scholar). on the and cellular for lipid roles in PAP activity be W.-I. Lin Y.-P. Wang E. Merrill Jr., A.H. Carman G.M. J. Biol. Chem... 1993; 268: 13830-13837Google Scholar, W.-I. Carman G.M. Scholar). in PA is between CDP-DAG and DAG, and CDP-DAG is used for the synthesis of and of PAP activity by phospholipids PA DAG for PE and PC synthesis via the Kennedy pathway or for the synthesis of the of PAP PA content and causes the of UASINO-containing genes that enzymes for phospholipid synthesis via CDP-DAG (23Carman G.M. Henry S.A. J. Biol. Chem... 2007; 282: 37293-37297Google Scholar). are and products of metabolism in yeast Biochim. Biophys. Acta.. 2002; Scholar). between the synthesis of PE and synthesis through sphingoid base metabolism G.M. Henry S.A. Prog. Lipid Res... 1999; Scholar). In addition, DAG is a product of the enzyme that is for the synthesis of a major yeast Biochim. Biophys. Acta.. 2002; Scholar). The of PAP activity by sphingoid an increase in PA which phospholipid synthesis by discussed and a mechanism for the regulation of the synthesis of phospholipids and by and which are for the synthesis of phospholipids G.M. Henry S.A. Prog. Lipid Res... 1999; Scholar), are of PAH1-encoded PAP activity W.-I. Carman G.M. J. Biol. Chem... 1994; Scholar). have revealed that the mechanism of by and is affecting the and for In addition, has shown that and are with to suggesting that PAP activity by a mechanism the of the W.-I. Carman G.M. J. Biol. Chem... 1994; Scholar). is known that cellular levels with the synthesis of phospholipids and TAG W.-I. Carman G.M. J. Biol. Chem... 1994; Scholar). levels of elevated PA content and phospholipid synthesis, whereas levels of PA content and an increase in the synthesis of TAG W.-I. Carman G.M. J. Biol. Chem... 1994; Scholar). content an increase in PA content and derepression of UASINO-containing phospholipid synthesis genes Carman G.M. J. Biol. Chem... Scholar). The of PAP activity by and by are with the regulation of lipid synthesis observed in cells that have in and W.-I. Carman G.M. J. Biol. Chem... 1994; Scholar, Carman G.M. J. Biol. Chem... Scholar). by PAP has been identified as a by a of the yeast C. J.J. J. S. 2007; Scholar, S.A. S.A. J. J. Res... 2007; Scholar). in have shown that PAP is a for protein kinase M. K. 2003; Scholar), J. H. J. H. R. N. L. De C. M. M. M. 2005; Scholar, N. S. 2005; Scholar), and J. M. M. 2005; Scholar). In PAP is by in a cell (20Santos-Rosa H. Leung J. Grimsey N. Peak-Chew S. Siniossoglou S. EMBO J.. 2005; 24: 1931-1941Google Scholar). of PAP has identified of (Fig. 2) (21O'Hara L. Han G.-S. Peak-Chew S. Grimsey N. Carman G.M. Siniossoglou S. J. Biol. Chem... 2006; 281: 34537-34548Google Scholar). within the motif are for (21O'Hara L. Han G.-S. Peak-Chew S. Grimsey N. Carman G.M. Siniossoglou S. J. Biol. Chem... 2006; 281: 34537-34548Google Scholar). of indicate that the has an effect on enzyme a purified mutant enzyme elevated PAP activity (21O'Hara L. Han G.-S. Peak-Chew S. Grimsey N. Carman G.M. Siniossoglou S. J. Biol. Chem... 2006; 281: 34537-34548Google Scholar). the overexpression of the mutant enzyme causes by the of the UASINO-containing gene (21O'Hara L. Han G.-S. Peak-Chew S. Grimsey N. Carman G.M. Siniossoglou S. J. Biol. Chem... 2006; 281: 34537-34548Google Scholar). mutant cells the phosphatase that is for dephosphorylation of PAP exhibit the phenotypes of the pah1Δ mutant (e.g. derepression of phospholipid synthesis genes and aberrant nuclear/ER membrane (20Santos-Rosa H. Leung J. Grimsey N. Peak-Chew S. Siniossoglou S. EMBO J.. 2005; 24: 1931-1941Google Scholar). In to enzyme the of PAP is affected by the that the mutant enzyme is in the membrane M. and M. lipins 1 and 2 are also (19Grimsey N. Han G.-S. O'Hara L. Rochford J.J. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 29166-29174Google Scholar, I. Jr., S. 2002; Scholar, J. Jr., J. Biol. Chem... 2007; 282: Scholar), that the of PAP is evolutionarily lipin 1 was known to have PAP activity (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar), it had been identified in as a major protein in to insulin I. Jr., S. 2002; Scholar). of lipin which is on the signaling pathway I. Jr., S. 2002; Scholar), at (Fig. 2) J. Jr., J. Biol. Chem... 2007; 282: Scholar). The of lipin 1 in has effect on its PAP but its between the cytosolic and membrane fractions of the cell J. Jr., J. Biol. Chem... 2007; 282: Scholar). a cytosolic association J. Jr., J. Biol. Chem... 2007; 282: Scholar), a that is distinct from its substrate In the PAP activity of lipins 1 and yeast PAP, lipin 1 and 2 are during the phase of cell at a and PAP are by the (19Grimsey N. Han G.-S. O'Hara L. Rochford J.J. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 29166-29174Google Scholar). shown for lipin 1 in the forms of lipins 1 and 2 in cells are in the cytosolic whereas the forms are in the membrane (19Grimsey N. Han G.-S. O'Hara L. Rochford J.J. Carman G.M. Siniossoglou S. J. Biol. Chem... 2008; 283: 29166-29174Google Scholar). indicate that has effects on PAP by activity and substrate The identification and of the yeast PAH1 gene and its protein product have established the role of PAP in the synthesis of phospholipids and TAG (11Han G.-S. Wu W.-I. Carman G.M. J. Biol. Chem... 2006; 281: 9210-9218Google Scholar, 12Lin Y.-P. Carman G.M. J. Biol. Chem... 1989; 264: 8641-8645Google Scholar). In addition, PAP activity in yeast plays a major role in cellular PA which in the regulation of phospholipid synthesis genes and of the nuclear/ER membrane G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar, 20Santos-Rosa H. Leung J. Grimsey N. Peak-Chew S. Siniossoglou S. EMBO J.. 2005; 24: 1931-1941Google Scholar, 21O'Hara L. Han G.-S. Peak-Chew S. Grimsey N. Carman G.M. Siniossoglou S. J. Biol. Chem... 2006; 281: 34537-34548Google Scholar, G.M. Henry S.A. J. Biol. Chem... 2007; 282: 37293-37297Google Scholar). The of PAP regulation is by the role enzyme plays in and peripheral in in studies with yeast PAP have led to an of the biochemical properties of the enzyme and its activity is by and a key of PAP regulation is through which is to be by protein known to control of cell physiology. The functions of the NLIP and HAD-like in yeast and mammalian PAP enzymes are not mutation of the conserved within the NLIP domain has shown that is for PAP activity G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar, J. Jr., J. Biol. Chem... 2007; 282: Scholar). In the structure of PAP, the NLIP domain is from the HAD-like domain that contains the catalytic sequence (Fig. 2) G.-S. Siniossoglou S. Carman G.M. J. Biol. Chem... 2007; 282: 37026-37035Google Scholar, Jr., Cell Metab... 2006; Scholar). The conserved in the NLIP domain may in it in to the catalytic sequence of the the mutation to may protein affecting enzyme be the structure of PAP In information of the PAP enzymes from yeast and mammalian cells also studies into the mechanism of enzyme and membrane and to the identification of specific enzyme and that may have in lipid and for on the