Regulatory Functions of Phospholipase A2.

Phospholipase A2 (PLA2) plays crucial roles in diverse cellular responses, including phospholipid digestion and metabolism, host defense and signal transduction. PLA2 provides precursors for generation of eicosanoids, such as prostaglandins (PGs) and leukotrienes (LTs), when the cleaved fatty acid is arachidonic acid, platelet-activating factor (PAF) when the sn-1 position of the phosphatidylcholine contains an alkyl ether linkage and some bioactive lysophospholipids, such as lysophosphatidic acid (lysoPA). As overproduction of these lipid mediators causes inflammation and tissue disorders, it is extremely important to understand the mechanisms regulating the expression and functions of PLA2. Recent advances in molecular and cellular biology have enabled us to understand the molecular nature, possible function, and regulation of a variety of PLA2 isozymes. Mammalian tissues and cells generally contain more than one enzyme, each of which is regulated independently and exerts distinct functions. Here we classify mammalian PLA2s into three large groups, namely, secretory (sPLA2), cytosolic (cPLA2), and Ca2+-independent PLA2s, on the basis of their enzymatic properties and structures and focus on the general undestanding of the possible regulatory functions of each PLA2 isozyme. In particular, the roles of type II sPLA2 and cPLA2 in lipid mediator generation are discussed.

Acyl Chain Preference in Foam Cell Formation from Mouse Peritoneal Macrophages.

Macrophage foam cells play critical roles in the initiation and development of atherosclerosis by synthesizing and accumulating cholesteryl ester (CE) in lipid droplets. However, in analyzing lipid metabolism in foam cell formation, studies have focused on the sterol group, and little research has been done on the acyl chains. Therefore, we adapted a model system using liposomes containing particular acyl chains and examined the effect of various acyl chains on foam cell formation. Of the phosphatidylserine (PS) liposomes tested containing PS, phosphatidylcholine, and cholesterol, we found that unsaturated (C18:1), but not saturated (C16:0 and C18:0), PS liposomes induced lipid droplet formation, indicating that foam cell formation depends on the nature of the acyl chain of the PS liposomes. Experiments on the uptake and accumulation of cholesterol from liposomes by adding [14C]cholesterol suggested that foam cell formation could be induced only when cholesterol was converted to CE in the case of C18:1 PS liposomes. Both microscopic observations and metabolic analysis suggest that cholesterol incorporated into either C16:0 or C18:0 PS liposomes may stay intact after being taken in by endosomes. The [14C]C18:1 fatty acyl chain in the C18:1 PS liposome was used to synthesize CE and triacylglycerol (TG). Interestingly, the [14C]C16:0 in the C18:1 PS liposome was metabolized to sphingomyelin rather than being incorporated into either CE or TG, which could be because of enzymatic acyl chain selectivity. In conclusion, our results indicate that the acyl chain preference of macrophages could have some impact on their progression to foam cells.

Cathepsin G-induced malignant progression of MCF-7 cells involves suppression of PAF signaling through induced expression of PAFAH1B2.

Breast cancer is primarily classified into ductal and lobular types, as well as into noninvasive and invasive cancer. Invasive cancer involves lymphatic and hematogenous metastasis. In breast cancer patients with distant metastases, a neutrophil-derived serine protease; cathepsin G (Cat G), is highly expressed in breast cancer cells. Cat G induces cell migration and multicellular aggregation of MCF-7 human breast cancer cells; however, the mechanism is not clear. Recently, platelet-activating factor (PAF)-acetylhydrolase (PAF-AH), the enzyme responsible for PAF degradation, was reported to be overexpressed in some tumor types, including pancreatic and breast cancers. In this study, we investigated whether PAF-AH is involved in Cat G-induced aggregation and migration of MCF-7 cells. We first showed that Cat G increased PAF-AH activity and elevated PAFAH1B2 expression in MCF-7 cells. The elevated expression of PAFAH1B2 was also observed in human breast cancer tissue specimens by immunohistochemical analysis. Furthermore, knockdown of PAFAH1B2 in MCF-7 cells suppressed the cell migration and aggregation induced by low concentrations, but not high concentrations, of Cat G. Carbamoyl PAF (cPAF), a nonhydrolyzable PAF analog, completely suppressed Cat G-induced migration of MCF-7 cells. In addition, PAF receptor (PAFR) inhibition induced cell migration of MCF-7 cells even in the absence of Cat G, suggesting that Cat G suppresses the activation of PAFR through enhanced PAF degradation due to elevated expression of PAFAH1B2 and thereby induces malignant phenotypes in MCF-7 cells. Our findings may lead to a novel therapeutic modality for treating breast cancer by modulating the activity of Cat G/PAF signaling.

Autotaxin has lysophospholipase D activity leading to tumor cell growth and motility by lysophosphatidic acid production.

Autotaxin (ATX) is a tumor cell motility-stimulating factor, originally isolated from melanoma cell supernatants. ATX had been proposed to mediate its effects through 5'-nucleotide pyrophosphatase and phosphodiesterase activities. However, the ATX substrate mediating the increase in cellular motility remains to be identified. Here, we demonstrated that lysophospholipase D (lysoPLD) purified from fetal bovine serum, which catalyzes the production of the bioactive phospholipid mediator, lysophosphatidic acid (LPA), from lysophosphatidylcholine (LPC), is identical to ATX. The Km value of ATX for LPC was 25-fold lower than that for the synthetic nucleoside substrate, p-nitrophenyl-tri-monophosphate. LPA mediates multiple biological functions including cytoskeletal reorganization, chemotaxis, and cell growth through activation of specific G protein-coupled receptors. Recombinant ATX, particularly in the presence of LPC, dramatically increased chemotaxis and proliferation of multiple different cell lines. Moreover, we demonstrate that several cancer cell lines release significant amounts of LPC, a substrate for ATX, into the culture medium. The demonstration that ATX and lysoPLD are identical suggests that autocrine or paracrine production of LPA contributes to tumor cell motility, survival, and proliferation. It also provides potential novel targets for therapy of pathophysiological states including cancer.

Expression of a novel 90-kDa protein, Lsd90, involved in the metabolism of very long-chain fatty acid-containing phospholipids in a mitosis-defective fission yeast mutant.

The fission yeast lsd1/fas2 strain carries a temperature-sensitive mutation of the fatty-acid-synthase alpha-subunit, exhibiting an aberrant mitosis lsd phenotype, with accumulation of very-long-chain fatty-acid-containing phospholipid (VLCFA-PL). A novel 90-kDa protein, Lsd90 (SPBC16E9.16c), was found to be newly expressed in small particle-like structures in lsd1/fas2 cells under restrictive conditions. Two mismatches leading to a double frame shift were found between the sequences of the lsd90(+) gene registered in the genomic database and the sequences determined experimentally at the amino acid, cDNA and genomic DNA levels. Unexpectedly, overexpression and disruption of the lsd90(+) gene in either lsd1/fas2 or wild-type cells did not affect either cell growth or expression of the lsd phenotype. The amounts of VLCFA-PL that accumulated in lsd90-overexpressing lsd1/fas2 cells were significantly lower than those in lsd1/fas2 cells, suggesting the involvement of Lsd90 in the metabolism of VLCFA-PL.

Controlled indomethacin release from mucoadhesive film: in vitro and clinical evaluations.

To develop a film formulation allowing controlled release for long-term analgesia, we selected ethyl cellulose (EC) as a novel additive, prepared a film formulation using indomethacin (IM film), and evaluated it in vitro and clinically. In the in vitro experiments, the effects of the EC concentration on the release rate of IM and on the adhesion force to the mucous membrane were investigated. The addition of 10% EC resulted in more sustained slow release compared with no EC, and the adhesion of the film with 10% EC added was similar to that of films containing carboxyvinyl polymer, which we reported previously showed significantly increased adhesion. A two-layered film consisting of an adhesive layer with 2% or 1% IM and 10% EC and a nonadhesive layer with 2% polyethylene glycol as a softening agent, was investigated for clinical use. Film consisting of an adhesive layer with 2% IM and 10% EC exhibited rapid onset of potent analgesia and was expected to prolong the duration of analgesia. These results suggest that IM film with EC added may be useful clinically, since it shows both immediate analgesic effects and prolonged duration of release.

In-vitro and clinical evaluation of an oral mucosal adhesive film containing indomethacin.

To develop a new mucoadhesive film containing an analgesic combining clinical efficacy and patient comfort, we prepared and evaluated a two-layered film consisting of an adhesive layer containing indomethacin (IM) as the active ingredient and carboxyvinyl polymer (CP) as a bonding agent and a nonadhesive layer containing polyethylene glycol (PEG) to improve film texture. In in vitro and in vivo adhesive tests, the optimal concentration of CP that could be applied to the mucous membrane was 0.2% or 0.3%. Stability testing determined that the optimal storage conditions and expiration period were 4 degrees C without shade and 4 weeks, respectively. The film was clinically evaluated in patients with oral pain. IM at concentrations of 0.5% and 1% provided optimum analgesic effects, and the effects were the greatest in the 1% IM group. The addition of PEG to the nonadhesive layer reduced the number of patients experiencing discomfort at the site where the film was applied. Therefore this film formulation may be useful for local analgesic application due to its low dose requirement, moderate adhesion, and comfortable texture.

[Accreditation of pharmacy education in Japan].

The need of society for professional pharmacists has been growing. In response to social needs, the six-year pharmacy education system, which is mandatory for registration for the examination to become a licensed pharmacist, was established under the Pharmacists Law and the Fundamentals of Education Act in academic year 2006. In accordance with the amendment of the Fundamentals of Education Act, it is obligatory to develop an accreditation system for six-year pharmacy education in Japan. The Committee for the Accreditation System for Pharmacy Education in Japan was set up under the Committee of Pharmacy Education Reform of the Pharmaceutical Society of Japan to investigate the accreditation system and to draw up a draft of the evaluation standard. The draft was distributed at the end of January 2007 to request feedback from each pharmaceutical university and will be revised within the next few years simultaneously with trials for accreditation.

Plasma platelet activating factor-acetylhydrolase (PAF-AH).

The platelet-activating factor-acetylhydrolase (PAF-AH) is an enzyme which catalyzes the hydrolysis of acetyl ester at the sn-2 position of PAF. The family of PAF-AHs consists of two intracellular isoforms (Ib and II), and one secreted isoform (plasma). These PAF-AHs show different biochemical characteristics and molecular structures. Plasma PAF-AH and intracellular isoform, II degrade not only PAF but also oxidatively fragmented phospholipids with potent biological activities. Among these PAF-AHs, plasma PAF-AH has been the target of many clinical studies in inflammatory diseases, such as asthma, sepsis, and vascular diseases, because the plasma PAF-AH activity in the patients with these diseases is altered when compared with normal individuals. Finding a genetic deficiency in the plasma PAF-AH opened the gate in elucidating the protecting role of this enzyme in inflammatory diseases. The most common loss-of-function mutation, V279F, is found in more than 30% of Japanese subjects (4% homozygous, 27% heterozygous). This single nucleotide polymorphism in plasma PAF-AH and the resulting enzymatic deficiency is thought to be a genetic risk factor in various inflammatory diseases in Japanese subjects. Administration of recombinant plasma PAF-AH or transfer of the plasma PAF-AH gene improves pathology in animal models. Therefore, substitution of plasma PAF-AH would be an effective in the treatment of the patients with the inflammatory diseases and a novel clinical approach. In addition, the detection of polymorphisms in the plasma PAF-AH gene and abnormalities in enzyme activity would be beneficial in the diagnosis of the inflammatory diseases.

Structure and function of phosphatidylserine-specific phospholipase A1.

Phospholipase A1 (PLA1) is an enzyme that hydrolyzes the sn-1 fatty acids from phospholipids and produces 2-acyl-lysophospholipids. Although PLA1 activities are detected in many tissues and cell lines, a limited number of PLA1s have been purified and cloned so far. These include phosphatidylserine (PS)-specific PLA1 (PS-PLA1) from rat platelets, PLA1 from vespid venom, and phosphatidic acid (PA)-preferential PLA1 (PA-PLA1). Structurally, the former two PLA1s belong to the lipase family, where they form a subfamily among the lipase family. An alignment of the PLA1s with other members of the lipase family revealed two molecular characteristics of PLA1: the presence of extremely short lids and deleted beta9 loops. The two surface loops have been implicated in the ligand recognition in human pancreatic lipase (PL) and guinea pig PL-related protein 2. Under physiological conditions, accessibility of PS-PLA1 to its substrate is limited as it is a secreted enzyme and PS is normally located in the inner leaflet of the lipid bilayer. However, PS-PLA1 efficiently hydrolyzes PS exposed on the surface of cells such as apoptotic cells and activated platelets, and produces 2-acyl-lysophosphatidylserine (lysoPS), which is a lipid mediator for mast cells, T cells and neural cells. Identification of PS-PLA1 reveals the presence of PLA1 subfamily within the lipase family and suggests that PLA1 has a role in the production of lysophospholipid mediators.

Red blood cells highly express type I platelet-activating factor-acetylhydrolase (PAF-AH) which consists of the alpha1/alpha2 complex.

Although red blood cells account for about 30% of total PAF-AH activity found in the blood, the physiological function of this enzyme is unknown. To understand the role and regulatory mechanism of this enzyme, we purified it from easily obtainable pig red blood cells. PAF-AH activity was mainly found in the soluble fraction of the red blood cells. Two peaks of enzyme activity appeared with increasing concentration of imidazole on column chromatography on nickel-nitroacetic acid (Ni-NTA) resin. We called these peaks of small and large enzyme activities fractions X and Y, respectively, and then further purified the enzymes by sequential chromatofocusing on Mono P and gel filtration on TSK G-3000. In the final preparation from fraction Y, two proteins bands corresponding to 26 kDa and 28 kDa were related to enzyme activity. Determination of the partial amino acid sequences of the proteins of 26 kDa and 28 kDa revealed that these proteins were identical to alpha(1) and alpha(2), respectively, both of which are catalytic subunits of Type I intracellular PAF-AH. On Western analysis, the 26 kDa and 28 kDa protein bands cross-reacted with specific monoclonal antibodies to alpha(1) and alpha(2), respectively. Since the apparent molecular weight of the natural enzyme was estimated to be about 60 kDa, the enzyme activity in fraction Y was thought to be that of a heterodimer consisting of alpha(1) and alpha(2). On the other hand, the enzyme activity in fraction X was thought to be that of a homodimer consisting of alpha(2). Other blood cells such as polymorphonuclear leukocytes and platelets only contained the alpha(2)/alpha(2) homodimer. It has been reported that the alpha(1)/alpha(2) heterodimer is poorly expressed in adult animals except for in the spermatogonium. Taken altogether, these results suggest that high expression of the alpha(1)/alpha(2) heterodimer is important for the physiological function of mature red blood cells.

Overview of PAF-Degrading Enzymes.

Because the acetyl group of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF) is essential for its biological activity, the degradation of PAF is the most important mechanism that regulates the level of PAF. The enzyme that catalyzes the hydrolysis of acetyl group at the sn-2 position of PAF was termed PAF-acetylhydrolase (PAF-AH). Subsequent research revealed that the PAF-AH family includes intracellular forms called PAF-AH I and PAF-AH II as well as an extracellular isoform, plasma PAF-AH. PAF-AH I forms a complex consisting of catalytic subunits α1, α2, and ß regulatory subunits. PAF-AH I was identified from the brain, and previous studies focused on the role of PAF-AH I in brain development. However, subsequent studies found that PAF-AH I is involved in diverse functions such as spermatogenesis, amyloid-ß generation, cancer pathogenesis, and protein trafficking. Another intracellular enzyme, PAF-AH II, has no homology with PAF-AH I, although this enzyme shares sequence similarity to plasma PAF-AH. Because PAF-AH preferentially hydrolyzes oxidatively modulated or truncated phospholipids, it is considered to play a protective role against oxidative stress. Homologs of this enzyme are widely distributed among evolutionarily diverse organisms. For example, studies of Caenorhabditis elegans PAF-AH II demonstrate its contribution to epidermal morphogenesis. Extracellular plasma PAF-AH associates strongly with plasma lipoproteins. Because PAF-AH is mainly associated with LDL particles, it is considered to play an anti-inflammatory role by removing oxidized phospholipids generated in LDLs exposed to oxidative stress. In this overview, we describe the crucial roles of these three PAF-degrading enzymes in cell function and cell pathology.

Platelet-activating factor acetylhydrolase (PAF-AH).

Platelet-activating factor (PAF) is one of the most potent lipid messengers involved in a variety of physiological events. The acetyl group at the sn-2 position of its glycerol backbone is essential for its biological activity, and its deacetylation induces loss of activity. The deacetylation reaction is catalyzed by PAF-acetylhydrolase (PAF-AH). A series of biochemical and enzymological evaluations revealed that at least three types of PAF-AH exist in mammals, namely the intracellular types I and II and a plasma type. Type I PAF-AH is a G-protein-like complex consisting of two catalytic subunits (alpha1 and alpha2) and a regulatory beta subunit. The beta subunit is a product of the LIS1 gene, mutations of which cause type I lissencephaly. Recent studies indicate that LIS1/beta is important in cellular functions such as induction of nuclear movement and control of microtubule organization. Although substantial evidence is accumulating supporting the idea that the catalytic subunits are also involved in microtubule function, it is still unknown what role PAF plays in the process and whether PAF is an endogenous substrate of this enzyme. Type II PAF-AH is a single polypeptide and shows significant sequence homology with plasma PAF-AH. Type II PAF-AH is myristoylated at the N-terminus and like other N-myristoylated proteins is distributed in both the cytosol and membranes. Plasma PAF-AH is also a single polypeptide and exists in association with plasma lipoproteins. Type II PAF-AH as well as plasma PAF-AH may play a role as a scavenger of oxidized phospholipids which are thought to be involved in diverse pathological processes, including disorganization of membrane structure and PAF-like proinflammatory action. In this review, we will focus on the structures and possible biological functions of intracellular PAF-AHs.

Molecular species of phospholipids with very long chain fatty acids in skin fibroblasts of Zellweger syndrome.

The ratio of C 26:0/C 22:0 fatty acids in patient lipids is widely accepted as a critical clinical criterion of peroxisomal diseases, such as Zellweger syndrome and X-linked adrenoleukodystrophy (X-ALD). However, phospholipid molecular species with very long chain fatty acids (VLCFA) have not been precisely characterized. In the present study, the structures of such molecules in fibroblasts of Zellweger syndrome and X-ALD were examined using LC-ESI-MS/MS analysis. In fibroblasts from Zellweger patients, a large number of VLCFA-containing molecular species were detected in several phospholipid classes as well as neutral lipids, including triacylglycerol and cholesteryl esters. Among these lipids, phosphatidylcholine showed the most diversity in the structures of VLCFA-containing molecular species. Some VLCFA possessed longer carbon chains and/or larger number of double bonds than C 26:0-fatty acid (FA). Similar VLCFA were also found in other phospholipid classes, such as phosphatidylethanolamine and phosphatidylserine. In addition, VLCFA-containing phospholipid species showed some differences among fibroblasts from Zellweger patients. It appears that phospholipids with VLCFA, with or without double bonds, as well as C 26:0-FA might affect cellular functions, thus leading to the pathogenesis of peroxisomal diseases, such as Zellweger syndrome and X-ALD.

Atropisomerism observed in indometacin derivatives.

To elucidate the active conformation of indometacin that differentiates between cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), the stereochemistry around the N-benzoylated indole moiety of indometacin was studied. Resolution of stable atropisomers as representative conformations was found to be possible by restricting rotation about the N-C7' and/or C7'-C1' bond. Only the aR-isomer showed specific inhibition of COX-1, and COX-2 was not inhibited by either atropisomer.

Expression of phosphatidylserine-specific phospholipase A(1) mRNA in human THP-1-derived macrophages.

The expression of phosphatidylserine-specific phospholipase A(1) (PS-PLA(1)) is most upregulated in the genes of peripheral blood cells from chronic rejection model rats bearing long-term surviving cardiac allografts. The expression profile of PS-PLA(1) in peripheral blood cells responsible for the immune response may indicate a possible biological marker for rejection episodes. In this study, PS-PLA(1) mRNA expression was examined in human THP-1-derived macrophages. The effects of several immunosuppressive agents on this expression were also examined in in vitro experiments. A real-time RT-PCR analysis revealed that PS-PLA(1) mRNA expression was found in human THP-1-derived macrophages. This expression was enhanced in the cells stimulated with lipopolysaccharide (LPS), a toll-like receptor (TLR) 4 ligand. Other TLR ligands (TLR2, 3, 5, 7, and 9) did not show a significant induction of PS-PLA(1) mRNA. The time course of the mRNA expression profiles was different between PS-PLA(1) and tumor necrosis factor-α (TNF-α), which showed a maximal expression at 12 and 1 h after LPS stimulation, respectively. Among the observed immunosuppressive agents, corticosteroids, prednisolone, 6α-methylprednisolone, dexamethasone, and beclomethasone inhibited PS-PLA(1) expression with half-maximal inhibitory concentrations less than 3.0 nM, while methotrexate, cyclosporine A, tacrolimus, 6-mercaptopurine, and mycophenoic acid showed either a weak or moderate inhibition. These results suggest that the expression of PS-PLA(1) mRNA in THP-1-derived macrophages is activated via TLR4 and it is inhibited by corticosteroids, which are used at high dosages to suppress chronic allograft rejection.

pH-dependent translocation of alpha-tocopherol transfer protein (alpha-TTP) between hepatic cytosol and late endosomes.

BACKGROUND: alpha-Tocopherol transfer protein (alpha-TTP), a member of the Sec14 protein family, plays an important role in transporting alpha-tocopherol, a major lipid-soluble anti-oxidant, in the cytosolic compartment of hepatocytes and is known as a product of the causative gene for familial isolated vitamin E deficiency. It has been shown that the secretion of hepatocyte alpha-tocopherol taken up with plasma lipoproteins is facilitated by alpha-TTP. To explore the mechanism of alpha-TTP mediated alpha-tocopherol secretion, we investigated drugs which may affect this secretion. RESULTS: We found that, in a hepatocyte cell culture system, intracellular alpha-tocopherol transport is impaired by chloroquine, an agent known for its function of elevating the pH in acidic compartments. Under chloroquine treatment, the diffuse cytosolic distribution of alpha-TTP changes to a punctate pattern. Double-staining experiments with endocytosis markers revealed that alpha-TTP accumulates transiently on the cytoplasmic surface of late endosomal membranes. This phenomenon is specific for hepatoma cell lines or primarily cultured hepatocytes. Other members of the Sec14 family, such as cellular retinaldehyde-binding protein (CRALBP) and supernatant protein factor (SPF), do not show this accumulation. Furthermore, we elucidate that the obligatory amino acid sequence for this function is located between amino acids 21 and 50, upstream of the N-terminal end of the lipid-binding domain. CONCLUSION: We hypothesize that a liver-specific target molecule for alpha-TTP exists on the late endosomal membrane surface. This transient binding may explain the mechanism of how alpha-tocopherol is transferred from late endosomes to cytosolic alpha-TTP.

Targeted disruption of intracellular type I platelet activating factor-acetylhydrolase catalytic subunits causes severe impairment in spermatogenesis.

Intracellular type I platelet activating factor-acetylhydrolase is a phospholipase that consists of a dimer of two homologous catalytic subunits alpha1 and alpha2 as well as LIS1, a product of the causative gene for type I lissencephaly. LIS1 plays an important role in neuronal migration during brain development, but the in vivo function of the catalytic subunits remains unclear. In this study, we generated alpha1- and a2-deficient mice by targeted disruption. alpha1(-/-) mice are indistinguishable from wild-type mice, whereas alpha2(-/-) male mice show a significant reduction in testis size. Double-mutant male mice are sterile because of severe impairment of spermatogenesis. Histological examination revealed marked degeneration at the spermatocyte stage and an increase of apoptotic cells in the seminiferous tubules. The catalytic subunits are expressed at high levels in testis as well as brain in mice. In wild-type mice, alpha2 is expressed in all seminiferous tubule cell types, whereas alpha1 is expressed only in the spermatogonia. This expression pattern parallels the finding that deletion of both subunits induces a marked loss of germ cells at an early spermatogenic stage. We also found that the LIS1 protein levels, but not the mRNA levels, were significantly reduced in alpha2(-/-) and double-mutant mice, suggesting that the catalytic subunits, especially alpha2, are a determinant of LIS1 expression level.

Type II platelet-activating factor-acetylhydrolase is essential for epithelial morphogenesis in Caenorhabditis elegans.

Type II platelet-activating factor-acetylhydrolase [PAF-AH (II)] is an N-myristoylated enzyme that contains a lipase/esterase catalytic motif and selectively hydrolyzes the sn-2 acetyl ester of PAF and other short-chain acyl groups attached to phosphoglycerides. However, the physiological role of this enzyme remains to be elucidated. PAF-AH (II) is conserved in a variety of species ranging from a simple multicellular organism, Caenorhabditis elegans, to mammals. C. elegans possesses two homologous PAF-AH (II) genes, named paf-1 and paf-2. In this study, we generated these two loss-of-function mutants to elucidate the in vivo PAF-AH (II) function. Surprisingly, mutants of paf-2, a major isoform of C. elegans PAF-AH (II)s, exhibits gross defects in epithelial sheet formation, resulting in unsuccessful subsequent morphogenesis with complete penetrance. Moreover, paf-2 RNA interference worms show a variable abnormal morphology, including ectopic protrusions and a lumpy shape at the late embryonic and early larval stages due to epithelial organization defects. Consistent with these phenotypes, PAF-AH (II) is predominantly expressed in epithelial cells of C. elegans. This study demonstrates that PAF-AH (II) is essential for epithelial morphogenesis.