Induction of lymphocyte cytotoxicity by modification of the effector or target cells with periodate or with neuraminidase and galactose oxidase.

Treatment of mouse spleen cells with periodate (NaIO4) or with neuraminidase and galactose oxidase (NAGO) induces blastogenesis and renders the cells cytotoxic to mastocytoma (P815) target cells. Treatment of target cells (P815 cells and turkey erythrocytes) with NaIO4 or with NAGO renders them susceptible to cytolysis by untreated mouse spleen cells. The cytotoxicity induced by NaIO4 is reduced upon reacting the NaIO4-treated, effector or target cells with borohydride or hydroxylamine. Thus the formation of free surface aldehydes on either the effector or target cell induced a cytotoxic effect. It is postulated that cross-linkage via a Schiff base between effector and target cell initiates the cytotoxic effect. Cytotoxicity induced by NaIO4 or NAGO is immunologically nonspecific and is independent of major antigenic differences between effector and target cells. Phagocytic cells are not involved in NaIO4-or NAGO-induced cytotoxicity toward P815 target cells.     

The requirement for macrophage-lymphocyte interaction in T lymphocyte proliferation induced by generation of aldehydes on cell membranes.

Guinea pig T lymphocyte proliferation induced by sodium periodate (NaIO4) or neuraminidase-galactose oxidase (NG) occurs when lymphocytes and macrophages are cultured together after treatment of either purified T lymphocytes or macrophages with these agents. Regardless of which cell initially bears the modified surface carbohydrate, lymphocyte proliferation requires the presence of viable homologous macrophages and fails to occur when they are replaced with fibroblasts, erythrocytes, L2C leukemia cells, thymocytes, PMN, line I hepatoma cells, or murine macrophages. Lymphocyte proliferation resulting from NaIO4 or NG treatment of lymphocytes is diminished when these cells are treated with proteolytic enzymes or aged in in vitro culture for 48 hr. By contrast, proteolytic enzyme treatment or in vitro aging has no effect on the ability of NaIO4 or NG-treated macrophages to induce lymphocyte proliferation. The requirement for macrophage-lymphocyte interaction in NaIO4 or NG-induced lymphocyte proliferation is indicative of a central role for the macrophage in the initiation of T lymphocyte proliferation.     

Biological effects of activation of human peripheral blood mononuclear cells by mitogenic oxidizing agents. I Alloantigen-independent activation of alloimmune memory cells

Mechanisms of activation of alloimmune memory cells by immunologically nonspecific signals were investigated utilizing the mitogenic oxidizing agents, neuraminidase and galactose oxidase (NAGO) and sodium periodate (IO₄^?). Direct activation of primary long-term human mixed-lymphocyte culture (MLC) cells (memory cells) with either NAGO or IO₄^? resulted in increased specific secondary cytolytic activity. Kinetics of the proliferative and cytotoxic responses resulting from such treatment of memory cells paralleled those resulting from treatment of memory cells with irradiated cells that were the stimulators in the primary MLC. Indirect activation of memory cells by NAGO or IO₄^?-treated and irradiated syngeneic cells also resulted in increased specific secondary cytolytic activity. In contrast, peripheral blood mononuclear cells (PBM) activated by the mitogenic oxidizing agents did not develop cytolytic activity toward syngeneic or multiple allogeneic target cells, despite extensive proliferative responses. Cytotoxicity generated by either direct or indirect activation of memory cells by IO₄^? was prevented by treatment of the oxidized cells with the reducing agent, sodium borohydride. Incubation of memory cells in supernatants from 24-hr cultures of PBM activated with either NAGO or IO₄^? resulted in proliferation and in an increase in cytolytic activity in memory cells, but not in PBM. These findings indicate that alloimmune memory cells can be activated by immunologically nonspecific lymphocyte-derived signals that do not depend on alloantigen or lectin.     

The effects of neuraminidase and galactose oxidase on murine lymphocytes. I. Evidence for the differential delivery of signal(s) leading to cell proliferation and the differentiation of cytotoxic T cells.

The sequential treatment of normal C57BL/6 mouse spleen cell populations with neuraminidase (NA) and galactose oxidase (GO) resulted in cell proliferation, but not in the differentiation of cytotoxic T cells. In contrast, C57BL/6 spleen cells derived from animals primed 5 to 8 months earlier with alloantigen (P815 mastocytoma cells of the DBA/2 strain) both proliferated and demonstrated T cell-mediated cytotoxicity after NAGO stimulation. T cells differentiating into cytotoxic cells after NAGO treatment demonstrated properties similar to alloantigen-specific 'memory' T cells. These were: 1) cytotoxicity developed only from 'primed' cell populations, 2) cytotoxicity developed within 24 hr after NAGO treatment, 3) DNA synthesis was not required for the differentiation of cytotoxic cells during the first 24 hr of culture but both DNA synthesis and cell proliferation were required for the cytotoxicity developing after 24 hr, and 4) all cytotoxicity induced by NAGO showed specificity for the priming alloantigen. It was found, furthermore, that cytotoxicity could be induced at much lower GO concentrations than needed for increased DNA synthesis. We interpret this finding as an indication that NAGO can differentially deliver two 'signals' to T lymphocytes: one leading to cell proliferation, the other causing the differentiation of memory T cells into cytotoxic effectors.     

Interrelationship between sodium cyanate and pH in the regulation of tumor cell division

Previous studies have suggested that the selective inhibitory effects of sodium cyanate on tumor metabolism in vivo may be related to a lower interstitial pH in tumors. In the present work, the influence of extracellular pH on the actions of sodium cyanate was studied with one rat hepatoma cell line (HTC) and two human colon tumor cell lines (HT29 and LS174T) and with rat hepatocytes to determine if the effects are accompanied by changes in intracellular pH. With some tumor cells, an inhibition of cell proliferation was observed when the cells were exposed to an acidic medium (pH 6.6). However, the LS174T line of human tumor cells divided at pH 6.6 essentially as fast as at pH 7.4. In the concentration range of 0.02-0.1 mg/ml, a greater inhibitory effect of cyanate on cell proliferation was observed at the lower pH. Intracellular pH was found to be influenced by the sodium ion concentration of the medium to a similar degree in the three tumor lines that were examined. The intracellular pH was found to be significantly affected by cyanate in rat hepatocytes and in two of the tumor cell lines (HT29 and LS174T). The data suggested that not only does extracellular pH influence the inhibitory effect of cyanate on tumor cell proliferation but also that cyanate can affect the regulation of intracellular pH in normal and neoplastic cells.     

Metabolic fate of cell surface glycoproteins during immunoglobulin-induced internalization

Goat antibodies directed against a subset of the externally oriented plasma membrane glycoproteins of hepatoma tissue culture (HTC) cells were used to follow the metabolic fate of the membrane antigens and the specifically bound immunoglobulin molecules in this cell type in cultures. Analyses of the immunoprecipitates from cells labeled in situ with neuraminidase and galactose oxidase, followed by reduction with tritiated sodium borohydride, indicate that about 40% of the galactose-labeled plasma membrane glycoproteins are recognized by the antiserum. Fluorescent microscopic analyses of cells treated with fluorescein-conjugated immunoglobulins and analyses of trypsin accessibility indicate that probably all of the antibodies bound to the cell surface are patched and internalized within about 4 hr when the cells are subsequently cultured at 37 degrees C in the presence of rabbit anti-goat immunoglobulins. At the same time, the antigens are also interiorized. Analyses of the cellular localization of the interiorized antigens and antibodies by cell fractionation on Percoll gradients show that the immunoglobulins to the cell surface antigens and the antigens themselves migrate to the same region of the Percoll gradient as lysosomal hydrolases. Although the antibodies bind to the cell surface glycoproteins and bring about patching and interiorization, there is no effect on the degradation of the plasma membrane antigens labeled via the galactose oxidase/borohydride reduction method. Furthermore, the iodinated antibodies directed against these membrane glycoproteins behave in their turnover properties like membrane antigens; the cell-bound specific immunoglobulins have the same half-life as the membrane glycoproteins. When the cells that had been reacted with the goat antibodies to membrane glycoprotein were cultured in the presence of rabbit anti-goat immunoglobulins, degradation of the former antibodies was effectively decreased. Similar results were obtained with concanavalin A and antibodies directed against this plant lectin.     

Tumor-induced alteration in macrophage accessory cell activity on autoreactive T cells

Using a tumor-model system, differences in the accessory cell capabilities on autoreactive T cells of splenic macrophages from normal and tumor-bearing hosts (TBH) were assessed in the syngeneic mixed lymphocyte reaction. Tumor development caused a drop in autoreactivity. At 0 and 7 days of tumor growth, no drop in reactivity occurred when TBH macrophages were used as accessory cells and L3T4+ autoreactive T cells from normal mice were used as responder cells. However, by day 14, there was a 32% drop in reactivity, and by day 21 only 22% of the T cell reactivity remained when TBH macrophages were used as accessory cells. Alterations in macrophage Ia antigen during tumor growth were first investigated as the potential cause of reduced autoreactivity. Before tumor growth (day 0) 59% of the splenic macrophages were found to be Ia+. Day-7 TBH macrophages showed no difference in Ia antigen expression when compared to day 0 macrophages. However, by day 14, TBH macrophages showed a 9% decrease, and by day 21 they showed a 36% decrease in the number which were Ia+. Concomitant with the decrease in the number of Ia+ cells was a decrease in the density of Ia antigen expression on day-14 and -21 TBH macrophages. In day-14 and -21 TBH macrophages, two populations were seen that were Ia+. The first had a 10%-20% decrease in Ia antigen expression per cell while the second population had a greater than 50% drop in Ia antigen expression per cell. By titrating and mixing TBH macrophages with normal host macrophages, we assessed whether they could actively mediate suppression of autoreactive T cells. A titratable suppressive phenomenon was demonstrated using day-21 TBH macrophages. In contrast, day-7 and -14 TBH macrophages titrated with normal host macrophages had no effect on the syngeneic mixed lymphocyte reactivity. Lastly, we investigated whether the macrophage-mediated suppression was caused by increased prostaglandin secretion. Addition of indomethacin to cultures increased autoreactive T cell reactivity stimulated by normal or TBH macrophages (59% and 99% increase, respectively). Although indomethacin reduced suppression mediated by TBH macrophages, autoreactivity did not return to levels induced by untreated or indomethacin-treated cells from a normal host. Taken together, the data suggested that tumor growth modulates the function of macrophage accessory cells with autoreactive T cells in at least two ways: by decreasing Ia antigen expression and by increasing suppressor activity.     

Dichloroacetate Enhances Adriamycin-Induced Hepatoma Cell Toxicity In Vitro and In Vivo by Increasing Reactive Oxygen Species Levels

A unique bioenergetic feature of cancer, aerobic glycolysis is considered an attractive therapeutic target for cancer therapy. Recently, dichloroacetate (DCA), a small-molecule metabolic modulator, was shown to reverse the glycolytic phenotype, induce reactive oxygen species (ROS) generation, and trigger apoptosis in various tumor cells. In this work, the capacity of DCA to enhance Adriamycin (ADM) efficacy in hepatoma cells by modulating glucose metabolism and redox status was evaluated. Two human hepatoma (HCC-LM₃ and SMMC-7721) and a normal liver (LO₂) cell lines were treated with DCA or ADM alone, or in combination. Exposure of hepatoma cells to DCA/ADM combination resulted in significantly decreased cell viability and increased percentage of apoptotic cells as well as intracellular ROS levels, in comparison with treatment with DCA or ADM alone. However, simultaneous treatment with the thiol antioxidant N-acetylcysteine (NAC, 10 mmol/L) reduced the elevated ROS levels and protected hepatoma cells from the cytotoxic effects of DCA/ADM combination. L-buthionine-[S,R]-sulfoximine, an inhibitor of glutathione synthesis, enhanced hepatoma cell sensitivity to DCA/ADM combination. Interestingly, treatment with DCA/ADM combination did not significantly increase cytotoxicity in normal hepatocytes in comparison with the drugs administered individually. Finally, DCA reduced tumor growth and enhanced ADM efficacy on HCC-LM₃ hepatoma in mice. Overall, our data suggest that DCA enhances ADM cytotoxicity in hepatoma cells by increasing intracellular ROS levels and provide a strong biochemical rationale for the use of DCA in combination with ADM for treatment of hepatoma.     

Immunological Properties of TtT/M-87 Cell Line Established from Murine Pituitary Tumor-Associated Macrophages

TtT/M-87 cell is a macrophage cell line established from thyrotropic pituitary tumor tissues in mouse. In this paper, we report the immunological properties of M-87 cells as a model of tumor-associated macrophage. Contrasting with resident peritoneal macrophages, M-87 cells constitutively secreted small but significant amounts of TNF-α and IL-1α, which were detectable in both biological assays (cytotoxic activity for L929 and co-mitogenic activity for Con A-induced T cell proliferation, respectively) and ELISA, and produced larger amounts of these cytokines upon stimulation with LPS. They expressed MHC class II molecules on their cell surface without stimulation by IFN-γ. The accessory or antigen-presenting cell activity in antibody-producing response of spleen lymphocytes to sheep red blood cells was shown to be much higher in M-87 cells than normal peritoneal macrophages. In addition, when normal spleen lymphocytes were cultured with allogeneic tumor cells, such as EL-4 and S-180, in the presence of M-87 cells, lymphocytes reactive to stimulator cells were activated to manifest inhibitory effect on the tumor cell growth and also to manifest specific cytotoxic effect on the allogeneic tumor cells. These results show that M-87 cells derived from tumor-associated tissue are activated macrophages and that they are inhibitory to tumor cell growth and augmentative in the induction of T-cell-mediated immune responses.     

Interaction between cisplatin-treated macrophages and Dalton's lymphoma cells in vitro

Murine peritoneal macrophages treated with cisplatin (10 micrograms/ml) showed increased binding to Dalton's lymphoma cells in vitro. Macrophages and target cells both extend cytoplasmic extensions towards each other, which finally join and fuse to form a distinct cytoplasmic bridge between the two cells. At later stages of coincubation the macrophages and tumor cells get closely bound with several short cytoplasmic connections. Finally the plasmalemmae between the two cells fuse over a large surface area and the tumor cell is phagocyted. No tumor cell was found to form cytoplasmic bridges when incubated with untreated macrophages. The base of cytoplasmic bridge and the cytoplasmic bridge between the macrophage and tumor cells stained for actin and fibronectin, but not for tubulin. We also report the transfer of lysosomes from the cytoplasm of cisplatin-treated macrophages to the tumor cell cytoplasm through cytoplasmic bridges. It is further reported that cisplatin-induced macrophage cytotoxicity against DL cells is inhibited by nifedipine and chlorpromazine.     

The selective activation of T8+ cells by neuraminidase and galactose oxidase is mediated by activated T4+ cells

The response of highly enriched populations of human T8+ lymphocytes to the oxidative mitogenic enzymes neuraminidase (NA) and galactose oxidase (GO) was enhanced by NAGO-primed T4+ lymphocytes. No similar enhancement occurred when the cells were primed with phytohemagglutinin (PHA). In the absence of subclass contamination (1%), the T8+ and T4+ cells responded equally to NAGO by the criterion of DNA replication. The addition of a small number, 2-10%, of NAGO-T4+ cells to the NAGO-T8+ cells enhanced DNA synthesis by as much as 8.5-fold. Augmentation of the cellular response did not occur unless the T4+ cells were activated by NAGO. The converse situation, 2-10% of NAGO-T8+ cells in a primarily NAGO-T4+ cell population, did not increase the DNA synthetic response of the NAGO-T4+ cells. The NAGO-T4+ cells did not augment the early event of increased phosphatidylinositol metabolism or the midcycle event of induction of receptors for interleukin 2 (IL2) and transferrin. The NAGO-T4+ cells therefore increased the probability that fully activated T8+ lymphocytes crossed the G1/S boundary. The basis for this effect was not an enhanced responsiveness of the NAGO-T8+ cells to IL2 or to other soluble growth mediators in medium conditioned by NAGO-activated lymphocytes. The results of this investigation thus implicate a control point in the NAGO-T8+ lymphocyte cell cycle that is positively modulated by the NAGO-T4+ cells themselves or by a product of their activation.     

Biosynthesis of various types of collagen by human hepatoma cells in vitro

A cloned human hepatoma cell line (HH2-1) produced and formed collagen fibers in vitro. The relative rate of collagen synthesis by the cells was increased with an enhancement of the cell density. An analysis of the components of the collagen using sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the cells synthesized interstitial collagen, types I and III, and other collagenous proteins. Thus, human hepatoma cells may play an important role in the formation of stromal collagen in the tumor.     

Tumor cell killing by macrophages activated in vitro with lymphocyte mediators: I. Development of a short term in vitro microcytotoxicity assay

We describe a short term in vitro microcytotoxicity assay to study the killing by macrophages of adhering tumor cells prelabeled with [³H]proline. With this assay, killing of line 1 hepatoma cells can be demonstrated within 6 hr of cocultivation with normal macrophages activated in vitro with the lymphocyte mediator macrophage activating factor (MAF).The data show that the decrease in residual adhering radioactivity, on which the calculations of percent kill are based, results from the lysis as well as from the detachment of tumor cells. However, detached tumor cells fail to exclude trypan blue and are no longer capable of DNA and protein synthesis. This suggests that the detachment of intact but nonviable tumor cells precedes actual target cell lysis in this system.     

Alpha-fetoprotein enhances the proliferation of human hepatoma cells in vitro

Although the biological functions of alpha-fetoprotein ( AFP ) have been extensively studied, little is known about its effect on tumor cell growth. Our previous work has found that human AFP significantly stimulates the growth of mouse hepatoma cells in vitro. The purpose of the present study is to observe the effect of AFP on the proliferation of human hepatoma cells in vitro. Using a MTT- microculture tetrazolium assay, we found that the proliferation of human hepatoma cells was enhanced by in vitro treatment of AFP. However, the same concentrations of AFP had no effect on HL - 60 human leukemia cell proliferation, indicating that the human hepatoma cell proliferation - promoting role of AFP was not simply due to non-specific addition of exogenous protein and the proliferation enhancement of AFP showed certain tumor cell specificity. On the other hand, the growth stimulation of AFP could be diminished by rabbit anti - human AFP antibody. The anti- AFP antibody alone suppressed the growth of BEL - 7404 human hepatoma cells, not affecting HL - 60 cell proliferation. BEL - 7404 cell proliferation was not inhibited by normal rabbit immunoglobulins to demonstrate the specificity of anti-AFP effect. Taken together, it is concluded that AFP enhances the proliferation of human hepatoma cells in vitro, and this effect is seemingly mediated by an AFP/receptor autocrine pathway.     

Downregulation of miR-210 expression inhibits proliferation, induces apoptosis and enhances radiosensitivity in hypoxic human hepatoma cells in vitro

Hypoxia is a common feature of solid tumors and an important contributor to tumor radioresistance. miR-210 is the most consistently and robustly induced microRNA under hypoxia in different types of tumor cells and normal cells. In the present study, to explore the feasibility of miR-210 as an effective therapeutic target, lentiviral-mediated anti-sense miR-210 gene transfer technique was employed to downregulate miR-210 expression in hypoxic human hepatoma SMMC-7721, HepG2 and HuH7 cells, and phenotypic changes of which were analyzed. Hypoxia led to an increased hypoxia inducible factor-1α (HIF-1α) and miR-210 expression and cell arrest in the G(0)/G(1) phase in all cell lines. miR-210 downregulation significantly suppressed cell viability, induced cell arrest in the G(0)/G(1) phase, increased apoptotic rate and enhanced radiosensitivity in hypoxic human hepatoma cells. Moreover, apoptosis-inducing factor, mitochondrion-associated, 3 (AIFM3) was identified as a direct target gene of miR-210. AIFM3 downregulation by siRNA attenuated radiation induced apoptosis in miR-210 downregulated hypoxic human hepatoma cells. Taken together, these data suggest that miR-210 might be a potential therapeutic target and specific inhibition of miR-210 expression in combination with radiotherapy might be expected to exert strong anti-tumor effect on hypoxic human hepatoma cells.     

Tumor infiltrating leukocytes (tils) during progressive tumor growth and BCG-mediated tumor regression

Tumor regression was induced by intralesional injection with BCG, 7 days after inoculation of line 10 hepatocellular carcinoma cells into strain 2 guinea pigs. Tumor-infiltrating leukocytes (TILS) were characterized immunohistochemically with 11 monoclonal antibodies (MoAbs) during the induction phase of line 10-immunity, and during immune-mediated regression of the tumor, at days 12 and 28 after tumor cell inoculation, respectively. At day 5 after BCG-injection (day 12 after tumor cell inoculation), there were no major differences between the TIL subpopulations of the BCG-treated and untreated tumors. The TILS were mainly T-cells, as identified by MoAbs against Pan T-cells (CT5), T-cytotoxic/suppressor cells (CT6) and T-helper/inducer cells (H155). A limited number of macrophages was also present. However, at day 21 after BCG-treatment (28 days after tumor cell inoculation), the fibrous stroma was increased dramatically in most of the BCG-treated tumors, and as a result, the tumor cell islets were smaller than in control tumors. In the BCG treated tumors, the numbers of T-cells and macrophages were increased. In growing and regressing tumors, MHC class I and II antigens were strongly expressed in TILS and in the tumor stroma. Line 10 tumor cells prior to inoculation expressed no MHC class I or II antigens. In the centers of the tumor islets at days 12 and 28, expression of these antigens was not found. However, MHC class I and II antigens were expressed on tumor cells at sites where they lay close to the fibrous stroma or TILS. This observation was made in progressively growing tumors and was most apparent in BCG-treated tumors.     

Cell-mediated immune response to syngeneic UV induced tumors: I. The presence of tumor associated macrophages and their possible role in the in Vitro generation of cytotoxic lymphocytes

A primary in vitro sensitization system employing a chromium release assay was utilized to investigate reactivity of murine spleen cells toward syngeneic ultraviolet (uv) light induced fibrosarcomas. These tumors are immunologically rejected in vivo when implanted into normal syngeneic mice but grow progressivly when implanted into syngeneic mice that had previously been irradiated with subcarcinogenic levels of uv light. Following appropriate sensitization, spleen cells from both normal and uv irradiated mice are capable of developing cytotoxic lymphocytes in vitro against the uv induced tumors. It was subsequently discovered that in situ uv induced tumors all contained macrophages of host origin that became demonstrable only after enzymatic dissociation of the tumor tissue. These macrophages were immunologically active in vitro as their presence in the stimulator cell population was necessary to achieve an optimum anti-tumor cytotoxic response following in vitro sensitization. Anti-tumor reactivity generated by mixing spleen cells and tumor cells in the absence of tumor derived macrophages could be greatly enhanced by the addition of normal syngeneic peritoneal macrophages. When in vitro anti-tumor reactivity of spleen cells from normal and uv treated mice was compared under these conditions we again found no significant difference in the magnitude of the responses. In addition, the cytotoxic cells generated in response to uv induced tumors appeared to be highly cross reactive with respect to their killing potential. Cross reactive killing was observed between all uv induced tumors tested as well as with a syngeneic benz[a]pyrene (BP) induced fibrosarcoma. No cytotoxicity was observed against normal syngeneic PEC's even through these cells were shown to be susceptible to lysis by anti-H-2^k effector cells. It was concluded that: (a) A significant number of host-derived macrophages are present in uv tumor tissue. (b) These macrophages are important for the in vitro generation of tumor specific cytotoxicity. (c) Spleen cells from uv treated mice are capable of recognizing and responding against uv tumor associated antigens in vitro. Cytotoxic effector cells generated in response to uv induced tumors appear to have specificity for tumor associated antigens (TAA) present on all uv tumors tested as well as a syngeneic BP induced tumor. The relationship between in vivo and in vitro reactivity against uv tumors is discussed.     

Macrophage-mediated cytostasis of neoplastic hemopoietic cells: cytofluorometric analysis of the reversible cell cycle block

Nonactivated mouse peritoneal macrophages inhibit the proliferation of neoplastic hemopoietic cells in vitro. This effect is dependent upon the number of adherent macrophages present in cultures of hemopoietic tumor cells and can be documented by various parameters used as indices of cell proliferation. The two-layer soft agar culture system permits analysis of the regulatory functions of macrophage-derived diffusible substances under conditions of extremely low cell density and where macrophage-tumor cell contact is prevented by the gel matrix. The ability of the underlayers of macrophages to inhibit colony formation by hemopoietic tumor cells indicates that such an effect can be mediated by factor(s) elaborated by macrophages. Evidence that the mode of action of macrophages on tumor cell proliferation is cytostatic rather than cytotoxic is the capability of the macrophages to retard tumor cell growth in a particular phase of the cell cycle with retention of cell viability. Growth inhibition could be demonstrated to be reversible, with tumor cells entering normal cell cycle distributions shortly after being removed from macrophages or macrophage-derived factors. Cytofluorometric analysis of cell cycle inhibition correlated with viable cell counts and mitotic indices and confirms the suitability of this method for studying tumor cell proliferation.     

The inhibitory effect of transthyretin gene on growth of human hepatoma cells

Transthyretin(TTR) gene was highly expressed in normal liver and it has been found to be deleted in part of DNA samples from human hepatic cancer.Its mRNA expression was suppressed in most hepatoma samples.In order to study the biological effect of TTR gene on the growth of hepatoma cells,a recombinant vector containing TTR cDNA was constructed by pCMV,then it was transfected into hepatoma cell lines SMMC-7721 and Q3.It has been demonstrated that the inhibition of growth rate of TTR cDNA transfected hepatoma cells was about 50% in strength compared with that of the control.This inhibition was further enhanced when the transfected hepatoma cells were treated with all-trans retinoic acid.Hepatoma cells of cell lines PLC/PRF/5,SMMC-7721 and Q3 as well as hepatoma cells SMMC-7721 transfected with pCMV or pCMV-TTR were analyzed for TTR expression by Northern hybridization.The low level of TTR expression was found in both hepatoma cell lines and in SMMC-7721 cells transfected with pCMV alone.However,a remarkable TTR mRNA expression was observed in hepatoma SMMV-7721 cells transfected with pCMV-TTR.It seems possible that TTR gene might be a candidate of cancer suppressor gene for human hepatic cancer.