Study of properties of cholinephosphotransferase from fetal guinea pig lung mitochondria and microsomes

Surfactant phospholipid metabolism

Pulmonary surfactant is essential for life and is composed of a complex lipoprotein-like mixture that lines the inner surface of the lung to prevent alveolar collapse at the end of expiration. The molecular composition of surfactant depends on highly integrated and regulated processes involving its biosynthesis, remodeling, degradation, and intracellular trafficking. Despite its multicomponent composition, the study of surfactant phospholipid metabolism has focused on two predominant components, disaturated phosphatidylcholine that confers surface-tension lowering activities, and phosphatidylglycerol, recently implicated in innate immune defense. Future studies providing a better understanding of the molecular control and physiological relevance of minor surfactant lipid components are needed. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.

Molecular cloning and characterization of the guinea pig cholinephosphotransferase gene

Cholinephosphotransferase (CPT), the terminal enzyme in the de novo synthesis of phosphatidylcholine (PC), has an important role in regulating the acyl group of PC in mammalian cells. A 593bp cDNA coding for the 3(')-end of the CPT gene has been cloned from guinea pig liver using degenerative oligos based on the human CPT gene. It has 85% amino acid homology with the human CPT enzyme and amino acid variations were found to cluster at few points. Restriction enzyme polymorphisms were found particularly with respect to BamHI and NcoI. Hydrophobic and helix plot analysis of the sequence shows a similar pattern to human counterpart except for amino acid residues 142-179 and 173-179. PCR analysis suggested that a predominant pseudogene may be present in guinea pig and also the intronic sequences were much shorter when compared to the human CPT gene. We are the first to report on the C-terminal 195 amino acid residues of the CPT gene from any animal species alike in many aspects of cellular metabolism. The probable differences in genomic organization and its expression in different cancer cells have been discussed here having CPT as an important target for cancer drug development.

Differential expression of cholinephosphotransferase in normal and cancerous human mammary epithelial cells

Membrane phospholipids as well as fatty acid profile of cell membrane phospholipids are altered in tumorigenicity and malignancy. Synthesis of total cellular phosphatidylcholine (PC) can be used as a marker for membrane proliferation in neoplastic mammary gland tissues. Cholinephosphotransferase (CPT), the terminal enzyme in the de novo synthesis of PC, has an important role in regulating the acyl group of PC in mammalian cells. In this study, the effect of neoplasia on CPT was examined. The gene shows an elevated expression in cancerous (11-9-14) breast epithelial cell line when compared to that of normal non-tumorigenic (MCF-12A) breast epithelial cell line. Four nucleotide substitutions are observed in the cancer cell line. Of these, three are null mutations, but the third one shows an interesting serine to tyrosine substitution (at amino acid position 89 of our partial sequence which corresponds to position 323 of the CPT sequence reported as NM_020244 in GenBank) in 11-9-14 cells. The tyrosine is present in the right context of KSELYQDT, which directs tyrosine phosphorylation at the tyrosine site. Biochemical approach also reveals a 1.5-fold stimulation in CPT activity in 11-9-14 cells compared to that of the MCF-12A cells.

Mainstream and sidestream cigarette smoke exposure increases Ca2+-dependent phospholipid binding proteins in guinea pig alveolar type II cells

We have earlier identified the presence of a 36 kDa Ca2+-dependent phospholipid-binding protein (PLBP) in guinea pig alveolar type II cells. PLBP has been suggested to act as a mediator in facilitating and regulating intracellular surfactant assembly and delivery to the plasma membrane of type II cells for secretion into alveolar space. It has been reported that cigarette smoke exposure (CSE) causes a decrease in the surfactant activity in bronchial washings. We have also reported earlier that mainstream (MS) and sidestream (SS) CSE causes desensitization of beta-adrenoreceptors in guinea pig alveolar type II cells. Since both Ca2+ and beta-adrenoreceptors are involved in surfactant secretion and PLBP is involved in surfactant delivery, it is important to know whether CSE causes any change in the PLBP level in alveolar type II cells. In the present study, we have demonstrated that MS and SS CSE causes a significant increase in the levels of PLBP in alveolar type II cells (107 and 150%, respectively) and in lung lavage (42 and 125%, respectively) in comparison to that in sham control (430 ng/mg protein in alveolar type II cells and 780 ng/mg protein in lung lavage). The mechanism by which smoke exposure causes an elevation in the levels of PLBP in alveolar type II cells and lung lavage remains to be investigated.

Development of pancellular toxicity in guinea pig lung by ingestion of oleylanilide

Toxic oil syndrome (TOS), characterized by widespread thromboembolism, vasculotoxicity, and ARDS, develops in humans ingesting denatured edible oils. The mechanism(s) involved in targeted vasculocentric damage in this multi-system disorder is not known. Oleylanilide (OA) was synthesized and fed to male, young adult guinea pigs by gavage for 30 days at doses of 35, 50, and 100 mg/kg/day in groups of six animals each respective to weight. Controls were fed olive oil. Oleylanilide fed animals gained less weight than controls. At the end of experiment, right lungs were inflation fixed in appropriate fixative for histology and transmission electron microscopy (TEM) and left lungs were frozen at -70 degrees C for biochemical analyses. The activity of glycerophosphate acyltransferase (GAT) and cholinephosphotransferase (CPT), two key enzymes involved in phospholipid biosynthesis, were decreased in lung due to OA ingestion. All doses of OA induced marked perivascular and peribronchoiolar monocytic infiltrates that often formed prominent nodules; segmental vascular smooth muscle cell proliferation and derangement of myocytic polarity, subendothelial foamy infiltrates, and edema; nuclear pyknosis and dropout in vascular and bronchial targetoid myocytes; and denudation of bronchiolar epithelial cells. Alveoli contained large numbers of monocytes, macrophages, red cells, edema, and debris. Transmission electron microscopy showed type I cell cytoplasmic ballooning and disintegration of type I cell; contracted and blebbed endothelial cells, fibrin thrombi in capillaries, intracellular megalamellar bodies in type II cells, and surfactant lamellae; and liposomes and fine granular precipitates within alveoli, and contraction and lift off of bronchiolar epithelial cells. Monocytes, mast cells, and eosinophils infiltrated bronchial walls. Furthermore, there was deposition of electron dense particles on the surface of the alveolar wall.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of thyroid hormone in de novo synthesis of cholinephosphotransferase in guinea pig lung mitochondria and microsomes

It is known that thyroid hormone enhances the biosynthesis of phosphatidylcholine in the lung. The purpose of the present study was to investigate the effects of thyroid hormone on the activity of cholinephosphotransferase, the terminal enzyme in the CDP-choline pathway, in guinea pig lung mitochondria and microsomes. Intramuscular injection of triiodothyronine (T3, 0.25-4 mg/kg body wt) stimulated the activities of both mitochondrial and microsomal enzymes in a dose-dependent manner. However, the stimulation was much more pronounced in the microsomes than in the mitochondria. The stimulatory effect of T3 was blocked by the intraperitoneal injection of both actinomycin D and cycloheximide in the microsomes, whereas in the mitochondria, the hormonal effect was blocked only by cycloheximide. Thus, it is suggested that T3 stimulates not only the nucleocytoplasmic system for the de novo synthesis of the enzyme, but possibly also the regulation of the transport of the synthesized protein into the mitochondria. Furthermore, administration of T3 produced an increase in the uptake and incorporation of [14C]choline into phospholipids of lung slices in vitro. However, this effect was blocked by intraperitoneal injection of both actinomycin D and cycloheximide. Thus, the change in CPT activity by T3 in mitochondria is not reflected by enhanced incorporation of choline into phosphatidylcholine.

Effects of aging on cholinephosphotransferase activity on guinea pig lung mitochondria and microsomes

It is known that the composition of phospholipids in lung changes with age. The final step in the de novo synthesis of phosphatidylcholine, a major component of lung surfactant, by the CDP-choline pathway, requires the enzyme cholinephosphotransferase (CPT). Even though CPT has earlier been proposed to be located exclusively in the endoplasmic reticulum, we have recently demonstrated its presence also in the mitochondria. We have earlier reported a gestational variation of CPT activity in fetal mitochondria and microsomes. In the present study we examined the subcellular distribution of CPT activity in lung as a function of age. After birth, the microsomal CPT activity continued to increase until adulthood (24 wks of age), thereafter it gradually decreased. On the otherhand, the CPT activity of mitochondria continued to increase with the advancement of age and beyond 72 wks of age, it was approximately 2-fold higher than that of the microsomal fraction.

Identification of calcium-dependent phospholipid-binding proteins (annexins) from guinea pig alveolar type II cells

A new group of calcium-regulating proteins, called annexins or Ca(++)-dependent phospholipid-binding proteins (PLBP), have been detected in different species, organs and cell types. In the present study, we have identified and quantitated PLBP from guinea pig lung, lavage fluid and alveolar type II cells to elucidate the possible role of PLBP in lung surfactant biogenesis and secretion. Lungs were lavaged and type II cells from lavaged lung were isolated by elastase digestion and purified by centrifugal elutriation. For the quantitative identification of PLBP, we performed ELISA assays and Western blot analysis by using an antiserum raised in guinea pigs against a pure rabbit lung 36 kDa PLBP. The lavage fluid, cytosol from lung and type II cells contained 784, 167 and 435 ng per mg protein, respectively, of PLBP. The SDS-PAGE electrophoretic pattern and Western blot confirmed that all lung samples have band corresponding to a 36 kDa protein. This indicates that both alveolar type II cells and lavage fluid have higher levels of PLBP than whole lung cytosol.