The structural basis for the phospholipid remodeling by lysophosphatidylcholine acyltransferase 3.
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ABSTRACT:
SUBMITTER: Zhang Q
PROVIDER: S-EPMC8617236 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:BackgroundThe involvement of lipid metabolism in tumourigenesis and the progression of clear cell renal cell carcinoma (ccRCC) have been reported. However, the role of phospholipid profile alterations in ccRCC has not yet been systematically explored. In the present study, we compared the phospholipid compositions between ccRCC and paired normal renal tissues.MethodsThe phospholipid compositions of paired ccRCC and normal renal tissues were evaluated using liquid chromatography tandem mass spectrometry (LC/MS/MS). To evaluate the mRNA and protein levels of lysophosphatidylcholine acyltransferase (LPCAT), which converts lysophosphatidylcholine (LPC) to phosphatidylcholine (PC), qRT-PCR, western blotting and immunohistochemistry were performed. The correlations of LPCAT1 expression with clinicopathological features and prognosis were assessed. In addition, siRNAs were used to knockdown LPCAT1 expression in ccRCC cell lines, and its effect on cell proliferation, cell cycle, migration and invasion were investigated.ResultsThe phospholipid compositions of ccRCC and normal renal tissues were significantly different. Multiple LPC species were decreased and corresponding PC species were increased in cancer tissues. The mRNA and protein levels of LPCAT1 were up-regulated in ccRCC tissues compared with normal renal tissues, and LPCAT1 expression was significantly correlated with unfavourable pathological features (higher tumour grade, higher TNM stage and larger tumour size) and overall survival. In cell line experiments, LPCAT1 knockdown depleted PCs, inhibited cell proliferation, migration and invasion and induced cell cycle arrest at the G0/G1 phase.ConclusionSelective changes in PC and LPC composition were observed in ccRCC tissues. The overexpression of LPCAT1 promotes the development and progression of ccRCC, likely through the conversion of LPC to PC.
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Project description:The mammalian RBC lacks de novo lipid synthesis but maintains its membrane composition by rapid turnover of acyl moieties at the sn-2 position of phospholipids. Plasma-derived fatty acids are esterified to acyl-CoA by acyl-CoA synthetases and transferred to lysophospholipids by acyl-CoA:lysophospholipid acyltransferases. We report the characterization of three lysophosphatidylcholine (lysoPC) acyltransferases (LPCATs), products of the AYTL1, -2, and -3 genes. These proteins are three members of a LPCAT family, of which all three genes are expressed in an erythroleukemic cell line. Aytl2 mRNA was detected in mouse reticulocytes, and the presence of the product of the human ortholog was confirmed in adult human RBCs. The three murine Aytl proteins generated phosphatidylcholine from long-chain acyl-CoA and lysoPC when expressed in Escherichia coli membranes. Spliced variants of Aytl1, affecting a conserved catalytic motif, were identified. Calcium and magnesium modulated LPCAT activity of both Aytl1 and -2 proteins that exhibit EF-hand motifs at the C terminus. Characterization of the product of the Aytl2 gene as the phosphatidylcholine reacylating enzyme in RBCs represents the identification of a plasma membrane lysophospholipid acyltransferase and establishes the function of a LPCAT protein.
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Project description:Lecithin:retinol acyltransferase-like proteins, also referred to as HRAS-like tumor suppressors, comprise a vertebrate subfamily of papain-like or NlpC/P60 thiol proteases that function as phospholipid-metabolizing enzymes. HRAS-like tumor suppressor 3, a representative member of this group, plays a key role in regulating triglyceride accumulation and energy expenditure in adipocytes and therefore constitutes a novel pharmacological target for treatment of metabolic disorders causing obesity. Here, we delineate a catalytic mechanism common to lecithin:retinol acyltransferase-like proteins and provide evidence for their alternative robust lipid-dependent acyltransferase enzymatic activity. We also determined high resolution crystal structures of HRAS-like tumor suppressor 2 and 3 to gain insight into their active site architecture. Based on this structural analysis, two conformational states of the catalytic Cys-113 were identified that differ in reactivity and thus could define the catalytic properties of these two proteins. Finally, these structures provide a model for the topology of these enzymes and allow identification of the protein-lipid bilayer interface. This study contributes to the enzymatic and structural understanding of HRAS-like tumor suppressor enzymes.
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Project description:Pulmonary surfactant is a complex of phospholipids and proteins lining the alveolar walls of the lung. It reduces surface tension in the alveoli, and is critical for normal respiration. Pulmonary surfactant phospholipids consist mainly of phosphatidylcholine (PC) and phosphatidylglycerol (PG). Although the phospholipid composition of pulmonary surfactant is well known, the enzyme(s) involved in its biosynthesis have remained obscure. We previously reported the cloning of murine lysophosphatidylcholine acyltransferase 1 (mLPCAT1) as a potential biosynthetic enzyme of pulmonary surfactant phospholipids. mLPCAT1 exhibits lysophosphatidylcholine acyltransferase (LPCAT) and lysophosphatidylglycerol acyltransferase (LPGAT) activities, generating PC and PG, respectively. However, the enzymatic activity of human LPCAT1 (hLPCAT1) remains controversial. We report here that hLPCAT1 possesses LPCAT and LPGAT activities. The activity of hLPCAT1 was inhibited by N-ethylmaleimide, indicating the importance of some cysteine residue(s) for the catalysis. We found a conserved cysteine (Cys(211)) in hLPCAT1 that is crucial for its activity. Evolutionary analyses of the close homologs of LPCAT1 suggest that it appeared before the evolution of teleosts and indicate that LPCAT1 may have evolved along with the lung to facilitate respiration. hLPCAT1 mRNA is highly expressed in the human lung. We propose that hLPCAT1 is the biosynthetic enzyme of pulmonary surfactant phospholipids.
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Project description:The alteration of the choline metabolite profile is a well-established characteristic of cancer cells. In colorectal cancer (CRC), phosphatidylcholine is the most prominent phospholipid. In the present study, we report that lysophosphatidylcholine acyltransferase 1 (LPCAT1; NM_024830.3), the enzyme that converts lysophosphatidylcholine into phosphatidylcholine, was highly overexpressed in colorectal adenocarcinomas when compared to normal mucosas. Our microarray transcription profiling study showed a significant (p < 10(-8)) transcript overexpression in 168 colorectal adenocarcinomas when compared to ten normal mucosas. Immunohistochemical analysis of colon tumors with a polyclonal antibody to LPCAT1 confirmed the upregulation of the LPCAT1 protein. Overexpression of LPCAT1 in COS7 cells localized the protein to the endoplasmic reticulum and the mitochondria and increased LPCAT1 specific activity 38-fold. In cultured cells, overexpressed LPCAT1 enhanced the incorporation of [(14)C]palmitate into phosphatidylcholine. COS7 cells transfected with LPCAT1 showed no growth rate alteration, in contrast to the colon cancer cell line SW480, which significantly (p < 10(-5)) increased its growth rate by 17%. We conclude that LPCAT1 may contribute to total choline metabolite accumulation via phosphatidylcholine remodeling, thereby altering the CRC lipid profile, a characteristic of malignancy.
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Project description:Glycerophospholipids have important structural and functional roles in cells and are the main components of cellular membranes. Glycerophospholipids are formed via the de novo pathway (Kennedy pathway) and are subsequently matured in the remodeling pathway (Lands' cycle). Lands' cycle consists of two steps: deacylation of phospholipids by phospholipases A2 and reacylation of lysophospholipids by lysophospholipid acyltransferases (LPLATs). LPLATs play key roles in the maturation and maintenance of the fatty acid composition of biomembranes, and cell differentiation. We examined whether LPLATs are involved in chondrogenic differentiation of ATDC5 cells, which can differentiate into chondrocytes. Lysophosphatidylcholine acyltransferase 4 (LPCAT4) mRNA expression and LPCAT enzymatic activity towards 18:1-, 18:2-, 20:4-, and 22:6-CoA increased in the late stage of chondrogenic differentiation, when mineralization occurred. LPCAT4 knockdown decreased mRNA and protein levels of chondrogenic markers as well as Alcian blue staining intensity and alkaline phosphatase activity in ATDC5 cells. These results suggest that LPCAT4 plays important roles during the transition of chondrocytes into hypertrophic chondrocytes and/or a mineralized phenotype.
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Project description:Lipid droplet (LD) accumulation is a now well-recognised hallmark of cancer. However, the significance of LD accumulation in colorectal cancer (CRC) biology is incompletely understood under chemotherapeutic conditions. Since drug resistance is a major obstacle to treatment success, we sought to determine the contribution of LD accumulation to chemotherapy resistance in CRC. Here we show that LD content of CRC cells positively correlates with the expression of lysophosphatidylcholine acyltransferase 2 (LPCAT2), an LD-localised enzyme supporting phosphatidylcholine synthesis. We also demonstrate that LD accumulation drives cell-death resistance to 5-fluorouracil and oxaliplatin treatments both in vitro and in vivo. Mechanistically, LD accumulation impairs caspase cascade activation and ER stress responses. Notably, droplet accumulation is associated with a reduction in immunogenic cell death and CD8+ T cell infiltration in mouse tumour grafts and metastatic tumours of CRC patients. Collectively our findings highlight LPCAT2-mediated LD accumulation as a druggable mechanism to restore CRC cell sensitivity.
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Project description:Eukaryotic cells are compartmentalized to form organelles, whose functions rely on proper phospholipid and protein transport. Here we determined the crystal structure of human VAT-1, a cytosolic soluble protein that was suggested to transfer phosphatidylserine, at 2.2 Å resolution. We found that VAT-1 transferred not only phosphatidylserine but also other acidic phospholipids between membranes in vitro Structure-based mutational analyses showed the presence of a possible lipid-binding cavity at the interface between the two subdomains, and two tyrosine residues in the flexible loops facilitated phospholipid transfer, likely by functioning as a gate to this lipid-binding cavity. We also found that a basic and hydrophobic loop with two tryptophan residues protruded from the molecule and facilitated binding to the acidic-lipid membranes, thereby achieving efficient phospholipid transfer.
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Project description:Retinal degenerative diseases, such as retinitis pigmentosa and Leber congenital amaurosis, are a leading cause of untreatable blindness with substantive impact on the quality of life of affected individuals and their families. Mouse mutants with retinal dystrophies have provided a valuable resource to discover human disease genes and helped uncover pathways critical for photoreceptor function. Here we show that the rd11 mouse mutant and its allelic strain, B6-JR2845, exhibit rapid photoreceptor dysfunction, followed by degeneration of both rods and cones. Using linkage analysis, we mapped the rd11 locus to mouse chromosome 13. We then identified a one-nucleotide insertion (c.420-421insG) in exon 3 of the Lpcat1 gene. Subsequent screening of this gene in the B6-JR2845 strain revealed a seven-nucleotide deletion (c.14-20delGCCGCGG) in exon 1. Both sequence changes are predicted to result in a frame-shift, leading to premature truncation of the lysophosphatidylcholine acyltransferase-1 (LPCAT1) protein. LPCAT1 (also called AYTL2) is a phospholipid biosynthesis/remodeling enzyme that facilitates the conversion of palmitoyl-lysophosphatidylcholine to dipalmitoylphosphatidylcholine (DPPC). The analysis of retinal lipids from rd11 and B6-JR2845 mice showed substantially reduced DPPC levels compared with C57BL/6J control mice, suggesting a causal link to photoreceptor dysfunction. A follow-up screening of LPCAT1 in retinitis pigmentosa and Leber congenital amaurosis patients did not reveal any obvious disease-causing mutations. Previously, LPCAT1 has been suggested to be critical for the production of lung surfactant phospholipids and biosynthesis of platelet-activating factor in noninflammatory remodeling pathway. Our studies add another dimension to an essential role for LPCAT1 in retinal photoreceptor homeostasis.
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