Uptake and intracellular fate of polyethylenimine in vivo

Branched polyamines are extensively used as nonviral vectors for plasmid DNA in transfection experiments. Moreover, recently it has been shown that these compounds are able to eliminate prions from infected cells in cultures. It has been proposed that in both cases endosomes or lysosomes are the site of action. This raises the question of how these molecules are taken up by the cells and what is their intracellular fate. In the work presented here, the question has been addressed by investigating the uptake and the intracellular distribution of branched polyethyleneimine (25 kD) by centrifugation methods. The polyamine was labelled with (125)I-tyramine cellobiose and injected to the rat. The radioactive polymer is taken up after injection into the liver, kidney, spleen, and lungs and remains in these organs for many days. In the liver, it is found mainly in the hepatocytes. Intracellular distribution of radioactivity present in that organ was investigated by differential and isopycnic centrifugations. Early after injection, radioactivity exhibits a distribution pattern similar to that of alkaline phosphodiesterase, a plasma membrane marker. Later, the distribution pattern becomes similar to that of cathepsin C, a lysosomal enzyme. Radioactivity and hydrolase distributions in a sucrose gradient are similarly modified by a pretreatment of the rat with Triton-WR1339, a specific density perturbant of lysosomes. These results indicate that polyethyleneimine is endocytosed and reaches lysosomes. For many days it persists in these organelles probably due to its resistance to lysosomal hydrolases.

Endosomes, lysosomes: their implication in gene transfer

Plasmid DNA, naked or bound to a non-viral vector, is taken up by endocytosis. As a result, it has to travel through the intracellular endocytic pathway involving endosomes and lysosomes. However, some DNA molecules must escape these organelles to reach the nucleus where transcription takes place. In this paper, we consider different factors that could affect the trafficking of plasmid DNA and influence transfection efficiency.

Subcellular localization of mannose 6-phosphate glycoproteins in rat brain

The intracellular transport of soluble lysosomal enzymes relies on the post-translational modification of N-linked oligosaccharides to generate mannose 6-phosphate (Man 6-P) residues. In most cell types the Man 6-P signal is rapidly removed after targeting of the precursor proteins from the Golgi to lysosomes via interactions with Man 6-phosphate receptors. However, in brain, the steady state proportion of lysosomal enzymes containing Man 6-P is considerably higher than in other tissues. As a first step toward understanding the mechanism and biological significance of this observation, we analyzed the subcellular localization of the rat brain Man 6-P glycoproteins by combining biochemical and morphological approaches. The brain Man 6-P glycoproteins are predominantly localized in neuronal lysosomes with no evidence for a steady state localization in nonlysosomal or prelysosomal compartments. This contrasts with the clear endosome-like localization of the low steady state proportion of mannose-6-phosphorylated lysosomal enzymes in liver. It therefore seems likely that the observed high percentage of phosphorylated species in brain is a consequence of the accumulation of lysosomal enzymes in a neuronal lysosome that does not fully dephosphorylate the Man 6-P moieties.

Uptake by rat liver and intracellular fate of plasmid DNA complexed with poly-L-lysine or poly-D-lysine

Efficiency of transfection is probably dependent on the rate of intracellular degradation of plasmid DNA. When a non-viral vector is used, it is not known to what extent the plasmid DNA catabolism is subordinated to the catabolism of the vector. In the work reported here, the problem was approached by following the intracellular fate in rat liver, of plasmid [35S]DNA complexed with a cationic peptide poly-L-lysine that can be hydrolyzed by cellular peptidases or with its stereoisomer, poly-D-lysine, that cannot be split by these enzymes. Complexes of DNA with poly-L-lysine and poly-D-lysine are taken up to the same extent by the liver, mainly by Kupffer cells, but the intracellular degradation of nucleic acid molecules is markedly quicker when poly-L-lysine is injected. The association of DNA with the polycations inhibits DNA hydrolysis in vitro by purified lysosomes but similarly for poly-L-lysine and poly-D-lysine. The intracellular journey followed by [35S]DNA complexed with poly-L- or poly-D-lysine was investigated using differential and isopycnic centrifugation. Results indicate that [35S]DNA is transferred more slowly to lysosomes, the main site of intracellular degradation of endocytosed macromolecules, when it is given as a complex with poly-D-lysine than with poly-L-lysine. They suggest that the digestion of the vector in a prelysosomal compartment is required to allow endocytosed plasmid DNA to rapidly reach lysosomes. Such a phenomenon could explain why injected plasmid DNA is more stable in vivo when it is associated with poly-D-lysine.

Delta F508 CFTR localizes in the endoplasmic reticulum-Golgi intermediate compartment in cystic fibrosis cells

We have studied the localization of mutant cystic fibrosis transmembrane regulator delta F508CFTR in pancreatic adenocarcinoma cells (CFPAC), which naturally express the mutant protein. Our goal was to investigate whether delta F508CFTR is strictly retained in the endoplasmic reticulum (ER) or alternatively whether it can be transported beyond the ER and reach the endoplasmic reticulum-Golgi intermediate compartment (ERGIC). This compartment, defined by the presence of the 53-kDa protein ERGIC-53, was identified by subcellular fractionation and by immunofluorescence. Part of the delta F508CFTR population and ERGIC-53 showed similar distributions in membrane fractions analyzed on Nycodenz density gradients. Both proteins were present in density fractions distinct from the ones containing the ER marker proteins calnexin and Sec61. Immunofluorescence microscopy of CFPAC cells revealed some colocalization of delta F508CFTR with ERGIC-53. Following incubation of CFPAC cells at 15 degrees C, a condition known to block ER to Golgi transport, both ERGIC-53 and delta F508CFTR subcellular localizations were altered. By contrast, this temperature shift had no effect on the localization of the ER marker Sec61. Our observations indicate that the abnormal protein delta F508CFTR can leak out of the ER and reach the ERGIC. These results support the idea that this intermediate compartment plays a role in the trafficking events leading to retention and finally degradation of the misfolded delta F508CFTR protein.

Cationic lipids destabilize lysosomal membrane in vitro

Addition of cationic lipids to plasmid DNA considerably increases the efficiency of transfection. The mechanism has not yet been elucidated. A possibility is that these compounds destabilize biological membranes (plasma, endosomal, lysosomal), facilitating the transfer of nucleic molecules through these membranes. We have investigated the problem by determining if a cationic lipid N-(1-(2,3-dioleoxy)propyl)-N,N,N,-trimethylammonium methyl-sulfate (DOTAP, Boehringer, Mannheim, Germany) affects the integrity of rat liver lysosomal membrane. We have measured the latency of beta-galactosidase, a lysosomal enzyme, and found that incubation of lysosomes with low concentrations of DOTAP causes a striking increase in free activity of the hydrolase and even a release of the enzyme into the medium. This indicates that lysosomal membrane is deeply destabilized by the lipid. The phenomenon depends on pH, it is less pronounced at pH 5 than at pH 7.4. Anionic compounds, particularly anionic amphipathic lipids, can to some extent prevent this phenomenon. It can be observed with various cationic lipids. A possible explanation is that cationic liposomes interact with anionic lipids of lysosomal membrane, allowing a fusion between the lipid bilayers which results in a destabilization of the organelle membrane.

Supramolecular assemblies from lysosomal matrix proteins and complex lipids

Most lysosomal hydrolases are soluble enzymes. Lamp-II (lysosome-associated membrane protein-II) is a major constituent of the lysosomal membrane. We studied the aggregation of a series of lysosomal molecules. The aggregation-sensitive lysosomal marker enzymes were optimally aggregated at intralysosomal pH. A similar pH dependence was recorded for aggregation of Lamp-II. The pH-dependent loss of solubility of isolated Lamp-II required components of the lysosome extract. Conditions of mild acid pH promoting aggregation triggered the formation of complexes with lipids of lysosomal origin. We fractionated a membrane-free lysosome extract by gel-filtration chromatography and could reconstitute assemblies in vitro from separated fractions. We found some selectivity in the lysosomal proteins binding to complex lipids, phosphatidylcholine, sphingomyelin, and phosphatidylethanolamine being most effective. We propose that the formation at pH 5.0 of such supramolecular assemblies between lysosomal proteins and lipids occurs within the intralysosomal environment. Some possible consequences of such an intralysosomal matrix formation on organelle function are discussed.

Cationic lipids delay the transfer of plasmid DNA to lysosomes

Plasmid 35S DNA, naked or associated with different cationic lipid preparations was injected to rats. Subcellular distribution of radioactivity in the liver one hour after injection, was established by centrifugation methods. Results show that at that time, 35S DNA has reached lysosomes. On the contrary, when 35S DNA was complexed with lipids, radioactivity remains located in organelles whose distribution after differential and isopycnic centrifugation, is clearly distinct from that of arylsulfatase, lysosome marker enzyme. Injection of Triton WR 1339, a specific density perturbant of lysosomes, four days before 35S DNA injection causes a density decrease of radioactivity bearing structures, apparent one hour after naked 35S DNA injection but visible only after more than five hours, when 35S DNA associated with a cationic lipid is injected. These observations show that cationic lipids delay the transfer to lysosomes, of plasmid DNA taken up by the liver.

Soluble form of Lamp II in purified rat liver lysosomes

Lamp II (for lysosomal associated membrane protein II) is an integral type I glycoprotein. It consists of a very large and heavily glycosylated luminal domain, a single transmembrane segment, and a short cytoplasmic tail. We show that in highly purified lysosomes from rat liver, Lamp II, immunodetected with a monoclonal antibody on Western blots, it surprisingly distributed between a membrane bound form and a "soluble" form. The partition of the protein between the membrane and the content of lysosomes is strongly pH dependent. The soluble Lamp II population is sensitive to pH dependent aggregation as it is for many lysosomal content enzymes.

Phagocytosis by rat liver: relationships between phagosomes and lysosomes

To study the transfer of phagocytosed components from phagosomes to lysosomes, we have investigated phagocytosis by rat liver of killed Staphylococcus aureus labelled with (125)I tyramine cellobiose. Lysosomes were identified by injecting the animals with Triton WR1339, a non ionic detergent that is endocytosed by the liver and accumulates in lysosomes, causing a marked decrease of their density; that allows these organelles to be well separated from other particles in a density gradient. Bacteria were quickly taken up by the liver; their uptake is followed by a slow degradation as ascertained by the increase of acid-soluble radioactivity in the homogenates with time. Triton WR1339 injection does not affect the uptake and the degradation of the particles. Differential centrifugation of homogenates shows that at any time after injection, most of the radioactivity is recovered in the mitochondrial fractions. Distributions of acid precipitable and acid soluble radioactivities amongst subcellular structures present in mitochondrial fractions were studied by isopycnic centrifugation in sucrose gradients, at increasing times after bacteria injection. Results show that: 1) acid-precipitable radioactivity is quasi-exclusively present in gradient fractions of high density, well separated from the fractions where there are recovered lysosomes; 2) with time, acid-soluble radioactivity is more and more associated with lysosomes, however, a significant proportion can be detected for many hours after injection, in gradient fractions where acid-precipitable radioactivity is located. The most plausible explanation of our observations is that phagocytosed particles are degraded in phagosomes and that the degradation products are delivered to lysosomes, probably by a vesicular process.

Deleterious effects of xanthine oxidase on rat liver endothelial cells after ischemia/reperfusion

Previous studies have demonstrated that reactive oxygen species are involved in ischemic injury. The present work was undertaken to determine in vivo the role of xanthine oxidase in the oxygen free radical production during rat liver ischemia and to examine the activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) during the same period. Our results indicate a 4-fold increase in xanthine oxidase activity between 2 and 3 hours of normothermic ischemia, in parallel with a decrease in cell viability. Moderate hypothermia delays both events. Under the same conditions, the activity of oxygen radical scavenging enzymes remains unchanged. Moreover, we have compared in vitro the susceptibility of isolated liver cells to an oxidative stress induced by O2.-, H2O2 and .OH. Our results reveal that endothelial cells are much more susceptible to reactive oxygen species than hepatocytes, probably because they lack H2O2-detoxifying enzymes. These findings suggest that xanthine oxidase might play a major role in the ischemic injury mainly at the level of the sinusoidal space where most endothelial cells are located.

Uptake of exogenous DNA by rat liver: effect of cationic lipids

We have investigated by using centrifugation methods, the uptake and the intracellular fate of 35S DNA by rat liver and the effect on these processes of N-(1-(2,3-dioleoxyloxy)propyl)-N,N,N,-trimethylammonium-methyl-sul fate(DOTAP, Boehringer, Mannheim, Germany), an artificial cationic lipid frequently used in transfection experiments. Labeled DNA molecules are quickly taken up by the liver but a progressive degradation takes place with time. Subcellular distribution of the radioactivity was established after differential and isopycnic centrifugation. Results indicate that 35S DNA enters liver cells by endocytosis and reaches lysosomes. The uptake of 35S DNA is not modified if the molecule is associated with DOTAP but marked differences are observed after internalization of the macromolecule. When DOTAP is used, radioactive products remain for a long time in low density organelles distinct from lysosomes indicating that the transfer of internalized DNA to these organelles is delayed by the cationic lipid. These results suggest that cationic lipids could favor transfection by preventing the delivery of DNA to lysosomes, allowing these molecules to be kept intact and available for transfer from endosomes to cytosol for a long time.

Uptake by rat liver of bovine growth hormone free or bound to a monoclonal antibody

In the work reported here, we have compared the elimination from the blood, the uptake by the liver and the intracellular distribution of bovine growth hormone, free(Gh) or bound to a monoclonal antibody (GhAb). Results show that: a) the elimination from the blood is more rapid for Gh than for GhAb; b) both molecules are quickly taken up by the liver; c) probably after travelling through endosomes, Gh and GhAb get to lysosomes where they are degraded. However, Gh mostly ends in hepatocyte lysosomes while GhAb is recovered to a large extent in sinusoidal cell lysosomes; and d) binding by isolated hepatocytes is markedly less efficient for GhAb than for Gh.

Uptake of tyramine by rat hepatocytes

Observations on the uptake of tyramine by hepatocytes indicate that the amine is taken up by simple diffusion and a transporter mediated system, with a Km of 39 microM and a Vmax of 270 pmol/min/10(5) cells. The carrier-mediated process is pH- and temperature-dependent and requires an activation energy of 12.9 kcal/mol. An overshoot uptake is achieved a few minutes after adding this amine to the cell suspension, suggesting that active transport is involved. This is supported by the finding that partial inhibition of the uptake can be induced by oligomycin, azide, cyanide and dinitrophenol. NO3-, SCN- and SO4(2-), which change the membrane potential significantly, and depress the transporter mediated uptake further, suggesting that the membrane potential is the driving force for the entry of this amine across hepatic membrane. Cysteine is essential for the normal carrier function; whereas, histidine, tryptophan, arginine and lysine do not directly deal with the activity of the carrier. Many substances, but not amino acids, H, M, and N receptor agonists, can inhibit the uptake of tyramine. It is possible that other amines can enter hepatocytes by using this transporter.

Chloroquine allows to distinguish between hepatocyte lysosomes and sinusoidal cell lysosomes

We have examined the effect of chloroquine on rat liver lysosomal enzyme distributions after isopycnic centrifugation in a sucrose gradient. Chloroquine injection causes the large majority of cathepsin C, acid phosphatase and N acetyl glucosaminidase to migrate towards lower density regions; on the other hand only about 50% of arylsulfatase and acid deoxyribonuclease are subjected to such a density shift. To specifically mark hepatocyte lysosomes and sinusoidal cell lysosomes, rats were injected with galactosylated bovine serum albumin (A) or mannosylated bovine serum albumin (B) labelled with 125I tyramine cellobiose; A is selectively endocytosed by hepatocytes, B by sinusoidal cells. The radioactivity distribution is affected by chloroquine in the same way as cathepsin C, after injection of A though it is not influenced by chloroquine after the injection of B. These results show that chloroquine does not modify the density of liver sinusoidal cell lysosomes when it decreases the density of hepatocyte lysosomes. Such a difference could result from the fact that sinusoidal cell lysosomes do not accumulate chloroquine to the same extent as hepatocyte lysosomes. Chloroquine treatment could be useful to distinguish between hepatocyte lysosomes and sinusoidal cell lysosomes.

Effect of various flavonoids on lysosomes subjected to an oxidative or an osmotic stress

When a light mitochondrial fraction (L fraction) of rat liver is incubated in the presence of an oxygen free radical generating system (xanthine-xanthine oxidase), the free activity of N-acetylglucosaminidase (NAGase) increases as a result of the deterioration of the lysosomal membrane. Various flavonoids are able to prevent this phenomenon, others are ineffective. Comparative activity studies suggest the importance of the presence of two OH groups in orthosubstitution in the B ring and of an OH in the 3 position. Flavan-type flavonoids behave like their related flavonoids; d-catechin also opposes lysosome disruption. Kaempferol, quercetin, 7,8-dihydroxyflavone and d-catechin inhibit lipoperoxidation occurring in an L fraction incubated with the xanthine oxidase system as ascertained by malondialdehyde (MDA) production. For kaempferol and quercetin, such an inhibition parallels the prevention of NAGase release; this is not the case for the two other compounds where inhibition of NAGase release takes place at a flavonoid concentration lower than that required to oppose MDA production. Morphological observations performed on purified lysosomes confirm the biochemical results. Some flavonoids are also able to prevent release of NAGase caused by the incubation of an L fraction in isoosmotic glucose. Only flavone and hydroxyflavones are effective. It is proposed that the protective effect of flavonoids on lysosomes subjected to oxygen free radicals does not only originate from their scavenger and antilipoperoxidant properties; a more direct action on lysosomal membrane making it more resistant to oxidative aggression has to be considered. The prevention by some flavonoids of lysosome osmotic disruption in isoosmotic glucose could be the result of an inhibition of glucose translocation through the lysosomal membrane.

Uptake of tyramine cellobiose by rat liver

The uptake of 125I-tyramine cellobiose (TC) by isolated rat hepatocytes and by total rat liver is markedly higher than that of 14C-sucrose and 125I-PVP, suggesting that TC does not enter the cells by fluid phase endocytosis. The distribution of radioactivity after differential centrifugation shows that the compound is shared out amongst sedimentable structures and unsedimentable fraction. Analysis by isopycnic centrifugation indicates that quickly after its penetration into the cells, most of sedimentable 125I-TC is associated with lysosomes. Such an intracellular localization is confirmed by the distributions observed after free flow electrophoresis and by the fact that radioactivity and cathepsin C, a lysosomal hydrolase, are simultaneously released from a mitochondrial fraction treated with glycyl-L-phenylalanine-2-naphthylamide. Pretreatment of the rats with chloroquine, an acidotropic drug that accumulates in lysosomes, prevents to some extent the entry of 125I-TC into these organelles. Experiments performed with purified lysosomes show that 14C-sucrose does not cross the lysosomal membrane when 125I-TC accumulates linearly with time in the fractions. These results are explained by supposing that the linkage of tyramine to cellobiose allow the disaccharide to diffuse through the plasma and the lysosome membranes, and that the accumulation of the molecule in these organelles results from its weak basic properties. 125I-TC could be an interesting molecule with which to study acidotropism in the whole animal and in isolated and cultured cells.

Endocytosis of superoxide dismutase by rat liver

We have investigated the endocytosis by rat liver of superoxide dismutase (SOD) labelled with 125I. (125I) SOD is quickly taken up by the liver where it remains in significant amounts for at least 150 min. Adsorptive endocytosis is probably involved. Distribution of radioactivity was established after differential and isopycnic centrifugation and compared with that of cathepsin C, a lysosomal enzyme. Results show that the behavior of radioactivity is similar to that of the hydrolase. SOD activity is only marginally affected by incubation in the presence of a purified lysosome extract; moreover, when (125I) SOD is treated in the same conditions, only a few percent of radioactivity becomes acidosoluble. These observations indicate that SOD taken up by the liver accumulates in lysosomes where it can stay for a relatively long time owing to its relative resistance to lysosomal hydrolases.

Biochemical characterization of subcellular particles in fetal and neonatal rats

By a variety of methods, such as ultracentrifugation in different media, hypoosmotic activation and hydrostatic compression, subcellular particles were characterized at different perinatal ages and compared to the adult rats. Fetal mitochondria elicited a higher density, an increased osmotic space and a greater resistance to compression. The size of these particles was larger than in the adults. Mitochondria in the 1-day-old animals were freely permeable to sucrose and their external membrane was more resistant to hypoosmotic activation. Lysosomes were shown to decrease their sucrose permeability and their resistance to hypoosmotic activation with development. Moreover, the size of the lysosomes increased with development.

Subcellular localization of acid carboxypeptidase in rat liver and human fibroblasts

The subcellular distribution of acid carboxypeptidase was investigated in rat liver, normal human skin (CRL 1501) and lung (WI-38) fibroblasts, galactosialidosis skin fibroblasts (GM 00806) and transformed lung fibroblasts (WI-38 VA 13). Results of differential and isopycnic centrifugations and osmotic activation experiments clearly indicate that the enzyme is located in lysosomes, in agreement with observations suggesting that carboxypeptidase is the protective protein of the 'Galjaard complex' which is defective in galactosialidosis.

Cytotoxicity and effect of glycyl-D-phenylalanine-2-naphthylamide on lysosomes

Glycyl-D-phenylalanine-2-naphthylamide (Gly-D-Phe-2-NNap) is a cytotoxic agent as exemplified by its effect on Vero cells in culture. This effect is inhibited to some extent by nigericin. On the other hand, Gly-D-Phe-2-NNap induces an increase of free activity of N-acetylglucosaminidase when incubated with a mitochondrial fraction of rat liver at pH 7.5. The phenomenon is inhibited by chloroquine, NH4Cl and nigericin, substances that are known to increase the intralysosomal pH. The latency of enzymes located in other subcellular structures - mitochondria, peroxisomes and endoplasmic reticulum - is not affected by Gly-D-Phe-2-NNap. Moreover, that compound does not cause a release of FITC-Dextran present in endosomes. Apparently Gly-D-Phe-2-NNap is a specific lytic agent for lysosomes. It is proposed that the molecule behaves like a lysosomotropic substance that is able to attack the lysosomal membrane from the interior of the organelle. Its cytotoxic properties could be explained by its effect on lysosomes.

Intracellular degradation by liver endothelial cells

Investigations were carried out on the intracellular fate of formaldehyde treated bovine serum albumin (F-BSA), in liver non-parenchymal cells. This paper reports the observations and results obtained by us. The first part of our work involved the injecting of the compound into either a) normal rats, b) rats injected with Triton WR 1339 or c) rats treated with mannan. Fractions obtained after differential and isopycnic centrifugation in sucrose gradients, were analysed by SDS-gel electrophoresis and fluorography. The degradation takes place in a two step process. The molecule is first split into radiolabeled compounds that are still acid precipitable. This is followed by the appearance of acid soluble radioactive molecules. In a sucrose gradient the first kind of degradation products exhibit a distribution totally different from that of acid soluble degradation compounds. In the second part of our experiments, fairly pure fractions of the organelles, known to be involved in the endocytic pathway i.e. endosomes, transfer lysosomes and accumulation lysosomes (marked by the presence of either Triton WR 1339 or mannan) were isolated and incubated with [125I]-F-BSA. These experiments revealed that endosomes, isolated by us, are incapable of degradation. Accumulation lysosomes arising exclusively from liver non-parenchymal cells (in which mannan had accumulated) though rich in certain hydrolases eg. arylsulfatase did not have an efficient proteolytic machinery. Our results, both from in vivo and in vitro studies, suggest that the first degradation step occurs in one type of structure (probably not endosomes), a sort of hybrid endosome-lysosome (as they are not affected by glycyl-1-phenyl-2-napthylamide) and the second step in a different type of lysosomes, what we have designated transfer lysosomes.

The permeability of lysosomes to sugars. Effect of diethylstilbestrol on the osmotic activation of lysosomes induced by glucose

We have investigated the effect on the osmotic activation of rat liver lysosomes, by glucose penetration, of different substances known to inhibit the glucose transport through the plasma membrane. Diethylstilbestrol is the most efficient, particularly when purified lysosomes are used. It has no effect on osmotic activation induced by hypo-osmotic sucrose or by iso-osmotic KCl. It is proposed that diethylstilbestrol reacts with specific sites involved in the glucose translocation through the lysosomal membrane. These sites could not be identified by binding experiments, presumably owing to the considerable unspecific binding of the compound to the membrane.

Fate of asialofetuin endocytosed by rat liver

We have investigated the endocytosis by rat liver of asialofetuin coupled to [125I] tyramine cellobiose: [125I] TCASF. Subcellular distribution of radioactive compounds was established after differential and isopycnic centrifugation and by analysing the fractions by SDS electrophoresis. Labelling secondary lysosomes was performed by injecting rats with Triton WR 1339 four days before injecting the protein. Results show that after being associated with endosomes [125I] TCASF is recovered in organelles where they are subjected to a first degradation, the density of these organelles is practically not affected by Triton WR 1339 injection. Later the degradation products are associated with lysosomes whose density is markedly lowered by Triton WR 1339 treatment. These observations suggest that the first intracellular organelles where [125I] TCASF is subjected to digestion are distinct from the secondary lysosome population. This could be in agreement with the hypothesis that supposes that endosomes acquire enzymes from primary lysosomes before fusion with secondary lysosomes.

Uptake and intracellular transport in rat liver of formaldehyde-treated bovine serum albumin labelled with 125I-tyramine-cellobiose

1. Endocytosis of formaldehyde-treated bovine serum albumin by rat liver sinusoidal cells has been followed by injecting rats with the protein labelled with 125I-tyramine cellobiose (125I-TCfBSA). 125I-TCfBSA is quickly taken up by the liver; the radioactivity present in the organ reaches a plateau 5-10 min after injection and is maintained for up to at least 180 min. During the first 5 min most of radioactivity remains acid-precipitable. After which, labelled acid-soluble components are produced at a constant rate for up to 30-40 min. 2. Differential centrifugation shows that radioactivity is first recovered mainly in the microsomal fraction. Within a few minutes it exhibits a distribution pattern similar to that of lysosomal enzymes, being chiefly located in the mitochondrial fractions. 3. Isopycnic centrifugation in a sucrose gradient of the microsomal fraction isolated 1 min after injection indicates a similar distribution for radioactivity and alkaline phosphodiesterase. Later, the microsomal radioactivity distribution curve is shifted towards higher densities and becomes distinct from that of the plasma-membrane enzyme. After isopycnic centrifugation in a sucrose gradient of the total mitochondrial fraction a considerable overlapping of acid-precipitable and acid-soluble radioactivity distributions is observed without significant changes with time. The same is observed in a Percoll gradient except that after a relatively long time (greater than 30 min) of injection a marked shift of radioactivity distribution towards higher densities occurs. 4. A pretreatment of rats with Triton WR 1339, a density perturbant of liver lysosomes, causes a striking shift of acid-soluble radioactivity distribution in a sucrose gradient towards lower densities while having markedly less influence on the acid-precipitable distribution. As a result, a distinction between the distribution of both kinds of radioactivity becomes clearly apparent. A preinjection of yeast invertase, modifies the acid-soluble distribution without having a significant effect on the acid-precipitable distribution up to 30 min after 125I-TCfBSA injection. 5. Glycyl-1-phenylalanine-2-naphthylamide largely releases acid-soluble radioactivity associated with the mitochondrial fraction, whatever the time after 125I-TCfBSA injection. On the other hand the proportion of acid-precipitable radioactivity present in the fraction that can be released is almost zero at 10 min after injection, and it later increases. 6. The results presented here are best explained by supposing that, after being trapped in small pinocytic vesicles, 125I-TCfBSA is quickly delivered to the endosomes.(ABSTRACT TRUNCATED AT 400 WORDS)

Subcellular localization of transglutaminase. Effect of collagen

1. The subcellular distribution of transglutaminase was investigated by using the analytical approach of differential and isopycnic centrifugation as applied to three organs of the rat: liver, kidney and lung. After differential centrifugation by the method of de Duve, Pressman, Gianetto, Wattiaux & Appelmans [(1955) Biochem. J. 63, 604-617], transglutaminase is mostly recovered in the unsedimentable fraction S and the nuclear fraction N. After isopycnic centrifugation of the N fraction in a sucrose density gradient, a high proportion of the enzyme remains at the top of the gradient; a second but minor peak of activity is present in high-density regions, where a small proportion of 5'-nucleotidase, a plasma-membrane marker, is present together with a large proportion of collagen recovered in that fraction. 2. Fractions where a peak of transglutaminase was apparent in the sucrose gradient were examined by electron microscopy. The main components are large membrane sheets with extracellular matrix and free collagen fibers. 3. As these results seem to indicate that some correlation exists between particulate transglutaminase distribution and those of collagen and plasma membranes, the possible binding of transglutaminase by collagen (type I) and by purified rat liver plasma membrane was investigated. 4. The binding studies indicated that collagen is able to bind transglutaminase and to make complexes with plasma-membrane fragments whose density is higher than that of plasma-membrane fragments alone. Transglutaminase cannot be removed from such complexes by 1% Triton X-100, but can be to a relatively large extent by 0.5 M-KCl and by 50% (w/v) glycerol. 5. Such results suggest that the apparent association of transglutaminase with plasma membrane originates from binding in vitro of the cytosolic enzyme to plasma membrane bound to collagen, which takes place during homogenization of the tissue, when the soluble enzyme and extracellular components are brought together.

Intracellular pathway followed by invertase endocytosed by rat liver

Yeast invertase, when injected into rats, is endocytosed by the liver, mainly by sinusoidal cells. The work reported here aims at investigating the organelles involved in the intracellular journey of this protein. Experiments were performed on rats injected with 125I-invertase (25 micrograms/100 g body wt) and killed at various times after injection. Homogenates were fractioned by differential centrifugation, according to de Duve, Pressman, Gianetto, Wattiaux and Appelmans [(1955) Biochem. J. 63, 604-617]. Early after injection the radioactivity was recovered mainly in the microsomal fraction P; later it was found in the mitochondrial fractions (ML). At all times a peak of relative specific activity was observed in the light mitochondrial fraction L. After isopycnic centrifugation in a sucrose gradient, structures bearing 125I-invertase, present in P, exhibited a relatively flattened distribution with a density of around 1.17 g/ml, relatively similar to that of alkaline phosphodiesterase a plasma membrane marker. The organelles located in ML were endowed with a more homogeneous distribution, their median equilibrium density increasing up to 30 min after injection (1.20 g/ml----1.23 g/ml); with time the radioactivity distribution became more closely related to the distribution of arylsulfatase, a lysosomal enzyme. ML fractions, isolated 10 min and 180 min after 125I-invertase injection, were subjected to isopycnic centrifugation in Percoll gradient with, as solvent, 0.25 M, 0.5 M and 0.75 M sucrose. The change of density of the particles bearing 125I-invertase, as a function of the sucrose concentration, paralleled the change of density of the lysosomes as ascertained by the behaviour of arylsulfatase. The distribution of radioactivity and arylsulfatase in a sucrose gradient was established after isopycnic centrifugation of the ML fraction of rats injected with 125I-invertase, the animals having received or not an injection of 900 micrograms/100 g body weight of unlabelled invertase 15 h before killing. In agreement with our previous results, a shift towards higher densities of about 25% or arylsulfatase takes place in rats pretreated with unlabelled invertase. At 10 min, invertase preinjection did not change the radioactivity distribution curve. Later, it caused a progressive shift of the distribution towards higher-density regions of the gradient where the arylsulfatase, which had been shifted, was located.(ABSTRACT TRUNCATED AT 400 WORDS)

Differences in the cellular location of substances endocytosed by rat liver as observed from the distribution patterns obtained after isopycnic centrifugation in a sucrose gradient

We have investigated the distribution of several substances endocytosed by rat-liver, after isopycnic centrifugation in a sucrose gradient of the MLP fractions (de Duve, Pressman, Gianetto, Wattiaux and Appelmans (1955) Biochem.J. 63, 604-617) isolated at increasing times after injection. It has been observed that there are changes in the distribution pattern with time depending on whether the substance is taken up by parenchymal or sinusoidal cells. The results suggest that centrifugation experiments can be informative with respect to the cellular location of a molecule endocytosed by the liver.

Effect on lysosomes of invertase endocytosed by rat-liver

The intracellular localization of invertase endocytosed by rat liver was investigated by analytical centrifugation in sucrose and Percoll gradients of mitochondrial fractions originating from rats killed 15 h after injection. After isopycnic centrifugation in a sucrose gradient, invertase is located in higher density zones than acid hydrolases. The difference between the distribution of invertase and that of acid hydrolases increases with the amount of invertase injected. When the invertase dose is sufficiently high, a change of lysosomal enzyme distribution is clearly visible. It consists in the shift of a proportion of these enzymes to higher density regions where invertase is located. The proportion of hydrolase activity affected by invertase is different for each enzyme measured; it is the least pronounced for acid phosphatase, and most for acid deoxyribonuclease and arylsulfatase. A pretreatment of the rat with Triton WR 1339 considerably decreases the equilibrium density of structures bearing invertase. Nevertheless invertase distribution is quite distinct from that of the bulk of lysosomal enzymes that are recovered in lower density zones of the gradient; on the other hand the invertase injection to rats treated with Triton WR 1339 causes a spreading of the acid hydrolase distribution towards higher density zones. The distribution of acid hydrolases and invertase in a Percoll gradient depends on the sucrose concentration of the solvent. It is shifted towards higher densities when the sucrose concentration increases. The phenomenon is more important for invertase. These results are best explained by supposing that invertase accumulates in a distinct population of lysosomes that can be individualized as a result of the density increase they are subjected to by the invertase they accumulate. It is proposed that these lysosomes mainly originate from non-parenchymal cells of the liver.

The effect of pressure on fetal and neonatal liver mitochondrial membranes

The effects of pressure on late fetal and neonatal rat liver mitochondria have been investigated. High hydrostatic pressure, as produced by isopycnic centrifugation in sucrose and glycogen gradients, altered the mitochondrial membranes of 1- and 7-day-old rats. Most of the mitochondrial enzymes, chosen for their known submitochondrial location, had a trimodal distribution in the sucrose gradients. In the glycogen gradients, a shift of the mitochondria to a lower density was noticed. Fetal liver mitochondria were resistant to the hydrostatic pressure exerted during isopycnic centrifugation experiments under different conditions such as sucrose and glycogen density gradients. The submitochondrial compartment tracer enzymes exhibited an unimodal distribution. Experimental temperatures set at 15 degrees C had a protective effect from hydrostatic pressure alterations in the neonatal liver mitochondria, whereas no effects were noticeable in the fetal mitochondria. Experiments in a hydraulic compression chamber showed that outer membranes of fetal mitochondria were more fragile and the inner membranes more resistant to compression than in the early stages after birth.

Drosophila melanogaster aldehyde dehydrogenase

Subcellular fractionation by differential centrifugation confirms the presence of aldehyde dehydrogenase in D. melanogaster. It is found principally in the heavy mitochondrial fraction.

Trapping of mannitol in rat-liver mitochondria and lysosomes

When injected into rats, a certain amount of mannitol is taken up by the liver and is associated with sedimentable structures. Isopycnic centrifugation in a sucrose gradient shows that a large part of mannitol is present in mitochondria, what remains is located in the lysosomes. The hypotonic release of mannitol present in organelles shows that the polyol is shared between mitochondria and lysosomes. The trapping of mannitol in lysosomes could result from the heterophagic or autophagic function of the lysosomes; the mechanism of its accumulation in mitochondria is still unexplained.

Presence of a transglutaminase activity in rat liver lysosomes

The intracellular distribution of rat liver transglutaminase has been investigated by centrifugation methods. When measured in presence of Ca++ the enzyme is mainly present in the unsedimentable fraction of the homogenate. When assayed in absence of Ca++, the enzymatic activity exhibits a distribution pattern like that of lysosomal markers, both after differential and isopycnic centrifugation. The enzyme shows the phenomenom of structure linked latency and can be unmasked parallel with acid phosphatase by freezing and thawing. The origin of this transglutaminase is discussed; it is proposed that it is a genuine constituent of lysosomes.

Intralysosomal hydrolysis of glycyl-L-phenylalanine 2-naphthylamide

Glycyl-L-phenylalanine 2-naphthylamide (Gly-L-Phe-2-NNap), a cathepsin C substrate, induces an increase of the free and unsedimentable activities of this enzyme when incubated with a total mitochondrial fraction of rat liver. 1 mM-ZnSO4 considerably inhibits the cathepsin C total activity, measured with Gly-L-Phe-2-NNap as the substrate, in the presence of Triton X-100. The inhibition is markedly less pronounced when the free activity is determined; a high activity remains that depends on the integrity of the lysosomes; it decreases as the free activity of N-acetylglucosaminidase increases when lysosomes are subjected to treatments able to disrupt their membrane. Cathepsin C activity is reduced when thioethylamine hydrochloride is omitted from the incubation medium. Under these conditions at 37 degrees C, the free activity equals the total activity, although the lysosomes are intact, as indicated by the low free activity of N-acetylglucosaminidase. 1 mM-ZnSO4 strikingly inhibits the total activity, whereas more than 80% of the free activity remains. These observations are presented as evidence that Gly-L-Phe-2-NNap can possibly cause a disruption of the lysosomes as a result of its hydrolysis inside these organelles. In the presence of ZnSO4, intralysosomal hydrolysis becomes apparent, owing to a preferential inhibition by Zn2+ of extralysosomal hydrolysis; in the absence of thioethylamine hydrochloride, it is measurable because the disruption of lysosomes by Gly-L-Phe-2-NNap is delayed as a result of a slow-down of the reaction. The usefulness of Gly-L-Phe-2-NNap and related dipeptidyl naphthylamides in lysosomal-membrane-permeability studies is emphasized.

Subcellular distribution of particle-bound neutral peptidases capable of hydrolyzing gonadoliberin, thyroliberin, enkephalin and substance P

Subcellular fractions from rat anterior pituitary homogenates were obtained by differential and gradient centrifugation, identified with the help of marker enzymes and screened for peptidases capable of hydrolyzing gonadoliberin, thyroliberin, enkephalin and substance P. Since each neuropeptide is susceptible to cleavage by more than one enzyme, specific substrates or inhibitors have been used for the selective determination of the individual peptidasic activities. Among the various enzymes tested, the angiotensin-converting enzyme, the thermolysin-like metalloendopeptidase ('enkephalinase'), a thyroliberin-degrading enzyme and some aminopeptidasic activities were found to be associated with the plasma membrane. Other aminopeptidases, a gonadoliberin-degrading and a substance-P-degrading enzyme are associated with the mitochondria and thus are most likely not involved in the biological inactivation of neuropeptides.

Freeze-fracture study of isolated lysosomes of rat liver

Freeze-fracture electron microscopy was utilized to pursue the morphological characterization of isolated lysosomes. Combining biochemical data of purity and morphological criteria of identification, it was possible to describe the convex and concave fracture faces of lysosomes. We have compared these with the corresponding faces of tritosomes i.e. lysosomes isolated after injection of Triton WR-1339 into the animal.

A centrifugation study of rat-liver mitochondria, lysosomes and peroxisomes during the perinatal period

We have investigated the intracellular distribution of several enzymes on homogenates of late foetal, early postnatal and adult rat livers. Homogenates were subjected to differential centrifugations in 0.25 M sucrose and four fractions were isolated which corresponded to the N (nuclear) ML (total mitochondrial) P (microsomal) and S (soluble) fractions of de Duve et al. (1955). In general the age of the animal did not significantly affect the distribution pattern. Reference enzymes of mitochondria, lysosomes and peroxisomes were mainly recovered in the total mitochondrial fraction (ML). Glucose-6-phosphatase and esterase, both located in the endoplasmic reticulum, were chiefly associated with the microsomal fraction P together with galactosyltransferase (a reference enzyme of the Golgi apparatus). 5'-Nucleotidase, (a plasma membrane enzyme) exhibits a bimodal distribution and is mainly recovered in the N and the P fractions. Such results indicate that the membrane composition of the fractions isolated by the fractionation scheme was used, does not appreciably differ for the late foetal, early postnatal and adult rat livers. An analytical fractionation of the mitochondrial (ML) fraction of livers at different stages of development was performed by isopycnic centrifugation in sucrose gradients and in glycogen gradients using sucrose solutions of various concentrations as the solvents. The distribution of mitochondria, lysosomes and peroxisomes were assessed by establishing the distribution of their reference enzymes. Some physical characteristics of the particles were deduced from the manner in which the distributions were influenced by the sucrose concentration of the centrifugation medium. The distribution of liver mitochondrial enzymes one day prenatal differs strikingly from that of enzymes one day postnatal; foetal mitochondria seem characterized by a high osmotic space and a high hydrated matrix density; neonatal mitochondria seem devoid of an osmotic space and the density of their hydrated matrix is markedly lower than that of the foetal mitochondria. As ascertained by the distribution of mitochondrial enzymes in a sucrose 2H2O gradient, the high density of a foetal mitochondria matrix does not mainly originate from a lower amount of hydration water. The behavior of lysosomal enzymes in media with increasing concentrations of sucrose suggests that lysosomes originating from late foetal rat liver are endowed with a very small osmotic space. As for the peroxisomes, our results do not display significant behavior differences in centrifugations that would indicate physicochemical changes of these particles during the perinatal period.

Isolation of rat liver lysosomes by isopycnic centrifugation in a metrizamide gradient

A preparation, similar to the light mitochondrial fraction of rat liver (L fraction of de Duve et al, (1955, Biochem. J. 60: 604-617), was subfractionated by isopycnic centrifugation in a metrizamide gradient and the distribution of several marker enzymes was established. The granules were layered at the top or bottom of the gradient. In both cases, as ascertained by the enzyme distributions, the lysosomes are well separated from the peroxisomes. A good separation from mitochondria is obtained only when the L fraction if set down underneath the gradient. Taking into account the analytical centrifugation results, a procedure was devised to purify lysosomes from several grams of liver by centrifugation of an L fraction in a discontinuous metrizamide gradient. By this method, a fraction containing 10--12% of the whole liver lysosomes can be prepared. As inferred from the relative specific activity of marker enzymes, it can be estimated that lysosomes are purified between 66 and 80 times in this fraction. As ascertained by plasma membrane marker enzyme activity, the main contaminant could be the plasma membrane components. However, cytochemical tests for 5'AMPase and for acid phosphatase suggest that a large part of the plasma membrane marker enzyme activity present in the purified lysosome preparation could be associated with the lysosomal membrane. The procedure for the isolation of rat liver lysosomes described in this paper is compared with the already existing methods.

Lateral phase separations and structural integrity of the inner membrane of rat-liver mitochondria. Effect of compression. Implications in the centrifugation of these organelles

When maintained in the vicinity of the lower transition temperature of their membrane lipids, rat-liver mitochondria undergo lysis as shown by the release of malate dehydrogenase, (an enzyme located within the mitochondrial matrix), in the surrounding medium. Structural changes take place in the membranes of mitochondria subjected to increasing pressure at 0 degrees C, when the pressure reaches 750 kg/cm2. Freeze-fracture electron microscopy shows the appearance of smooth areas devoid of particles in fracture faces of mitochondrial membranes, together with zones, where aggregated particles can be seen. Concurrently, a suppression of the malate dehydrogenase structure-linked latency is observed. These structural changes can be prevented by increasing the temperature at which compression is performed. The freeze-etching observations suggest that lateral phase separations occur in mitochondrial membranes subjected to high pressure. This can be explained by supposing that pressure promotes the gel-phase appearance in a lipid system and raises the transition temperature since the transition liquid crystal lead to gel is accompanied by a decrease in volume. The deterioration of mitochondria subjected to high pressure is interpreted as a result of the lateral phase separation induced by compression in the membranes. These results are discussed with respect to our interpretation of the damaging effects that hydrostatic pressure, generated by centrifugation, exerts on rat-liver mitochondria.