Pit cells (Hepatic natural killer cells) of the rat induce apoptosis in colon carcinoma cells by the perforin/granzyme pathway

Cells in the liver microenvironment regulate the process of liver metastasis

The research of liver metastasis is a developing field. The ability of tumor cells to invade the liver depends on the complicated interactions between metastatic cells and local subpopulations in the liver (including Kupffer cells, hepatic stellate cells, liver sinusoidal endothelial cells, and immune-related cells). These interactions are mainly mediated by intercellular adhesion and the release of cytokines. Cell populations in the liver microenvironment can play a dual role in the progression of liver metastasis through different mechanisms. At the same time, we can see the participation of liver parenchymal cells and nonparenchymal cells in the process of liver metastasis of different tumors. Therefore, the purpose of this article is to summarize the relationship between cellular components of liver microenvironment and metastasis and emphasize the importance of different cells in the occurrence or potential regression of liver metastasis.

Tissue-Resident NK Cells: Development, Maturation, and Clinical Relevance

Natural killer (NK) cells belong to type 1 innate lymphoid cells (ILC1) and are essential in killing infected or transformed cells. NK cells mediate their effector functions using non-clonotypic germ-line-encoded activation receptors. The utilization of non-polymorphic and conserved activating receptors promoted the conceptual dogma that NK cells are homogeneous with limited but focused immune functions. However, emerging studies reveal that NK cells are highly heterogeneous with divergent immune functions. A distinct combination of several activation and inhibitory receptors form a diverse array of NK cell subsets in both humans and mice. Importantly, one of the central factors that determine NK cell heterogeneity and their divergent functions is their tissue residency. Decades of studies provided strong support that NK cells develop in the bone marrow. However, evolving evidence supports the notion that NK cells also develop and differentiate in tissues. Here, we summarize the molecular basis, phenotypic signatures, and functions of tissue-resident NK cells and compare them with conventional NK cells.

Probing the unseen structure and function of liver cells through atomic force microscopy

With the arrival of atomic force microscopy (AFM) about thirty years ago, this new imaging tool opened up a new area for the exploration of biological samples, ranging from the tissue and cellular level down to the supramolecular scale. Commercial instruments of this new imaging technique began to appear in the five years following its discovery in 1986 by Binnig, Quate & Gerber. From that point onwards the AFM has attracted many liver biologists, and the number of publications describing structure-function relationships on the diverse set of liver cells has grown steadily ever since. It is therefore timely to reflect on the achievements of AFM in disclosing the cellular architecture of hepatocytes, liver sinusoidal endothelial cells, Kupffer cells, stellate cells and liver-associated natural killer cells. In this thematic paper, we present new data and provide an in-depth overview of the current AFM literature on liver cell biology. We furthermore include a future outlook on how this scanning probe imaging tool and its latest developments can contribute to clarify various structural and functional aspects of cells in liver health and disease.

Liver natural killer cells: subsets and roles in liver immunity

The liver represents a frontline immune organ that is constantly exposed to a variety of gut-derived antigens as a result of its unique location and blood supply. With a predominant role in innate immunity, the liver is enriched with various innate immune cells, among which natural killer (NK) cells play important roles in host defense and in maintaining immune balance. Hepatic NK cells were first described as 'pit cells' in the rat liver in the 1970s. Recent studies of NK cells in mouse and human livers have shown that two distinct NK cell subsets, liver-resident NK cells and conventional NK (cNK) cells, are present in this organ. Here, we review liver NK cell subsets in different species, revisiting rat hepatic pit cells and highlighting recent progress related to resident NK cells in mouse and human livers, and also discuss the dual roles of NK cells in liver immunity.

Xenobiotic and Endobiotic Mediated Interactions Between the Cytochrome P450 System and the Inflammatory Response in the Liver

The liver is a unique organ in the body as it has significant roles in both metabolism and innate immune clearance. Hepatocytes in the liver carry a nearly complete complement of drug metabolizing enzymes, including numerous cytochrome P450s. While a majority of these enzymes effectively detoxify xenobiotics, or metabolize endobiotics, a subportion of these reactions result in accumulation of metabolites that can cause either direct liver injury or indirect liver injury through activation of inflammation. The liver also contains multiple populations of innate immune cells including the resident macrophages (Kupffer cells), a relatively large number of natural killer cells, and blood-derived neutrophils. While these cells are primarily responsible for clearance of pathogens, activation of these immune cells can result in significant tissue injury during periods of inflammation. When activated chronically, these inflammatory bouts can lead to fibrosis, cirrhosis, cancer, or death. This chapter will focus on interactions between how the liver processes xenobiotic and endobiotic compounds through the cytochrome P450 system, and how these processes can result in a response from the innate immune cells of the liver. A number of different clinically relevant diseases, as well as experimental models, are currently available to study mechanisms related to the interplay of innate immunity and cytochrome P450-mediated metabolism. A major focus of the chapter will be to evaluate currently understood mechanisms in the context of these diseases, as a way of outlining mechanisms that dictate the interactions between the P450 system and innate immunity.

Natural history of hepatic metastases from colorectal cancer - pathobiological pathways with clinical significance

Colorectal cancer hepatic metastases represent the final stage of a multi-step biological process. This process starts with a series of mutations in colonic epithelial cells, continues with their detachment from the large intestine, dissemination through the blood and/or lymphatic circulation, attachment to the hepatic sinusoids and interactions with the sinusoidal cells, such as sinusoidal endothelial cells, Kupffer cells, stellate cells and pit cells. The metastatic sequence terminates with colorectal cancer cell invasion, adaptation and colonisation of the hepatic parenchyma. All these events, termed the colorectal cancer invasion-metastasis cascade, include multiple molecular pathways, intercellular interactions and expression of a plethora of chemokines and growth factors, and adhesion molecules, such as the selectins, the integrins or the cadherins, as well as enzymes including matrix metalloproteinases. This review aims to present recent advances that provide insights into these cell-biological events and emphasizes those that may be amenable to therapeutic targeting.

A review of mast cells and liver disease: What have we learned?

BACKGROUND

Mast cells are recognized as diverse and highly complicated cells. Aside from their notorious role in allergic inflammatory reactions, mast cells are being implicated in numerous disease processes from heart disease to cancer. Mast cells have been implicated in liver pathogenesis including hepatitis and host allograft rejection after liver transplantation.

AIMS

The aim of this review is to discuss the traditional function of mast cells, their location and anatomy with regards to hepatic vasculature and the role of mast cells in hepatic diseases including liver regeneration and rejection. Finally, we will touch on the role of mast cells in liver cancer. In conclusion, we hope that the reader comes away with a better understanding of the diverse and potential role(s) that mast cells may play in liver pathologies.

The prometastatic microenvironment of the liver

The liver is a major metastasis-susceptible site and majority of patients with hepatic metastasis die from the disease in the absence of efficient treatments. The intrahepatic circulation and microvascular arrest of cancer cells trigger a local inflammatory reaction leading to cancer cell apoptosis and cytotoxicity via oxidative stress mediators (mainly nitric oxide and hydrogen peroxide) and hepatic natural killer cells. However, certain cancer cells that resist or even deactivate these anti-tumoral defense mechanisms still can adhere to endothelial cells of the hepatic microvasculature through proinflammatory cytokine-mediated mechanisms. During their temporary residence, some of these cancer cells ignore growth-inhibitory factors while respond to proliferation-stimulating factors released from tumor-activated hepatocytes and sinusoidal cells. This leads to avascular micrometastasis generation in periportal areas of hepatic lobules. Hepatocytes and myofibroblasts derived from portal tracts and activated hepatic stellate cells are next recruited into some of these avascular micrometastases. These create a private microenvironment that supports their development through the specific release of both proangiogenic factors and cancer cell invasion- and proliferation-stimulating factors. Moreover, both soluble factors from tumor-activated hepatocytes and myofibroblasts also contribute to the regulation of metastatic cancer cell genes. Therefore, the liver offers a prometastatic microenvironment to circulating cancer cells that supports metastasis development. The ability to resist anti-tumor hepatic defense and to take advantage of hepatic cell-derived factors are key phenotypic properties of liver-metastasizing cancer cells. Knowledge on hepatic metastasis regulation by microenvironment opens multiple opportunities for metastasis inhibition at both subclinical and advanced stages. In addition, together with metastasis-related gene profiles revealing the existence of liver metastasis potential in primary tumors, new biomarkers on the prometastatic microenvironment of the liver may be helpful for the individual assessment of hepatic metastasis risk in cancer patients.

The tumor cell-host organ interface in the early onset of metastatic organ colonisation

Metastatic lesions are the leading cause of death among cancer patients. These lesions usually originate from clonal proliferation of single tumor cells dispersed from the primary tumor into the circulation which finally arrest in the capillary bed of distant organs. The microenvironment within the circulation of potential metastatic target organs provides a variety of pro- and anti- metastatic stimuli regulating the onset of organ colonisation by metastatic tumor cells. Mechanical shear stress, anoikis and cell mediated cytotoxicity within the microcirculation probably clear most circulating tumor cells. Adhesion, and eventually extravasation, are essential initial interactions of circulating tumor cells with distant organs and can provide escape from the cytotoxic environment within the circulation. Adhesion to the capillary wall is mostly controlled by the organ-specific availability of adhesion molecules on tumor cells, the endothelium, and the composition of the underlying extracellular matrix. The availability of pro-adhesive and pro-migratory paracrine signals provided by the organ specific microenvironment can further initiate the onset of metastatic organ colonisation. Tumor cell and microenvironment factors regulating survival within the microcirculation, adhesion and extravasation of tumor cells are highlighted in the review.

Adoptive transfer of TRAIL-expressing natural killer cells prevents recurrence of hepatocellular carcinoma after partial hepatectomy

BACKGROUND

Antitumor activity of the liver natural killer (NK) cells reportedly decreases after partial hepatectomy, suggesting that patients with such depressed immune status are susceptible to the recurrence of hepatocellular carcinoma (HCC). We hypothesize that adoptive immunotherapy using activated NK cells can be a novel strategy to improve the depressed immune status in patients with HCC after hepatectomy or partial liver transplantation. In the present study, we have tested this hypothesis by using a mouse model.

METHODS

Intraportal injection of 1-5 x 10(6) Hepa1-6 cells (hepatoma cell line) did not result in liver metastases in untreated B6 mice, but led to the growth of liver metastases after extensive partial hepatectomy. Utilizing this murine HCC metastasis model, we investigated the antitumor activity of both remnant liver and exogenously transferred NK cells.

RESULTS

The anti-HCC activity of liver NK cells significantly decreased after partial hepatectomy. The expression of CD69 and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) on liver NK cells was temporarily downregulated. The adoptive transfer of NK cells, including a TRAIL-expressing fraction, extracted from the liver perfusates of poly I:C-stimulated B6 mice inhibited the growth of liver metastasis in B6 or (B6xBALB/c) F1 (B6CF1) mice that underwent hepatectomy and received intraportal Hepa1-6 injection.

CONCLUSIONS

These findings indicate that adoptive immunotherapy using activated NK cells extracted from normal liver perfusates may be a novel technique for reconstituting the depressed immune status in cases of living donor liver transplantation involving HCC patients, recipients of a partial liver graft.

Cross-presentation of antigens from apoptotic tumor cells by liver sinusoidal endothelial cells leads to tumor-specific CD8+ T cell tolerance

Development of tumor-specific T cell tolerance contributes to the failure of the immune system to eliminate tumor cells. Here we report that hematogenous dissemination of tumor cells followed by their elimination and local removal of apoptotic tumor cells in the liver leads to subsequent development of T cell tolerance towards antigens associated with apoptotic tumor cells. We provide evidence that liver sinusoidal endothelial cells (LSEC) remove apoptotic cell fragments generated by induction of tumor cell apoptosis through hepatic NK1.1+ cells. Antigen associated with apoptotic cell material is processed and cross-presented by LSEC to CD8+ T cells, leading to induction of CD8+ T cell tolerance. Adoptive transfer of LSEC isolated from mice challenged previously with tumor cells promotes development of CD8+ T cell tolerance towards tumor-associated antigen in vivo. Our results indicate that hematogenous dissemination of tumor cells, followed by hepatic tumor cell elimination and local cross-presentation of apoptotic tumor cells by LSEC and subsequent CD8+ T cell tolerance induction, represents a novel mechanism operative in tumor immune escape.

Structural and functional aspects of the liver and liver sinusoidal cells in relation to colon carcinoma metastasis

Nowadays, liver metastasis remains difficult to cure. When tumor cells escape and arrive in the liver sinusoids, they encounter the local defense mechanism specific to the liver. The sinusoidal cells have been widely described in physiologic conditions and in relation to metastasis during the past 30 years. This paper provides an “overview” of how these cells function in health and in diseases such as liver metastasis.

Liver immunobiology

Tle liver has a number of important functions in innate and adaptive immunity. Contributions to the innate (nonspecific) immune system include production of acute phase proteins, nonspecific phagocytosis of particles, nonspecific pinocytosis of molecules, and nonspecific cell killing. Hepatic involvement in innate immunity contributes to the systemic response to local inflammation, clearance of particles and soluble molecules from the circulation, and killing of invading cells such as neoplastic cells. Liver involvement in the adaptive (specific) immune system includes deletion of activated T cells, induction of tolerance to ingested and self-antigens, extrathymic proliferation of T cells, and deletion of many of the signaling and effector molecules. Hepatic involvement in adaptive immunity allows clearance of activated T cells and signaling molecules following inflammatory reactions, and promotes immunologic tolerance toward potentially antigenic proteins that are absorbed from the intestinal tract. The liver is a major site of extrathymic T cell development, which assumes increasing significance with aging in mammals. Perturbations in hepatic structure or function can result in significant ramifications in both the innate and adaptive immune systems.

Hepatic local cellular immune status and prognosis of hepatocellular carcinoma

AIM: To investigate the local cellular immune status in the tissues of liver cirrhosis (LC) and hepatocellular carcinoma (HCC) and its relationship with the prognosis of the patients.

METHODS: Surgical specimens from 60 cases of HCC, 62 cases of LC, and 23 normal liver tissues were stained of CD₃, CD₅₇, CD₂₀, CD₆₈ and GrB with streptavidin-horseradish peroxidase detection system to assess the number and the distribution of hepatic local immunocytes.

RESULTS: The numbers of T lymphocytes (60.5±18.9), B lymphocytes (40.3±29.9) and NK cells (6.8±5.1) in the liver of HCC patients were significantly higher than those in the liver of LC patients (53.0±18.7, t = 2.21, P = 0.029<0.05; 21.5±18.2, t = 4.19, P = 0.000<0.01; 4.2±2.9, t = 3.53, P = 0.001<0.01, respectively) and normal controls (45.4±11.7, t = 3.57, P = 0.001<0.01; 8.1±5.9, t = 7.97, P = 0.000<0.01; 4.8±2.3, t = 2.54, P = 0.013<0.05, respectively ); while the number of macrophages (Mf)(24.6±13.4)was significantly lower than that in the liver of LC patients(41.0±13.5, t = 6.74, P = 0.000<0.01)and normal controls (40.3±8.9, t = 6.17, P = 0.000<0.01). The numbers of T and B lymphocytes in the liver of LC patients were significantly higher than those in normal controls (T cells: 53.0±18.7 vs 45.4±11.7, t = 2.23, P = 0.029<0.05; B cells: 21.5±18.2 vs 8.1±5.9, t = 5.14, P = 0.000<0.01). GrB positive cells in the liver mostly consisted of CD₅₇ positive cells and a few CD₃ positive cells. The numbers of NK cells, B lymphocytes and GrB positive cells in the cancerous tissues of stages I and II were significantly higher than that of stages III and IV (8.3±5.3 vs 5.3±4.5, t = 5.38, P = 0.024<0.05; 49.1±29.8 vs31.0±27.5, t = 2.44, P = 0.018<0.05; 6.8±5.3 vs 4.1±3.2, t = 2.32, P = 0.024<0.05, respectively). The numbers of T lymphocytes, NK cells, Mj and GrB positive cells in HCC with metastasis in 15 months were significantly lower than those without metastasis (53.1±16.0 vs 65.5±21.1, t = 2.41, P = 0.02<0.05; 2.9±3.1 vs 9.4±4.5, t = 6.33, P = 0.000<0.01; 20.9±11.3vs 30.1±14.4, t = 2.62, P = 0.012<0.05; 2.5±1.6 vs 7.0±4.3, t = 5.02, P = 0.000<0.01, respectively). The numbers of T lymphocytes, NK cells, B lymphocytes and GrB positive cells decreased gradually with the progressing of disease in the HCC patients.

CONCLUSION: The numbers of T lymphocytes, NK cells, B lymphocytes, Mf and GrB positive cells might be important markers to assess the hepatic local immune status and useful factors to predict the prognosis of HCC patients.

Interactions between rat colon carcinoma cells and Kupffer cells during the onset of hepatic metastasis

Liver sinusoids harbor populations of 2 important types of immunocompetent cells, Kupffer cells (KCs) and natural killer (NK) cells, which are thought to play an important role in controlling hepatic metastasis in the first 24 hr upon arrival of the tumor cells in the liver. We studied the early interaction of KCs, NK and CC531s colon carcinoma cells in a syngeneic rat model by confocal laser scanning microscopy. Results showed a minority of KCs (19% periportal and 7% pericentral) involved in the interaction with 94% of tumor cells and effecting the phagocytosis of 92% of them. NK cell depletion decreased the phagocytosis of tumor cells by KCs by 33% over a period of 24 hr, leaving 35% of the cancer cells free, as compared to 6% in NK-positive rats. Surviving cancer cells were primarily located close to the Glisson capsule, suggesting that metastasis would initiate from this region.

Nitric oxide from rat liver sinusoidal endothelial cells induces apoptosis in IFN gamma-sensitized CC531s colon carcinoma cells

BACKGROUND/AIMS

Investigation of apoptosis is pivotal in searching for mechanisms that eliminate colon cancer cells getting trapped in liver sinusoids at the time of surgical removal of the primary tumor. This study focuses on nitric oxide (NO), Fas/FasL and the involvement of interferon-gamma (IFNgamma) in liver sinusoidal endothelial cells (LSECs) and in the colon carcinoma cell line CC531s.

METHODS

Apoptosis was quantified and visualized in vitro by specific DNA fragmentation, specific staining and electron microscopy. In vivo experiments were also conducted.

RESULTS

In co-cultures of LSECs with CC531s, apoptosis of CC531s was observed only when they were pre-treated with IFNgamma, and was unaffected by blocking the Fas/FasL pathway. However, LSECs continuously produced NO, and apoptosis was inhibited by NO-inhibitors (NMMA and dexamethasone). When IFNgamma-sensitized CC531s were injected into rats, liver weight was lower, in contrast to control conditions where liver weight was higher.

CONCLUSIONS

(i) LSECs induce apoptosis in IFNgamma-sensitized CC531s in vitro; (ii) LSECs express FasL; (iii) Fas on CC531s becomes active after IFNgamma-treatment; however, (iv) blocking the Fas/FasL pathway had no effect; (v) apoptosis was inhibited by NO-inhibitors; (vi) the immune system uses this IFNgamma-activated pathway to support LSECs in killing tumor cells.

Immuno-localization of Fas and FasL in rat hepatic endothelial cells: influence of different fixation protocols

Immunocytochemistry has been widely used to localize molecules involved in apoptosis. In this short report, we describe with the aid of confocal laser scanning microscopy the immunolocalization of Fas and FasL on liver sinusoidal endothelial cells, and show how the localization of these two molecules differ when the cells are fixed with different fixation protocols. Methanol fixation shows diffuse staining of Fas and FasL in the cytoplasm, as well as in the nucleus. In contrast, paraformaldehyde fixation reveals the presence of Fas and FasL polarized at one side of the cell and only in the cytoplasm. After fixation with a combination of paraformaldehyde and glutaraldehyde the polarization is still present although the fluorescence is concentrated and located as bright dots in the cytoplasm. In conclusion, paraformaldehyde preserves the (nuclear) membrane-associated structures better then methanol and results in a more accurate localization of Fas and FasL. Understanding the different outcome of these common used fixation protocols will assist investigators to select the most suitable method for visualizing membrane-bound Fas and FasL.

CC531s colon carcinoma cells induce apoptosis in rat hepatic endothelial cells by the Fas/FasL-mediated pathway

The mechanisms involved in colorectal carcinoma with liver metastasis are not well known. Metastasizing colon carcinoma cells express more FasL than primary colon carcinoma cells and cancer cells induce apoptosis in hepatocytes by the Fas/FasL pathway. Therefore, this study focused on Fas/FasL expression and functionality in rat liver sinusoidal endothelial cells (LSECs) and CC531s colon carcinoma cells in vitro and in vivo. RT-PCR and immunochemistry revealed Fas and FasL in LSECs and CC531s, respectively. Functionality of Fas was assessed in vitro by incubation with human recombinant FasL (1-100 ng/ml) with or without enhancer. At concentrations of 10 and 100 ng/ml with enhancer, respectively 21% and 44% of endothelial cells showed signs of apoptosis using Hoechst 33342/propidium iodide staining and electron microscopy. In co-cultures, apoptosis could be detected in endothelial cells neighboring the CC531s and could be inhibited by an antagonistic FasL antibody. Moreover, 18 h after mesenteric injection of CC531s, the sinusoidal endothelium revealed disruption. In conclusion, (i). CC531s cells induce apoptosis in LSECs in vitro by using Fas/FasL; (ii). CC531s cells damage the sinusoidal endothelial lining in vivo; and (iii). this might provide FasL-positive tumor cells a gateway towards the hepatocytes.

Antimycin A-induced defenestration in rat hepatic sinusoidal endothelial cells

Liver sinusoidal endothelial cells (LSECs) possess fenestrae arranged in sieve plates. Hepatic endothelial fenestrae are open pores approximately 100 to 200 nm in diameter. Alterations in their number or diameter by hormones, xenobiotics, and diseases have important implications for hepatic microcirculation and function. Numerous reports of hepatotoxin-induced defenestration suggest that the cytoskeleton and the energy status of hepatic endothelial cells play a key role in the regulation of fenestrae. Therefore, we investigated the effect of antimycin A, an inhibitor of mitochondrial energy production, on the number of fenestrae in cultured LSECs using high-resolution microscopy and immunocytochemistry. Prolonged incubation (greater than 30 min) with antimycin A resulted in defenestrated cells and coincided with the appearance of F-actin dots, whereas the distribution of G-actin remained unchanged. Adenosine triphosphate (ATP) was depleted dramatically to less than 5% within 30 minutes within the LSECs. After treatment with antimycin A, unusual elevated fenestrated complexes were apparent, organized as a meshwork of anastomosing fenestrae at the center of and above the sieve plates. The position and appearance of these novel structures and their association with defenestration suggest that they are implicated in the process of defenestration. In conclusion, the results of experiments with antimycin A suggest that ATP is needed to maintain fenestrae and the underlying fenestrae-associated cytoskeleton rings that maintain fenestrae patency. Antimycin A-induced defenestration of LSECs is associated with the development of a structure in the sieve plate that appears to be intrinsically involved in defenestration.

MHC class I expression protects rat colon carcinoma cells from hepatic natural killer cell-mediated apoptosis and cytolysis, by blocking the perforin/granzyme pathway

BACKGROUND: Hepatic natural killer (NK) cells, the most cytotoxic cells of the natural occurring NK cells, are located in the liver sinusoids and are thus in a strategic position to kill arriving metastasising tumour cells, like colon carcinoma cells. It is known that major histocompatibility complex (MHC) class I on tumour cells negatively regulates NK cell-mediated cytolysis, but this is found using blood- or spleen-derived NK cells. Therefore, using isolated rat hepatic NK cells and the syngeneic colon carcinoma cell line CC531s, we investigated whether this protective role of MHC class I is also operative in hepatic NK cells, and addressed the mechanism of MHC class I protection. RESULTS: When MHC class I on CC531s cells was masked by preincubation with monoclonal antibody OX18, hepatic NK cell-mediated cytolysis (51Cr release) as well as apoptosis (DNA fragmentation, nucleus condensation and fragmentation) increased. When hepatic NK cells were preincubated with the granzyme inhibitor 3,4-dichloroisocoumarin, or when extracellular Ca2+ was chelated by ethylene glycol-bis(beta-aminoethyl ether)-N, N-tetraacetic acid, the enhanced cytolysis and apoptosis were completely inhibited. The involvement of the perforin/granzyme pathway was confirmed by showing that the enhanced cytolysis was caspase-independent. CONCLUSIONS: MHC class I expression protects CC531s colon carcinoma cells from hepatic NK cell-mediated apoptosis and cytolysis, by blocking the perforin/granzyme pathway.

Distinct intracellular signaling in tumor necrosis factor-related apoptosis-inducing ligand- and CD95 ligand-mediated apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in tumor cells but not in healthy cells. Similar to CD95 ligand (CD95L), TRAIL signaling requires ligand-receptor interaction; the downstream signaling molecules, such as Fas-associated death domain and caspase-8, also seem similar. Using cells stably expressing TRAIL and CD95L, we show that both TRAIL and CD95L induce apoptosis in the rat colon carcinoma cell line CC531. The mitochondrial damage (loss of mitochondrial membrane potential (MMP) and release of cytochrome c) observed after co-incubation with TRAIL-expressing cells occurs much earlier than that observed with CD95L-expressing cells. The decrease in MMP induced by both ligands was caspase-8-mediated; no difference in caspase-8 activation by TRAIL and CD95L was found. TRAIL, but not CD95L, induced activation of caspase-10. bcl-2 overexpression could not prevent TRAIL-induced mitochondrial dysfunction, whereas it completely prevented CD95L-mediated loss of MMP and cytochrome c release. The selective effect of TRAIL on tumor cells and the apparent inability of bcl-2 to block TRAIL-induced apoptosis suggest that TRAIL may offer a lead for cancer therapy in the future.

Early detection of cytotoxic events between hepatic natural killer cells and colon carcinoma cells as probed with the atomic force microscope

The atomic force microscope (AFM) is a powerful tool to investigate surface and submembranous structures of living cells under physiological conditions at high resolution. These properties enabled us to study the interaction between live hepatic natural killer (NK) cells, also called pit cells, and colon carcinoma cells in vitro by AFM. In addition, the staining for filamentous actin and DNA was performed and served as a reference, because actin and nuclear observations at the light microscopic level during the cytotoxic interaction between these two cell types have been presented earlier. In this study, we collected evidence that conjugation of hepatic NK cells with CC531s colon carcinoma cells results in a decreased binding of CC531s cells to the substratum as probed with the AFM in contact mode as early as 10 min after cell contact (n = 11). To avoid the lateral forces and smearing artefacts of contact mode AFM, non-contact imaging was performed on hepatic NK/CC531s cell conjugates, resulting in identical observations (n = 3). In contrast, the first cytotoxic signs, as determined with the nuclear staining dye Hoechst 33342, could be observed 3 h after the start of the co-culture. This study illustrates that the AFM can be used to probe early cytotoxic effects of effector to target cell contact in nearby physiological conditions. Other routine cytotoxicity tests detect the first cytotoxic effects after 1.5-3 h co-incubation at the earliest.

Rat hepatic natural killer cells (pit cells) express mRNA and protein similar to in vitro interleukin-2 activated spleen natural killer cells

Pit cells are liver-specific natural killer (NK) cells that can be divided into high- (HD) and low-density (LD) subpopulations. The characteristics of pit cells were further investigated in this report. LD and HD pit cells express the specific NK-activation markers gp42, CD25, and ANK44 antigen. LD cells and IL-2-activated NK cells have a high mRNA expression of perforin, granzymes, interferon-gamma, and tumor necrosis factor-alpha. LD pit cells, unlike spleen NK cells, have a weak response to IL-2 with regard to proliferation, cytotoxicity, and production of NK-related molecules. The characteristics of HD cells are intermediate between LD and spleen NK cells. These results show that pit cells, especially LD cells, possess characteristics similar to IL-2-activated NK cells. This is the first evidence on a molecular level that pit cells could be considered in vivo activated NK cells.

Major hepatic resection may suppress the growth of tumours remaining in the residual liver

Little is known as to how hepatectomy is associated with the growth of hepatic tumours, which may reside in the remaining liver after curative resection for hepatocellular carcinoma. Using an intra-hepatic tumour implantation model in rats, the effects of hepatectomy on tumour growth in the remaining liver were investigated. On post-operative day 7, the tumour weight in the remaining liver following 30% hepatectomy was 0.321+/-0.058 g (mean +/- SD) which was significantly greater than that (0.245+/-0.040 g) in sham operations (P<0.05). However, the tumour weight (0.156+/-0.067 g) in the remaining liver following 60% hepatectomy was significantly lower than that in sham animals (P< 0.005). The number of TdT-mediated dUTP nick-end labelling (TUNEL) positive tumour cells was significantly increased in 60% hepatectomy as compared with the sham and 30% hepatectomy group. The mRNA expression of TGF-beta1, TNF-alpha and Fas in the tumour portion of 60% hepatectomy, was higher than that in 30% hepatectomy group. Plasma levels of TGF-beta1 were inversely correlated with intra-hepatic tumour weights. These results suggest that major hepatic resection may lead to an increased induction of apoptosis for the remaining hepatic tumour.

Participation of CD45, NKR-P1A and ANK61 antigen in rat hepatic NK cell (pit cell)-mediated target cell cytotoxicity

AIM: Several triggering receptors have been described to be involved in natural killer (NK) cell-mediated target cytotoxicity. In these studies, NK cells derive d from blood or spleen were used. Pit cells are liver-specific NK cells that possess a higher level of natural cytotoxicity and a different morphology when com pared to blood NK cells. The aim of this study was to characterize the role of t he NK-triggeringmoleculesNKR-P1A,ANK61antigen,and CD45 in pit cell-media ted killing of target cells.

METHODS: ⁵¹Cr-release and DNA fragmentation were used to quantify target cell lysis and apoptosis, respectively.

RESULTS: Flow cytometric analysis showed that pit cells expressed CD45, NK R-P1A, and ANK61 antigen. Treatment of pit cells with monoclonal antibody (mAb) to CD45 (ANK74) not only inhibited CC531s or YAC-1 target lysis but also apopto sis induced by pit cells. The mAbs to NKR-P1A (3.2.3) and ANK61 antigen (ANK61) had no effect on pit cell-mediated CC531s or YAC-1 target cytolysis or apoptosis, while they did increase the Fcγ receptor positive (Fcγ R⁺) P815 cytolysis and apoptosis. This enhanced cytotoxicity could be inhibited by 3,4-dichloroi socoumarin, an inhibitor of granzymes.

CONCLUSION: These results indicate that CD45 participates in pit cell-med iated CC531s and YAC-1 target cytolysis and apoptosis. NKR-P1A and ANK61 antig en on pit cells function as activation structures against Fcγ R⁺ P 815 cells, which was mediated by the perforin/granzyme pathway.

Involvement of LFA-1 in hepatic NK cell (pit cell)-mediated cytolysis and apoptosis of colon carcinoma cells

BACKGROUND/AIMS

Previous studies have shown that hepatic natural killer (NK) cells, also called pit cells, have a higher cytotoxicity against certain tumor cells and have a higher expression of the cell adhesion molecule CD11a as compared with blood NK cells. We further investigated the involvement of the adhesion molecules, reported to be involved in target cell killing by blood NK cells, in pit cell-mediated colon carcinoma cell killing.

METHODS

51Cr-release and DNA fragmentation were used to quantify target cell lysis and apoptosis, respectively. Adhesion of pit cells to CC531s monolayers was quantitated.

RESULTS

Flow cytometric analysis showed that pit cells expressed CD2, CD11a, CD18 and CD54. CC531s cells expressed only CD54. Treatment of freshly isolated pit cells with monoclonal antibodies (mAbs) to CD11a and CD18 inhibited not only the pit cell-mediated CC531s cytolysis but also the pit cell-induced apoptosis of CC531s cells. The combination of mAbs to CD11a, CD18 and CD54 further increased the inhibition of pit cell-mediated CC531s cytolysis and apoptosis. Anti-CD2 mAb did not affect these processes. The binding of pit cells to CC531s cells was also inhibited by anti-CD11a, and CD18 mAbs, but not by anti-CD2 mAb. Anti-CD54 mAb reduced the target cell killing and the binding only slightly.

CONCLUSIONS

These results indicate that CD11a/CD18 (LFA-1) present on pit cells plays an important role in pit cell-mediated target cell adhesion, lysis and apoptosis. This finding might explain why pit cells, which have a higher expression of LFA-1 as compared to blood NK cells, are more cytotoxic against tumor cells as compared to blood NK cells.