Mechanisms of α-fetoprotein synthesis in hepatoma cells

Summary Immunoreaction of -fetoprotein (AFP) was detected not only in well-differentiated hepatocellular carcinoma but also in hepatocytes forming foci in livers with hyperplastic nodules during 3-methyl-4-dimethylaminoazobenzene hepatocarcinogenesis. The subcellular location of AFP in hepatoma cells was in the rough endoplasmic reticulum, perinuclear space and well-developed Golgi apparatus around the nucleus. In livers with hyperplastic nodules it was also in some parts of the smooth endoplasmic reticulum and Golgi regions in hepatocytes in the vicinity of submembranous areas or bile canaliculi. These findings suggest that the Golgi apparatus in hepatoma cells acts mainly as an organelle for glycosylation of AFP and that the Golgi complexes in the hepatocytes in livers with hyperplastic nodules are organelles for secretion of AFP.Combined light microscopic immunoperoxidase study and autoradiography with ³H-thymidine revealed a higher cumulative labeling index in AFP-positive hepatoma cells than in non-tumorous areas. Combined electron microscopic immunoperoxidase study and autoradiography showed that hepatoma cells with AFP immunoreactivity only in the rough endoplasmic reticulum had a significantly higher labeling index than did cells with AFP immunoreactivity in both rough endoplasmic reticulum and Golgi apparatus. These findings suggest that AFP is synthesized in hepatoma cells before or during the stage of their DNA synthesis and is then transported to the Golgi apparatus.     

Demonstration by light and ultrastructural immunoperoxidase study of alpha-fetoprotein-positive non-hepatoma cells and hepatoma cells during 3'-methyl-4-dimethylaminoazobenzene hepatocarcinogenesis

Immunoreaction of alpha-fetoprotein (AFP) has been described in cholangiolar "oval" cells in the early stage of 3'-methyl-4-dimethylaminoazobenzene hepatocarcinogenesis. The subcellular location of AFP in the oval cells was in the perinuclear space, rough endoplasmic reticulum and Golgi apparatus. In livers with hyperplastic nodules there were two different types of foci containing AFP-positive cells. One type had a normal nucleocytoplasmic ratio and was seen in well-preserved hepatic trabecular structures, and the other had less cytoplasm and occurred in trabecular structures in disarray. AFP-immunoreactivity in the former type was visible in the perinuclear space and rough endoplasmic reticulum but scarce in the Golgi apparatus, and in the latter type it was present in the proliferative smooth endoplasmic reticulum and in several parts of Golgi apparatus in the submembranous or pericanalicular areas. In livers with hepatocarcinoma, AFP immunoreaction was detected in well-differentiated hepatocellular carcinomas, and the subcellular location of AFP was in the perinuclear space, rough endoplasmic reticulum and many developed Golgi complexes. Therefore, AFP-positive cells in livers with hyperplastic nodules are a new cell population in hepatocarcinogenesis, and each type is morphologically different from the oval cell.     

Ultrastructural changes in the liver of the sand lamprey,Lampetra reissneri,during sexual maturation

Ultrastructural changes of hepatocytes were examined in the sand lamprey,Lampetra reissneri, during various phases of the life cycle. In hepatocytes of ammocoetes, the rough endoplasmic reticulum was composed of short cisternae and the Golgi apparatus were scarcely developed, showing no sexual differences at this stage of life cycle. In hepatocytes of female lampreys at the metamorphic stages 4 to 5, the rough endoplasmic reticulum was developed to form long parallel cisternae and the Golgi apparatus were well-developed. The rough endoplasmic reticulum developed further to form stacks of long parallel cisternae extending over the cytoplasm in hepatocytes of females at the young adult stage, and became composed of both long parallel and vesicular cisternae in the cells of females at the adult stage. The Golgi apparatus were invariably welldeveloped in hepatocytes of young adult and adult females. No consipcuous development was observed in profiles of the rough endoplasmic reticulum and the Golgi apparatus in hepatocytes of males during and after metamorphosis. The ultrastructural changes of the rough endoplasmic reticulum and the Golgi apparatus observed in hepatocytes of female sand lampreys are considered to have an intimate relation to the activity of vitellogenin synthesis in the liver, and it is suggested that the hepatocytes begin to rapidly synthesize vitellogenin in the sand lamprey at the metamorphic stages 4 to 5.     

ELECTRON MICROSCOPIC RADIOAUTOGRAPHIC DETECTION OF SITES OF PROTEIN SYNTHESIS AND MIGRATION IN LIVER

The sites of synthesis of proteins and their subsequent migration in rat liver have been studied during a 75 min period after labeling of liver-slice proteins by exposure to leucine-H³ for 2 min. Incorporation of the label into protein began after 1 min and was maximal by 4 min. Electron microscopic radioautography showed that synthesis of proteins in hepatocytes occurs mainly on ribosomes, particularly those in rough endoplasmic reticulum and, to some extent, in nuclei and mitochondria. Most of the newly formed proteins leave the endoplasmic reticulum in the course of 40 min, and concurrently labeled proteins appear in Golgi bodies, smooth membranes, microbodies, and lysosomes. A likely pathway for the secretion of some or all plasma proteins is from typical rough endoplasmic reticulum to a zone of reticulum which is partially coated with ribosomes, to the Golgi apparatus, and thence to the cell periphery. The formation of protein by reticuloendothelial cells was measured and found to be about 5% of the total protein formed by the liver.     

Kallikrein- and prolactin-producing cells in the rat anterior pituitary are the same

Kallikrein-positive cells in the anterior pituitary of female rats were identified to be the same as prolactin-producing cells by using an immunoelectron microscopic method. The kallikrein immunoreactivity was localized at the Golgi apparatus, the rough endoplasmic reticulum, and secretory granules, suggesting that kallikrein is synthesized in the prolactin-producing cells and also may be secreted into the blood vessels.     

Ultrastructural location of albumin and fibrinogen in primary cultures of new-born rat liver tissue

In primary cultures of new-born rat liver tissue, albumin and frbrinogen, two proteins normally synthesized by the liver and secreted into plasma were demonstrated by specific antibodies labelled with peroxidase in about 50 and 70% of the hepatocytes; these proteins were not demonstrated in the other types of cells, in particular fibroblasts, present in primary cultures. These two proteins were detected on the ribosomes of the rough endoplasmic reticulum and were also present in the lumina of the rough and smooth endoplasmic reticulum and in the Golgi apparatus. It is concluded that

1. 1. In primary cultures of liver tissue, only the hepatocytes synthesize albumin and fibrinogen.

2. 2. Proliferating cultured hepatocytes are able to synthesize albumin and fibrinogen.

3. 3. The presence of detectable albumin and fibrinogen in the lumina of the rough and smooth endoplasmic reticulum and in the Golgi apparatus in hepatocytes of primary cultures and their absence in the lumina of the rough and smooth endoplasmic reticulum and in the Golgi apparatus in the hepatocytes of adult rat liver might indicate an alteration in the translocation of albumin and fibrinogen through these organelles in cultured hepatocytes.

     

Protein synthesis in the livers of aging mice studied by electron microscopic radioautography.

The application of 3H-leucine results in labeling of the liver cells of mice in which protein is synthesized at various ages of the animals. Quantitative changes of protein synthesis in the hepatocytes of aging mice were studied by electron microscopic radioautography. The silver grains in the hepatocytes were mainly located over the rough surfaced endoplasmic reticulum, mitochondria, Golgi apparatus, cytoplasmic matrix, and a few over the nuclei. The number of silver grains in the cytoplasm and nuclei of the hepatocytes gradually increased after birth, reached the maximum at 1 month after birth, thereafter it continued to decrease with aging until the 24th month. The number of silver grains in the hepatocyte cytoplasm was more than that in nuclei at various ages. The number of silver grains in the rough surfaced endoplasmic reticulum and mitochondria gradually increased from embryo to 1 month after birth, thereafter it continued to decrease with aging until the 24th month. The number of silver grains in the Golgi apparatus showed almost no change from fetal stage to 6 months after birth, thereafter it continued to decrease with aging until the 24th month. The number of silver grains in the cytoplasmic matrix gradually increased from fetal stage to 2 months after birth, then decreased with aging until the 24th month. These changes reflect the quantity of protein synthesized in each cell organelle at various ages of animals.     

Secretion of collagen by insects: Autoradiographic study of l-proline 3H-5 incorporation by the firebrat Thermobia domestica

The biosynthesis of collagenous endoskeletal endosterna by fibroblasts was studied by electron microscope autoradiography after tritium-labelled proline administration in the firebrat Thermobia domestica at various time intervals. Autoradiographs were quantitatively analyzed and the relative concentration of label was determined for various cellular compartments. The labelling in the rough endoplasmic reticulum, ground cytoplasm, Golgi apparatus and endosterna was compared during the secretion of radioactive products. The label, initially located in the rough endoplasmic reticulum was found in the Golgi apparatus before it accumulated in the endosternum. The involvement of the rough endoplasmic reticulum and Golgi apparatus in the transport of secreted collagen is discussed, comparing our results with current knowledge of collagenous secretion.     

Ultrastructural localization of Cu, Zn-SOD in hepatocytes of patients with various liver diseases

The ultrastructural localization of copper, zinc-superoxide dismutase (Cu, Zn-SOD) in the liver of patients with acute hepatitis, chronic hepatitis, liver cirrhosis and alcoholic fatty liver was studied by means of the indirect immunoperoxidase technique. In hepatocytes Cu, Zn-SOD was found to be localized in perinuclear cisternae, rough endoplasmic reticulum (rER), vesicles and Golgi apparatus. The Cu, Zn-SOD was also detected around the lipid droplets in hepatocytes as well as on the cytoplasmic membrane in cases of liver cirrhosis. These findings suggest that Cu, Zn-SOD is produced in the rER in hepatocytes and protects the cells from cellular injury caused by superoxide anion radical in various disorders of the liver.     

Nitric oxide synthase is localized predominantly in the Golgi apparatus and cytoplasmic vesicles of vascular endothelial cells

The localization of nitric oxide synthase (NOS) in vascular endothelial cells of submucosal blood vessels from the guinea-pig ileum was examined using NADPH diaphorase histochemistry at the light microscopic level, and endothelial NOS immunohistochemistry at the light and electron microscopic level. The pattern of staining observed following NADPH diaphorase histochemistry and endothelial NOS immunohistochemistry was identical. Endothelial cells of the arterioles, capillaries and venules showed small patches of intense, perinuclear staining. Under the electron microscope, endothelial NOS immunoreactivity was found predominantly in association with the Golgi apparatus and with the membranes of some vesicles. Small regions of the plasma membrane and the rough endoplasmic reticulum also showed some immunoreactivity. The presence of NOS in the Golgi apparatus and in vesicles raises the possibility that NOS may be exteriorized by endothelial cells, and hence that nitric oxide is synthesized extracellularly.     

Immunolocalization of the oligosaccharide trimming enzyme glucosidase II

We used immunoelectron microscopy to localize glucosidase II in pig hepatocytes. The enzyme trims the two inner alpha 1,3-linked glucoses from N-linked oligosaccharide precursor chains of glycoproteins. Immunoreactive enzyme was concentrated in rough (RER) and smooth (SER) endoplasmic reticulum but not detectable in Golgi apparatus cisternae. Transitional elements of RER and smooth membraned structures close to Golgi apparatus cisternae contained labeling for glucosidase II. Specific labeling was also found in autophagosomes. These results indicate strongly that glucosidase II acts on glycoproteins before their transport to, and processing in Golgi apparatus cisternae, and suggest that an important transitional region for glucosidase II exists between RER and Golgi apparatus cisternae. Degradation in autophagolysosomes could form a normal catabolic pathway for glucosidase II.     

Cytochemical localization of terminal N-acetyl-D-galactosamine residues in cellular compartments of intestinal goblet cells: implications for the topology of O-glycosylation

The O-linked oligosaccharides of mucin-type glycoproteins contain N- acetyl-D-galactosamine (GalNAc) that is not found in N-linked glycoproteins. Because Helix pomatia lectin interacts with terminal GalNAc, we used this lectin, bound to particles of colloidal gold, to localize such sugar residues in subcellular compartments of intestinal goblet cells. When thin sections of low temperature Lowicryl K4M embedded duodenum or colon were incubated with Helix pomatia lectin- gold complexes, no labeling could be detected over the cisternal space of the nuclear envelope and the rough endoplasmic reticulum. A uniform labeling was observed over the first and several subsequent cis Golgi cisternae and over the last (duodenal goblet cells) or the two last (colonic goblet cells) trans Golgi cisternae as well as forming and mature mucin droplets. However, essentially no labeling was detected over several cisternae in the central (medial) region of the Golgi apparatus. The results strongly suggest that core O-glycosylation takes place in cis Golgi cisternae but not in the rough endoplasmic reticulum. The heterogenous labeling for GalNAc residues in the Golgi apparatus is taken as evidence that termination of certain O- oligosaccharide chains by GalNAc occurs in trans Golgi cisternae.     

Subcellular fractionation studies on the post-translational processing of pro-adrenocorticotropic hormone/endorphin in rat intermediate pituitary

The subcellular localization of the post-translational processing steps which occur in the conversion of pro-adrenocorticotropic hormone (ACTH)/endorphin into beta-endorphin-sized molecules in rat intermediate pituitary has been studied. Primary cell cultures were incubated in radioactively labeled amino acids, and a subcellular fraction containing secretory granules was separated from a subcellular fraction containing rough endoplasmic reticulum and Golgi apparatus by centrifugation of homogenates on gradients on Percoll (Pharmacia Fine Chemicals). The radiolabeled beta-endorphin-related material in the granule and rough endoplasmic reticulum/Golgi apparatus fractions was quantitated by immunoprecipitation and sodium dodecyl sulfate polyacrylamide gel electrophoresis. A pulse-chase labeling experiment demonstrated that newly synthesized beta-endorphin-related material first appeared in the rough endoplasmic reticulum/Golgi apparatus fraction and after longer incubations (chase) appeared in the secretory granule fraction. After 2 h of chase incubation, about 85% of the beta-endorphin-related material synthesized during the 30-min pulse incubation had been transferred from the rough endoplasmic reticulum/Golgi apparatus to the secretory granule fraction. The conversion of most of the newly synthesized pro-ACTH/endorphin into beta-lipotropin occurred in the rough endoplasmic reticulum/Golgi apparatus fraction, whereas the conversion of most of the beta-lipotropin into beta-endorphin-sized molecules occurred in the secretory granule fraction.     

Immunocytochemical localization of renin in juxtaglomerular cells

The involvement of various organelles in the synthesis, transport, and packaging of renin in the juxtaglomerular cells of newborn mice has been investigated by immunocytochemistry with the protein A-gold technique. Highly specific rabbit antibodies against mouse submandibular renin were used. Mild fixation and embedding in glycol methacrylate allowed enough sensitivity to identify a steep gradient of labeling from rough endoplasmic reticulum to Golgi complex to secretory granules. Routine fixation and embedding in Epon produced labeling differentials that allowed delineation of hitherto ill-defined types of secretory granules and vacuoles. The classical pattern of synthesis, transport, and packaging of secretory proteins involves the rough endoplasmic reticulum and Golgi complex and seems to apply to renin secretion. Immunoreactive renin is packaged as rhomboid crystals at the trans face of the Golgi complex. The limiting membrane of these rhomboids fuses to form coalescing protogranules where the crystals eventually yield their individuality maturing into secretory granules. Vacuoles containing a flocculent material, with or without a dense core, show significant immunocytochemical labeling. These vacuoles are not associated with the Golgi complex but occupy cytoplasmic areas well endowed with rough endoplasmic reticulum. As judged from their morphological features and their immunoreactivity, the vacuoles do not seem to follow the sequence of events typical of protogranules and coalescing protogranules. They possibly represent a parallel pathway of renin synthesis and transport, involving the nuclear envelope and bypassing the Golgi complex.     

Electron-immunocytochemical localization of calcitonin and calcitonin-gene-related peptide in human c cells of the thyroid

A preembedding immunocytochemical technique enabled us to demonstrate normal human parafollicular (C) cells at the electron-microscopic level. The normal human C cells had numerous large secretory granules with a diameter of approximately 200 nm, well-developed rough endoplasmic reticulum and Golgi complex in their cytoplasm. Calcitonin immunoreactivity and calcitonin-gene-related peptide (CGRP) immunoreactivity were present only in the C cells whose secretory granules were heavily labeled. Both calcitonin and CGRP immunoreaction deposits were seen in the cytosol but not in the cisterna of endoplasmic reticulum, Golgi apparatus or mitochondrial matrix. The two peptides produced from a single calcitonin gene were stored in the secretory granules of the C cells.     

DAB致大鼠肝癌过程中免疫组化及免疫电镜研究

本文采用二甲氨基偶氮苯(DAB)诱发的大鼠肝癌模型,运用组织病理学、血清学、免疫组化及免疫电镜技术相结合的方法,对诱癌过程中各个不同时期肝脏的组织病理学变化及肝癌阳性标志物AFP的表达进行了动态观察。结果显示:早在血清AFP浓度上升和由卵圆细胞转变而来的小肝细胞表达AFP之前,肝小叶中就出现了散在的AFP阳性肝细胞,我们认为这种AFP阳性肝细胞可作为肝细胞癌前病变的早期征象之一。在AFP阳性的肝细胞内,AFP主要定位于核周间隙、粗面内质网和高尔基复合体。     

Sites of sulfatation in the chondrocytes of the articular cartilage of the rabbit

35S sulfate uptake by the articular cartilage chondrocytes, from biopsies of rabbit, have been studied by high resolution autoradiography. The Golgi apparatus, rough endoplasmic reticulum, cytosol, cytoplasmic membrane and extracellular space were considered as cell compartments in the quantitative analysis of the autoradiograms. The results obtained show: 1) a high activity of radiosotope incorporation in the Golgi apparatus; 2) a fast rhythm of transfer of the substances labelled in the Golgi apparatus to the cell membrane; 3) significant labelling of the rough endoplasmic reticulum, throughout the experiment. It is concluded: 1) The grains observed in the rough endoplasmic reticulum show a significant radioisotope uptake on this level, and this evidence some sulfotransferase activity. 2) The high 35S sulfate uptake level which is observed in the Golgi apparatus demonstrates that the highest sulfotransferase enzyme activity is located in this cell area, thus showing that the "early" sulfation that began in the rough endoplasmic reticulum was completed by a "late" sulfation in the Golgi apparatus. It is here that complete chondromucoprotein building takes place before being excreted. 3) The high transfer level of the labelled substances from the Golgi apparatus shows that the sulfated product secretion for building the cartilage matrix takes place rapidly since a great label increase can be already observed at the beginning of the chase period in the outer surrounding area of the chondrocyte membrane.     

Morphology of the liver of the brook lamprey, Lampetra lamottenii before and during infection with the nematode, Truttaedacnitis stelmioides, hepatocytes, sinusoids, and perisinusoidal cells.

Routine light microscopy and transmission and scanning electron microscopy were used to describe and compare the livers of larval lampreys, Lampetra lamottenii before and during infection of the bile ducts by the nematode, Truttaedacnitis stelmioides. The hepatocytes of uninfected animals differ from other lamprey species in that they contain abundant glycogen, smooth endoplasmic reticulum (SER), and lipoprotein indicating that the liver may be involved in glucose metabolism. Infestation of the biliary tree by T. stelmioides coincides with alterations to the hepatocytes. These changes include dilation of the bile canaliculi, smooth endoplasmic reticulum (SER), rough endoplasmic reticulum (RER), and Golgi apparatus, swollen mitochondria in cells showing a high degree of hypertrophy, and an abundance of dense bodies. Following infection, the sinusoidal lumina became dilated and contain a moderate electron-dense precipitate, an abundance of melanomacrophages, lipocytes, and mononuclear cells. There is also a widening of the fenestrae of the sinusoidal endothelium following infection. Many of the changes in hepatocytes and sinusoids following parasite infections closely resemble those observed in hepatocytes in various pathologies and following experimental bile duct ligation and, therefore, are likely a consequence of increased biliary pressure due to bile duct obstruction.     

Antibodies to the Golgi complex and the rough endoplasmic reticulum

Rabbits were immunized with membrane fractions from either the Golgi complex or the rough endoplasmic reticulum (RER) by injection into the popliteal lymph nodes. The antisera were then tested by indirect immunofluorescence on tissue culture cells or frozen, thin sections of tissue. There were may unwanted antibodies to cell components other than the RER or the Golgi complex, and these were removed by suitable absorption steps. These steps were carried out until the pattern of fluorescent labeling was that expected for the Golgi complex or RER. Electron microscopic studies, using immunoperoxidase labeling of normal rat kidney (NRK) cells, showed that the anti-Golgi antibodies labeled the stacks of flattened cisternae that comprise the central feature of the Golgi complex, many of the smooth vesicles around the stacks, and a few coated vesicles. These antibodies were directed, almost entirely, against a single polypeptide with an apparent molecular weight of 135,000. The endoplasmic reticulum (ER) in NRK cells is an extensive, reticular network that pervades the entire cell cytoplasm and includes the nuclear membrane. The anit-RER antibodies labeled this structure alone at the light and electron microscopic levels. They were largely directed against four polypeptides with apparent molecular weights of 29,000, 58,000, 66,000, and 91,000. Some examples are presented, using immunofluorescence microscopy, where these antibodies have been used to study the Golgi complex and RER under a variety of physiological and experimental condition . For biochemical studies, these antibodies should prove useful in identifying the origin of isolated membranes, particularly those from organelles such as the Golgi complex, which tend to lose their characteristic morphology during isolation.     

Immunocytochemical localization of alpha-fetoprotein in the developing and carbon tetrachloride-treated rat liver.

The immunocytochemical localization of alpha-fetoprotein (AFP)-producing cells was observed in pre- and postnatal and carbon tetrachloride (CCl4)-treated rat livers in comparison with that of albumin (ALB)-producing cells. According to immunoblotting data, considerable numbers of AFP-positive hepatocytes were observed in the differentiating liver between prenatal day 19 and postnatal day 0 (6 h after birth). Analyses by serial section profiles of these cells revealed that certain AFP-positive hepatocytes are also stained with ALB antiserum. Immunoelectron microscopy of the AFP-producing cells revealed that immunoreactive gold particles are preferentially localized in rough endoplasmic cisternae, Golgi apparatus and Golgi-derived vesicles near the cell surface. In addition, the release of the content of the Golgi-derived vesicles into the differentiating bile canaliculi as well as into the space of Disse by exocytosis is apparent. In CCl4-treated rat liver, immunoreactions to AFP are localized exclusively in newly formed hepatocytes of the regenerative tissue. These AFP-positive cells have not established the hepatic cell cords, and the adjacent ones are conjugated to each other mainly by simple attachment devices as in the case of those in pre- and postnatal rat liver.