Morphological and functional heterogeneity of Zajdela rat ascites hepatoma cells

This work studies the mechanisms of dysdifferentiation at cell neoplastic transformation based on the example of heterogeneity of the cell populations that form malignant tumors. Two natural fractions of Zajdela rat hepatoma cells are revealed that differ in the type of growth in the primary culture. Cells of one fraction are attached to substrate and are growing in monolayer (S-fraction), whereas cells of the other fraction are floating in the culture medium (F-fraction). Using the method of supravital observation of the primary culture cells (of 1–2 passages) at the limit of resolution of DIC microscopy, it has been established that both fractions contain cells of several types. Some of these cells are specific to one of the fractions and others are present in both fractions, but with different frequencies. Using the same method, it has been shown that, at the long-term separate cultivation of the fractions in vitro (more than 50 passages), both the cell composition and the initial ratio of cells of different types are changed in both of them. According to the data of flow DNA cytometry, cells of both fractions are hypotetraploid and have insignificant differences in the amount of DNA. After adaptation to conditions of cultivation in vitro, S-fraction cells have been found to have elevated proliferative activity compared to the cells of F-fractions; after long cultivation, the fractions already differ significantly (2.3 times) by this criterion. The content of the cell surface laminin, a marker of hepatocellular carcinomas, is higher on cells of the F-fraction than on those of the S-fraction. The interfraction differences are confirmed by immunologic estimations of the resistance of hepatoma cells to lyses of natural killer cells; cells of the S-fraction of the primary culture are 2.4 times more sensitive than cells of the F-fraction, while, after long-term cultivation, cells of the F-fraction become almost resistant to the cytotoxic action of natural killer cells. Based on the obtained data, the most probable pathways of the dysdifferentiation of rat hepatocytes upon the establishment of Zajdela hepatoma and at the long-term cultivation of cells of this tumor in vitro are discussed.     

Study of surface heteroorganic antigens of rat hepatoma cells participating in the cell proliferation process

The study of the antigen diversion of cells of rat hepatocellular tumors, which is caused by the expression of normal antigens peculiar to renal definitive tissues (so-called “heteroorganic renal antigens”) is continued. Using an immune serum of narrow specificity, in the plasma membrane fractions of Zajdela ascites hepatoma cells and of cultivated HTC hepatoma cells, heteroorganic antigens 110–115 and 125–130 kDa are revealed; the heteroorganic antigen 75–80 kDa is only detected for the Zajdela hepatoma cells. The participation of these heteroorganic antigens in the cell proliferation process is shown by the methods of radioisotope analysis and DNA flow cytometry.     

Investigation of the surface heteroorganic antigens of rat hepatoma cells involved in process of cell proliferation

The investigation of antigenic diversion of hepatoma cells resulting from the expression of heteroorganic kidney antigens has been continued. Tumor-associated heteroorganic antigens 110-115 and 125-130 kDa were detected by immunoserum of narrow specificity in fractions of plasmatic membranes of cells of rat ascitic hepatoma Zajdela and cultured hepatoma HTC; the antigen 75-80 kDa was revealed only for hepatoma Zajdela cells. It has been shown by methods of radioisotope analysis and flow DNA-cytometry that heteroorganic antigens 110-130 kDa can be involved in process of cell proliferation.     

Calmodulin in Zajdela hepatoma cell growth

Calmodulin levels were measured in Zajdela hepatoma cells growing both in vivo and in culture, with respect to the distribution of the cells into G1 and S+G2 phases of the cell cycle and growth conditions. These levels, expressed on a per-microgram of protein basis, were significantly elevated at the G1-S boundary and maintained throughout the remainder of the cell cycle. This elevation of calmodulin took place independently of the culture conditions. Taken together with previous observations, these data suggest that a threshold concentration for calmodulin is required for progression through the cell cycle, DNA synthesis and cell division.     

Antigenic divergence in a primary rat hepatocyte culture after exposure to the hepatic carcinogen N-diethylnitrosamine

Using the indirect immunofluorescence method, the appearance of membrane hetero-organic antigens of kidney origin associated with the Zajdela hepatoma cells was observed on the surface of cells of the rat liver primary culture following a single hepatocarcinogen N-diethylnitrosamine (DENA) treatment before and after explantation. A correlation of antigenic alterations after a single DENA treatment in vivo and in vitro was discovered. No antigens under investigation were discovered in cultured hepatocytes of intact adult rats.     

Detection and identification of the tumor-associated antigens in the fraction enriched with plasma membranes of the Zajdela hepatoma cells

Tumor-associated antigens 45, 57, 80 and 130 kDa were detected using tumor-specific rabbit immune serum in the fraction enriched with plasma membrane of the rat Zajdela hepatoma cells and isolated on the immunosorbent. Revealed proteins were identified as integrin beta-1, ecto-nucleotide pyrophosphatase/phosphodiesterase-3 (E-NPP3), basigin, epithelial cell adhesion molecule (EpCAM), alpha-fetoprotein (AFP) and protein chaperones--glucose-regulated protein 78 (GRP78) and protein disulfide-isomerase (PDI) A1 by mass spectrometry technique. Functions and characteristics of these proteins in tumor cells and some aspects of the Zajdela hepatoma cells origin are discussed.     

Initiation of unscheduled synthesis on DNA sites associated with a nuclear matrix of irradiated hepatoma cells

A study was made of the distribution of unscheduled DNA synthesis (induced by UV- or gamma-radiation and resistant to hydroxyurea) between the DNA sites in the nuclear matrix and total nuclear DNA of Zajdela ascites hepatoma cells. It was shown that during the first 1.5 to 5 min of the postirradiation incubation the rate of the unscheduled synthesis of DNA was considerably higher in the DNA fraction, firmly associated with the nuclear matrix proteins, than in the total nuclear DNA.     

Uptake in vitro of nucleic acid precursors and nucleic acids by Zajdela ascitic hepatoma cells.

Zajdela ascitic hepatoma cells are shown to take up pyrimidine bases at much lower rates than obtained in slices from normal rat liver. The rates of uptake of adenine and uridine by the Zajdela cells are, however, as high as in the slices. Like the slices, again, the Zajdela cells take up E. coli RNA and DNA at very low rates but, unlike the slices, thses cells degrade rapidly the RNA taken up. The Zajdela cells resemble parenchymal cell suspensions derived from normal rat liver in regard to the uptake of pyrimidine bases and the ability to degrade heterologous RNA.     

Formation, size, and solubility in chloroform/methanol of products of protein synthesis in isolated mitochondria of rat liver and Zajdela hepatoma.

The number, size, solubility in chloroform/methanol and some aspects of the formation of the components labeled by radioactive amino acids in isolated mitochondria of rat liver and Zajdela hepatoma were studied. Isolated mitochondria were labeled with radioactive amino acids under various conditions, and the distribution of radioactivity in sodium dodecylsulfate-polyacrylamide gels after electrophoresis of mitochondrial membrane fraction was analysed. 1. Isolated mitochondria of rat liver and Zajdela hepatoma incroporated radioactive amino acids almost exclusively into the membrane fraction. Electrophoretic analysis of this fraction revealed the presence of 15 distinct peaks of radioactivity with corresponding apparent molecular weights of 10 000 to 58 000. The electrophoretic mobility of the labeled components was identical and the general pattern of the radioactivity distribution in the gel for the rat liver and the tumour mitochondria was very similar. 2. Components of the membrane fraction of rat liver mitochondria labeled in vitro displayed an unequal solubility in acidic (2 mM HC1) chloroform/methanol (2/1) mixture; as detected by sodium dodecylsulfate-polyacrylamide gel electrophoresis a single labeled component with apparent molecular weight of 10 000 was soluble in neutral chloroform/methanol. 3. Inverse relation was observed between amino acid incorporation activity of isolated mitochondria and the portion of the label incorporated into the component with apparent molecular weight 10 000. The identity of this component with that soluble in neutral chloroform/methanol mixture has been indicated. 4. The rate of incorporation of [3H]leucine by isolated Zajdela hepatoma mitochondria into the components with lower (10 000-25 000) apparent molecular weights decreased with time, whereas that into components with higher (above 25 000) apparent molecular weight remained approximately constant within the time interval tested (30 min). 5. From the total radioactivity incorporated into the membrane fraction during 5-min pulse labeling of isolated Zajdela hepatoma mitochondria by [3H]leucine up to 25% was recovered in the region of the gel corresponding to a component with apparent molecular weight 10 000. After 25 min chase the radioactivity in this region decreased about 3.5 times while the specific radioactivity of the total membrane fraction did not change significantly. The pattern of radioactivity distribution observed after the pulse was preserved by chloramphenicol. 6. Unlabeled sonicated mitochondria or postribosomal supernatant from rat liver regenerating in the presence of chloramphenicol were incubated with neutral chloroform/methanol extract of in vitro with [14C]leucine labeled rat liver mitochondria. After this incubation several labeled components with apparent molecular weights above 10 000 were recovered in the electrophoreograms of the originally unlabeled fractions.     

Variable association of DNA polymerase with the cytoskeletal fractions of resting and dividing cells

A DNA polymerase activity associated with the detergent insoluble cytoskeletal fraction has been identified in dividing and non-dividing rat hepatocytes and a hepatoma (the Zajdela Ascitic Hepatoma). About 35 % of the enzyme is found associated with the cytoskeletal fraction of non-dividing cells as compared to about 3–6 % of the enzyme in dividing cells even though the dividing cells contain larger amounts of the extranuclear enzyme. The properties of the enzyme are similar to those of DNA polymerase-v. It is suggested that the association of the enzyme with the cytoskeletal fraction has functional significance.     

Establishment and characterization of clonal lines with cancer stem- and progenitor-cell properties from monolayer Zajdela hepatoma

The aim of this study was to investigate the biology of cancer stem cells (CSC) from a metastatic tumor. Previously, we explanted the cells of rat ascites Zajdela hepatoma in vitro. We established a permanent monolayer cell line via selection of adhesive cells from multicellular floating islets. In the present work, we cloned these cells by a limiting-dilution method and established five novel clonal sublines of the hepatoma: three holoclonal sublines containing CSC and two meroclonal sublines. After a long-term cultivation (approximately 30 passages, freezing, and thawing), the cell of clonal sublines retained the features of CSC. They have a tumor-initiating potential and produce mainly holoclones upon recloning in the complete growth medium and large nonadhesive hepatospheres in the serum-free medium. Morphometric analysis showed that the cells of holoclonal and meroclonal sublines differed in the cell shape, area, nucleus size, and nuclear-cytoplasmic ratio. We have found for the first time that holoclonal cells of Zajdela hepatoma have a fibroblast-like morphology and form contacts with each other due to membrane protrusions. We suggest that the fibroblast-like morphology of CSC is an attribute of a metastatic tumor and demonstrates the capability of these cells for individual migration.     

Synthesis and targeting of hexokinase to mitochondria in hepatoma cells

The synthesis and turnover of hexokinase has been measured in Zajdela hepatoma ascites cells labeled for short periods with [35S]methionine. Digitonin fractionation of the labeled cells into a soluble and a membrane fraction showed that only a small part of the newly labeled hexokinase is transferred to mitochondrial binding sites. The soluble enzyme disappears, however, with a half-life of less than 2 h. Glucose had no effect on the stability of the soluble enzyme in intact cells. Our experiments suggest that Zajdela cell hexokinase is synthesized in excess of binding sites and that the excess enzyme is not stable.     

The expression of hetero-organic antigens of kidney origin on the surfaces of cultured rat hepatocytes under the influence of the narrow-band fractions of non-histone chromosomal proteins]

Narrow fractions of nonhistone chromosomal proteins (NHCP) eluted with 0.4-0.5 M NaCl from the phosphocellulose column stimulate expression of hetero-organic antigens of kidney origin on the membrane of intact hepatocytes cultured in suspension. These fractions of NHCP were isolated from the intact rats kidney, from cells of hepatoma 27 and Zajdela hepatoma, and from the carcinogenic liver after a single diethylnirozamine injection. The membrane hetero-organic antigens were identified by means of indirect immunofluorescence using specific immune serum.     

Comparative investigation of antigens associated with plasmatic membranes of rat hepatoma and myogenic cells using anti-kidney serum

The investigation of antigenic diversion of tumor cells resulting from the expression of heteroorganic antigens has been continued. Tumor-associated heteroorganic antigens with mol. weight 200-210 kDa (identified before as laminin), 105-130, 75-80 and 43 kDa were detected by anti-kidney serum in fractions of plasmatic membranes of cells of rat ascitic Zajdela hepatoma and cultured HTC hepatoma; the antigen 43 kDa was isolated on immunosorbent and identified by mass spectrometry as beta-actin. Anti-kidney serum revealed laminin in fractions of plasmatic membranes of cultured L8 and L6J1 myoblasts, and L6J1 myotubes; apparently, synthesis of laminin by hepatoma and myogenic cells is not connected with their proliferative activity. Besides, anti-kidney serum detected components 38, 42, 44, 48, 62, 78 and 120 kDa, expression of which on myogenic cells surface might be consequence of active cell proliferation and (or) differentiation.     

Resurgence of glycogen synthesis and storage capacity in cultured hepatoma cells.

This paper describes a new cultured hepatoma cell line referred as ZHC cells, derived from the ascitic Zajdela rat hepatoma. Since 1963, the dedifferenciated in vivo transplanted ascitic cells were characterized by the absence of glycogen as in generally the case in all fast growing hepatic tumors. In 1974, we succeeded in adapting these tumor cell to in vitro defined growth conditions, where we observed the progressive recovery of the ability to synthesize and to store large amounts of glycogen, as shown by histochemical, ultrastructural and biochemical studies. It can now be considered as an established cell line in which the reverted phenotype has been stable for 3 years.     

Membrane antigens of Zajdela ascitic hepatoma]

The membrane antigens of Zajdela ascitic hepatoma cells were investigated. Living cells were studied by immunofluorescence method, and solublized membrane preparations by the precipitation reacting in agar gel. Testing of the tumor cells with organospecific anti-kidney serum caused a specific fluorescence of tumor cells surface. This can be due to incorporation into the antigenic structure of the Zajdela hepatoma cell membranes of at least one organospecific antigen. Treatment of the tumor cells with organospecific anti-liver serum led to specific fluorescence of tumor cells surface. In solubilizates of the tumor cells one of the three organospecific antigens peculiar for the normal liver cells, was detected.     

Fraction from human and rat liver which is inhibitory for proliferation of liver cells

A comparative study was undertaken with human and rat liver of a fraction reported to have growth inhibitory activity when prepared from rat liver. Fractions which were soluble in 70% ethanol and insoluble in 87% ethanol were prepared from liver cytosols. Electrophoretic analysis under denaturing conditions indicated that there were several quantitative or qualitative differences in the fractions from the two species. Fractions from both human and rat liver were found to be inhibitory for the incorporation of 3H-thymidine into DNA of foetal chick hepatocytes. Under conditions in which the rat fraction inhibited precursor incorporation into DNA of rat liver epithelial cells there was not a significant inhibitory effect with the fraction from human liver. DNA synthesis in a rat hepatoma cell line was not significantly inhibited by preparations from either species. The data suggested that corresponding fractions from both rat and human liver could have inhibitory effects on precursor incorporation into DNA but the magnitude of the effects and target cell specificity may differ.     

Primary cultured murine hepatocytes but not hepatoma cells regulate the cell number through density-dependent cell death

The mechanisms by which hepatocytes regulate their cell numbers in culture have been examined. We found that when murine hepatocytes were cultured at an overconfluent stage, the number of viable cells were reduced to that of the confluent stage 48 h later by cell death. Cell death was accompanied by LDH release, and it was observed only in primary cultured hepatocytes but not in hepatoma cells. Genomic DNA analysis using electrophoresis showed that DNA fragmentation, a biochemical hallmark of apoptosis, was induced in superconfluent cultures of hepatocytes in a cell-density-dependent fashion, but not in pre-confluent cells. DNA fragmentation was rapidly induced 2 h after the beginning of the in vitro culture and continued up to 24 h later. Flow cytometry analysis demonstrated that the nuclei from the hepatocytes in a high density culture were condensed and that the DNA content was reduced. These data suggest that the mechanism of cell death is apoptosis. The DNA fragmentation seen in the high density hepatocyte culture was not observed in hepatoma cell lines. Moreover, apoptosis was induced in hepatocytes of MRL/lpr mice, suggesting that the Fas antigen was not involved in the apoptotic process. Apoptosis was inhibited by a protein synthesis inhibitor, cycloheximide, and by a calmodulin antagonist, W-7. Taken together, the results indicate that high density culture of murine hepatocytes though not hepatoma cells regulate their cell numbers by an apoptotic mechanism. The apoptosis is dependent on de novo protein synthesis and intracellular calcium metabolism.     

Distribution and metabolism of protein-bound hydroxyproline in an elongating tissue, the Avena coleoptile

A study has been made of the distribution and metabolism of protein-bound hydroxyproline in an elongating tissue, the excised Avena coleoptile. The hydroxyproline-containing proteins of this tissue have been separated into 3 fractions on the basis of their solubilities. The cytoplasmic, trichloroacetic acid-insoluble proteins (S-fraction) contain the bulk of the proline of the cells but only 20% of the hydroxyproline. The cytoplasm also contains a previously unrecognized trichloroacetic acid-soluble, non-dialyzable fraction (DS-fraction) which is low in proline but contains 20% of the hydroxyproline. The remaining 60% of the hydroxyproline is in the wall-bound, cold alkali-soluble fraction (extensin).

Incorporation of free proline into the proline and hydroxyproline of all fractions is linear with time for at least 12 hours. The specific activity of the proline at any time is the same in all 3 fractions while the specific activity of the hydroxyproline is 4-times greater in the S-fraction than in the W-fraction. During a pulse-chase experiment the specific activity of the proline decreases 25 to 40% in all fractions during the chase. The labeling of hydroxyproline in the wall increases during the chase while that of the DS-fraction remains constant. In the S-fraction, the labeling in hydroxyproline rapidly drops 30 to 35% during the chase but then remains constant. It is concluded that the majority of the hydroxyproline-proteins in the cytoplasm are not transported to the wall. It is suggested that a sizeable portion of the cytoplasmic hydroxyproline may be located in enzymatic proteins.